Basic Concepts in BondingCovalent Bonding• Atoms share electrons in covalent bonds, forming

a molecular compound.• Covalent bonding occurs between two non-

metals or between a non-metal and a metalloid.• The simplest unit of a molecular compound is a

molecule.

Basic Concepts in BondingIonic Bonding• In an ionic compound, bonding typically occurs

between a metal and a non-metal or a metal and a polyatomic ion.

• Ionic compounds are held together by ionic bonds formed from the electrostatic attractions between charged particles. – Cations – positively charged ion– Anions – negatively charged ion

• Ionic compounds consist of large numbers of ions held together in a lattice structure.

• As a result, they do not exist as single molecules. Instead, a formula unit represents the simplest ratio of atoms in an ionic compound.

Chemical Formulas– Subscripts in a formula indicate the number of each

atom that is present (no subscript = only 1 atom). • i.e. C6H12O6 has 6 C atoms, 12 H atoms, and 6 O atoms.

– Subscripts outside of parentheses affect all atoms inside the parentheses. • i.e. (NH4)2CO3 has 2 N atoms, 8 H atoms, 1 C atom, and 3 O

atoms. – How many oxygen atoms in each of the following?• CaSO4

• Al(OH)3

• Mg(C2H3O2)2

Valence Electrons• Valence electrons – the outermost electrons in an

atom that are involved in forming bonds. • The Octet Rule – atoms tend to form chemical

bonds in order to reach a total of 8 valence electrons.

• Using the octet rule, it is possible to predict the type of ion that an element is likely to form in a compound (see next slide).

Remember: elements in the same group have the same number of valence electrons. Atoms tend to form bonds to reach eight valence electrons in their outer energy level.

Writing Formulas for Ionic Compounds1. Find the charge of each ion in the compound2. Check to see if the + and – charges are equal.3. If the charges are not equal, the charge on one ion

will become the subscript on the other. 4. If necessary, simplify to the molecular formula.

Atom Ion Atom Ion Formula

Calcium Oxygen

Sodium Sulfur

Potassium Fluorine

Beryllium Chlorine

Aluminum Oxygen

• Naming Ionic Compounds– The name of the metal is always written first,

followed by the name of the non-metal with the ending changed to “-ide”.

Atom Atom Formula Compound Name

Calcium Oxygen CaO

Sodium Sulfur Na2S

Potassium Fluorine KF

Beryllium Chlorine BeCl2

Aluminum Oxygen Al2O3

• Polyatomic Ions – Consist of multiple atoms covalently bonded

together that have gained or lost electrons. Ammonium Ion Sulfate Ion (NH4)+ (SO4)2-

• Write formulas for the following compounds: – Sodium Nitrate– Aluminum Hydroxide– Potassium Chromate– Calcium Phosphate

• Name the following compounds: – Ca(ClO3)2

– Ba(OH)2

–MgCO3

– Li3PO4

• Using the octet rule in this way is helpful, however there are many metals which can have a variety of different oxidation states.

• The metals listed in the table below have only one oxidation state.

Group 1A elements +1 ionGroup 2A elements +2 ion

Aluminum +3 ionZinc +2 ion

Cadmium +2 ionSilver +1 ion

• For all other metals, the stock naming system must be used. For example: – Fe2+ can bond with Cl- to form FeCl2

– Fe3+ can bond with Cl- to form FeCl3

–We cannot refer to both compounds as “iron chloride”, so the stock naming system must be used.

– FeCl2 is called “iron (II) chloride”. – FeCl3 is called “iron (III) chloride”.– The roman numeral given in parentheses indicates the

oxidation state (charge) that iron forms in each compound.

• Write formulas for the following compounds: –Manganese (II) oxide– Nickel (III) nitrate– Cobalt (II) sulfate– Gold (I) chloride

• Name the following compounds: – CuCl2

– Fe2O3

– PbSO4

– SnO2

Binary Molecular Compounds– Two elements can often form

covalent bonds in different ratios, so prefixes are used when naming them.

– i.e. nitrogen and oxygen can form a variety of compounds:

NO = Nitrogen MonoxideNO2 = Nitrogen DioxideN2O = Dinitrogen MonoxideN2O3 = Dinitrogen TrioxideN2O5 = Dinitrogen Pentoxide

Number Prefix1 Mono-2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-7 Hepta-8 Octa-9 Nona-

10 Deca-

• Write formulas for the following compounds: – Carbon tetrachloride– Iron (III) hydroxide– Sulfur hexafluoride– Zinc oxide

• Name the following compounds: – P2O3

– AlCl3

– CuSO4

– CO

• Write formulas for the following compounds: – Phosphorus trihydride–Magnesium sulfate– Titanium (IV) chloride– Sodium hydrogen phosphate

• Name the following compounds: – NaClO2

– Cu2S– SiF4

– Ba(NO3)2