Topic B2 - Redox and Periodicity
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What is disproportionation?
a reaction where the same element from the same species is both oxidized and reduced
What is oxidation?
-loss of electrons -gain of oxygen -increase in oxidation state
What is reduction?
-gain of electrons -loss of oxygen -decrease in oxidation state
How was the periodic table initially arranged?
by atomic weight
What is periodicity?
repeating trends and patterns across the periodic table
Why does atomic radius increase down a group?
as there are more electron shells
Why does atomic radius decrease across a period?
-increased nuclear charge (more protons) -similar shielding -greater attraction between electrons and nucleus
What is the definition of the first ionisation energy?
energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous +1 ions
First ionisation energy equation example
X (g) —> X +1 (g) + e-
What factors affect ionisation energy?
-atomic radius (or ionic) -nuclear charge/ no. protons -shielding (no. shells)
Why is there a large increase in ionisation energy between electron shells?
electros being removed are closer to nucleus -greater attraction -more energy required to remove electron
Why is there an increase in ionisation energy across a period?
-smaller atomic radius -greater nuclear charge -stronger attraction between electron being removed + the nucleus
Why is there a decrease in ionisation energy down a group?
-atomic radius increases -same nuclear charge -weaker attraction between electron being removed + nucleus
Why does B have a lower ionisation energy than Be?
-as in B electron is being removed from a 2p orbital -2p orbital is further from nucleus -less attraction
Why does O have a lower ionisation energy than N?
-O has a pair of electrons in 2p orbital -pair of electrons repel -so it is easier to remove election
Why does Mg have a higher ionisation energy than Na?
-has more delocalised electrons (charge of 2+) -stronger electrostatic attraction
What is the oxidation number for elements?
0
What is H oxidation number in hydrides (e.g. NaH)?
-1
What is O oxidation number in peroxides (e.g. H2O2)?
-1
What is O oxidation number when bonded to F (F2O)?
+2
Sum of oxidation numbers =
total charge
What do Roman numerals show in names of compounds?
oxidation state (number) of element, with no sign - e.g. iron (II) = Fe2+ with oxidation number +2