periodictrends

A Short Review of Atomic Structure, Periods & Groups
2005 - Mr. Gilliland, Honors Physical Science @ Sarasota High

In Chapter 5 & 6 you learned how scientists, through indirect evidence, discovered the structure of the atom. An atom consists of three particles:

Particle	Symbol	Charge	Location	Mass	Importance
Proton	P⁺	Positive	Nucleus	1 AMU	Identifies the element
Neutron	N^o	Neutral	Nucleus	1 AMU	Isotopes
Electron	e^-	Negative	energy levels outside the nucleus	O AMU	Determines chemical activity

You also learned that electrons are found in certain energy levels outside the nucleus. The MAXIMUM number of electrons in an energy level is:

Energy Level
Maximum number of electrons

1st 2

2nd 8

3rd 18

4th 32

5th 18

6th 8

7th 2

Using the periodic table you can construct the Bohr model of an atom.

The period number tells you how many electron energy levels there are in the atom. Hydrogen and Helium (period 1 elements) have one energy level, period 2 elements have 2 e- energy levels, period 3 elements have 3 e- energy levels... and so on.
The family (group) number tells you the number of electrons in the outer energy level (valence electrons). The electrons in the last energy level are called valence electrons.

Lithium is in period 2, group 1A (Alkali Metals). Here is a model of a Lithium atom:

View movie of Families and Groups

Click on the element that has an e- configuration of 2,8,18,6?

Energy Level	Maximum number of electrons
1st	2
2nd	8
3rd	18
4th	32
5th	18
6th	8
7th	2