1. The Periodic TableSection 2 The Role of Electrons 〉 Why do elements within a group of the periodic table have similar chemical properties? 〉 The periodic trends in the periodic table are the result of electron arrangement.

2. The Periodic TableSection 2 The Role of Electrons, continued Valence electrons account for similar properties. An element’s location in the periodic table is related to electron arrangement. –Example: Lithium and sodium, in Group 1, each have one valence electron.

3. The Periodic TableSection 2 Ion Formation 〉 What happens to an atom that gains or loses electrons? 〉 If an atom gains or loses electrons the atom has a net electric charge, because it no longer has an equal number of electrons and protons. The charges do not cancel completely.

4. The Periodic TableSection 2 Ion Formation, continued Group 1 elements form positive ions. Group 17 elements form negative ions. –The single valence electron is easily removed. –The addition of one valence electron fills the outer energy level.

5. The Periodic TableSection 2 How Are Elements Classified? 〉 What are the three main categories of elements? 〉 All elements are either metals, nonmetals, or semiconductors.

6. The Periodic TableSection 2 How Are Elements Classified?, continued Elements in each category have similar properties. –metal: an element that is shiny and that conducts heat and electricity well –nonmetal: an element that conducts heat and electricity poorly –semiconductor (or metalloid): an element or compound that conducts electric current better than an insulator does but not as well as a conductor does