Electron configuration

Electron configuration

by Roy Mathews

​In an atom, the negatively charged electrons are found outside the nucleus in different shells or energy levels. The way electrons are placed in their electron shells is called electron configuration or simply electron arrangement. Number of electrons in the outer shell of an atom is called valence electrons. These are the electrons that are either transferred or shared with other atoms during chemical reactions.

​Rules

​(Note: These rules apply only for the first 20 elements)

• ​The first shell, the one closest to the nucleus, can hold only a maximum of 2 electrons.

• ​The second and third shell can hold a maximum of 8 electrons.

• ​Any extra electrons are placed in the fourth shell.

• ​Inner shells are filled before any electrons are placed in the outer shell.

Multiple Choice

State the maximum number of electrons that can be placed in the first electron shell of an atom.

• 1

• 2

• 6

• 8

Multiple Choice

State the maximum number of electrons that can be placed in the second electron shell of an atom.

• 2

• 8

• 16

• 24

Multiple Choice

State the maximum number of electrons that can be placed in the third electron shell of an atom.

• 2

• 14

• 16

• 8

Multiple Choice

A chlorine atom has 17 electrons. Its electron configuration must be:

• 2. 8. 7

• 10. 7

• 3. 7. 7

• 8. 2. 7

Multiple Choice

The electron arrangement of a calcium atom can be written as 2. 8. 8. 2. What must be the atomic number of calcium?

• 40

• 20

• 2

• 18

Multiple Choice

The electron arrangement of a calcium atom can be written as 2. 8. 8. 2. How many valence electrons are there in a calcium atom?

• 2

• 8

• 20

• 18

Multiple Choice

This diagram shows the electron arrangement of a sulfur atom. How many protons must be there in a sulfur atom?

• 2

• 8

• 18

• 16

Multiple Choice

A sulfur atom has 16 neutrons in its nucleus and its electron arrangement is shown in the diagram. What would be the atomic mass of sulfur?

• 16

• 2

• 8

• 32

Open Ended

Write down the electron arrangement for a potassium ( ₁₉K) atom.

Open Ended

Write down the electron arrangement for a Neon (₁₀Ne) atom an Argon (₁₈Ar) atom. Explain in what ways these two atoms are similar.

Open Ended

Write down the electron arrangement for an oxygen atom (₈O)