UNIT 3

Molecules

MoleculesChemistry happens among the

electrons.

Bonds occur between atoms as a result of interactions among the electrons.

When the interaction is to share electrons, the bond is said to be covalent and the entity formed is a molecule.

Formed from nonmetals.

H

H – O – H

Structural formula

O

This is a molecule of water.

H2O

chemical (molecular) formula

H

Properties of Molecular Compounds

held together by covalent bonds

form discrete molecules soft low melting point generally nonconductive includes all organic

compounds

held together by ionic bonds

do NOT form discrete molecules

hard, rigid, brittle high melting points conductive when melted

or when dissolved in water

Properties of Ionic Compounds

Diatomic Molecules

When two atoms of the same element form a covalent bond, the result is a diatomic molecule.

Seven nonmetal elements exist as diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2

H H+ H – H

(H2)

Hydrogen exists naturally as a diatomic molecule.

1 18

1 H22 13 14 15 16 17

2 N2 O2 F2

33 4 5 6 7 8 9 10 11 12

Cl2

4 Br2

5 I2

6

7

Elements that exist as diatomic molecules

Molecular Formulas

A molecular formula shows the number and type of elements in a molecule, e.g., the molecular formula for glucose is C6H12O6. An empirical formula gives only the relative number and type of elements, e.g., the empirical formula for glucose is CH2O.

When only one atom of an element is present, no subscript is written.

The molecular formula for water is H2O. The empirical formula for water is H2O.

Nomenclature (Naming)

Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Naming Binary Molecular Compounds

1. Name the element farther to the left on the periodic table. (Exception: O is written last unless it’s bonded to F.)

2. If both elements are in the same group, name the lower one first.

3. Give the anion name of the second element (-ide ending).

4. Greek prefixes give the number of each atom in the formula. mono- 1

di- 2

tri- 3

tetra- 4

penta- 5

hexa- 6

hepta- 7

octa- 8

nona- 9

deca- 10

CO carbon monoxide

CO2 carbon dioxide

P4O10 tetraphosphorus decaoxide

N2O dinitrogen monoxide

Nomenclature (Naming)

Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Acids Are compounds that produce hydrogen ions (H+) in water.

They are molecular compounds that ionize in water. “aq” is short for aqueous which means water.

HCl(g) H+(aq) + Cl - (aq)

or, more correctly, the hydronium ion (H3O+)

HCl(g) + H2O H3O+ (aq) + Cl - (aq)

In general, acids are compounds of with a formula of HX, H2X, H3X, etc. where X can be an anion from Group 6A or 7A or X can be an oxyanion.

Naming Acids with an Anion Name Which Ends in –ide

NOT IN SOLUTION, the name of the acid is just the name of the binary molecular compound: HCl(g) is hydrogen chloride

IN SOLUTION, replace hydrogen with hydro- change –ide to –ic add the word “acid” HCl(aq) is hydrochloric acid

Nomenclature (Naming)

Inorganic compounds binary ionic compounds hydrates binary molecular compounds acids with anion name of -ide acids with anion name of -ate or -ite

Naming Ternary (Acids with an Anion That Ends in –ate or -ite)

Modify the oxyanion name: -ate anion becomes –ic

nitrate becomes nitric -ite anion becomes –ous

nitrite becomes nitrousthen add the word “acid”

sulfuric acidsulfurous acid

sulfate: SO42- H2SO4

sulfite: SO32- H2SO3

perchlorate: ClO4- HClO4

chlorate: ClO3- HClO3

chlorite: ClO2- HClO2

hypochlorite: ClO- HClO

perchloric acidchloric acidchlorous acidhypochlorous acid

Names of Common Chemicals

common name or use

chemical name formula

water water H2O

ammonia, window cleaner

ammonia NH3(aq)

natural gas Methane (70%) CH4

vinegar acetic acid (5% solution)

CH3COOH

or HC2H3O2

Names of Common Chemicals

common name or use

chemical name formula

hydrogen peroxide hydrogen peroxide H2O2

drinking alcohol ethanol, ethyl alcohol C2H5OH

rubbing alcohol isopropyl alcohol, 2-propanol

CH3CH(OH)CH3

nail polish remover acetone CH3COCH3