Name: how transition metal complexes are named
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 2 min 54 s
Channel: JoVE

K12 Standards

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Ohio’s Learning Standards and Model Curriculum

9-12

Physical Science

Study Of Matter

Bonding and compounds

Coordination Compounds and Nomenclature

I composti di coordinazione sono specie neutre costituite da un complesso neutro o da ioni complessi caricati e da controioni con carica opposta. Lo ione complesso è uno ione metallico centrale legato a molecole o ioni noti come ligandi. I ligandi sono composti con una o più coppie di elettroni.

Agiscono come basi di Lewis donando una coppia di elettroni allo ione metallico, che agisce come un acido di Lewis per formare un legame covalente coordinato. Insieme, costituiscono una sfera di coordinamento. Nel 1893, Alfred Werner propose una teoria della coordinazione per spiegare perché specifiche molecole stabili reagiscono e violano la teoria della valenza per formare composti di coordinazione.

Studiando vari complessi cobalto-ammoniaca, Werner ha ipotizzato che l'atomo di metallo centrale esibisca due tipi di interazioni di valenza. La valenza primaria è il numero di ossidazione del metallo centrale, mentre la valenza secondaria è il numero di ligandi legati a esso, detto anche numero di coordinazione. Pertanto, se il numero di ligandi limitati diminuisce, i controioni possono legarsi direttamente allo ione metallico, mantenendo la valenza secondaria.

La teoria della coordinazione di Werner è usata oggi per scrivere formule chimiche di composti di coordinazione. Iniziate con il simbolo dello ione metallico, quindi elencate tutti i ligandi in ordine alfabetico. Mettete le parentesi quadre intorno allo ione complesso ed elencate i contatori per ultimi.

Usate pedici numerici per indicare il numero di ligandi e controioni coinvolti. Per una nomenclatura sistematica dei composti di coordinazione, innanzitutto, nominate gli ioni complessi. Iniziate elencando i ligandi in ordine alfabetico.

Un ligando anionico termina con la lettera o, mentre un ligando neutro è indicato dal suo nome molecolare con poche eccezioni come acqua e ammina. Usate prefissi greci come di-tri-o tetra-per indicare il numero di ligandi. Se un prefisso è già presente nel nome del ligando, alternare i prefissi a bis-tri-o tetrakis-con il nome del ligando tra parentesi.

Quindi nominate il nome del metallo e il suo stato di ossidazione utilizzando numeri romani tra parentesi. Nel caso di un complesso anionico, il nome del metallo ha il suffisso ate. Infine, il composto di coordinazione è nominato aggiungendo prima il nome del catione, seguito dall'anione.

Pertanto, i due composti di coordinazione sono chiamati amminechlorobis(etilendiammina)cobalto(III)bromuro e diaquatetraclorocobaltato di ammonio(III)

composti di coordinazione e nomenclatura

Nella maggior parte dei composti degli elementi del gruppo principale, gli elettroni di valenza degli atomi isolati si combinano per formare legami chimici che soddisfano la regola dell'ottetto. Ad esempio, i quattro elettroni di valenza del carbonio si sovrappongono agli elettroni di quattro atomi di idrogeno per formare CH_4. L'unico elettrone di valenza lascia il sodio e si aggiunge ai sette elettroni di valenza del cloro per formare l'unità di formula ionica NaCl (Figura 1a). I metalli di transizione normalmente non si legano in questo modo. Formano principalmente legami covalenti coordinati, una forma di interazione acido-base di Lewis in cui entrambi gli elettroni nel legame vengono forniti da un donatore (base di Lewis, ad esempio molecola di ammoniaca) a un accettore di elettroni (acido di Lewis, ad esempio ione cobalto) (Figura 1b). L'acido di Lewis nei complessi di coordinazione, chiamato ione metallico centrale (o atomo), è spesso un metallo di transizione o un metallo di transizione interna. I donatori di basi di Lewis, chiamati ligandi, possono essere un'ampia varietà di sostanze chimiche: atomi, molecole o ioni. L'unico requisito è che abbiano una o più coppie di elettroni, che possono essere donate al metallo centrale. Molto spesso, ciò comporta un atomo donatore (atomo di azoto, Figura 1b) con una coppia solitaria di elettroni che può formare un legame coordinato con il metallo.

<img alt="Image1" src="/files/ftp_upload/11455/11455_Image_1.svg" style="text-align: center; height: 150px;" />

Figura 1 (a) I legami covalenti implicano la condivisione di elettroni, mentre i legami ionici implicano il trasferimento di elettroni associati a ciascun atomo di legame, come indicato dagli elettroni colorati. (b) Tuttavia, i legami covalenti coordinati implicano che gli elettroni di una base di Lewis vengano donati a un centro metallico. Le coppie solitarie di sei molecole di ammoniaca formano legami con lo ione cobalto per formare un complesso ottaedrico.

La sfera di coordinazione è costituita dallo ione o atomo metallico centrale più i suoi ligandi attaccati. Le parentesi in una formula racchiudono la sfera di coordinazione; le specie fuori parentesi non rientrano nella sfera di coordinamento. Il numero di coordinazione dello ione o atomo metallico centrale è il numero di atomi donatori ad esso legati. Il numero di coordinazione dello ione argento in [Ag(NH_3)2]^+ è due; per lo ione rame(II) in [CuCl_4]^2^−, il numero di coordinazione è quattro; mentre per lo ione cobalto(II) in [Co(H_2O)6]^2+ il numero di coordinazione è sei.

La denominazione dei complessi

La nomenclatura dei complessi è modellata su un sistema suggerito da Alfred Werner, un chimico svizzero e premio Nobel, il cui eccezionale lavoro più di 100 anni fa gettò le basi per una comprensione più chiara di questi composti. Per denominare i complessi vengono utilizzate le seguenti cinque regole:

<ol>
	<li>Se un composto di coordinazione è ionico, bisogna nominare prima il catione e poi l'anione, secondo la nomenclatura usuale.</li>
	<li>Dai un nome prima ai ligandi, poi al metallo centrale. Assegna un nome ai ligandi in ordine alfabetico. I ligandi negativi (anioni) vengono nominati aggiungendo -o al nome della radice del gruppo. Per la maggior parte dei ligandi neutri viene utilizzato il nome della molecola. Le quattro eccezioni comuni sono acqua (H_2O), ammina (NH_3), carbonile (CO) e nitrosile (NO). Ad esempio, denominare [Pt(NH_3)_2Cl_4] come diamminotetracloroplatino(IV).</li>
	<li>Se è presente più di un ligando di un dato tipo, il numero è indicato dai prefissi di- (per due), tri- (per tre), tetra- (per quattro), penta- (per cinque) ed esa- (per sei). A volte, i prefissi bis- (per due), tris- (per tre) e tetrakis- (per quattro) vengono utilizzati quando il nome del ligando include già di-, tri- o tetra-, o quando il nome del ligando inizia con una vocale. Ad esempio, lo ione bis(bipiridil)osmio(II) utilizza bis- per indicare che ci sono due ligandi attaccati all'Ossio e ciascun ligando bipiridilico contiene due gruppi piridinici (C_5H_4N).</li>
</ol>

Quando il complesso è un catione o una molecola neutra, il nome dell'atomo metallico centrale è scritto esattamente come il nome dell'elemento ed è seguito da un numero romano tra parentesi per indicarne lo stato di ossidazione.

Quando il complesso è un anione, alla radice del nome del metallo viene aggiunto il suffisso -ate, seguito dalla designazione numerica romana del suo stato di ossidazione. A volte si usa il nome latino del metallo quando il nome inglese è scomodo. Ad esempio, si usa ferrato invece di ironato, plumbate invece di piombo e stannate invece di tinate.

Lo stato di ossidazione del metallo è determinato in base alle cariche di ciascun ligando e alla carica complessiva del composto di coordinazione. Ad esempio, in [Cr(H_2O)_4Cl_2]Br, la sfera di coordinazione (tra parentesi) ha una carica di 1+ per bilanciare lo ione bromuro. I ligandi dell'acqua sono neutri e i ligandi del cloruro sono anionici con una carica di 1− ciascuno. Per determinare lo stato di ossidazione del metallo, la carica complessiva viene posta pari alla somma dei leganti e del metallo: +1 = −2 + x, quindi lo stato di ossidazione (x) è pari a +3.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/19-2-coordination-chemistry-of-transition-metals">Openstax, Chemistry 2e, Chapter 19.2 Coordination Chemistry of Transition Metals</a>.

Composti di coordinazione e nomenclatura

Nella maggior parte dei composti degli elementi del gruppo principale, gli elettroni di valenza degli atomi isolati si combinano per formare legami chimici che soddisfano la regola dell'ottetto. Per...

Education

Didattica

JoVE Core

Chemistry

Chimica

Transition Metals and Coordination Complexes

Metalli di transizione e complessi di coordinazione

transition-metals-and-coordination-complexes

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

how transition metal complexes are named

Transition metal complexes are named by following rules for ligands, metal ions, and oxidation state. These compounds form when a central metal ion or atom, often a transition metal or inner transition metal, accepts electron pairs from ligands. A ligand is a Lewis base that can be an atom, molecule, or ion with one or more lone pairs to donate.

In these complexes, the bond is a coordinate covalent bond. That means both electrons in the bond come from the donor, such as ammonia, and are accepted by the metal center, such as a cobalt ion. The coordination sphere includes the metal plus its attached ligands. Brackets show the coordination sphere in a formula, and anything outside the brackets is not part of it.

The coordination number tells how many donor atoms are bonded to the central metal. For example, [Ag(NH3)2]+ has a coordination number of two, [CuCl4]2− has a coordination number of four, and [Co(H2O)6]2+ has a coordination number of six. These examples show how different ligands can surround the metal in different numbers.

The naming system for complexes follows rules suggested by Alfred Werner. If the coordination compound is ionic, name the cation first and the anion second. Then name the ligands first, followed by the central metal, and list the ligands in alphabetical order.

Negative ligands are named by changing the stem of the name to end in -o. Most neutral ligands keep their usual molecular name, but aqua, ammine, carbonyl, and nitrosyl are common exceptions. If more than one ligand is present, use prefixes such as di-, tri-, tetra-, penta-, and hexa-. The prefixes bis-, tris-, and tetrakis- are used when the ligand name already contains a prefix or begins with a vowel.

A cationic or neutral complex keeps the metal name unchanged and adds a Roman numeral for the oxidation state. An anionic complex uses the -ate ending on the metal name, followed by the Roman numeral. Latin-based names are sometimes used when the English form sounds awkward, such as ferrate, plumbate, and stannate.

The oxidation state of the metal is found from the charges of the ligands and the total charge of the complex. In [Cr(H2O)4Cl2]Br, the bracketed coordination sphere has a 1+ charge to balance bromide. The water ligands are neutral, and each chloride ligand has a 1− charge, so the chromium oxidation state is +3.

How Transition Metal Complexes Are Named

properties of transition metals

Transition Metals in the Periodic Table

Transition metals are the d-block elements and the inner transition metals in the f-block. They are defined by partially filled d orbitals. In the periodic table, the transition elements are in groups 3 through 11, and the inner transition metals appear in the two rows below the main body of the table. The d-block is often grouped into transition series. The first transition series runs from Sc through Cu. The second series runs from Y through Ag. The third series includes La and Hf through...

coordination compounds and nomenclature

Transition metal complexes are named by following rules for ligands, metal ions, and oxidation state. These compounds form when a central metal ion or atom, often a transition metal or inner transition metal, accepts electron pairs from ligands. A ligand is a Lewis base that can be an atom, molecule, or ion with one or more lone pairs to donate. In these complexes, the bond is a coordinate covalent bond. That means both electrons in the bond come from the donor, such as ammonia, and are...

metal-ligand bonds

Coordination Complexes and Chelation

Coordination complexes form when a metal ion bonds to ligands. These compounds appear in familiar examples such as hemoglobin in blood, chlorophyll in green plants, vitamin B-12, and the catalyst used to make polyethylene. Transition metal ions are especially likely to form these complexes. In a coordination complex, the metal acts as a Lewis acid. The ligand acts as a Lewis base and donates both electrons in the coordinate covalent bond. A ligand can be an atom, molecule, or ion, as long as...

coordination number and geometry

Transition Metal Shapes from Coordination Number

Transition metal complexes are often identified by their coordination number and the shape around the metal ion. The coordination number is the number of donor atoms bonded to the central metal. In many complexes, the most common shapes are octahedral, tetrahedral, and square planar. Coordination number and molecular geometry are linked in a clear pattern. A coordination number of 2 gives a linear shape, as in [Ag(NH3)2]+. A coordination number of 3 gives a trigonal planar shape, as in...

structural isomerism

Linkage and Ionization Isomers

Isomers are different chemical species that share the same chemical formula. In coordination compounds, structural isomerism includes linkage isomers and coordination-sphere isomers. These two forms show how the same atoms can be arranged in different ways around a metal center. Linkage isomers form when a ligand can attach to a transition metal through two different atoms. The cyanide ligand, CN−, can bind through carbon or nitrogen. The thiocyanate ligand, SCN−, can bind through sulfur or...

stereoisomerism

Isomer Shapes in Coordination Complexes

Isomer shapes in coordination complexes can change a compound’s properties even when the chemical formula stays the same. Isomers are different chemical species with the same formula. In transition metal complexes, the atoms stay connected through the same types of bonds, but their arrangement in space can differ. One common form is geometric isomerism. In these complexes, ligands (the ions or molecules attached to the metal) can sit in cis or trans positions. The octahedral [Co(NH3)4Cl2]+ ion...

valence bond theory

Metal Ligand Bonds in Coordination Complexes

Coordination complexes form metal-ligand bonds through valence bond theory. In this model, Linus Pauling explained bonding with hybridization and overlap of atomic orbitals. The central metal atom or ion acts as a Lewis acid. It uses empty orbitals of suitable energy to accept electron pairs from ligands, which act as Lewis bases. These coordinate covalent bonds help explain the color, geometry, and magnetic behavior seen in coordination compounds. The type of hybridization helps determine the...

crystal field theory - octahedral complexes

crystal-field-theory-octahedral-complexes

Octahedral d-Orbital Splitting in Crystal Fields

Crystal field theory explains how ligands affect the d orbitals in transition metal complexes. This electrostatic model helps predict the colors, magnetic behavior, and some structures of coordination compounds. It focuses on the nonbonding electrons on the central metal ion, not on the metal-ligand bonds. In crystal field theory, the metal ion and ligands are treated as very small point charges. Because electrons are negative, electrons donated by the ligands repel the electrons in the...

crystal field theory - tetrahedral and square planar complexes

crystal-field-theory-tetrahedral-and-square-planar-complexes

Crystal Field Splitting in Non-Octahedral Shapes

Crystal field theory also explains d orbital splitting in tetrahedral and square planar complexes. These shapes do not follow the same pattern as an octahedral complex, so the d orbitals respond to ligand placement in different ways. In tetrahedral complexes, the four ligands sit between the axes. None of the d orbitals points directly at the ligands, but the d x2−y2 and d z2 orbitals lie along the Cartesian axes and overlap less with the ligands than the d xy, d xz, and d yz orbitals. The d...

colors and magnetism

Color and Spin in Coordination Complexes

Color in coordination complexes comes from how metal electrons absorb light. When atoms or molecules absorb light at the right frequency, electrons move to higher-energy orbitals. For many main-group atoms and molecules, the absorbed light is ultraviolet and cannot be seen. In coordination compounds, the energy gap between d orbitals often matches visible light, so the compound can absorb and emit colors that the human eye detects. Small changes in orbital energy can cause large shifts in the...

key terms and concepts

Learn how transition metal complexes are named, including ligands, coordination number, oxidation state, and rules like di-, bis-, and -ate.

How Transition Metal Complexes Are Named | JoVE K12

chemistry

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New York State Science Learning Standards

High School

HS. Structure and Properties of Matter

HS-PS2-6.

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

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Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Molecules and Compounds

Atoms and Molecules

Everything in the universe is made up of matter, and matter is composed of a combination of elements. An atom is the smallest unit of ...

Classification of Elements and Compounds

Pure substances consist of only one type of matter. A pure substance can be an element or a compound. An element consists of only one type of atom, while ...

What is Energy?

The universe is composed of matter in different forms, and all forms of matter contain energy. &#xA0;The different forms of energy on Earth originate from ...

Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

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Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

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Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

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Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

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Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

Phase Transitions: Melting and Freezing

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Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

• Heterogeneous vs. homogeneous 
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Content elaboration: Matter was introduced in the elementary grades and the learning progression continued through middle school to include differences in the physical properties of solids, liquids and gases. Elements, compounds, mixtures, molecules, kinetic and potential energy and the particulate nature of matter were introduced. Content in Chemistry (e.g., electron configuration, molecular shapes, bond angles) will build on concepts in this course. Matter can be classified in broad categories, such as homogeneous and heterogeneous, according to its composition or by its chemical properties (e.g., reactivity, flammability, pH) and physical properties (e.g., color, solubility, odor, hardness, density, conductivity, melting point and boiling point, viscosity, malleability). Solutions are homogeneous mixtures of a solute dissolved in a solvent. The amount of a solid solute that can dissolve in a solvent generally increases as the temperature increases since the particles have more kinetic energy to overcome the attractive forces between them. Water is often used as a solvent since so many substances will dissolve in water. Aqueous solutions can be classified as acidic (below 7 on the pH scale), neutral (7 on the pH scale), or basic (above 7 on the pH scale), but the discussion of hydroxide and hydrogen ions as they relate to the pH scale is reserved for Chemistry. Physical properties can be used to separate the substances in mixtures, including solutions. Phase changes can be represented by graphing the temperature of a sample vs. the time it has been heated. Investigations include collecting data during heating, cooling and solid-liquid-gas phase changes. At times, the temperature will change steadily, indicating a change in the motion of the particles and the kinetic energy of the substance. However, during a phase change, the temperature of a substance does not change, indicating there is no change in kinetic energy. Since the substance continues to gain or lose energy during phase changes, these changes in energy are potential and indicate a change in the position of the particles. When heating a substance, a phase change will occur when the kinetic energy of the particles is great enough to overcome the attractive forces between the particles; the substance then melts or boils. [cite: 91, 92] Conversely, when cooling a substance, a phase change will occur when the kinetic energy of the particles is no longer great enough to overcome the attractive forces between the particles; the substance then condenses or freezes. [cite: 92, 93] Phase changes are examples of changes that can occur when energy is absorbed from the surroundings (endothermic) or released into the surroundings (exothermic). When thermal energy is added to a solid, liquid or gas, most substances increase in volume because the increased kinetic energy of the particles causes an increased distance between the particles. This results in a change in density of the material. Generally, solids have greater density than liquids, which have greater density than gases due to the spacing between the particles. [cite: 96, 101] The density of a substance can be calculated from the slope of a mass vs. volume graph. Differences in densities can be determined by interpreting mass vs. volume graphs of the substances. Students should be able to calculate mass, volume or density, given two of the three values.

Classification of matter

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Quantum Numbers

It is said that the energy of an electron in an atom is quantized; that is, it can be equal only to certain specific values and can jump from one energy ...

• Models of the atom (components)
• Ions (cations and anions)
• Isotopes

Content elaboration: Content introduced in middle school, where the atom was introduced as a small, indestructible sphere, is further developed in this course. Over time, technology was introduced that allowed the atom to be studied in more detail. The atom is composed of protons, neutrons and electrons that have measurable properties, including mass and, in the case of protons and electrons, a characteristic charge. An atom is empty space with a very small positively charged nucleus. The nucleus is composed of protons and neutrons. The electrons move about in the empty space that surrounds the nucleus. Although current understanding goes beyond the Bohr Model, it can still be used to represent the atom and develop the idea of valence electrons. Experimental evidence that led to the development of historic atomic models is reserved for Chemistry. All atoms of a particular element have the same atomic number; an element may have different isotopes with different mass numbers. [cite: 112, 113] Atoms may gain or lose valence electrons to become anions or cations. Atomic number, mass number, charge and identity of the element can be determined from the numbers of protons, neutrons and electrons. Atomic mass calculations and explanations about configuration of electrons and how atomic spectra are produced are reserved for Chemistry.

Atoms

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

• Periodic law 
• Representative groups

Content elaboration: Content from the middle school level, specifically the properties of metals, nonmetals and metalloids and their positions on the periodic table, is further expanded in this course. The periodic table was arranged so that elements with similar chemical and physical properties are in the same group or family. When elements are listed in order of increasing atomic number, the same sequence of properties appears over and over again; this is the periodic law. [cite: 120, 121] Trends in simple observable properties, like density or melting point, can be examined within families or groups on the periodic table. These trends allow scientists to make predictions about new elements. Metalloids are elements that have some properties of metals and some properties of nonmetals. Metals, nonmetals, metalloids, periods and groups or families including the alkali metals, alkaline earth metals, halogens and noble gases can be identified by their position on the periodic table. Elements in Groups 1, 2 and 17 have characteristic ionic charges that will be used in this course to predict the formulas of compounds. Other trends in the periodic table (e.g., atomic radius, electronegativity, ionization energies) are reserved for Chemistry.

Periodic trends of the elements

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

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Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

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Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


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Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For ...

• Bonding (ionic and covalent)
• Nomenclature

Content elaboration: Middle school content introduced the concept that compounds are composed of atoms of two or more different elements joined together chemically. In this course, the chemical joining of atoms is studied in more detail. Atoms may be bonded together by losing, gaining or sharing valence electrons to form molecules or three-dimensional lattices. An ionic bond involves the attraction of two oppositely charged ions, typically a metal cation and a nonmetal anion formed by transferring electrons between the atoms. An ion attracts oppositely charged ions from every direction, resulting in the formation of a three-dimensional lattice. Covalent bonds result from the sharing of electrons between two atoms, usually nonmetals. Covalent bonding can result in the formation of structures ranging from small individual molecules to three-dimensional lattices (e.g., diamond). The bonds in most compounds fall on a continuum between the two extreme models of bonding: ionic and covalent. Using the periodic table to determine ionic charge, formulas of ionic compounds containing elements from groups 1, 2, 17, hydrogen and oxygen can be predicted. Given a chemical formula, a compound can be named using conventional systems that include Greek prefixes where appropriate. Prefixes will be limited to represent values from one to 10. Given the name of an ionic or covalent substance, formulas can be written. Naming organic molecules is beyond this grade level and is reserved for an advanced chemistry course. Prediction of bond types from electronegativity values, polar covalent bonds, and writing formulas/naming compounds that contain polyatomic ions or transition metals are reserved for Chemistry.

Chemical Equations

Chemical equations represent the identities and relative quantities of substances involved in a chemical reaction. The substances undergoing reaction are ...

Reaction Stoichiometry

A balanced chemical equation provides a great deal of information in a very succinct format. Chemical formulas provide the identities of the reactants and ...

Limiting Reactant

The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in ...

Reaction Yield

The theoretical yield of a reaction is the amount of product estimated to form based on the stoichiometry of the balanced chemical equation. The ...

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

• Chemical reactions
• Nuclear reactions

Content elaboration: In middle school, the law of conservation of matter was expanded to chemical reactions, noting that the number and type of atoms and the total mass are the same before and after the reaction. In this course, conservation of matter is expressed by writing balanced chemical equations. At this level, reactants and products can be identified from an equation and simple equations can be written and balanced given either the formulas of the reactants and products or a word description of the reaction. [cite: 143, 149] Stoichiometric relationships beyond the coefficients in a balanced equation and classification of types of chemical reactions are reserved for Chemistry. During chemical reactions, thermal energy is either transferred from the system to the surroundings (exothermic) or transferred from the surroundings to the system (endothermic). Since the environment surrounding the system can be large, temperature changes in the surroundings may not be detectable. Nuclear reactions involve changes to the nucleus and typically produce much larger energies than chemical reactions. The strong nuclear force is an attractive force that binds protons and neutrons together in the nucleus. While the nuclear force is extremely weak at most distances, over the very short distances present in the nucleus the force is greater than the repulsive electrical forces among protons. When the attractive nuclear forces and repulsive electrical forces in the nucleus are not balanced, the nucleus is unstable. Through radioactive decay, the unstable nucleus emits radiation in the form of very fast-moving particles and energy to produce a new nucleus. Nuclei that undergo this process are said to be radioactive. Radioactive decay can result in the release of different types of radiation (alpha, beta, gamma), each with a characteristic mass, charge, and potential to alter and penetrate the material it strikes. Alpha decay changes the identity of the element. Beta decay results from the decay of a neutron. When a radioisotope undergoes alpha or beta decay, the resulting nucleus can be predicted and the balanced nuclear equation can be written. For any radioisotope, the half-life is unique and predictable. Graphs can be constructed that show the amount of a radioisotope that remains as a function of time and can be interpreted to determine the value of the half-life. Half-life values are used in radioactive dating. Only whole number integers of half-lives will be addressed in this course. Other examples of nuclear processes include nuclear fission and nuclear fusion. Nuclear fission involves splitting a large nucleus into smaller nuclei, releasing large quantities of energy. Nuclear fusion is the joining of smaller nuclei into a larger nucleus accompanied by the release of large quantities of energy. Nuclear fusion is the process responsible for formation of elements in the universe beyond hydrogen and is the source of energy in the sun and other stars. Using nuclear reactions as an energy resource can be addressed. Further details about nuclear processes, including mass-energy equivalence and nuclear power applications, are addressed in Physics.

Reactions of matter

How Transition Metal Complexes Are Named

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