Lesson 2.2 - Element Patterns

Patterns in the periodic table

The periodic table has many patterns.

In this lesson, we will learn about how we can predict the properties of elements, using the periodic table.

Electron shells

The number of electron shells is the same as the period of the element.

Carbon (C) is in Period 2, and so has 2 electron shells.

Krypton (K) is in Period 4, and so has 4 electron shells.

Note: The outer shell may not be full. Carbon has 2 total shells, but only the first is full.

Outer electrons

The number of electrons in the outer shell is determined by the group of the element.

The number of outer electrons is almost always the same as the group.

The exception: Group 0 has a full outer shell (usually 8 electrons).

Element	Group	Outer electrons
Oxygen	6	6
Carbon	4	4
Sodium	1	1
Fluorine	7	7
Argon	0	8