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

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

Os compostos químicos são substâncias constituídas por dois ou mais elementos de proporções específicas. Para descrever com precisão estes compostos químicos foram desenvolvidas fórmulas. A fórmula química disponibiliza informação sobre os elementos e o número de íons ou átomos envolvidos.Os elementos são representados pelo seu símbolo químico, enquanto o número relativo de íons ou átomos é indicado com um número subscrito. Por exemplo, o açúcar ou sacarose é um composto que contém elementos de carbono, hidrogênio, e oxigênio-representados pelos seus símbolos C, H, e O.Os números doze, vinte e dois e onze indicam o número total de átomos de carbono, hidrogênio e oxigênio presentes no composto. Em geral, os elementos não estão por ordem alfabética, mas começam com o que tem mais carga positiva, ou elementos metálicos, seguido do que tem mais carga negativa, ou menos elementos metálicos, como o hidróxido de potássio.As fórmulas químicas estão divididas em moleculares, empíricas e estruturais. As fórmulas moleculares descrevem um composto através da indicação de cada elementos e do número exato de átomos presentes. A fórmula molecular da glicose é C_6H_12O_6, o que significa que a glicose é composta por seis átomos de carbono, doze átomos de hidrogênio e seis átomos de oxigênio.A fórmula empírica apresenta a mais simples proporção de número inteiro de átomos dos elementos presentes. Na glucose, a mais simples proporção de átomos de carbono, hidrogénio e oxigénio é 1:2:1 originando a fórmula empírica de CH_2O. A fórmula molecular de um composto é também um número inteiro múltiplo da sua fórmula empírica.Na glicose, a multiplicação da sua fórmula empírica com o número inteiro seis dá a sua fórmula molecular. Em contrapartida, a fórmula estrutural apresenta a relação entre os átomos individuais graficamente. Os símbolos químicos representam átomos, e as linhas curtas simbolizam as ligações químicas.As linhas simples representam ligações simples enquanto que duas ou três linhas simbolizam ligações duplas e triplas, respetivamente. Modelos ampliados da fórmula estrutural tais como o desenho em perspectiva, o modelo ball-and-stick, ou o modelo de preenchimento de espaço, disponibilizam várias perspectivas tridimensionais sobre a forma molecular. De entre as três fórmulas químicas, a fórmula estrutural disponibiliza a maior parte das informações sobre o material químico, seguida da fórmula molecular.A fórmula empírica é a menos informativa.

fórmulas químicas

Uma fórmula química apresenta informações sobre as proporções de átomos que constituem um determinado composto ou molécula química, principalmente utilizando símbolos de elementos e números. Às vezes outros símbolos, tais como traços, parênteses, parênteses rectos, vírgulas, sinais de mais e menos, também são usados. Uma fórmula química pode ser de três tipos – molecular, empírica, e estrutural.

<h4>Fórmula Molecular</h4>

A fórmula molecular representa uma molécula ou um composto químico utilizando símbolos químicos (para indicar os tipos de átomos) e números subscritos (para mostrar o número de átomos de cada tipo na molécula). Fórmulas moleculares também são usadas como abreviações para os nomes de compostos.

Alguns elementos consistem em átomos individuais discretos, como os gases nobres hélio, néon, e árgon. Tais elementos são chamados de gases monatómicos e têm fórmulas moleculares He, Ne e Ar, respectivamente. Poucos elementos existem como moléculas feitas de dois ou mais átomos do mesmo elemento ligados quimicamente. Por exemplo, elementos como hidrogénio, oxigénio, e azoto existem como moléculas diatómicas contendo dois átomos cada um e, assim, têm as fórmulas moleculares H2, O2, e N2, respectivamente. Da mesma forma, elementos como fósforo e enxofre existem como moléculas poliatómicas com fórmulas moleculares P4 e S8, respectivamente. 

É importante notar que um subscrito a seguir a um símbolo e um número à frente de um símbolo não representam a mesma coisa; por exemplo, H2 e 2H representam espécies distintamente diferentes. H2 é uma fórmula molecular; representa uma molécula diatómica de hidrogénio, composta por dois átomos do elemento que são ligados quimicamente. A expressão 2H, por outro lado, indica dois átomos de hidrogénio separados que não estão combinados como uma unidade. A expressão 2H2 representa duas moléculas de hidrogénio diatómico.

<h4>Fórmula Empírica </h4>

Os compostos são formados quando dois ou mais elementos se combinam quimicamente, resultando na formação de ligações. Por exemplo, hidrogénio e oxigénio podem reagir para formar água, e sódio e cloro podem reagir para formar cloreto de sódio ou sal de mesa. Algumas vezes descrevemos a composição desses compostos com uma fórmula empírica, que indica os tipos de átomos presentes e a mais simples relação de número inteiro do número de átomos (ou iões) no composto. Por exemplo, o dióxido de titânio (usado como pigmento em tinta branca e no tipo de protector solar espesso, branco, bloqueador) tem uma fórmula empírica de TiO2. Isto identifica os elementos titânio (Ti) e oxigénio (O) como os constituintes do dióxido de titânio e indica a presença de duas vezes mais átomos do elemento oxigénio do que átomos do elemento titânio.

Em muitos casos, a fórmula molecular de uma substância é derivada de uma determinação experimental tanto da sua fórmula empírica como da sua massa molecular (a soma das massas atómicas para todos os átomos que compõem a molécula). Por exemplo, pode-se determinar experimentalmente que o benzeno contém dois elementos, carbono (C) e hidrogénio (H), e que para cada átomo de carbono no benzeno há um átomo de hidrogénio. Assim, a fórmula empírica é CH. Uma determinação experimental da massa molecular revela que uma molécula de benzeno contém seis átomos de carbono e seis átomos de hidrogénio, de modo que a fórmula molecular para o benzeno é C6H6.

<h4>Fórmula Estrutural</h4>

A fórmula estrutural de um composto dá a mesma informação que a sua fórmula molecular (os tipos e números de átomos na molécula), mas também mostra como os átomos estão ligados na molécula. Por outras palavras, a fórmula estrutural representa a estrutura molecular de um composto graficamente. Mostra o arranjo provável dos átomos e como os átomos estão ligados no espaço tridimensional real, dando mais informações sobre a geometria molecular. As linhas são usadas para representar as ligações presentes entre os átomos. A fórmula também pode representar os ângulos de ligação aproximados, dando uma sensação da forma da molécula. 

Este texto é adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/2-4-chemical-formulas">Openstax Chemistry 2e, Section 2.4: Chemical Formulas.</a>

Fórmulas Químicas

Uma fórmula química apresenta informações sobre as proporções de átomos que constituem um determinado composto químico ou molécula, principalmente usando símbolos de ...

Education

Book

Química

Molecules, Compounds, and Chemical Equations

Moléculas, Compostos e Equações Químicas

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

Cientistas em Ação

key terms

Termos Principais

key relationships & equations

Relações e Equações Principais

chapter exercises

Exercícios do Capítulo

appendices

Apêndices

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

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The Scientific Method

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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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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

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Elements: Chemical Symbols and Isotopes

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

PS.Chm.1.1

Radioactivity and Nuclear Equations

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Types of Radioactivity

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Alpha (&#945;) decay is the ...

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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

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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

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

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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

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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

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

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Electron Affinity

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



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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

Types of Chemical Bonds

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Lewis Symbols and the Octet Rule

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Ionic Bonding and Electron Transfer

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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 ...

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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

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Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

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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:


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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

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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, ...

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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