Everything Science Grade 10

CHAPTER 4. THE ATOM 4.6

1s

2s

3s

4s

2p

3p

E N E R G Y

First mainenergy level

Second mainenergy level

Third mainenergy level

Figure 4.9: The positions of the first ten orbitals of an atom on an energy diagram.

• An electron will occupy an orbital on its own, rather than share an orbital with
  another electron. An electron would also rather occupy a lower energy orbitalwith
  another electron, before occupying a higher energy orbital. In other words, within
  one energy level, electrons will fill an s orbital before starting to fill p orbitals.


• The s subshell can hold 2 electrons


• The p subshell can hold 6 electrons

The way that the electrons are arranged in an atom is called itselectron configuration.

Tip

When there are two

electrons in an or-

bital, the electrons

are called anelectron

pair. If the orbital

only has one electron,

this electron is said to

be anunpaired elec-

tron. Electron pairs

are shown with ar-

rows pointing in op-

posite directions.

DEFINITION: Electron configuration

Electron configuration is the arrangement of electrons in an atom, molecule

or other physical structure.

Aufbau diagrams ESABH

An element’s electron configuration can be represented usingAufbau diagramsor energy
level diagrams. An Aufbau diagram uses arrows to represent electrons. You can use the
following steps to help you to draw an Aufbau diagram:

Chemistry: Matter and Materials 81