Periodic Table Groups and Periods
The Periodic Table is a chart that systematically organizes all known elements into a grid. Understanding its basic layout of rows (Periods) and columns (Groups) is the first step to predicting an element's properties and chemical behaviour.
Part of the ESAT Chemistry syllabus — revision for the Engineering and Science Admissions Test (ESAT), the UAT-UK admissions test for Cambridge, Imperial, Oxford and UCL.
Key points
- The Periodic Table arranges elements in order of increasing atomic number.
- Horizontal rows are called Periods.
- Vertical columns are called Groups.
- The modern IUPAC convention numbers the Groups from 1 to 18, from left to right.
- An element's Period number indicates the principal energy level of its outermost electrons.
- Elements in the same Group typically have similar chemical properties.
Definitions
- Period
- A horizontal row in the Periodic Table. Elements within the same period have the same number of electron shells.
- Group
- A vertical column in the Periodic Table. Elements in the same group have the same number of electrons in their outer shell (valence electrons), leading to similar chemical behaviour.
Worked example
An element is located in the second horizontal row and the sixteenth vertical column of the Periodic Table. What are its Period and Group numbers?
- 1
Identify the term for a horizontal row, which is a 'Period'.
Since the element is in the second horizontal row, its Period number is 2.
- 2
Identify the term for a vertical column, which is a 'Group'.
Since the element is in the sixteenth vertical column, its Group number is 16.
- 3
Combine these to state the final answer.
Answer: The element is in Period 2 and Group 16.
Common mistakes
- ×A foundational mistake is confusing the terms 'Period' and 'Group'. Ensure you have memorised that Periods are the horizontal rows and Groups are the vertical columns.
No-calculator tips
- ✓Use a mnemonic to remember the orientation: 'Groups go down' (like a group of people in a lift) and 'Periods go across' (like a punctuation period at the end of a horizontal sentence).