A* A-Level Inorganic Chemistry Notes:
,Periodicity:
Periodicity: Repeating patterns/trends of physical or chemical properties.
As we explored in the atomic structure topic, elements are arranged in specific blocks. The blocks they
are classified as, is dependent on which orbital their outer electron lies in.
1. Atomic Radius Trend:
Across a Period: Decreases
● Nuclear charge increases (more protons).
● Same shielding (electrons added to the same shell).
● Greater electrostatic attraction between nucleus and outer electrons.
Down a Group: Increases
● More electron shells (greater shielding).
● Weaker attraction between nucleus and outer electrons.
2. Across a Period: Generally increases
● Nuclear charge increases → Stronger attraction.
● Atomic radius decreases → Electrons held more tightly.
● Same shielding (electrons in the same shell).
However there is a small drop from magnesium to aluminium. This is because:
● Aluminum outer electrons are in a 3p orbital. The 3p orbital has a slightly higher energy than
3s orbital, so electrons are further from the nucleus. The 3p electrons are slightly easier to
remove due to the additional shielding from the 3s orbital.
, There is also a small drop between phosphorus and sulfur. This is because:
● In phosphorus, an electron is being removed from a singly occupied orbital, but in sulfur, an
electron is being removed from an orbital containing two electrons. Due to the repulsion,
between the two negatively charged electrons, it is easier to remove an electron.
Melting and boiling points:
● For Na, Mg, and Al that have metallic bonding, the melting/boiling point increases. This is
because the charge on the ions increases and the ions become smaller. Therefore greater
attraction between smaller positively charged ions and sea of delocalised electrons. More
energy needed to break the bonds.
● Si: Si is a giant covalent structure, with very strong covalent bonds. A Lot of energy is needed
to break the covalent bonds.
● Cl2, S8,P4: They are simple molecular structures, they have weak van der waals forces
between the molecules, which do not require much energy to break.
S8 would have a higher melting point than P4 as S8 is bigger. Therefore more van der waals forces
between the molecules which require more energy to break.
,Periodicity:
Periodicity: Repeating patterns/trends of physical or chemical properties.
As we explored in the atomic structure topic, elements are arranged in specific blocks. The blocks they
are classified as, is dependent on which orbital their outer electron lies in.
1. Atomic Radius Trend:
Across a Period: Decreases
● Nuclear charge increases (more protons).
● Same shielding (electrons added to the same shell).
● Greater electrostatic attraction between nucleus and outer electrons.
Down a Group: Increases
● More electron shells (greater shielding).
● Weaker attraction between nucleus and outer electrons.
2. Across a Period: Generally increases
● Nuclear charge increases → Stronger attraction.
● Atomic radius decreases → Electrons held more tightly.
● Same shielding (electrons in the same shell).
However there is a small drop from magnesium to aluminium. This is because:
● Aluminum outer electrons are in a 3p orbital. The 3p orbital has a slightly higher energy than
3s orbital, so electrons are further from the nucleus. The 3p electrons are slightly easier to
remove due to the additional shielding from the 3s orbital.
, There is also a small drop between phosphorus and sulfur. This is because:
● In phosphorus, an electron is being removed from a singly occupied orbital, but in sulfur, an
electron is being removed from an orbital containing two electrons. Due to the repulsion,
between the two negatively charged electrons, it is easier to remove an electron.
Melting and boiling points:
● For Na, Mg, and Al that have metallic bonding, the melting/boiling point increases. This is
because the charge on the ions increases and the ions become smaller. Therefore greater
attraction between smaller positively charged ions and sea of delocalised electrons. More
energy needed to break the bonds.
● Si: Si is a giant covalent structure, with very strong covalent bonds. A Lot of energy is needed
to break the covalent bonds.
● Cl2, S8,P4: They are simple molecular structures, they have weak van der waals forces
between the molecules, which do not require much energy to break.
S8 would have a higher melting point than P4 as S8 is bigger. Therefore more van der waals forces
between the molecules which require more energy to break.
