Molecules and Compounds. Bonding Chemical bonds are forces that cause a group of atoms to behave as a unit. Bonds result from the tendency of a system

Molecules and Molecules and CompoundsCompounds

BondingBonding

Chemical bonds are forces that cause Chemical bonds are forces that cause a group of atoms to behave as a unit. a group of atoms to behave as a unit.

Bonds result from the tendency of a Bonds result from the tendency of a system to seek its lowest possible energy.system to seek its lowest possible energy.

Bond breaking always requires Bond breaking always requires energy, and bond formation always energy, and bond formation always releases energy.releases energy.

Types of BondsTypes of Bonds

The type of bonding depends upon the The type of bonding depends upon the nature of the atoms that are combined.nature of the atoms that are combined.

A metal and a non-metal will form A metal and a non-metal will form ionic ionic bondsbonds when electrons are transferred from the when electrons are transferred from the metal to the non-metal. The resulting attraction metal to the non-metal. The resulting attraction between oppositely charged ions forms a stable between oppositely charged ions forms a stable crystal. crystal.

Ionic compounds are usually solids at room Ionic compounds are usually solids at room temperature, with high melting points. They temperature, with high melting points. They conduct electricity only when dissolved in water.conduct electricity only when dissolved in water.


When metals bond with each other, When metals bond with each other, the valence electrons are shared by the the valence electrons are shared by the atoms in the entire crystal. The electrons atoms in the entire crystal. The electrons are no longer associated with a specific are no longer associated with a specific nucleus, and are free to move throughout nucleus, and are free to move throughout the sample.the sample.

Metallic solids tend to be malleable Metallic solids tend to be malleable and ductile. Their melting points can be and ductile. Their melting points can be low (mercury is a liquid at room low (mercury is a liquid at room temperature) to quite high. They conduct temperature) to quite high. They conduct electricity and heat.electricity and heat.


When non-metals bond with each When non-metals bond with each other (water, carbon dioxide, nitrogen), other (water, carbon dioxide, nitrogen), electrons are shared between the atoms electrons are shared between the atoms to form a molecule. to form a molecule. When electrons in When electrons in the bonds are shared between atoms, a the bonds are shared between atoms, a covalent covalent bond is formed.bond is formed.

Covalent molecules are often Covalent molecules are often gaseous or liquids at room temperature. gaseous or liquids at room temperature. The solids tend to be soft and crumbly. The solids tend to be soft and crumbly.

Lewis StructuresLewis Structures

Lewis StructuresLewis Structures, also known as , also known as Lewis dot diagrams, show how the Lewis dot diagrams, show how the valence electrons are arranged valence electrons are arranged among the atoms in the molecule. among the atoms in the molecule.

For ionic compounds, it shows For ionic compounds, it shows the end result when the metal loses the end result when the metal loses its electrons to the non-metal.its electrons to the non-metal.

Lewis Structures – Ionic Lewis Structures – Ionic CompoundsCompounds

A dot (A dot (.. ) is used to represent ) is used to represent each valence electron. Consider each valence electron. Consider sodium chloride. The dot diagram for sodium chloride. The dot diagram for the sodium atom is:the sodium atom is:

NaNa

The dot diagram for the chlorine atom The dot diagram for the chlorine atom is:is:

ClCl

::: .

.


Note that electrons (dots) Note that electrons (dots) representing valence electrons are representing valence electrons are written singly or in pairs on either written singly or in pairs on either side of the atomic symbol, and above side of the atomic symbol, and above and below the symbol.and below the symbol.

NaNa ClClIt doesn’t matter which side has

the unpaired electron.:

: :..

Sodium donates its single valence Sodium donates its single valence electron to the chorine atom, and electron to the chorine atom, and chlorine accepts the extra electron. chlorine accepts the extra electron.

NaNa ClClAfter transfer, both ions have a

noble gas electron configuration.Na+ Cl

:: :

..


: :::-

Lattice EnergyLattice Energy

When metals react with non-When metals react with non-metals, a large amount of energy is metals, a large amount of energy is usually released. These reactions usually released. These reactions are usually are usually exothermicexothermic. .

The electron transfer from the The electron transfer from the metal to the non-metal usually metal to the non-metal usually requires energy, and is requires energy, and is endothermicendothermic..

The large release of energy The large release of energy comes from forming an ionic crystal.comes from forming an ionic crystal.


The crystal will have oppositely The crystal will have oppositely charged ions in contact with each charged ions in contact with each other and like charged ions other and like charged ions separated from each other. The separated from each other. The alternating charged ions form a alternating charged ions form a crystal latticecrystal lattice. As the lattice forms, . As the lattice forms, large amounts of energy are large amounts of energy are released.released.



Lattice energy is defined as the Lattice energy is defined as the energy released when a mole of an energy released when a mole of an ionic solid forms from its constituent ionic solid forms from its constituent gaseous ions. It is usually a large gaseous ions. It is usually a large negative quantity.negative quantity.


Based on CoulombBased on Coulomb’’s Law, the s Law, the lattice energy increases with smaller lattice energy increases with smaller ionic size.ionic size.


Based on CoulombBased on Coulomb’’s Law, the s Law, the lattice energy increases significantly lattice energy increases significantly with greater ionic charge.with greater ionic charge.

E = constant (qE = constant (q11)(q)(q22)/r)/r

Melting PointsMelting Points

As ionic crystals melt, the lattice As ionic crystals melt, the lattice is disrupted, and the ions become is disrupted, and the ions become free to move, and can conduct free to move, and can conduct electricity.electricity.

Ionic BondingIonic Bonding

The strength The strength of the attraction of the attraction between ions between ions increases increases significantly with significantly with increasing ionic increasing ionic charge, and charge, and results in high results in high melting points.melting points.

Ionic vs. Covalent Ionic vs. Covalent CompoundsCompounds

Ionic Compounds Ionic Compounds Crystalline solids Crystalline solids

(made of ions)(made of ions) High melting and High melting and

boiling pointsboiling points Conduct electricity Conduct electricity

when meltedwhen melted Many soluble in Many soluble in

water but not in water but not in nonpolar liquidsnonpolar liquids

Covalent CompoundsCovalent Compounds Gases, liquids, or Gases, liquids, or

solids (made of solids (made of molecules)molecules)

Low melting and Low melting and boiling pointsboiling points

Poor electrical Poor electrical conductors in all conductors in all phasesphases

Many soluble in Many soluble in nonpolar liquids but nonpolar liquids but not in waternot in water

Properties of NaCl and Properties of NaCl and CClCCl44

Naming Inorganic Naming Inorganic CompoundsCompounds

1. Binary Compounds1. Binary Compounds

Binary compounds contain only two Binary compounds contain only two elements. The elements are either elements. The elements are either a metal with a non-metal (ionic a metal with a non-metal (ionic bonding), or two non-metals bonding), or two non-metals (covalent bonding).(covalent bonding).

Naming Binary Naming Binary CompoundsCompounds

a) Metal + Non-metal:a) Metal + Non-metal:

When metals react with non-When metals react with non-metals, the metal loses electrons metals, the metal loses electrons and the non-metal gains electrons. and the non-metal gains electrons. The resulting attraction between The resulting attraction between oppositely charged ions creates oppositely charged ions creates ionic bondsionic bonds. .

Common Ionic ChargesCommon Ionic Charges

The charges of ions of elements The charges of ions of elements in groups 1A-7A (the main groups) in groups 1A-7A (the main groups) are usually predictable. are usually predictable.

Group 1A metals form +1 ions, Group 1A metals form +1 ions, group 2A metals form +2 ions, etc.group 2A metals form +2 ions, etc.

The non-metals of group 5A The non-metals of group 5A have a -3 charge, those of group 6A have a -3 charge, those of group 6A have a -2 charge, and the halogens have a -2 charge, and the halogens form ions with a -1 charge.form ions with a -1 charge.

Typical Ionic ChargesTypical Ionic Charges


For example, NaCl is calledFor example, NaCl is called

sodium chlorsodium chlorideide

Where Where ““chlorchlor”” is the root for the is the root for the element chlorine.element chlorine.


Three common transition metals Three common transition metals also have only one ionic charge, and also have only one ionic charge, and are also named the same way.are also named the same way.

They are: zinc ion (always +2), They are: zinc ion (always +2), silver ion (+1) and cadmium ion (+2)silver ion (+1) and cadmium ion (+2)

ZnS is zinc sulfide, as ZnS is zinc sulfide, as ““sulfsulf”” is is the root for sulfur.the root for sulfur.

Writing Formulas of Binary Writing Formulas of Binary CompoundsCompounds

Compounds have no net charges, so the Compounds have no net charges, so the formulas of ionic compounds must formulas of ionic compounds must contain equal numbers of positive and contain equal numbers of positive and negative charges.negative charges.

Magnesium bromide, made from Magnesium bromide, made from magnesium ion (Mgmagnesium ion (Mg2+2+) and bromide ion ) and bromide ion (Br(Br1-) has the formula

MgBrMgBr22

Binary Compounds with Binary Compounds with Variable Charge MetalsVariable Charge Metals

Most transition metals and the Most transition metals and the metals on the lower right side of the metals on the lower right side of the periodic table can have several ionic periodic table can have several ionic charges.charges.

The properties of the ion vary The properties of the ion vary greatly with charge, so the charge greatly with charge, so the charge must be specified in naming the ion must be specified in naming the ion or its compounds.or its compounds.

Typical Ionic ChargesTypical Ionic Charges



If an ion has variable charges, If an ion has variable charges, you you mustmust specify the charge in specify the charge in naming the metal.naming the metal.

If an ion has only one charge, If an ion has only one charge, it it is incorrectis incorrect to specify its charge. to specify its charge.

Naming FeNaming Fe22OO33

FeFe22OO33 is an iron oxide, but we must specify is an iron oxide, but we must specify the charge of the iron ion.the charge of the iron ion.

We know each oxide has a -2 charge, so We know each oxide has a -2 charge, so three oxide ions have a total charge of -6.three oxide ions have a total charge of -6.

The two iron ions therefore have a The two iron ions therefore have a charge of +6, with charge of +6, with eacheach iron having a charge iron having a charge of +3.of +3.

The name of the compound is iron(III) oxide.The name of the compound is iron(III) oxide.

Unusual IonsUnusual Ions

Mercury forms two ions, Mercury forms two ions, mercury(I) and mercury(II). The mercury(I) and mercury(II). The mercury(I) ion is mercury(I) ion is polyatomicpolyatomic, and , and exists as two mercury(I) ions bonded exists as two mercury(I) ions bonded together. Its formula is Hgtogether. Its formula is Hg22

2+2+..

Oxygen in compounds usually Oxygen in compounds usually exists as the oxide ion, Oexists as the oxide ion, O2-2-. Oxygen . Oxygen also exists as the peroxide ion, Oalso exists as the peroxide ion, O22

2-2-, , with each oxygen having a -1 charge. with each oxygen having a -1 charge.

Naming Polyatomic IonsNaming Polyatomic Ions

There are many ions, such as There are many ions, such as sulfate or nitrate, that contain more sulfate or nitrate, that contain more than one element. than one element.

Many of these ions contain Many of these ions contain oxygen and a non-metal.oxygen and a non-metal.

These ions can be found in a These ions can be found in a group of acids called the group of acids called the oxy acidsoxy acids (such as sulfuric acid, nitric acid, (such as sulfuric acid, nitric acid, etc.).etc.).

Polyatomic IonsPolyatomic Ions

The bonding within these polyatomic The bonding within these polyatomic ions (such as nitrate, sulfate and ions (such as nitrate, sulfate and phosphate) is covalent. The ionic charge phosphate) is covalent. The ionic charge results from the loss of one or more H results from the loss of one or more H ions to water, resulting in a negative ions to water, resulting in a negative charge on the anion formed. charge on the anion formed.

In water, the covalently bonded In water, the covalently bonded hydrogen is donated to water, forming hydrogen is donated to water, forming hydronium ions and the corresponding hydronium ions and the corresponding anion.anion.

Naming the Oxy AcidsNaming the Oxy Acids

The easiest way to learn the The easiest way to learn the names of the ions is to memorize a names of the ions is to memorize a short list of oxy acid names and their short list of oxy acid names and their formulas.formulas.

The names of the ions are The names of the ions are derived from the names of the acids.derived from the names of the acids.

Keep in mind that the acids Keep in mind that the acids must be aqueous solutions.must be aqueous solutions.

Common Oxy AcidsCommon Oxy Acids

AcidAcid NameName

HNOHNO33 Nitric acidNitric acid

HH22SOSO44 Sulfuric acidSulfuric acid

HClOHClO33 Chloric acid (or iodic or bromic Chloric acid (or iodic or bromic acid)acid)

HH33POPO44 Phosphoric acidPhosphoric acid

HH22COCO33 Carbonic acidCarbonic acid

Naming Complex IonsNaming Complex Ions

Once the list of acids is learned, the Once the list of acids is learned, the names of other acids and ions can be names of other acids and ions can be derived.derived.

Removal of the hydrogens in the acid Removal of the hydrogens in the acid as Has H++ ions results in ions that end in ions results in ions that end in ateate..

HNOHNO33 minus one H minus one H++ ion gives NO ion gives NO331-1-, ,

the nitrthe nitrateate ion. ion.

The oxy acids that end in The oxy acids that end in icic, produce , produce ions that end ions that end ateate..


Sulfuric acid is HSulfuric acid is H22SOSO44. Removing two . Removing two HH++ ions produces SO ions produces SO44

2-2-, the sulf, the sulfateate ion. ion.

Keep in mind that the formula of the Keep in mind that the formula of the ions must include the charge.ions must include the charge.

If only one of the HIf only one of the H++ ions is removed ions is removed from sulfuric acid, HSOfrom sulfuric acid, HSO44

1-1- is produced. is produced. This is called the hydrogen sulfate ion, This is called the hydrogen sulfate ion, also commonly known as the bisulfate ion.also commonly known as the bisulfate ion.


Carbonic acid, HCarbonic acid, H22COCO33, produces , produces two ions:two ions:

HCOHCO331-1-, the hydrogen carbonate , the hydrogen carbonate

or or bicarbonate ionbicarbonate ion

andand

COCO332-2-, the carbonate ion, the carbonate ion


Some of the oxy acids previously Some of the oxy acids previously listed also exist with one more oxygen in listed also exist with one more oxygen in the formula.the formula.

HClOHClO33, HBrO, HBrO33 and HIO and HIO33 , in aqueous , in aqueous solution are chloric, bromic and iodic acid solution are chloric, bromic and iodic acid respectively.respectively.

Adding an oxygen to the formulas Adding an oxygen to the formulas provides the formulas for the provides the formulas for the per per root root ic ic acid.acid.

HClOHClO44 is is perperchloric acid. The ion, ClOchloric acid. The ion, ClO441-1- is is

the the perperchlorchlorateate ion. ion.


Several of the oxy acids listed Several of the oxy acids listed previously can have one less oxygen previously can have one less oxygen atom in the formula. These acids atom in the formula. These acids have names that end in have names that end in ousous, and ions , and ions that end in that end in iteite..

HNOHNO33 is nitric acid. HNO is nitric acid. HNO22(aq) is (aq) is nitrnitrousous acid. The ion NOacid. The ion NO22

1-1- is the is the nitrnitriteite ion. ion.


Sulfuric acid, phosphoric acid, Sulfuric acid, phosphoric acid, chloric, bromic and iodic acids all can chloric, bromic and iodic acids all can have one less oxygen atom. The acids have one less oxygen atom. The acids are sulfurous acid, phosphorous acid, are sulfurous acid, phosphorous acid, chlorous acid, bromous acid and iodous chlorous acid, bromous acid and iodous acid.acid.

The ions are called sulfite, The ions are called sulfite, phosphite, chlorite, bromite and iodite phosphite, chlorite, bromite and iodite ion.ion.


The halogen oxy acids HClOThe halogen oxy acids HClO33, , HBrOHBrO33, and HIO, and HIO33 also exist with also exist with twotwo less oxygen atoms in the formula. less oxygen atoms in the formula. The name of the resulting acid has The name of the resulting acid has the name the name

hypo hypo rootroot ous ous acid. acid.

HClO(aq) is HClO(aq) is hypohypochlorchlorous ous acid, acid, and ClOand ClO1-1- is the hypochlorite ion. is the hypochlorite ion.

Naming Complex IonsNaming Complex Ions If you If you memorizememorize the list of acids ending the list of acids ending

in in icic, you can derive the names and , you can derive the names and formulas for many other acids and ions. formulas for many other acids and ions. AcidAcid NameName

HNOHNO33 Nitric acidNitric acid

HH22SOSO44 Sulfuric acidSulfuric acid

HClOHClO33 Chloric acid (or iodic or bromic Chloric acid (or iodic or bromic acid)acid)

HH33POPO44 Phosphoric acidPhosphoric acid

HH22COCO33 Carbonic acidCarbonic acid


In naming the ions from the acids on In naming the ions from the acids on the list, remember that the list, remember that icic ate.ate.

If there is one additional oxygen atom, If there is one additional oxygen atom, the acid has the name the acid has the name perper rootroot icic, and , and the ion has the name the ion has the name per per rootroot ate ate..

If there is one less oxygen atom, the If there is one less oxygen atom, the acid has a name ending in acid has a name ending in ousous. The . The ions will have names ending in ions will have names ending in iteite. . ((ousous ite ite))


If an acid has two less oxygen atoms If an acid has two less oxygen atoms than the than the ““icic”” list, its name has the list, its name has the form form hypohypo root root ousous. The ion will . The ion will have the name have the name hypohypo rootroot iteite..

Other Common FormulasOther Common Formulas

CHCH33COOHCOOH Acetic acidAcetic acid

CHCH33COOCOO1-1- Acetate ionAcetate ion

NHNH33 AmmoniaAmmonia

NHNH44++ Ammonium ionAmmonium ion

OHOH1-1- Hydroxide ionHydroxide ion

HH33OO++ Hydronium ionHydronium ion

MnOMnO441-1- Permanganate ionPermanganate ion

CrOCrO442-2- Chromate ionChromate ion

CrCr22OO772-2- Dichromate ionDichromate ion

Hydrated Ionic Hydrated Ionic CompoundsCompounds

HydratesHydrates are compounds that are compounds that contain a specific number of water contain a specific number of water molecules associated with each formula molecules associated with each formula unit. The water molecules are called unit. The water molecules are called waters of hydrationwaters of hydration, and can usually be , and can usually be removed by heating the compound.removed by heating the compound.

CuSOCuSO44..5H5H22O is copper(II) sulfate O is copper(II) sulfate

pentahydratepentahydrate

Covalent compounds exist as discrete molecules, whereas ionic compounds consist of an aggregate of cations and anions.

Covalent BondingCovalent Bonding

Covalent BondsCovalent Bonds

When two (or more) non-metals When two (or more) non-metals form bonds, electrons are shared. form bonds, electrons are shared. The result is a The result is a covalent bondcovalent bond..

Covalent bonds form because Covalent bonds form because the attraction of electrons for the the attraction of electrons for the nuclei in the atoms is greater than nuclei in the atoms is greater than the electron-electron repulsion or the electron-electron repulsion or the nucleus-nucleus repulsion.the nucleus-nucleus repulsion.


There is There is usually an usually an optimum bond optimum bond length or length or internuclear internuclear distance where distance where attractions attractions between electrons between electrons and the nuclei are and the nuclei are optimized and optimized and repulsions are repulsions are minimized.minimized.

Covalent BondingCovalent Bonding

Bond EnergyBond Energy

Bond formation releases energy, and bond breaking requires energy.

MoleculesMolecules

Molecules are neutral Molecules are neutral combinations of two or more atoms that combinations of two or more atoms that are bonded together and act as a unit.are bonded together and act as a unit.

Molecules may be elements (HMolecules may be elements (H22, , OO22, O, O33, F, F22), or compounds containing ), or compounds containing atoms of different elements bonded atoms of different elements bonded together. Molecules typically contain together. Molecules typically contain elements that are non-metals.elements that are non-metals.

The Diatomic ElementsThe Diatomic Elements

Several common Several common elementsprimarily exist in nature as elementsprimarily exist in nature as molecules containing two atoms. The molecules containing two atoms. The diatomic elements are:diatomic elements are:

HH22, N, N22, O, O22, F, F22, Cl, Cl22, Br, Br22 and I and I22

Lewis Structures – Covalent Lewis Structures – Covalent MoleculesMolecules

In many covalent molecules, the In many covalent molecules, the non-metals share valence electrons. non-metals share valence electrons. Electrons are shared so that each atom Electrons are shared so that each atom in the molecule has a full valence shell.in the molecule has a full valence shell.

HH.. ..HH

HH::H or HH or H....H or HH or H--H H

Each hydrogen has access to two Each hydrogen has access to two electrons, as does the noble gas helium. electrons, as does the noble gas helium.


For elements in period 2, the For elements in period 2, the non-metals generally share enough non-metals generally share enough valence electrons so that each atom valence electrons so that each atom obtains the same number of valence obtains the same number of valence electrons as neon (a total of eight electrons as neon (a total of eight electrons). electrons).

This may involve making This may involve making multiple (double or triple) bonds multiple (double or triple) bonds between atoms.between atoms.


Provide Lewis structures for Provide Lewis structures for elemental nitrogen, oxygen and elemental nitrogen, oxygen and fluorine.fluorine.

Molecular ShapesMolecular Shapes

Lewis structures are drawn on a Lewis structures are drawn on a flat piece of paper, many molecules flat piece of paper, many molecules are three dimensional. In addition, are three dimensional. In addition, the Lewis structure doesn’t the Lewis structure doesn’t necessarily give an accurate idea of necessarily give an accurate idea of the bond angles.the bond angles.

Molecular ShapesMolecular Shapes

Although the Lewis structure suggests a linear molecule, the bond angle in water is approximately 105o.

Naming Covalent Binary Naming Covalent Binary CompoundsCompounds

When two non-metals form a When two non-metals form a compound, they share electrons, rather compound, they share electrons, rather than transfer them. The resulting bond than transfer them. The resulting bond is called a is called a covalent bondcovalent bond..

The naming of these compounds is The naming of these compounds is fairly simple. The first element is named fairly simple. The first element is named first, and the second element is named as first, and the second element is named as the the root + ideroot + ide..

PrefixesPrefixes are used to indicate the are used to indicate the number of each atom present.number of each atom present.


These prefixes are used only for compounds containing two non-metals.

The prefix mono is never used for the first element in the compound.


The prefix The prefix monomono is never used for the is never used for the first element. COfirst element. CO22 is is carbon dioxidecarbon dioxide..

If the prefix ends in an If the prefix ends in an aa or or oo, and the , and the element that follows begins with a element that follows begins with a vowel, the last letter of the prefix is vowel, the last letter of the prefix is usually dropped. Nusually dropped. N22OO55 is called is called dintrogen pentoxidedintrogen pentoxide (and not (and not pentpentaoaoxide).xide).


Note that these prefixes are only Note that these prefixes are only used for binary covalent compounds. It used for binary covalent compounds. It is incorrect to use them for compounds is incorrect to use them for compounds containing a metal and a non-metal.containing a metal and a non-metal.


There are some compounds of There are some compounds of metalloids or metals in very high metalloids or metals in very high oxidation states that are sometimes oxidation states that are sometimes named using this system.named using this system.


For example, compounds such For example, compounds such as SnClas SnCl44 or PbCl or PbCl44 are covalent in are covalent in nature, and not ionic solids. They nature, and not ionic solids. They may be called tin(IV) chloride or tin may be called tin(IV) chloride or tin tetrachloride [or lead(IV) chloride or tetrachloride [or lead(IV) chloride or lead tetrachloride.lead tetrachloride.

Binary Compounds with Binary Compounds with HydrogenHydrogen

With metals, hydrogen can form With metals, hydrogen can form ionic compounds in which the ionic compounds in which the hydrogen has a -1 ionic charge. hydrogen has a -1 ionic charge. These compounds are named like These compounds are named like any binary ionic compound.any binary ionic compound.

NaH is sodium hydrideNaH is sodium hydride

CaHCaH22 is calcium hydride is calcium hydride


With non-metals, the bonding is With non-metals, the bonding is covalent. Hydrogen covalent. Hydrogen nevernever forms a forms a positive ion in nature.positive ion in nature.

Many of the compounds Many of the compounds containing hydrogen have common containing hydrogen have common names that do not follow the usual names that do not follow the usual nomenclature rules.nomenclature rules.


Examples include:Examples include:

water water HH22OO

ammoniaammonia NHNH33

phosphine phosphine PHPH33

hydrogen sulfidehydrogen sulfide HH22SS

Note that the order in which the Note that the order in which the elements are written is also irregular.elements are written is also irregular.

Binary Compounds with Binary Compounds with Hydrogen- AcidsHydrogen- Acids

Hydrogen also forms binary Hydrogen also forms binary compounds that act as acids in compounds that act as acids in water. These compounds water. These compounds dissociatedissociate in water to donate a proton to water.in water to donate a proton to water.

HCl(g) + HCl(g) + HH22O(l) O(l) H H33OO++(aq) (aq) + Cl + Cl––(aq)(aq)

hydrogen chloridehydrogen chloride hydronium hydronium

Naming Binary AcidsNaming Binary Acids

The naming of the pure compound and its aqueous acid solution differ.

HCl is a gas called hydrogen chloride. HCl(aq) is an acid called hydrochoric acid.

Naming Binary AcidsNaming Binary Acids

Name the following acids:Name the following acids:

HH22S(aq) , HBr(aq)S(aq) , HBr(aq)

MoleculesMolecules

Scientists studying the nature of Scientists studying the nature of matter focused much of their research matter focused much of their research in 1800s on the composition of in 1800s on the composition of compounds.compounds.

Since molecules are much too small Since molecules are much too small to observe, they typically observed the to observe, they typically observed the reactions of larger amounts of matter reactions of larger amounts of matter and used mass measurements to and used mass measurements to develop their theories of matter.develop their theories of matter.

Empirical FormulasEmpirical Formulas

The studies of water and hydrogen The studies of water and hydrogen peroxide lead to peroxide lead to empiricalempirical formulas. formulas. These are based on experiment, and These are based on experiment, and represent to simplest way of expressing represent to simplest way of expressing the ratio of atoms in a compound.the ratio of atoms in a compound.

The early scientists analyzed new The early scientists analyzed new chemical compounds to determine their chemical compounds to determine their composition and chemical formulas. composition and chemical formulas. Modern analytical laboratories still Modern analytical laboratories still provide this service.provide this service.

Molecular FormulasMolecular Formulas

Molecular formulas show the exact Molecular formulas show the exact number of each type of atom in a number of each type of atom in a molecule. For example, hydrogen molecule. For example, hydrogen peroxide has a molecular formula of peroxide has a molecular formula of HH22OO22. Its empirical formula shows that . Its empirical formula shows that there is one hydrogen for every oxygen, there is one hydrogen for every oxygen, so it is OH or HO. Neither of these so it is OH or HO. Neither of these formulas provides the structure or formulas provides the structure or arrangement of the bonds in the arrangement of the bonds in the molecule.molecule.

Percent CompositionPercent Composition

A chemical formula can be used A chemical formula can be used to calculate the percent composition to calculate the percent composition of a compound. Likewise, the of a compound. Likewise, the percent composition can be used to percent composition can be used to determine the empirical formula of a determine the empirical formula of a compound. This is extremely useful compound. This is extremely useful when trying to determine the when trying to determine the formula of a new, or unknown formula of a new, or unknown compound.compound.

Chemical CompositionChemical Composition

The formula obtained for the The formula obtained for the compound is the simplest whole compound is the simplest whole number ratio of the elements in the number ratio of the elements in the compound, or the compound, or the empirical formulaempirical formula. . It may differ from the actual It may differ from the actual formula. For example, hydrogen formula. For example, hydrogen peroxide is Hperoxide is H22OO22, but chemical , but chemical analysis will provide an empirical analysis will provide an empirical formula of HO.formula of HO.


To calculate the % composition of To calculate the % composition of a known compound, you determine a known compound, you determine the total mass of the molecule, and the total mass of the molecule, and the mass due to each of the elements the mass due to each of the elements in the compound.in the compound.

% by mass of element A = % by mass of element A =

total mass of Atotal mass of A (100%) (100%)

molecular massmolecular mass


To calculate the % composition of To calculate the % composition of a known compound, you determine a known compound, you determine the total mass of the molecule, and the total mass of the molecule, and the mass due to each of the elements the mass due to each of the elements in the compound.in the compound.

% by mass of element A = % by mass of element A =

total mass of Atotal mass of A (100%) (100%)

molecular massmolecular mass

% Composition Problem% Composition Problem

Problem: Calculate the percent Problem: Calculate the percent composition of ammonia.composition of ammonia.

Determining FormulasDetermining Formulas

It is generally more useful to It is generally more useful to obtain percent composition data obtain percent composition data (usually from a laboratory), and (usually from a laboratory), and determine the empirical formula of a determine the empirical formula of a compound. This will be the simplest compound. This will be the simplest whole number ratio of the elements, whole number ratio of the elements, and provides no information about and provides no information about the structure of the compound.the structure of the compound.

Determining Empirical Determining Empirical FormulasFormulasIf given % compositionIf given % composition::

1. Assume a quantity of 100 grams of 1. Assume a quantity of 100 grams of the compound.the compound.

2. Determine the number of moles of 2. Determine the number of moles of each element in the compound by each element in the compound by dividing the grams of each element dividing the grams of each element by the appropriate atomic mass.by the appropriate atomic mass.

3. To simplify the formula into small 3. To simplify the formula into small whole numbers, divide the moles of whole numbers, divide the moles of each element by the smallest number each element by the smallest number of moles.of moles.

Determining Empirical Determining Empirical FormulasFormulas

4. If necessary, multiply each 4. If necessary, multiply each number of moles by a factor that number of moles by a factor that produces whole number produces whole number subscripts.subscripts.

5. If you know the approximate 5. If you know the approximate molar mass of the compound, molar mass of the compound, determine the molecular formula.determine the molecular formula.

Chemical CompositionChemical Composition

Usually, the compound is Usually, the compound is combusted in the presence of oxygen. combusted in the presence of oxygen. Any carbon in the compound is Any carbon in the compound is collected as carbon dioxide (COcollected as carbon dioxide (CO22), and ), and any hydrogen is collected as water any hydrogen is collected as water (H(H22O).O).

% Composition Problem% Composition Problem

Caffeine contains 49.48% carbon, Caffeine contains 49.48% carbon, 5.15% hydrogen, 28.87% nitrogen, 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen. The compound and 16.49% oxygen. The compound has a molar mass of 194.2. has a molar mass of 194.2. Determine the empirical and Determine the empirical and molecular formula of caffeine. molecular formula of caffeine.


If given combustion dataIf given combustion data::

The ultimate goal is to get the The ultimate goal is to get the simplest whole number ratio of the simplest whole number ratio of the elements in the compound. Usually elements in the compound. Usually the compound contains carbon, the compound contains carbon, hydrogen and perhaps oxygen or hydrogen and perhaps oxygen or nitrogen.nitrogen.

1. Use the information about CO1. Use the information about CO22 to to determine the moles and mass of determine the moles and mass of carbon in the compound.carbon in the compound.


If given combustion dataIf given combustion data::

2. Use the information about H2. Use the information about H22O to O to determine the moles and mass of determine the moles and mass of

hydrogen hydrogen in the compound.in the compound.

3. The mass and moles of oxygen (or a 3. The mass and moles of oxygen (or a third element) can be obtained by third element) can be obtained by difference.difference.

4. Once moles of each element is 4. Once moles of each element is obtained, find the relative number of obtained, find the relative number of moles and empirical formula (as with moles and empirical formula (as with % composition).% composition).

Formulas Formulas from from Combustion Combustion DataData

This method assumes the compound contains only C and H.

Empirical Formula using Empirical Formula using Combustion Data- ProblemCombustion Data- Problem

A compound, which contains C, H A compound, which contains C, H and O, is analyzed by combustion. If and O, is analyzed by combustion. If 10.68 mg of the compound produces 10.68 mg of the compound produces 16.01 mg of carbon dioxide and 4.37 16.01 mg of carbon dioxide and 4.37 mg of water, determine the mg of water, determine the empirical formula of the compound.empirical formula of the compound.

If the compound has a molar mass If the compound has a molar mass of 176.1 g/mol, determine the of 176.1 g/mol, determine the molecular formula of the compound.molecular formula of the compound.

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Molecules and Compounds. Bonding Chemical bonds are forces that cause a group of atoms to behave as a unit. Bonds result from the tendency of a system