Classification of Elements

January 13, 2011

Objectives

1. Describe characteristics of metals, nonmetals, and metalloids

2. Define period, periodic law, family, malleable, ductile. valence electrons

3. Describe how elements are arranged on the periodic table

Henry Mosley (1914)

Determined that each atom has a unique number of positive charges.

Discovered isotopes

Rearranged Mendeleyev’s table by their atomic number

Periodic Law

Because properties of elements repeated in an orderly way, it was called periodic.

Properties of elements are a function of their atomic numbers. 

Elements are arranged:

Vertically into Groups or Families

Horizontally Into Periods

Valence Electrons

Number of electrons an element has in its outermost orbital

Families have the same number of valence electrons

Group number tells how many valence electrons each family will have

The group 2 atoms all have 2 electrons in their outer shells

Be (Beryllium)

Atom

Mg (Magnesium) Atom

If you looked at an atom from each element in a period

Each atom has the same number of electron shells.

The period 4 atoms each have 4 electron containing shells

K (Potassium)

AtomFe (Iron) Atom

Kr (Krypton)

Atom

4th Shell

Metals

shiny (they have luster) solids at room temperature good conductors malleable - capable of being

hammered out into thin sheets ductile - drawn out into wire or threads

Located to the left of the zigzag line Most elements are metals Usually have few valence electrons

Non-metals

Can be found as solids, liquids, or gases at room temperature

Typically dull and brittle Poor conductors All non-metals except hydrogen are

found on the right side of the zigzag line

Many valance electrons

Metalloids

Border both sides of the zigzag line each has some of the properties of a

metal and non metal can become good conductors under

certain conditions such as high temperatures

Also called semiconductors