Unit 2
Topic 1: Periodicity
The Periodic Table arranges the known elements according to proton number. All the
elements along a periodhave the same number of electron shells. All the elements down a
grouphave the same number of outer electrons, this number is indicated by the group
number.
Elements are classified into blockswithin the Periodic Table that show electron
configuration:
● s-block = groups 1 and 2
● p-block = groups 3 to 0
● d-block = transition metals
● f-block = radioactive elements
These different electron configurations are often linked to other trendswithin the Periodic
Table. Periodicity is the study of these trends.
Atomic Radius
Along a period, atomic radius decreases. This is due to an increased nuclear chargefor the
same number of electron shells. The outer electrons are pulled in closer to the nucleus as
the increased charge produces a greater attraction. As a result, the atomic radius for that
element is reduced.
Down a group, atomic radius increases. With each increment down a group, an electron
shell is added each time. This increases the distance between the outer electrons and the
nucleus, reducing the power of attraction. More shells also increases electron shielding
where the inner shells create a ‘barrier’ that blocks the attractive forces. Therefore the
nuclear attraction is reducedfurther and atomic radius increases.
Topic 1: Periodicity
The Periodic Table arranges the known elements according to proton number. All the
elements along a periodhave the same number of electron shells. All the elements down a
grouphave the same number of outer electrons, this number is indicated by the group
number.
Elements are classified into blockswithin the Periodic Table that show electron
configuration:
● s-block = groups 1 and 2
● p-block = groups 3 to 0
● d-block = transition metals
● f-block = radioactive elements
These different electron configurations are often linked to other trendswithin the Periodic
Table. Periodicity is the study of these trends.
Atomic Radius
Along a period, atomic radius decreases. This is due to an increased nuclear chargefor the
same number of electron shells. The outer electrons are pulled in closer to the nucleus as
the increased charge produces a greater attraction. As a result, the atomic radius for that
element is reduced.
Down a group, atomic radius increases. With each increment down a group, an electron
shell is added each time. This increases the distance between the outer electrons and the
nucleus, reducing the power of attraction. More shells also increases electron shielding
where the inner shells create a ‘barrier’ that blocks the attractive forces. Therefore the
nuclear attraction is reducedfurther and atomic radius increases.
