Name: reading molecular, empirical, and structural formulas
Uploaded: 2020-09-03T13:38:26.000Z
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K12 Standards

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

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.3

Chemical Formulas

Les composés chimiques sont des substances composées de deux éléments ou plus dans des proportions spécifiques. Pour décrire ces composés avec précision, des formules chimiques ont été développées. La formule chimique fournit des informations sur les éléments et le nombre d'ions ou d'atomes impliqués.Les éléments sont représentés par leur symbole chimique, tandis que le nombre relatif d'ions ou d'atomes est indiqué par un indice. Par exemple, le sucre de table ou le saccharose est un composé contenant les éléments carbone, hydrogène et O.Les nombres douze, vingt-deux et oxygène-représentés en utilisant leurs symboles C, H et onze indiquent le nombre total d'atomes de carbone, d'hydrogène et d'oxygène présents dans le composé. En général, les éléments ne sont pas listés par ordre alphabétique, mais plutôt en commençant par des éléments plus chargés positivement, ou métalliques, suivis d'éléments chargés plus négativement, ou moins métalliques, comme l'hydroxyde de potassium.Les formules chimiques sont classées comme moléculaires, empiriques et structurelles. Les formules moléculaires décrivent un composé en énumérant chaque élément et le nombre exact d'atomes présents. La formule moléculaire du glucose est C_6H_12O_6, ce qui signifie que le glucose est composé de six atomes de carbone, douze atomes d'hydrogène et six atomes d'oxygène.La formule empirique affiche le plus simple rapport nombre entier d'atomes d'éléments présents. Dans le glucose, le rapport le plus simple des atomes de carbone, d'hydrogène et d'oxygène est 1:2:1-ce qui lui donne la formule empirique CH_2O. La formule moléculaire d'un composé est également un multiple entier de sa formule empirique.Dans le glucose, la multiplication de sa formule empirique avec le nombre entier six donne sa formule moléculaire. En revanche, la formule structurelle présente graphiquement la relation entre les atomes individuels. Les symboles chimiques représentent les atomes, et les lignes courtes désignent des liaisons chimiques.Les lignes simples représentent des liaisons simples tandis que deux et trois lignes caractérisent les liaisons doubles et triples, respectivement. Les modèles étendus de la formule structurelle tels que le dessin en perspective, le modèle à bille et à bâton ou le modèle de remplissage d'espace fournissent diverses perspectives tridimensionnelles sur la forme moléculaire. Parmi les trois formules chimiques, une formule structurelle fournit le plus d'informations sur le matériau chimique, suivie de la formule moléculaire.La formule empirique est la moins informative.

formules chimiques

Une formule chimique présente des informations sur les proportions des atomes constituant un composé ou une molécule chimique en particulier, en utilisant principalement des symboles d'éléments et des nombres. Parfois, d'autres symboles, tels que des tirets, des parenthèses, des crochets, des virgules, des signes plus et moins sont également utilisés. Une formule chimique peut être l'un de ces trois types : moléculaire, empirique et structurelle. 
 
 <h4>Formule moléculaire </h4>
 
 La formule moléculaire représente une molécule ou un composé chimique à l'aide de symboles chimiques (pour indiquer les types d'atomes) et de nombres en indice (pour indiquer le nombre d'atomes de chaque type dans la molécule). Les formules moléculaires sont également utilisées comme abréviations pour les noms des composés. 
 
 Certains éléments sont constitués d'atomes individuels distincts, comme les gaz nobles hélium, néon et argon. Ces éléments sont appelés des gaz monoatomiques et ont les formules moléculaires respectives He, Ne et Ar. Peu d'éléments existent en tant que molécules constituées de deux atomes ou plus du même élément liés chimiquement. Par exemple, des éléments tels que l'hydrogène, l'oxygène et l'azote existent sous la forme de molécules diatomiques contenant chacune deux atomes, et elles ont donc les formules moléculaires respectives H2, O2 et N2. De même, des éléments tels que le phosphore et le soufre existent sous la forme de molécules polyatomiques avec les formules moléculaires respectives P4 et S8.  
 
 Il est important de noter qu'un indice qui suit un symbole et un nombre devant un symbole ne représente pas la même chose ; par exemple, H2 et 2H représentent clairement des espèces différentes. H2 est une formule moléculaire ; elle représente une molécule diatomique d'hydrogène, composée de deux atomes de l'élément qui sont liés chimiquement. L'expression 2H, d'autre part, indique deux atomes d'hydrogène distincts qui ne sont pas combinés ensemble comme une unité. L'expression 2H2 représente deux molécules d'hydrogène diatomique. 
 
 <h4>Formule empirique </h4>
 
 Les composés se forment lorsque deux éléments ou plus se combinent chimiquement, ce qui entraîne la formation de liaisons. Par exemple, l'hydrogène et l'oxygène peuvent réagir pour former de l'eau, et le sodium et le chlore peuvent réagir pour former du chlorure de sodium, ou du sel de table. Nous décrivons parfois la composition de ces composés avec une formule empirique, qui indique les types d'atomes présents et le rapport le plus simple de nombres entiers d'atomes (ou d'ions) dans le composé. Par exemple, le dioxyde de titane (utilisé comme pigment dans la peinture blanche et dans la crème solaire blanche, épaisse, de type écran total) a une formule empirique TiO2. Cela identifie les éléments titane (Ti) et oxygène (O) comme étant des constituants du dioxyde de titane et indique la présence de deux fois plus d'atomes de l'élément oxygène que d'atomes de l'élément titane. 
 
 Dans de nombreux cas, la formule moléculaire d'une substance est dérivée d'une détermination expérimentale de sa formule empirique et de sa masse moléculaire (somme des masses atomiques pour tous les atomes composant la molécule). Par exemple, on peut déterminer expérimentalement que le benzène contient deux éléments, le carbone (C) et l'hydrogène (H), et que pour chaque atome de carbone du benzène, il y a un atome d'hydrogène. Ainsi, la formule empirique est CH. Une détermination expérimentale de la masse moléculaire révèle qu'une molécule de benzène contient six atomes de carbone et six atomes d'hydrogène, de sorte que la formule moléculaire du benzène est C6H6. 
 
 <h4>Formule structurale </h4>
 
 La formule structurale d'un composé donne les mêmes informations que sa formule moléculaire (les types et les nombres d'atomes dans la molécule) mais montre également comment les atomes sont reliés dans la molécule. En d'autres termes, la formule structurale représente graphiquement la structure moléculaire d'un composé. Elle montre la disposition probable des atomes et la façon dont les atomes sont connectés dans l'espace réel tridimensionnel, donnant plus d'informations sur la géométrie moléculaire. Les lignes sont utilisées pour représenter les liaisons présentes entre les atomes. La formule peut également représenter les angles de liaisons approximatifs, ce qui donne une idée de la forme de la molécule.  
 
 Ce texte est adapté de <a href="https://openstax.org/books/chemistry-2e/pages/2-4-chemical-formulas">Openstax Chemistry 2e, Section 2.4 : Formules chimiques.</a>

Formules chimiques

Une formule chimique présente des informations sur les proportions d’atomes constituant un composé chimique ou une molécule particulière, principalement à l’aide de symboles de ...

Education

Enseignement

Book

Chimie

Molecules, Compounds, and Chemical Equations

Molécules, composés et équations chimiques

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

Des scientifiques en action

key terms

Termes clés

key relationships & equations

Relations et équations clés

chapter exercises

Exercices du chapitre

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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

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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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