Name: reading molecular, empirical, and structural formulas
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 52 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.3

Chemical Formulas

I composti chimici sono sostanze composte da due o più elementi in proporzioni specifiche. Per descrivere accuratamente questi composti sono state sviluppate formule chimiche. La formula chimica fornisce informazioni sugli elementi e sul numero di ioni o atomi coinvolti.

Gli elementi sono rappresentati dal loro simbolo chimico, mentre il numero relativo di ioni o di atomi è indicato con un numero al pedice. Per esempio, lo zucchero da tavola, o saccarosio, é un composto contenente carbonio, idrogeno e ossigeno, rappresentati utilizzando i simboli C, H e O.I numeri dodici, ventidue e undici indicano il numero totale di atomi di carbonio, idrogeno e ossigeno presenti all'interno del composto. In generale, gli elementi non sono elencati in ordine alfabetico, ma piuttosto iniziano con gli elementi carichi più positivamente, o metallici, seguiti dagli elementi carichi più negativamente, o meno metallici, come l'idrossido di potassio.

Le formule chimiche sono classificate come molecolari, empiriche e strutturali. Le formule molecolari descrivono un composto elencando ogni elemento e il numero esatto di atomi presenti. La formula molecolare del glucosio è C_6H_12O_6, il che significa che il glucosio è composto da sei atomi di carbonio, dodici di idrogeno e sei di ossigeno.

La formula empirica mostra il più semplice rapporto fra gli atomi degli elementi presenti. Nel glucosio, il rapporto più semplice tra atomi di carbonio, idrogeno e ossigeno è 1:2:1, conferendoglii la formula empirica CH_2O. La formula molecolare di un composto è anche un multiplo intero della sua formula empirica.

Nel glucosio, moltiplicando la formula empirica per il numero intero sei ne risulta la sua formula molecolare. Al contrario, la formula strutturale presenta graficamente la relazione fra i singoli atomi. I simboli chimici rappresentano gli atomi, e le linee brevi indicano i legami chimici.

Le singole linee rappresentano i singoli legami mentre due e tre linee caratterizzano, rispettivamente, i doppi e i tripli legami. I modelli estesi della formula strutturale, come il disegno prospettico, il modello asta e sfera o il modello di riempimento dello spazio, forniscono varie prospettive tridimensionali sulla forma molecolare. Fra le tre formule chimiche, una formula strutturale fornisce la maggior parte delle informazioni sul materiale chimico, seguita dalla formula molecolare.

La formula empirica è la meno informativa.

formule chimiche

Una formula chimica presenta informazioni sulle proporzioni degli atomi che costituiscono un particolare composto chimico o molecola, principalmente utilizzando simboli di elementi e numeri. A volte vengono utilizzati anche altri simboli, come trattini, parentesi, parentesi quadre, virgole e segni più e meno. Una formula chimica può essere di tre tipi: molecolare, empirica e strutturale.

Formula molecolare

La formula molecolare rappresenta una molecola o un composto chimico utilizzando simboli chimici (per indicare i tipi di atomi) e numeri in pedice (per mostrare il numero di atomi di ciascun tipo nella molecola). Le formule molecolari vengono utilizzate anche come abbreviazioni per i nomi dei composti.

Alcuni elementi sono costituiti da atomi discreti e individuali, come i gas nobili elio, neon e argon. Tali elementi sono chiamati gas monoatomici e hanno rispettivamente formule molecolari He, Ne e Ar. Pochi elementi esistono come molecole costituite da due o più atomi dello stesso elemento legati chimicamente. Ad esempio, elementi come idrogeno, ossigeno e azoto esistono come molecole biatomiche contenenti due atomi ciascuna e quindi hanno rispettivamente le formule molecolari H_2, O_2 e N_2. Allo stesso modo, elementi come il fosforo e lo zolfo esistono come molecole poliatomiche con formule molecolari rispettivamente P_4 e S_8.

È importante notare che un pedice che segue un simbolo e un numero davanti a un simbolo non rappresentano la stessa cosa; ad esempio, H_2 e 2H indicano due cose nettamente diverse. H_2 è una formula molecolare: rappresenta una molecola biatomica di idrogeno, costituita da due atomi dell'elemento legati chimicamente insieme. L'espressione 2H invece indica due atomi di idrogeno separati che non sono combinati come un'unità. L'espressione 2H_2 rappresenta due molecole di idrogeno biatomico.

Formula empirica

I composti si formano quando due o più elementi si combinano chimicamente, dando luogo alla formazione di legami. Ad esempio, l'idrogeno e l'ossigeno possono reagire per formare l’acqua, mentre il sodio e il cloro possono reagire per formare cloruro di sodio o sale da cucina. A volte descriviamo la composizione di questi composti con una formula empirica, che indica i tipi di atomi presenti e il rapporto intero più semplice del numero di atomi (o ioni) nel composto. Ad esempio, il biossido di titanio (utilizzato come pigmento nella vernice bianca e nelle creme solari spesse, bianche e protettive) ha una formula empirica di TiO_2. Ciò identifica gli elementi titanio (Ti) e ossigeno (O) come costituenti del biossido di titanio e indica la presenza di un numero doppio di atomi dell'elemento ossigeno rispetto agli atomi dell'elemento titanio.

In molti casi, la formula molecolare di una sostanza deriva da una determinazione sperimentale sia della sua formula empirica che della sua massa molecolare (la somma delle masse atomiche di tutti gli atomi che compongono la molecola). Ad esempio, si può determinare sperimentalmente che il benzene contiene due elementi, carbonio (C) e idrogeno (H), e che per ogni atomo di carbonio nel benzene c'è un atomo di idrogeno. Pertanto, la formula empirica è CH. Una determinazione sperimentale della massa molecolare rivela che una molecola di benzene contiene sei atomi di carbonio e sei atomi di idrogeno, quindi la formula molecolare del benzene è C_6H_6.

Formula strutturale

La formula strutturale di un composto fornisce le stesse informazioni della formula molecolare (i tipi e il numero di atomi nella molecola) ma mostra anche come gli atomi sono collegati nella molecola. In altre parole, la formula strutturale rappresenta graficamente la struttura molecolare di un composto. Mostra la probabile disposizione degli atomi e come essi sono collegati nello spazio tridimensionale reale, fornendo maggiori informazioni sulla geometria molecolare. Le linee vengono utilizzate per rappresentare i legami presenti tra gli atomi. La formula può anche rappresentare gli angoli di legame approssimativi, dando un’idea della forma della molecola.

Questo testo è adattato da <a href="https://openstax.org/books/chemistry-2e/pages/2-4-chemical-formulas">Openstax Chemistry 2e, Section 2.4: Chemical Formulas. </a>

Formule chimiche

Una formula chimica presenta informazioni sulle proporzioni degli atomi che costituiscono un particolare composto chimico o molecola, utilizzando principalmente simboli di ...

Education

Didattica

Book

Chimica

Molecules, Compounds, and Chemical Equations

Molecole, composti ed equazioni chimiche

molecules-compounds-and-chemical-equations

reading molecular, empirical, and structural formulas

Chemical formulas show the types and proportions of atoms in a compound or molecule. They use element symbols and numbers. Some formulas also use dashes, parentheses, brackets, commas, plus signs, and minus signs.

A molecular formula shows a molecule or compound with chemical symbols and subscript numbers. The symbols tell which atoms are present, and the subscripts show how many of each atom are in the molecule. Molecular formulas can also serve as short names for compounds.

Some elements exist as separate atoms. The noble gases helium, neon, and argon are monatomic gases, so their molecular formulas are He, Ne, and Ar. Other elements form molecules with two or more bonded atoms of the same element. Hydrogen, oxygen, and nitrogen are diatomic and have the formulas H2, O2, and N2. Phosphorus and sulfur are polyatomic and have the formulas P4 and S8.

It is important to tell the difference between a subscript and a number in front of a symbol. H2 means one diatomic hydrogen molecule. The expression 2H means two separate hydrogen atoms. The expression 2H2 means two hydrogen molecules.

An empirical formula shows the types of atoms present and the simplest whole-number ratio of those atoms or ions in a compound. Compounds form when two or more elements chemically combine and make bonds. Water and sodium chloride are common examples of compounds. Titanium dioxide has the empirical formula TiO2, which shows titanium and oxygen and means there are twice as many oxygen atoms as titanium atoms.

In many cases, a molecular formula is found from the empirical formula and the molecular mass. Molecular mass is the sum of the atomic masses of all atoms in a molecule. Benzene is one example. Experiments show that benzene contains carbon and hydrogen in a 1:1 ratio, so its empirical formula is CH. Its molecular mass shows that one molecule contains six carbon atoms and six hydrogen atoms, so its molecular formula is C6H6.

A structural formula gives the same atom count information as a molecular formula, but it also shows how the atoms are connected. It draws the molecular structure in a way that helps show the probable arrangement of atoms in three-dimensional space. Lines represent bonds between atoms. Structural formulas may also show approximate bond angles, which gives a sense of molecular shape.

Reading Molecular, Empirical, and Structural Formulas

reading-molecular-empirical-and-structural-formulas

chemical formulas

Chemical formulas show the types and proportions of atoms in a compound or molecule. They use element symbols and numbers. Some formulas also use dashes, parentheses, brackets, commas, plus signs, and minus signs. A molecular formula shows a molecule or compound with chemical symbols and subscript numbers. The symbols tell which atoms are present, and the subscripts show how many of each atom are in the molecule. Molecular formulas can also serve as short names for compounds. Some elements...

molecules and compounds

Atomic Elements, Molecules, and Bonds

Matter is made of elements, and elements are built from atoms. An atom is the smallest unit of an element that still keeps that element’s properties. A silver coin, for example, is made of silver atoms. Each atom keeps the unique properties of silver. Elements are pure substances made of identical atoms. They cannot be broken down into simpler substances by chemical changes. Most elements are atomic elements, which use single atoms as their basic unit. Carbon and sodium are examples of atomic...

classification of elements and compounds

Atomic vs Molecular Substances and Bonding

Pure substances are made of only one kind of matter. A pure substance can be an element or a compound. An element contains only one type of atom. A compound contains two or more types of atoms joined by a chemical bond. Elements are classified as atomic or molecular based on their basic units. Compounds are classified as ionic or molecular, also called covalent, based on the bonds they contain. Molecular compounds form when two or more different nonmetal atoms share electrons. Their basic...

ionic compounds: formulas and nomenclature

ionic-compounds-formulas-and-nomenclature

Ionic Charges, Formulas, and Naming Rules

Ionic compounds form when metals transfer electrons to nonmetals and create oppositely charged ions. The electrostatic attraction between the ions, called an ionic bond, holds the compound together. Many nonmetals gain electrons by moving toward the electron count of the next noble gas. Group 17 atoms usually gain one electron and form 1− ions, while group 16 atoms usually gain two electrons and form 2− ions. Oxygen is a clear example. A neutral oxygen atom has 8 protons and 8 electrons. When...

molecular models

Molecular Model Types in Chemistry

Molecular models help chemists and students visualize the structures and shapes of atoms and molecules. They represent the molecular architecture of chemical compounds in a way that is easier to study than formulas alone. Skeletal models are simple two-dimensional drawings of compounds. They show the molecular framework, or the bonds, without drawing every atom. In this model, many carbon and hydrogen atoms are not shown directly. Their positions are implied by the ends and junctions of the...

molecular compounds: formulas and nomenclature

molecular-compounds-formulas-and-nomenclature

Naming Covalent Compounds and Acids

Molecular compounds are covalent compounds made when atoms share electrons. Because there is no electron transfer, they do not contain ions. They are made of separate, neutral molecules. Since covalent compounds usually form from nonmetals, the periodic table can help students recognize many of them. In many cases, the positions of the elements can also help predict whether a compound is ionic or covalent, although there are exceptions. Molecular compounds are named differently from ionic...

organic compounds

Organic Molecules in Everyday Chemistry

Organic molecules are carbon-based compounds found in living things and in many everyday products. Most organic compounds have carbon as the main element, bonded to hydrogen and other carbon atoms. Some carbon-containing substances, such as carbonates, cyanides, and simple oxides like CO and CO2, are not classified as organic. Carbon can form up to four strong bonds, which helps explain why organic compounds can make chains and rings of many sizes and shapes. These molecules appear in...

formula mass and mole concepts of compounds

formula-mass-and-mole-concepts-of-compounds

Chemical Formula Mass and Percent Composition

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance. For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses. Ionic...

experimental determination of chemical formula

experimental-determination-of-chemical-formula

Finding Empirical and Molecular Formulas

Chemical formulas show the elemental makeup of a compound. When a formula is unknown, scientists often start by measuring the masses of the elements in the sample. Those mass data are then used to find the simplest whole-number ratio of atoms, which gives the empirical formula. To get from mass to atom ratio, the masses of the elements are first converted to moles using molar masses. Chemical formulas describe numbers of atoms, not masses, so this step is necessary. In one example, 1.71 grams...

chemical equations

Reading Chemical Equations and Balancing Them

Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products. The numbers in a chemical equation are shown with coefficients. A coefficient...

scientists in action

Scienziati in azione

key terms

Termini chiave

key relationships & equations

Relazioni ed Equazioni Chiave

chapter exercises

Esercizi del capitolo

appendices

Appendici

molecules, compounds, and chemical equations

Learn how molecular, empirical, and structural formulas show atom counts, ratios, and bonds. See examples like H2, TiO2, and C6H6.

Reading Molecular, Empirical, and Structural Formulas | JoVE K12

chemistry

PS.Chm.4.3

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Representing compounds

Virginia  Standards of Learning

HIgh School

CH.3

CH.3.a

Texas Essential Knowledge and Skills

High School

CHEM.8

CHEM.8.D

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.7

Georgia Standards of Excellence

SPS2.

Chemical Names and Chemical Formulas

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

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 ...

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 ...

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 ...

Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

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 ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

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

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

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

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

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 ...

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 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

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

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 ...

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

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 ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

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

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

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 ...

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

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 ...

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

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:


	...

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, ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

molecular-comparison-of-gases-liquids-and-solids

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 ...

comparing-intermolecular-forces-melting-point-boiling-point

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, ...

Construct an explanation to summarize the influences intermolecular forces have on the properties of chemical compounds.

PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Reading Molecular, Empirical, and Structural Formulas

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