2.1 Periodicity Flashcards
What happens to atomic radius across a period?
Atomic radii decrease 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.
What is the general trend of first ionisation energy across a period?
There is a general trend across to increase. This is due to increasing number of protons as the electrons are being added to the same shell.
Where are the drops in ionisation energy across period 3?
Aluminium and sulphur
Why is there a drop in first ionisation energy for Aluminium?
There is a small drop between Mg + Al. Mg has its outer electrons in the 3s sub shell, whereas Al is starting to fill the 3p subshell. Al’s electron is slightly easier to remove because the 3p electrons are higher in energy.
Why is there a drop in first ionisation energy at Sulphur?
There is a small drop between phosphorous and sulfur. Sulfur’s outer electron is being paired up with an another electron in the same 3p orbital.
When the second electron is added to an orbital there is a slight repulsion between the two negatively charged electrons which makes the second electron easier to remove.
What happens to melting and boiling points across period 3?
Melting and boiling points
For Na, Mg, Al- Metallic bonding : strong bonding
Si is Macromolecular: many strong covalent bonds between atoms.
Cl2 (g), S8 (s), P4 (S)- simple molecular : weak van der waals between molecules.
S8 has a higher mp than P4 because it has more electrons (S8 =128)(P4=60) so has stronger v der w between molecules
Ar is monoatomic weak van der waals between atoms
What is the trend in melting and boiling point in period 2?
Similar trend in period 2
Li,Be metallic bonding (high mp) B,C macromolecular (very high mp) N2,O2 molecular (gases! Low mp as small v der w)
Ne monoatomic gas (very low mp)
