Periodicity

What is the trend in ATOMIC RADIUS across period 3 [4]?

• Decreases.

• N.o. protons increases, the n.o. electron shells stays the same.

• So there is an increased nuclear charge.

• A greater electrostatic force of attraction, so electrons are pulled closer to the nucleus.

What is the trend in SUCCESSIVE IONISATION ENERGY across period 3 [4]?

• Increases (Al & S are exceptions).

• N.o. protons increases, shielding stays the same, so there is an increase in nuclear charge.

• Decrease in atomic radius.

• Theres a stronger force of attraction between the nucleus and outer electron, so more energy is required to remove the electron.

Why are Al [2] and S [2] exceptions in SUCCESSIVE IONISATION ENERGY trend?

• Al's outer electron is lost from its p orbital, while Mg's electron is lost from its s orbital.

• The p orbital is higher in energy, so it is further from the nucleus and more shielded.

• The electrons in S's p orbital begin to pair up, while the electrons in P's orbital are not paired up.

• The electron electron repulsion in S's orbital makes the removal of the electron easier.

What is the trend in MELTING POINTS across period 3 [5]?

• Increases from Na-Si, then decreases from Si-Ar.

• Na, Mg, Al are metals, have metallic bonding, delocalised electrons increase & cation charge increases so theres a stronger electrostatic force of attraction.

• Si has a giant covalent lattice structure, loads of covalent bonds, many bonds need to be broken so a high temp is needed.

• P, S, Cl are simple molecular, have weak van der waals forces, so less energy is needed.

• Ar is monatomic, has weaker van der waals forces, so less energy is needed.