Periods

Definition

Periods are the horizontal rows in the periodic table. They indicate the number of electron shells an atom possesses.

5 Must Know Facts For Your Next Test

1. There are 7 periods in the periodic table.
2. Elements in the same period have the same number of electron shells.
3. The atomic number increases from left to right across a period.
4. Chemical properties vary widely across a single period.
5. Period number corresponds to the highest energy level that contains electrons in ground state.

Review Questions

• How many periods are there in the periodic table?
• What do elements in the same period have in common?
• How does the atomic number change as you move across a period?

Related terms

Groups: Vertical columns in the periodic table, which contain elements with similar chemical properties.

Electron Shells: Regions around an atom's nucleus where electrons are found, corresponding to different energy levels.

Atomic Number: The number of protons in an atom's nucleus, determining its position on the periodic table.