Structure 3.1 Flashcards
Periodicity
When arranged, there is a repeating pattern in the chemical and physical properties
Atomic radius
Half the distance between two neighbouring nuclei
Atomic radius trend across a period
Nuclear charge increases, increase in electrostatic attraction, decrease in radius as electrons are pulled in
Trend down a group
Number of occupied electron shells increases, increase in atomic radii.
Isoelectric positive ions radius trend
Decrease in size across a period as electrons remains constant, but nuclear charge increases
Isoelectric negative ions
Decrease in size across a period as electrons remain constant but nuclear charge increases
Positive ions are smaller or larger than parent ions
Smaller (loss of outer energy level)
Negative ions are smaller or larger than parent ions
Larger (addition of electron = increased electron repulsion = increased radius)
Ionisation energy
Enthalpy change when an electron is removed from an atom in the gaseous state
IE across a period
Increases due to the increase in nuclear charge leading to greater electrostatic attraction
IE down a group
Nuclear charge increases but the shielding means it is about the same, so increased distance between electron and nucleus reduces attraction so decreases
Electron affinity
Enthalpy change when an electron is added to an atom in the gaseous state (exothermic)
Are second and third electron affinity exo or endo?
Endothermic as electron is repelled from the negative ion and needs to have energy to be added
Electron affinity trends
Increases across a period and up a group - this is rough rule
Electronegativity
Relative measure of the attraction that an atom has for a shared pair of electrons when it is covalently bonded to another atom
Why does electronegativity increase across a period?
Due to increase in nuclear charge - increased attraction between nucleus and bond electrons
Why does electronegativity decrease down a group?
Bonding electrons are further from the nucleus so reduced attraction
Alkali metals (5)
Silvery metals, very reactive, good conductors, low densities, form ionic compounds with non-metals
Halogens (3)
Coloured, very reactive, form ionic or covalent
Displacement reactions
A more reactive element (higher in group) displaces a less reactive element (lower in group) from a compound that contains the less reactive element.
Lewis Acid
Can accept an electron pair (non-metal oxides)
Lewis base
Can donate an electron pair (many metal oxides)
Lewis bases + metal oxides
React with water to form hydroxides.
Amphoteric
Can act as an acid or base
Acid rain
Solutions with a lower pH than 5.6 due to presence of sulfur and nitrogen oxides
Sulfur oxides in creating acid rain
Sulfur dioxide dissolves in rainwater to form sulfric or sulfurous
H2O + SO2 -> H2SO3
- It can also be oxidised to sulfur trioxide, forming sulfric acid
Nitrogen oxides in creating acid rain
Nitrogen dioxide dissolves in rainwater to form nitric or nitrous acid
Ocean acidification due to carbon dioxide
About 50% of CO2 produced by combustion of fossil fuels is dissolved in oceans. CO2 reacts with water to make carbonic acid.
CO2 (aq) + H2O (l) -> H2CO3 (aq)
Displacement reactions examples
Cl2 + 2Br- -> Br2 + 2Cl- (colourless to orange)
Cl2 + 2I-/Br2 + 2I- (colourless to dark orange/brown)
Base/acid across a period
Changes from basic to amphoteric to acidic
Metal oxides are
Bases (react with water to form hydroxides). Group 2 oxides also do this.
Non metal oxides
Acids (react with water to form more acid)
Oxygen oxidation states
-2, with peroxides is -1, with flourine is +2
Chlorine oxidation states
-1, with O or F is +1, in Cl04 is +7
Hydrogen oxidation states
+1, with group 1/2 metals is -1
Oxidation
An increase in oxidation state
Reduction
A decrease in oxidation state
Disproportionation
When the same element is reduced and oxidised in the same reaction
Why is there an increase in ionisation energy across a period?
Due to increase in nuclear charge increasing attraction between electrons and nuetrons.
Why is there a discontinuity in ionisation energy between Be/B, Al/Mg, O/N and Ne/P
- Higher energy level and so less energy to remove an electron
- Electrons are in spin pairs and repel each other
Ligand
Neutral molecule or ion that possess at least one non bonding pair of electrons that can form a coordinate bond
Monodentate and polydentate ligands
Mono-dentate - one bond with transition metal.
Polydentate - multiple bonds
Colour of a compound - what affects it?
As white light passes through, energy is absorbed and electrons promoted. When the electrons fall, the remaining light is transmitted and light is complementary to the absorbed light.
