GCSE Chemistry - Electron Arrangement

Understanding Electron Arrangement in Atoms

The Importance of Electron Shells

• Most atoms, like fluorine, have an incomplete outer shell of electrons, which is crucial for their stability.

• Atoms react with others to gain or lose electrons to achieve a full outer shell, essential for stability.

Drawing Electron Arrangements

• Sodium has an atomic number of 11, indicating it has 11 protons and electrons arranged in shells around the nucleus.

• The first shell holds two electrons; the second can hold up to eight. Electrons are added in specific positions before filling them completely.

Stability and Reactivity of Atoms

• A sodium atom is unstable with one electron in its outer shell instead of eight, prompting it to react with other atoms.

• Noble gases (Group 0), like neon, have full outer shells and do not react due to their stable configuration.

Calculating Electron Structures

• To find the electron arrangement for argon (atomic number 18), we fill the shells: 2 in the first, 8 in the second, and 8 in the third.

• This can also be represented numerically as "2, 8, 8" for clarity.

Examples of Electron Configurations

• Calcium (atomic number 20): It has two electrons in its fourth shell but needs to lose these two for stability.

• After losing two electrons, calcium becomes a calcium ion with a +2 charge due to having more protons than electrons.

Understanding Fluorine's Configuration

• Fluorine has an atomic number of nine: it contains two electrons in its first shell and seven in its second (written as "2, 7").