CHEMICAL BONDING and CHEMICAL INTERACTIONS PSc.2.2 OBJECTIVE: Understand chemical bonding and chemical interactions. Objectives PSc.2.2.1 –Infer valence electrons, oxidation number, and reactivity of an element based on its location on the Periodic Table. Bonding and Molecules The outer electrons are involved in bonding. These are called valence electrons. Bonding and Molecules Most stable atoms have eight valence electrons. When an atom has 8 valence electrons, it is said to have an octet of electrons. The Octet Rule Oxidation Number An oxidation number indicates how many electrons are lost, gained, or shared when bonding occurs. 1A 2A The elements in the A groups 8A 0 are called the representative 3A 4A 5A 6A 7A elements. 1A Group 1A elements have one valence electron. They form 1+ ions after losing the one valence electron. 1+ is referred to as the oxidation number for Group 1A elements. 2A Group 2A elements have two valence electrons. They form 2+ ions after losing the 2 valence electrons. 2+ is referred to as the oxidation number for Group 2A elements. Group 3A elements have three valence electrons. They form 3+ ions after losing the 3 valence electrons. 3+ is referred to as the oxidation number for Group 3A elements. 3A Group 4A elements have four valence electrons. They form 4+ ions after losing the 4 valence electrons. They could just as easily form 4- ions after gaining four additional electrons. 4A Group 4A elements could have a 4+ or 4oxidation number, depending on the element with which they are bonding. 4A Group 4A Two elements in Group 4A have multiple oxidation numbers of 2+ and 4+. These two elements are tin (Sn) and lead (Pb). Group 5A elements have five valence electrons. They form 3- ions after gaining 3 additional electrons. 3- is referred to as the oxidation number for Group 5A elements. 5A Group 6A elements have six valence electrons. They form 2- ions after gaining 2 additional electrons. 2- is referred to as the oxidation number for Group 6A elements. 6A Group 7A elements have seven valence electrons. They form 1- ions after gaining 1 additional electron. 1- is referred to as the oxidation number for Group 7A elements. 7A Group 8A elements have eight valence electrons, except helium which only has 2. Group 8A elements, with a full complement of valence electrons, are generally not reactive. 8A Question How many valence electrons are in an atom of each of the following elements? a) Magnesium (Mg) (2) b) Selenium (Se) (6) c) Tin (Sn) (4) Question Determine the oxidation number of each of the following elements. a) Potassium (K) b) Chlorine (Cl) c) Tin (IV) (Sn) (1+) (1-) (4+) Reactivity of Metals In general, the reactivity of metals increases from top to bottom and decreases from left to right. Reactivity of Metals Reactivity of Nonmetals In general, the reactivity of nonmetals increases from left to right and decreases from top to bottom.