Periodicity

define periodicity

The repeating pattern of physical and chemical properties going across a period

whats the trend for atomic radius across a period and down a group and why?

• across a period the atomic radius decreases due to an increase in nuclear charge but the same shielding, making electrostatic attraction increase and pull outer electrons closer to the nucleus

• down a group the atomic radius increases due to increased shielding further from the nucleus making electrostatic attraction weaker

what is the trend for ionisation energy in period 3

• there is a general increase due to increasing nuclear charge and same shielding

• there is a small drop from Mg to Al this is because Als outer electron is in the P subshell rather than the S subshell which is slightly higher in energy and so less energy is needed to remove the outer electron

• there is also a drop between P and S this is because sulfurs outer electron is in the same orbital as another one of its electrons which means there is a natural repulsion between the two electrons in the orbital

what is the trend for melting and boiling points in period 3

• increase between Na, Mg and Al, because of their metallic bonding, the boning gets stronger as the atomic radius decreases due to greater positive charge and delocalised electrons, more energy is needed to overcome the electrostatic attraction.

• Si is the highest, as it is macromolecular, many strong covalent bonds high energy needed to breakcovalent bonds

  decrease from S8 to P4 to Cl2, this is because they are simple molecules and have weak van der waals which get stronger as the molecule gets stronger.

• Ar is the lowest as it is monoatmoic therefore has very weak van der waals between molecules