Ionic Bonding Objectives: 1. Describe the characteristics of an ionic bond. 2. State the octet rule. 3. Draw a Lewis dot diagram to show the valence electrons of an atom. 4. Distinguish between cations, anions, and polyatomic ions. Key Terms: ionic bond, covalent bond, ionic compound, cation, anion, octet rule, monatomic ion, polyatomic ion, binary ionic compound, empirical formula

Ionic bonds & Compounds Ionic bonding is the result of the attraction of oppositely charged ions (atoms) or polyatomic ions (atom groups). Here are some simple rules for ion formation and naming. – Cations - positively charged ions, usually formed from the metals on IA, IIA, B & IIA & IVA groups – anions - negatively charged ions, usually formed from the nonmetals in VA, VIA & VIIA groups – Ionic compounds consist of entirely ionic bonds and have a net charge of 0 The ionic compound is electronically neutral (positive charges = negative charges) Ions and ionic compounds are frequently more stable than their parent atoms

Properties of Ionic Compounds The properties of ionic compounds are more similar to the nonmetals than the metals and include: – High melting points – relatively strong bonds crystalline structure Tend to be brittle - exhibits cleavage or fracture – Most dissolve in water to form electrolyte solutions - a solution that is a good conductor of electricity Poor conductors in the solid state

Octet Rule The octet rule was a major breakthrough in the understanding of chemical bonding. – States that atoms will gain or loose electrons to fill their valence orbitals. Or more simply stated. The atoms will loose or gain electrons to become more like the nearest noble gas. (Atoms generally have 8 valence electrons (H & He are the exception with 2 valence electrons) Most representative (main periodic) elements follow this ionic pattern (most transitional and rare elements do not) – Group IA (1) will loose 1 (1 + Charge) – Group IIA (2) will loose 2 (2 + Charge) – Group VIIA (17) will gain 1 (1 - Charge) – Group VIA (16) will gain 2 (2 - Charge) – Group VA (15) will gain 3 (3 - Charge)

Lewis Dot Diagrams Lewis Dot diagrams are an easy way to display the 4 valence orbitals involved in bonding. The element name is abbreviated and dots are filled in around the element based on the number of valence electrons present. – An imaginary box is drawn around the element – Dots (electrons) are filled in one side at a time, not doubling up until all 4 sides are full – No more than 2 dots can be present on any side Elements with only 2 electrons will have the dots on opposite sides