PERIODICITY

Question 1

Explain the trend of atomic radii across the period

Answer 1

-Atomic radii decrease as you move from left to right
across a period,
-because the increased number of protons create more positive charge attraction for
electrons
-which are in the same shell with similar
shielding

Question 2

explain the trend of ionic radii across the period

Answer 2

-when an atom forms a cation, size of cation is smaller than its respective atom as a shell is lesser.
-when an atom form an anion, size of anion is greater than its atom, as increase in electrons increases repulsion,
-so shell moves away from eachothers.

Question 3

explain the melting and boiling trend of the following:
-Na,Mg,Al
-Si
-Cl2,S8.P4
-Ar

Answer 3

-For Na, Mg, Al- Metallic bonding : strong bonding – gets stronger
the more electrons there are in the outer shell that are released to
the sea of electrons. A smaller positive centre also makes the
bonding stronger. Higher energy is needed to break bonds.
-Si is Macromolecular: many strong covalent bonds between
atoms, high energy needed to break covalent bonds– very high mp
+bp
-Cl2 (g), S8 (s), P4 (S)- simple Molecular : weak van der waals between
molecules, so little energy is needed to break them – low mp+ bp
-S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger van der w between molecules
-Ar is monoatomic weak van der waals between atoms