Group
A vertical column of the periodic table. Elements in a group have the same number of outer electrons, so they react in similar ways.
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Analogy
A group is like a family. Members share features because they share the same outer electrons.
Example
Group 1: 1 outer electronGroup 2: 2 outer electronsGroup 7: 7 outer electronsGroup 0: full outer shell
In practice
Lithium, sodium and potassium are all in group 1. Each has one outer electron.
Practice
Flashcards
- What do elements in the same group have in common?The same number of outer electrons, so similar reactions.
Interview questions
- Explain why the elements in group 1 have similar chemical properties and why reactivity increases down the group.
- Same number of outer electrons (one)
- Each loses one electron to react
- Lower in the group the outer electron is further from the nucleus
- Less attraction so electron is lost more easily
Questions people ask
How can you tell the group of an element from its electrons?
For main groups 1 to 7, the group number equals the number of outer electrons. Group 0, the noble gases, is the exception because those atoms have a full outer shell, meaning 8 electrons (2 for helium). So sodium with 2, 8, 1 is in group 1.
Why did Mendeleev leave gaps in his periodic table?
Dmitri Mendeleev arranged elements by atomic mass and by chemical behaviour. Where an element did not fit a pattern, he left a gap and predicted an undiscovered element would fill it. Later discoveries, such as gallium and germanium, matched his predictions, which won support for his table.