Name: chemical bonding and bond properties
Uploaded: 2020-09-03T13:38:28.000Z
Duration: 2 min 37 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.1

Types of Chemical Bonds

I legami chimici sono essenziali affinché gli atomi formino una varietà di composti, come sale, acqua o leghe. Comprendere la formazione dei legami chimici, o più specificamente l'attrazione tra gli atomi, aiuterà a capire e prevedere il comportamento molecolare. Il nucleo di un atomo è costituito da neutroni e protoni carichi positivamente, circondati dagli elettroni carichi negativamente.

Quando due atomi si avvicinano l'uno all'altro, gli elettroni di un atomo sono attratti dal nucleo dell'altro atomo e viceversa. Allo stesso tempo, i nuclei di entrambi gli atomi si respingono, così come gli elettroni di ciascun atomo. Quando queste interazioni portano a una riduzione netta dell'energia potenziale, si forma un legame chimico.

Esistono tre tipi di legami chimici. Un metallo e un non metallo, come il sodio e il cloro, formano un legame ionico. I metalli hanno basse energie di ionizzazione che consentono una più facile rimozione degli elettroni dall'atomo.

Questi elettroni sono prontamente accettati dai non metalli dati la loro elevata affinità e il desiderio di ottenere un guscio di valenza completo. Pertanto, il metallo trasferisce gli elettroni al non metallo formando un catione e un anione. Queste particelle cariche si attraggono a vicenda per creare un legame ionico.

Il secondo tipo sono i legami covalenti formati tra due non metalli, come un atomo di carbonio e due di ossigeno che formano anidride carbonica. I non metalli hanno energie di ionizzazione elevate che rendono difficile rimuovere e trasferire elettroni di valenza da un atomo all'altro, quindi gli elettroni sono condivisi tra gli atomi. Questi elettroni condivisi interagiscono con entrambi i nuclei degli atomi nel legame e abbassano l'energia potenziale.

L'ultimo tipo è il legame metallico formato fra due atomi di un metallo. Gli atomi del metallo perdono facilmente gli elettroni di valenza, formando un pool di elettroni secondo il più semplice modello del mare di elettroni. Gli elettroni di valenza si delocalizzano sull'intero metallo e gli atomi del metallo carichi positivamente sono attratti da questo pool di elettroni, che tiene insieme gli atomi stessi.

tipi di legami chimici

Le teorie del legame chimico furono sperimentate dal chimico americano Gilbert N. Lewis. Svilupp un modello chiamato modello di Lewis per spiegare il tipo e la formazione di diversi legami. Il legame chimico fondamentale per la chimica; spiega come gli atomi o gli ioni si legano insieme per formare le molecole. Spiega perch alcuni legami sono forti e altri sono deboli, o perch un carbonio si lega a due ossigeni e non a tre; perch l'acqua H_2O e non H_4O.

Legami ionici

Gli ioni sono atomi o molecole dotati di carica elettrica. Un catione (uno ione positivo) si forma quando un atomo neutro perde uno o pi elettroni dal suo guscio di valenza, mentre un anione (uno ione negativo) si forma quando un atomo neutro acquista uno o pi elettroni nel suo guscio di valenza. I composti formati da ioni sono chiamati composti ionici (o sali) e i loro ioni costituenti sono tenuti insieme da legami ionici: le forze elettrostatiche di attrazione tra cationi e anioni con carica opposta.

Le propriet dei composti ionici fanno luce sulla natura dei legami ionici. I solidi ionici presentano una struttura cristallina e tendono ad essere rigidi e fragili; tendono anche ad avere punti di fusione e di ebollizione elevati, il che suggerisce che i legami ionici sono molto forti. I solidi ionici sono anche cattivi conduttori di elettricit per lo stesso motivo: la forza dei legami ionici impedisce agli ioni di muoversi liberamente nello stato solido. La maggior parte dei solidi ionici, tuttavia, si dissolve facilmente in acqua. Una volta disciolti o fusi, i composti ionici sono ottimi conduttori di elettricit e calore perch gli ioni possono muoversi liberamente.

Legami covalenti

Gli atomi non metallici formano spesso legami covalenti con altri atomi non metallici. I legami covalenti si formano quando gli elettroni sono condivisi tra gli atomi e sono attratti dai nuclei di entrambi gli atomi. Se gli atomi che formano un legame covalente sono identici, come in H_2, Cl_2 e altre molecole biatomiche, allora gli elettroni nel legame devono essere condivisi equamente. Questo viene definito legame covalente puro. Quando gli atomi legati da un legame covalente sono diversi, gli elettroni di legame sono condivisi, ma non pi equamente. Invece, gli elettroni di legame sono pi attratti da un atomo che dall’altro, dando luogo ad uno spostamento della densit elettronica verso quell’atomo. Questa distribuzione ineguale di elettroni nota come legame covalente polare.

I composti che contengono legami covalenti presentano propriet fisiche diverse rispetto ai composti ionici. Poich l’attrazione tra le molecole, che sono elettricamente neutre, pi debole di quella tra ioni elettricamente carichi, i composti covalenti hanno generalmente punti di fusione e di ebollizione molto pi bassi rispetto ai composti ionici. Inoltre, mentre i composti ionici sono buoni conduttori di elettricit quando disciolti in acqua, la maggior parte dei composti covalenti sono insolubili in acqua; essendo elettricamente neutri, sono cattivi conduttori di elettricit in qualsiasi stato.

Legami metallici

I legami metallici si formano tra due atomi di metallo. Un modello semplificato per descrivere il legame metallico stato sviluppato da Paul Drü chiamato "modello del mare di elettroni". Basato sulle basse energie di ionizzazione dei metalli, il modello afferma che gli atomi metallici perdono facilmente i loro elettroni di valenza e diventano cationi. Questi elettroni di valenza creano un pool di elettroni delocalizzati che circondano i cationi sull'intero metallo.

I solidi metallici, come i cristalli di rame, alluminio e ferro. sono formati da atomi di metallo e tutti presentano un'elevata conduttivit termica ed elettrica, lucentezza metallica e malleabilit. Molti sono molto duri e piuttosto forti. A causa della loro malleabilit (la capacit di deformarsi sotto pressione o martellamento), non si frantumano e, quindi, costituiscono utili materiali da costruzione. I punti di fusione dei metalli variano ampiamente. Il mercurio un liquido a temperatura ambiente e i metalli alcalini fondono al di sotto dei 200 °C. Anche diversi metalli post-transizione hanno punti di fusione bassi, mentre i metalli di transizione fondono a temperature superiori a 1000 °C. Queste differenze riflettono le differenze nella forza del legame metallico tra i metalli.

Questo testo adattato da <a href="https://openstax.org/books/chemistry-2e/pages/7-1-ionic-bonding">Openstax, Chemistry 2e, Section 7.1: Ionic Bonding</a>, <a href="https://openstax.org/books/chemistry-2e/pages/7-2-covalent-bonding">Openstax, Chemistry 2e, Section 7.2: Covalent Bonding</a>, and <big><a href="https://openstax.org/books/chemistry-2e/pages/10-5-the-solid-state-of-matter">Openstax, Chemistry 2e, Section 10.5: The Solid State of Matter</a>.</big>

Tipi di legami chimici

Le teorie dei legami chimici sono state introdotte dal chimico americano Gilbert N. Lewis. Ha sviluppato un modello chiamato modello di Lewis per spiegare il tipo e ...

Education

Didattica

JoVE Core

Chimica

Chemical Bonding: Basic Concepts

Legami chimici: concetti fondamentali

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

chemical bonding and bond properties

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O.

Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence shell. An anion is a negative ion formed when a neutral atom gains one or more electrons in its valence shell. Ionic compounds, also called salts, are held together by electrostatic attraction between oppositely charged cations and anions.

The properties of ionic compounds show why ionic bonds are strong. Ionic solids usually have a crystalline structure and are rigid and brittle. They also tend to have high melting and boiling points. In the solid state, they are poor conductors of electricity because the ions cannot move freely. Many ionic solids dissolve readily in water. When they are dissolved or melted, they conduct electricity and heat well because the ions can move about freely.

Covalent bonding is common between nonmetal atoms. It forms when atoms share electrons, and the shared electrons are attracted by the nuclei of both atoms. When identical atoms bond, as in H2 and Cl2, the electrons are shared equally. This is called a pure covalent bond. When different atoms bond, the electrons are still shared, but not equally. This creates a polar covalent bond, where electron density shifts toward one atom.

Covalent compounds have different properties from ionic compounds. Because the attraction between neutral molecules is weaker than the attraction between charged ions, covalent compounds usually have much lower melting and boiling points. Most are insoluble in water. They are also poor conductors of electricity in any state because they are electrically neutral.

Metallic bonding forms between metal atoms. Paul Drude's electron sea model describes this bond by saying that metal atoms lose valence electrons easily and become cations. The valence electrons form a pool of delocalized electrons around the cations throughout the metal. Metallic solids, such as copper, aluminum, and iron, conduct heat and electricity well. They also have metallic luster and are malleable, so they can deform under pressure or hammering without shattering.

Metals can have very different melting points. Mercury is liquid at room temperature, and alkali metals melt below 200 degrees Celsius. Several post-transition metals also have low melting points. Transition metals, however, melt above 1000 degrees Celsius. These differences reflect differences in the strength of metallic bonding among metals.

Chemical Bonding and Bond Properties

types of chemical bonds

Chemical bonding explains how atoms and ions join to form molecules and compounds. American chemist Gilbert N. Lewis pioneered chemical bonding theory with the Lewis model. This model helps explain why bonds form, why some are stronger than others, and why compounds have fixed formulas like H2O instead of H4O. Ionic bonding involves ions, which are atoms or molecules with an electrical charge. A cation is a positive ion formed when a neutral atom loses one or more electrons from its valence...

the born-haber cycle

Predicting Ionic Stability with Lattice Energy

Lattice energy helps explain why ionic compounds are stable. It measures the strength of attraction between positive and negative ions in a crystal. In one common definition, lattice energy is the energy required to separate one mole of an ionic solid into gaseous ions, so it has a positive value. Another definition uses the opposite sign and describes the energy released when gaseous ions form a lattice. When checking data, it is important to confirm which convention is being used. In either...

lewis symbols and the octet rule

Valence Electrons, Lewis Symbols, and Bonding

Chemical bonds form when atoms or ions interact in ways that lower the potential energy of a molecule. Gilbert N. Lewis created a simple model to show bond formation using valence electrons, the electrons in the outer shell. In this model, electrons are shared or transferred to help atoms reach a stable electron configuration. The Lewis model helps describe two common bond types. An ionic bond forms when electrons move from a metal to a nonmetal. A covalent bond forms when two nonmetals share...

electronegativity

Electronegativity and Polar Bonds

Electronegativity helps explain why some covalent bonds are nonpolar and others are polar covalent. It is a measure of how strongly an atom attracts shared electrons toward itself. That pull controls how electron density is distributed in a bond. Linus Pauling proposed the first electronegativity values by studying bond energies in heteronuclear molecules such as hydrogen fluoride. He expected the bond energy of HF to be about the average of the bond energies of H2 and F2, or 296 kJ/mol. The...

ionic bonding and electron transfer

Ionic Compounds and Crystal Lattices

Ionic compounds form when positive and negative ions attract each other. A cation is a positive ion, and it forms when an atom loses one or more valence electrons. An anion is a negative ion, and it forms when an atom gains one or more valence electrons. Compounds made of these ions are called ionic compounds, or salts, and the force between them is an ionic bond. The properties of ionic solids help show how strong this attraction is. They usually form rigid, brittle crystals and have high...

trends in lattice energy: ion size and charge

trends-in-lattice-energy-ion-size-and-charge

Lattice Energy Patterns in Ionic Solids

Lattice energy shows how strongly ions hold an ionic solid together. It is the energy required to separate one mole of a solid into its gaseous ions. For sodium chloride, this process requires 769 kJ per mole. The opposite convention may also be used, where lattice energy is the energy released when gaseous ions form the solid. In either case, a larger magnitude means a more stable ionic compound. For ionic crystals, lattice energy follows a pattern based on charge and ion size. The...

covalent bonding and lewis structures

Shared Electrons in Covalent Molecules

Covalent molecules form when atoms share electrons instead of transferring them. This bonding usually happens between nonmetal atoms with similar tendencies to attract electrons. Because the atoms pull on the electrons in a shared way, the bond is held together by mutual attraction. Covalent compounds often have physical properties that differ from ionic compounds. The attraction between neutral molecules is weaker than the attraction between charged ions. As a result, many covalent compounds...

bond polarity, dipole moment, and percent ionic character

bond-polarity-dipole-moment-and-percent-ionic-character

How Bond Polarity Shapes Molecular Dipoles

Bond polarity depends on electronegativity, the ability of an atom to attract shared electrons. The absolute value of the electronegativity difference, or ΔEN, gives a rough guide to bond type. When the difference is very small or zero, the bond is covalent and nonpolar. When it is larger, the bond may be polar covalent or ionic. Examples show how this works in real compounds. H–H has a ΔEN of 0, so it is nonpolar. H–Cl has a ΔEN of 0.9, so it is polar covalent. Na–Cl has a ΔEN of 2.1, so it...

lewis structures of molecular compounds and polyatomic ions

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Drawing Lewis Structures with Valence Electron Counts

Drawing Lewis structures starts with counting valence electrons and building the atom arrangement step by step. Valence electrons are the outer-shell electrons that help show how atoms bond. For ions, a positive charge means one electron is removed for each plus sign, and a negative charge means one electron is added for each minus sign. The next step is to sketch the skeleton structure. The least electronegative atom usually goes in the center, while hydrogen is almost never central. Fluorine...

resonance

Resonance Forms in Lewis Structures

Resonance forms in Lewis structures help explain molecules and ions that cannot be shown correctly with just one drawing. In nitrite ion, NO2−, the Lewis structure can be drawn in two ways. The N-O and N=O bonds switch positions in the two drawings, but the atoms stay in the same arrangement. If nitrite really had one single bond and one double bond, the two bond lengths should be different. A double bond is shorter and stronger than a single bond between the same atoms. Experiments show that...

formal charges

Lewis Structures with Formal Charge

Lewis structures can sometimes show more than one reasonable arrangement for a molecule or polyatomic ion. Formal charge helps chemists choose the best Lewis structure when that happens. It is a useful way to compare possible structures in chemistry. Formal charge is the hypothetical charge an atom would have if bonding electrons were shared evenly between the atoms. It can also be found by starting with the valence electrons of the neutral atom, subtracting the nonbonding electrons, and then...

exceptions to the octet rule

Octet Rule Exceptions in Lewis Structures

Some covalent molecules do not follow the octet rule in their Lewis structures. Their central atoms can fall into three groups: odd-electron molecules, electron-deficient molecules, and hypervalent molecules. These cases show why a Lewis structure may not always give every atom eight valence electrons. Odd-electron molecules have an odd number of valence electrons, so one electron remains unpaired. Molecules with an odd number of electrons are called radicals. Nitric oxide, NO, is one example,...

bond energies and bond lengths

How Bond Energy Predicts Reaction Heat

Bond energy helps explain why molecules stay together and how much heat a reaction may release or absorb. A covalent bond is stronger when more energy is needed to separate the atoms. The energy needed to break one specific covalent bond in one mole of gaseous molecules is called bond energy, or bond dissociation energy. For a diatomic molecule, bond energy is the standard enthalpy change for an endothermic reaction that breaks that bond. The H-H bond is a common example. Its bond energy is...

bonding in metals

Electron Sea Model in Metals

Electron sea model explains how metallic bonding holds metals together. In this model, most metal atoms do not have enough valence electrons to form ionic or covalent bonds in the usual way. Their valence electrons are held loosely because metals have low electronegativity, and their ionization energy is low, so electrons are removed easily. When a metal atom loses these outer electrons, it becomes a positively charged metal ion. The freed electrons form a delocalized electron cloud around...

key terms and concepts

Explore ionic, covalent, and metallic bonding, plus the properties of each. Learn how electrons, ions, and metals explain structure, conductivity, and melting points.

Chemical Bonding and Bond Properties | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

Physical Science

PS.PSc.2.1

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Bonding and compounds

Structure And Properties Of Matter

Chemical bonding

Physical Geology

Minerals

Chemical bonding (ionic, covalent, metallic)

Tennessee Academic Standards

High School

Matter and Its Interactions

CHEM1.PS1.14

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Motion and Stability: Forces and Interactions

CHEM1.PS2.1

CHEM1.PS2.2

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.d

PS.3

PS.3.c

Minnesota Academic Standards in Science

1.2.1 9C.1.2.1.2

Arizona Science Standards

HS.P1

HS.P1U1.2

HS+C.P1

HS+C.P1U1.4

Texas Essential Knowledge and Skills

CHEM.6

CHEM.6.E

Alabama Course of Study Science

9-12.C.2.2.a

9-12.C.2.2.c

Florida Department of Education

SC.912.P.8

SC.912.P.8.6

Chemistry and Physics

IPC.7

IPC.7.A

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New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS1-3.

HS. Chemical Reactions

HS-PS1-2.

HS-PS1-4.

HS-PS1-12.

Georgia Standards of Excellence

SPS2.

Chemical Bonds

SC2.

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Bonding Types: From Nonpolar Covalent to Ionic

Scientific Laws and Theories

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Classifying Matter by State

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Classifying Matter by Composition

Matter: Pure Substances and Mixtures
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PS.Chm.1.1

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Nuclear Binding Energy

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Radioactive Decay and Radiometric Dating

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Nuclear Fission

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Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

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PS.Chm.1.2

Atomic Orbitals

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The Pauli Exclusion Principle

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The Energies of Atomic Orbitals

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The Aufbau Principle and Hund's Rule

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electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

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The Periodic Table

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Atomic Mass

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Molar Mass

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Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

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

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Ionization Energy

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Electron Affinity

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Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

Analyze the structure of atoms and isotopes.

Chemical Bonding and Bond Properties

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