1. Chapter 4 Section 4: Nonmetals and metalloids
Key concepts: What are the properties of nonmetals?
How are the metalloids useful?
Key terms: nonmetal, diatomic molecule, halogen, noble gas, metalloid, semiconductor

2. Properties of nonmetals
A nonmetal is an element that lacks most of the properties of a metal.
They are mostly poor conductors of electricity and heat and are reactive with other elements. Solid nonmetals are dull and brittle.
16 of them are gases at room temperature

3. Chemical properties
Most nonmetals are reactive. Fluorine (F) is the most reactive element known. Atoms of nonmetals usually gain or share electrons when they react with other atoms.

4. Families of nonmetals
The carbon family – in group 14, only carbon is a nonmetal.
The nitrogen family – in group 15, only nitrogen and phosphorous are nonmetals. They usually gain or share 3 electrons when reacting with other elements.
Nitrogen is an example of an element that occurs in nature in the form of a diatomic molecule. A diatomic molecule consists of 2 atoms.

5. Families continued
Oxygen family – group 16, three nonmetals: oxygen, sulfur, and selenium. These elements usually gain or share two electrons when reacting with other elements
Oxygen is highly reactive, so it can combine with ALMOST every other element.

6. Halogen family – group 17, contains Fluorine, chlorine, bromine, iodine, astatine. They are also known as HALOGENS, which means “salt forming”. A halogen atom usually gains or shares one electron when it reacts with other elements.
All of the halogens are very reactive.

7. Families continued
Noble gases – group 18: do not ordinarily form compounds. Usually unreactive.
Hydrogen – one proton and one electron Sometimes they have neutrons. It is rarely found by itself.

8. Metalloids
Along the border between the metals and the non metals are seven elements called metalloids. They have some characteristic of both metals and nonmetals. Brittle, hard, and somewhat reactive.
Their most useful property is their ability to conduct electricity in varying ways.
Good semiconductors – substances that conduct electricity under some conditions but not others.