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The Periodic Table

Chemistry: AQA A Level, topic 3.1.1

The Periodic Table - Groups and Periods

The periodic table is arranged into periods and groups.

The periodic table

The periodic table

  • The periodic table is the table that organises all the elements into groups and periods.
  • The elements are arranged in order of proton number, starting with hydrogen that has the proton number of 1.
Periods

Periods

  • A period is a row in the periodic table.
  • Elements in the same period have their valence electrons in the same shell.
  • The diagram highlights Period 3.
Period example

Period example

  • Magnesium and sulfur are in the same period.
  • In simple terms, they have the electron configuration 2,8,2 and 2,8,6 respectively.
  • So, their valence electrons are in the same shell.
Groups

Groups

  • A group is a column in the periodic table.
  • Elements in the same group have their electrons in similar orbitals.
  • They often have very similar properties.
  • A Group n element has n valence electrons.
    • E.g. Carbon is in Group 4 and has 4 valence electrons.
  • The diagram highlights Group 7.
Group example

Group example

  • The halogens are all in Group 7.
  • Fluorine's simplified electron configuration is 2,7.
  • Chlorine's is 2,8,7.
    • We see they both have the same number of valence electrons.
  • We also know that halogens have very similar chemical properties.

Periodic Table - Blocks

The periodic table can be organised into four sections. These are labelled s, p, d and f blocks.

The s block

The s block

  • The two leftmost columns make up the s block.
  • This is called the s block because elements in it have all their valence electrons in s orbitals.
  • Note, Helium is also an s block element because it has the electron configuration 1s2.
The p block

The p block

  • The six rightmost columns make up the p block.
  • This is called the p block because elements in the p block have a partially filled p sub-shell.
The d block

The d block

  • The d block lies between the s and p blocks.
  • Elements in the d block have a partially filled d sub-shell.
  • Elements in the d block are often called transition metals.
The f block

The f block

  • The f block is detached along the bottom of the periodic table.
  • Elements in the f block have a partially filled f sub-shell.
  • These elements are referred to as the lanthanides and the actinides (top and bottom row respectively).

Test yourself on The Periodic Table

  • Li, Be, B, C, N, O, F, Ne
    What is this list of elements an example of?

  • What do elements in the same group have?

  • An element has the configuration 2.8.6
    Which of the following configurations would represent an element in the same group?

  • Which of the following is an s block element that does NOT sit on the left-hand side of the periodic table?

  • Which block would the transition metal tungsten lie in?

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