Basic Concepts in Bonding Ionic Bonding In an

Basic Concepts in Bonding Ionic 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.

Basic Concepts in Bonding Covalent 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.

Chemical Formulas – Subscripts in a formula indicate the number of each atom that is present (no subscript = only 1 atom). • i. e. C 6 H 12 O 6 has 6 C atoms, 12 H atoms, and 6 O atoms. – Subscripts outside of parentheses affect all atoms inside the parentheses. • i. e. (NH 4)2 CO 3 has 2 N atoms, 8 H atoms, 1 C atom, and 3 O atoms. – How many oxygen atoms in each of the following? • Ca. SO 4 four • Al(OH)3 three • Mg(C 2 H 3 O 2)2 four

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 Compounds EX: What is the formula of calcium nitride? 1. Find the charge of each ion in the compound calcium Ca 2+ nitrogen N 3 - 2. 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. “crossover method” Ca 3 N 2 If necessary, simplify to the molecular formula.

• 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 Formula Compound Name Calcium Oxygen Ca. O calcium oxide Sodium Sulfur Na 2 S sodium sulfide Potassium Fluorine KF potassium fluoride Beryllium Chlorine Be. Cl 2 beryllium chloride Aluminum Oxygen Al 2 O 3 aluminum oxide

• 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 1 A elements Group 2 A elements Aluminum Zinc Cadmium Silver +1 ion +2 ion +3 ion +2 ion +1 ion

• For all other metals, the stock naming system with Roman Numerals is used. For example: – Fe 2+ can bond with Cl- to form Fe. Cl 2 – Fe 3+ can bond with Cl- to form Fe. Cl 3 – We cannot refer to both compounds as “iron chloride”, so the stock naming system must be used. – Fe. Cl 2 is called “iron (II) chloride”. – Fe. Cl 3 is called “iron (III) chloride”. – The roman numeral given in parentheses indicates the oxidation state (charge) that iron forms in each compound.

• Polyatomic Ions – Consist of multiple atoms covalently bonded together that have gained or lost electrons. Ammonium Ion (NH 4)+ Sulfate Ion (SO 4)2 -

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 Monoxide NO 2 = Nitrogen Dioxide N 2 O = Dinitrogen Monoxide N 2 O 3 = Dinitrogen Trioxide N 2 O 5 = Dinitrogen Pentoxide Number 1 2 3 Prefix Mono. Di. Tri- 4 5 6 7 8 9 10 Tetra. Penta. Hexa. Hepta. Octa. Nona. Deca-

• Write formulas for the following compounds: – Sodium Nitrate – Aluminum Hydroxide – Potassium Chromate – Calcium Phosphate • Name the following compounds: – Ca(Cl. O 3)2 – Ba(OH)2 – Mg. CO 3 – Li 3 PO 4

• Write formulas for the following compounds: – Manganese (II) oxide – Nickel (III) nitrate – Cobalt (II) sulfate – Gold (I) chloride • Name the following compounds: – Cu. Cl 2 – Fe 2 O 3 – Pb. SO 4 – Sn. O 2

• Write formulas for the following compounds: – Carbon tetrachloride – Iron (III) hydroxide – Sulfur hexafluoride – Zinc oxide • Name the following compounds: – P 2 O 3 – Al. Cl 3 – Cu. SO 4 – CO

• Write formulas for the following compounds: – Phosphorus trihydride – Magnesium sulfate – Titanium (IV) chloride – Sodium hydrogen phosphate • Name the following compounds: – Na. Cl. O 2 – Cu 2 S – Si. F 4 – Ba(NO 3)2