Periodicity
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How is the periodic table arranged?
By atomic number into periods and groups.
What does the period number tell you about an element?
The number of e- shells it has.
What does the group number tell u about an element?
The number of e- in outer shell.
Why do elements in the same group have similar properties?
They have the same number of outer shell e-.
What is the exception to the group number rule?
Group 0 elements have full outer shells with 8 e-
What are the blocks of the periodic table?
s,p,d,f
What does the block of an element tell you?
Which orbitals the outer e- are in.
What is periodicity?
The repeating patter of physical and chemical properties across a period.
What is organic chemistry?
The study of groups and periods of the periodic table and trends in their properties.
What happens to atomic radius across a period?
It decreases.
Why does atomic radius decrease across a period?
The number of protons increases, increasing nuclear charge.
How does increased nuclear charge affect electrons?
Greater electrostatic attraction pulls outer electrons closer.
Why is shielding same across a period?
All outer electrons are on the same shell.
Define 1st ionisation energy.
Energy needed to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
How does 1st ionisation change across a period?
It increases.
Why does ionisation energy increase across a period?
Increased nuclear charge causes stronger attraction to outer electrons, same shielding.
Between which groups does the ionisation energy drop occur?
2 and 3.
Why does ionisation energy drop from Mg to Al?
The outer electron moved from a 3s to a 3p sub-shell with more shielding.
Between which groups does the second ionisation energy drop?
5 and 6.
Why does ionisation energy drop from P to S?
The outer elecrton enters a doubly occupied 3s orbital, increasing repulsion.
How does melting point change from Na to Mg to Al?
They increase.
Why do Na, Mg and Al have increasing melting points?
Stronger metallic bonding due to higher ion charge, smaller radius and more delocalised electrons.
Why is silicon’s melting point the highest in period 3?
It forms a giant covalent structure with strong covalent bonds.
What structure does silicon form?
A giant covalent macromolecule with tetrahedral bonding like diamond.