Periodicty

Question 1

How does the atomic radius change in period 3

Answer 1

Across the period, the atomic radii decrease
This is because the number of protons (the nuclear charge) and the number of electrons increases by one every time you go an element to the right
The elements in a period all have the same number of shells (so the shielding effect is the same)
This means that as you go across the period the nucleus attracts the electrons more strongly pulling them closer to the nucleus
Because of this, the atomic radius (and thus the size of the atoms) decreases across the period

Question 2

How does the ionic radius change across a period

Answer 2

Decrease
Bc nuclear charge increase
And fewer electrons are gained

Question 3

How does 1st IE change across a period

Answer 3

There is a general increase in IE1 across a period
The nuclear charge increases
The atomic radius decreases
There are stronger attractive forces between the nucleus and outer electrons
It therefore gets harder to remove any electrons

Small ‘dips’ are observed between Mg - Al and P - S - see atomic structure topic

Question 4

how do the melt points in period 3 change

Answer 4

Increase then decrease
Look at bonding to see why

Na, Mg and Al are metallic elements which form positive ions arranged in a giant lattice in which the ions are held together by a ‘sea’ of delocalised electrons around them. - increase in amount of e- they donate - so stronger metallic bonding - stronger electrostatic forces - so increase
Na will donate one electron into the ‘sea’ of delocalised electrons, Mg will donate two and Al three electrons
As a result of this, the metallic bonding in Al is stronger than in Na
This is because the electrostatic forces between a 3+ ion and the larger number of negatively charged delocalised electrons is much larger compared to a 1+ ion and the smaller number of delocalised electrons in Na

P, S, Cl and Ar are non-metallic elements and exist as simple molecules (P4, S8, Cl2 and Ar as a single atom)
The covalent bonds within the molecules are strong, however, between the molecules, there are only weak VDW so no decreases