Unit 4 Flashcards
Atomic radius
Distance between the nucleus of an atom and the outermost electron shell
Trends in atomic radius
- They generally decrease across each period as atomic number increases with extra electrons added to the outer shell. The larger the nuclear charge, the greater the pull of the nuclei on the electrons reducing atomic radius
- They generally increase down each group as number of shells increase, electrons in inner shell repel electrons in outershell, shielding from positive nuclear charge weakening the pull of nuclei on electrons increasing atomic radius
Ionic radius
measure of the size of an ion
Ionic radius trends
- Ionic radius decreases down a group (same as atomic radius)
- Trend across a period depends on positive or negative charge
- Ions with negative charges are formed by atoms accepting extra electrons while the nuclear charge remains the same. This extra electron repulsion with other valence electrons increases ionic radius Greater the negative charge, larger the ionic radius
- Ions with positive charge lose electrons, nuclear charge but lower electrons undergo electrostatic forces of attraction towards nucleus, decreasing ionic radius. Greater the positive charge, lower the ionic radius
Ionization energy
amount of energy required to remove one mole of electrons from one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
Ionization energy trends
- Increases across a period as nuclear charge increases but distance between nucleus and outer shell as well as shielding by inner electrons remains the same
- Decrease down the group due to increased distance between nucleus / outer electrons, increased shielding by inner electrons. This outweighs increased nuclear charge
Ionization energy exceptions
- Group 2 and 3 discontinuity: Due to existence of s and p orbitals
- Group 5 and 6 discontinuity: Due to electron to electron repulsion from double filled p orbital
Electron affinity
The amount of energy released when one mole of electrons is gained by one mole of atoms of an element in the gaseous state to form one mole of gaseous ions
- Measured under standard conditions
- First EA is always exothermic
Electron affinity trends
- Generally decrease down a group as atoms become larger, the attraction for additional electrons decrease since effective nuclear charge decreased from increased shielding
- Less exothermic down a group
Exception to Electron affinity trensd
- Fluorine EA smaller than expected because small atom and an additional electron in the 2p subshell experiences considerable repulsion with the other valence electrons
Electronegativity
ability of an atom to attract a pair of electrons towards itself in a covalent bond. Arises from nucleus ability to attract negatively charged electrons in outer shell.
Electronegativity trends
- Increases across a period as nuclear charge and shielding remains same but nucleus has increased attraction for bonding of pair of electrons across period resulting in smaller atomic radius
- Decreases down the group as nuclear charge increases but extra shell which increases shielding and distance between nucleus and valence electrons resulting in larger radius. Results in decreased attraction between nucleus and valence electrons.
Properties of group 1 metals
- soft and easy to cut, getting softer and denser as you move down the group
- Have shiny silvery surfaces when freshly cut
- Conduct heat and electricity
- all have low melting points and low densities and the melting point decreases going down the group as the atomic radius increases and the metallic bonding gets weaker
Group 1 metal reactions with halide ions
- React vigorously halogen ions, becomes more vigorous down the group because each element gets larger meaning electrons further away from nucleus and shielding effect increases.
Group 1 metal reactions with water
- React readily with oxygen and water vapour in air so kept under oil to stop from reacting
- Reacts similarly with water, vigorously to produce alkalne metal, hydroxide solution, and hydrogen gas
Metal + water -> Metal hydroxide + Hydrogen gas
Reactivity trend of group 17 halogens
- Reactivity decreases down the group as number of shells increases, electrons increase and thus shielding increases. Means outer electrons further away form nucleus so weaker forces of attraction
Halogen reactions with halide ions
Occurs when more reactive halogen displaces less reactive one from aqueous solution of its halide. Reactiivty increases up the group
Oxide trends across a period
The broad trend is that oxides change from basic through amphoteric to acidic across a period
Oxide reactions with water
Na2O + H2O -> 2NaOH (PH14)
MgO + H2O -> Mg(OH)2 (PH10)
P4O10 + 6H2O -> 4H3PO4 (PH2)
2NO2 + H2O -> HNO3 + HNO2 (PH1)
SO2 + H2O -> H2SO3 (PH1)
SO3 + H2O -> H2SO4 (PH1)
Oxide reaction with water patterns
- The metallic oxides form hydroxides when they react with water
- non-metallic oxides form oxoacids when they react with water
- Metal and non-metal elements generally form ionic compounds so the elements Na to Al have giant ionic structures
-The oxides become more ionic as you go down the group as the electronegativity decreases - The oxides become less ionic as you go across a period as the electronegativity increases
-The oxides of non-metals such as S, N and P form molecular covalent compounds
Combustion
Relatively fast, thermochemical reaction that requires:
- Fuel
- Oxygen
- Source of ignition / Trigger
Combustion of metals
All metals can oxidise but not combust and only if they have high surface area.
- Less reactive metals dont combust whereas more reactive metals like s block metals will combust in air
Combustion of non metals
Non-metals show a variety of oxidation states in the different oxides that they form during combustion
- p block non metals form covalent oxides when they undergo combustion and are acidic
Complete combustion and word equation
When fuels such as hydrocarbons and alcohols are burnt in excess oxygen, complete combustion takes place
- carbon and hydrogen will be oxidised
Fuel + Oxygen -> Carbon Dioxide + Water
Combustion of hydrocarbons word equation
Hydrocarbon + Oxygen -> Carbon Dioxide + Water
Combustion of alcohols word equation
Alcohols react with oxygen in the air when ignited and undergo complete combustion to form carbon dioxide and water
Alcohol + Oxygen -> Carbon Dioxide + Water
Reactive metal reactions factors
Extent depends on reactivity of metals and strength of acid
- Very reactive metals react dangerously with acids and usually not carried out / Low reactive metals don’t react at all
- Stronger acids react more vigorously with metals than weak acids
Faster reactions seen as:
- More effervescence (fizzing / shaking)
- Dissolves faster
Relative ease of oxidation and reduction trend of group 1 and 2 metals
Metal more or less likely to be oxidised
EG: 2Li + 2H2O -> 2LiOH + H2
- Lithium oxidised from Li to Li+, this reaction more vigorous down group 1 as reaction becomes more violent, thus relative ease of oxidation increases. Same pattern in group 2
Oxidising power of halogens
Halogens react with metals by gaining electron to become anion (-1 charge). Therefore, they’re oxidising agents
- Oxidise the metal by removing electron from metal
- Halogens become reduced as they gain extra electron from metal atom
- Oxidizing power of halogens decreases going down the group
Metal and metal ion reactions
- Metal higher in reactivity displaces less reactive metal
EG: Mg + CuSO4 -> MgSO4 + Cu - Mg -> Mg2+ 2e- = Oxidation
- Cu2+ 2e- -> Cu = Reduction
- More reactive metal acts as reducing agent
