CHEM 1113: Chemical Bonding and Molecular Geometry

Chemical bond

Refers to the forced holding atoms together to form molecules and solids

Crystal lattice

Structure in which every cation is surrounded by anions and vice versa

Lattice energy

Is the energy released when the solid crystal forms from separate ions in the gas state; it is always exothermic

Formula unit

Basic unit of an ionic compound; smallest, electrically neutral collection of ions

Metals that form only one type of ion

The first type contains a metal whose charge is invariant from one compound to another (e.g., alkali and alkaline earth metals)

Metals that form more than one type of ion

The second type are metals that can vary in charge from one compound to another (e.g., transition metals, inner transition metals, and p-block metals)

Oxyanions

Polyatomic ions that contain oxygen and another elements

Hydrates

Ionic compounds containing a specific number of water molecules associated with each formula unit

Why atoms bond

Chemical bonds form to lower the potential energy between charged particles that compose atoms

Pure (non-polar) covalent bonds

0.0-0.4, electrons shared equally

Polar covalent bonds

0.4-2.0, electrons shared unequally

Ionic bonds

2.0-3.3, electrons transferred

Electronegativity

The ability of an tom to attract bonding electrons to itself

Polymers

A very large molecule that is made up of a number of smaller molecules repeatedly linked together

Monomers

The small molecules that are linked together to form a polymer

Resonance structures

Used when two or more valid Lewis structures can be drawn for the same compound

Formal charge

An electron bookkeeping system that allows us to discriminate between alternative Lewis structures

Bond energy

The amount of energy in the gaseous state that it takes to break one mole of a bond in a compound

Bond breaking

Endothermic; delta H breaking is positive

Bond making

Exothermic; delta H making is negative

VSEPR Theory

Electron groups around the central atom will be most stable when they are as far apart as possible

Acetate

C2H3O2-

Carbonate

CO3 2-

Hydrogen carbonate (or bicarbonate)

HCO3-

Hydroxide

OH-

Nitrite

NO2-

Nitrate

NO3-

Chromate

CrO4 2-

Dichromate

Cr2O7 2-

Phosphate

PO4 3-

Hydrogen phosphate

HPO4 2-

Dihydrogen phosphate

H2PO4-

Ammonium

NH4+

Hypochlorite

ClO-

Chlorite

ClO2-

Chlorate

ClO3-

Perchlorate

ClO4-

Permanganate

MnO4-

Sulfite

SO3 2-

Hydrogen sulfite (or bisulfite)

HSO3-

Sulfate

SO4 2-

Hydrogen sulfate (or bisulfate)

HSO4-

Cyanide

CN-

Peroxide

O2 2-

Lewis Bonding Theory

Predicts many properties of molecules, such as molecular stability, shape, size, and polarity

Bond length

The distance between the nuclei of bonded atoms

Relationship between bond length and its strength

The longer the bond, the weaker it is

Relationship between electrons shared and bond length

The more electrons two atoms share, the shorter the covalent bond

Bond length trend from left to right across a period

Bond length decreases

Bond length trend from top to bottom on a column

Bond length increases