1: Periodicity Flashcards
What is atomic radius?
Half the width of an atom.
How does atomic radius change across a period?
Decreases
Why does atomic radius decrease across a period?
As number of protons increases, positive charge of the nucleus increases.
The nucleus attracts to the electrons, and due to higher charge, they are drawn closer to the nucleus, decreasing the radius.
Why does shielding have no effect on atomic radius across a period?
Electrons are added onto the outermost shell, which is the same across a period.
Why does melting point increase from Na to Mg?
Na has a +1 charge and therefore 1 delocalised electron. Mg has a higher charge of 2+ and 2 delocalised electrons, so there is double the electrostatic attraction.
Describe the difference in atomic radius between Al and Mg.
Al has a smaller atomic radius than Mg due to a higher nuclear charge, which draws electron shells closer to the nucleus and decreases the radius.
Why does silicon have a very high melting point?
It is macromolecular, meaning it is held by covalent bonds only, which require lots of energy to be overcome.
Give the numbers of molecules in P, S and Cl.
P4
S8
Cl2
Why does sulfur have a slightly higher melting point than phosphorus and chlorine?
It is a larger molecule and larger molecules have stronger van der waals forces.
Why does ionisation energy generally increase across period 3?
The nuclear charge increases, meaning attraction to outer electrons also increases/
Why is there a drop in ionisation energy between Mg and Al? (2 reasons)
What are these factors strong enough to override?
Al’s outermost electron is in the 3p orbital, so it is further from the nucleus. This means there is less attraction to the electron, so it is lost more easily.
There is more shielding from the 3s.
These 2 factors override the effect of nuclear charge
What is the drop in ionisation energy between group 5 and 6 across period 3 caused by?
Why is it easier to remove an electron from a full orbital?
The electron in phosphorus is removed from a singly occupied orbital but in the sulfur, the electron is removed from a fully occupied orbital pair.
It is easier to remove an electron from a full orbital due to the repulsion
Explain why the second ionisation energy of calcium is lower than second ionisation of potassium.
Ca+ outer electron further from nucleus.
Additional shielding
Identify the s block metal with the highest first ionisation energy.
Beryllium
Explain why atomic radius decreases across period 3 from sodium to chlorine.
Nuclear charge increases but number of shells stays the same
