Groups and Periods

Part of the Atomic Structure section of Coddy's Chemistry journey. Lesson 30 of 45.

A row is a period: the period number is the number of shells an atom uses. Sodium, 2, 8, 1, uses three shells: period 3.

The first four periods with group numbers above the columns and period numbers beside the rows, sodium and chlorine ringed

Columns are groups, rows are periods

A column is a group. Atoms in a group have the same number of outer electrons, so they react alike.

Groups 1 and 2: the group number is the number of outer electrons. Groups 13 to 18: add 10. Chlorine, 1s² 2s² 2p⁶ 3s² 3p⁵, has 7 electrons in shell 3, so it is in period 3, group 17.

Chlorine as shells: 2, 8, 7, with the outer shell ringed

Chlorine: 3 shells (period 3), 7 outer electrons (group 17)

Challenge

Six cards come with their configurations: N 1s² 2s² 2p³, Ne 1s² 2s² 2p⁶, Mg 1s² 2s² 2p⁶ 3s², P 1s² 2s² 2p⁶ 3s² 3p³, Cl 1s² 2s² 2p⁶ 3s² 3p⁵ and K 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹. Put each one in its box.

Try it yourself

Periodic tablePut each card in its cell