The Periodic Table Section 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.

The Periodic Table Section 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.

The Periodic Table Section 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.

The Periodic Table Section 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.

The Periodic Table Section 2

How Are Elements Classified?

〉What are the three main categories of elements?

〉All elements are either metals, nonmetals, or semiconductors.

The Periodic Table Section 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