C5, C6, C7, C8

Redox, chemical bonding, group chemistry and separation techniques

C5 - REDOX

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Redox

• Oxidation is loss of electrons and gain of oxygen

• Reduction is gain of electrons and loss of oxygen

• When this happens at once, this is redox (OIL RIG)

Oxidising vs reducing agent

• Oxidising agent

  • Accepts electrons and undergoes reduction

• Reducing agent

  • Donates electrons and undergoes oxidation

Oxidation number rules

• Un-combined elements have an oxidation number of 0

• Atoms in molecules bonded to identical atoms (diatomic molecules) have oxidation number of 0

• Monatomic ion's ON is same as its charge (Fe3+ has ON of +3)

• In molecular ion, sum of ON is equal to overall charge

• Neutral compounds have ON sum of 0

• Combined oxygen has ON of -2 except in peroxides where its -1

  • In OF2 its +2

• Combined hydrogen usually has an ON of +1 except in metal hydrides where its -1

• Oxidation number of compound containing 2 non-metals is given to more electronegative element

Roman numerals

• Roman numerals are used after element's name to specify its oxidation number

  • Iron (II) has ON of +2

  • Iron (III) has ON of +3

-ate compounds

• Ions ending in -ate are made up of oxygen and another element

• Element bonding to oxygen has variable oxidation number

  • Roman numerals are used after compound's name to differentiate between these numbers

Oxidation numbers

• Oxidation

  • Increase of oxidation numbers

• Reduction

  • Decrease of oxidation number

• E.G. Na + 1/2 Cl2 ---> NaCl2

  • Sodium is oxidised because oxidation number increases from 0 to +1

  • Chlorine is reduced because oxidation number decreases from 0 to -1

Disproportionation

• When single element is both oxidised and reduced

• e.g. in Cl2 + 2OH- ----> ClO- + Cl- + H2O

  • Cl is both oxidised (increase in ON)

  • Cl is both reduced (decrease in ON)

C6 - CHEMICAL BONDING, STRUCTURE AND PROPERTIES

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Element, compound and mixture

• Element

  • Pure substance that have the same proton number and cannot be broken into simpler substances

• Compound

  • Pure substance made of two or more different elements chemically bonded

• Mixture

  • Two or more different substances not joined together

Ionic bond

• Ion

  • Atom with a negative or positive charge

• Ide

  • 2 elements

• Ate

  • 3 elements

• Ionic bonding

  • Oppositely charged ion (cations + anions) are attracted to each other and held together by strong electrostatic forces of attraction

• Formation of ions

  • Group no --> loses/gains an electron for a full outer shell

  • Means it has pos/neg charge

  • More protons than electrons/ more electrons than protons

Structure of ionic compound

Alternating regular arrangement of ions in a lattice held together by ESFA between oppositely charged ions

Properties of ions

• High BP/MP

  • Strong electrostatic forces of attraction

  • More energy needed to break them

  • Intermolecular forces between molecules that must be overcome

• Conductive

  • When aqueous or molten

  • Ions are unable to move when in lattice

    • ESFA

  • Unable to conduct charge

  • When liquid, ions are free to move

  • Can conduct charge

Strength of ionic bond

• Ionic charge

  • Higher charge greater strength

• Ionic size

  • Smaller ions have greater attraction

Common ions

• OH-

• SO₄2-

• NO₃-

• CO₃2-

• NH₄+

• HCO₃-

Covalent molecules

• Covalent bonding

  • Shared pair of electrons between non-metals on the outer shell

• Molecules

  • Group of covalently bonded atoms

• Bonding

  • Group no --> need certain no of electrons for full outer shell

  • Share pairs of electrons to get full outer shell

  • Typically water, methane, ammonia

  • 1 pair = 1 bond

Covalent properties

• Low BP/MP

  • Weak intermolecular forces of attraction

    • Less energy needed to overcome it

• Poor conductor

  • No charged particles

  • Nothing to conduct charge

Giant covalent: diamond and graphene

• Diamond

  • Strong

    • 4 covalent bonds per carbon atom

    • Rigid and hard

      • Good for cutting tools

  • High BP/MP

    • Because of strong bonds

    • More energy required

  • Poor conductor

    • No delocalised electrons

• Graphene

  • Regular shape (3 covalent bonds per carbon atom)

    • 1 free/spare electron (delocalised e^-)

      • Good conductor

  • High BP/MP

    • 3 strong bonds

  • Light and strong

Giant covalent: graphite and fullerene

• Fullerene

  • Simple covalent (has discreet formula)

  • 3 bonds per carbon atom (delocalised e^-)

    • Conductor

  • Low BP/MP

    • Less energy is required to overcome intermolecular forces of attraction

  • Hollow + ball shape

    • Transporting medicine

• Graphite

  • Weak intermolecular forces of attraction between LAYERS

    • Layers can slide over each other

    • Slippery --> lubricant

  • Covalent bonds between carbon atoms

  • Delocalised e^- (3 bonds per atoms)

    • Can conduct electricity (electrodes)

Metallic bonding

• Giant lattice of atoms

• Give up the shell and share the electrons

• Forms a sea of delocalised electrons

• Electrostatic attraction between e^- and newly made cations

Metallic properties

• Malleability

  • Arranged in lattice

  • Force applied means layers can slide over each other

• Conductivity

  • Delocalised electrons can conduct charge

  • Free to move in lattice

• High BP/MP

  • Strong electrostatic forces of attraction between delocalised electrons and cations

  • More energy needed to overcome it

C7 - GROUP CHEMISTRY

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Group 1 physical properties

• Alkali metals

• Physical properties

  • Soft

  • Low density

  • Low melting points

Group 1 Chemical: reaction with water

• They all have 1 electron in outer shell

  • Will react similarly

• Reaction with water

  • Produce metal hydroxide and hydrogen

  • Energy of reaction can sometimes make hydrogen burn

  • Reaction of lithium = fizzes steadily

  • Reaction of sodium = melts to form a ball, fizzes

  • Reaction of potassium, quickly melts to form a ball,

Group 1 Chemical: reaction with oxygen

• Form metal oxides

• Potassium is either metal peroxide (two oxygen) or superoxide (1 oxygen)

• Chlorine is oxide

• Sodium is oxide or peroxide

Group 1 reactivity

• Further from nucleus easier to lose electron

• Less electrons easier to lose

Halogen physical properties

• Live as molecules

• Melting and boiling points increase as you go down

  • Molecules become larger

  • More intermolecular forces

  • Harder to overcome

• Colour and states

  • Chlorine: green, gas

  • Bromine: brown, liquid

  • Iodine: purple/black, solid

Halogen chemical properties

• Reaction with metals

  • Form salts

• Less reactive as you go down table

  • Atoms larger

  • More shells further from nucleus

• Reaction with hydrogen

  • Form hydrogen HALIDE

    • e.g. chlorine --> chloride

    • Dissolve in water to form acidic solution

  • High reaction = explosion

Halogen displacement

• A more reactive halogen replaces a less reactive halide ion

• Chlorine displaces bromide ions

• Cl_{2 (aq)} + 2Br^-_(aq) ---> 2Cl^-_(aq) + Br_{2 (aq)}

• 
  

Noble gases physical properties

• Exist as single atoms

• Low boiling points

  • Increase due to more covalently bonded molecules

• Low densities

  • Gases

Noble gases chemical properties

• Inert

  • When element reacts, they lose/gain electron

  • They already have full outer shell anyways

Noble gases uses

• Helium

  • Less dense than air

  • Used for balloons

  • Non flammable

• Argon

  • Shield gas for welding

  • Denser than air so oxidation does not occur at weld

C8 - SEPARATION TECHNIQUES

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Chemical processes

Needed to displace constituent elements from compounds

Physical processes

• Used to separate mixtures

• Including dissolved/insoluble solids

• Miscible/immiscible liquids

When to use: distillation, crystallisation, chromatography, filtration and fractional distillation

• Distillation

  • Solid + liquid w VERY different BP

• Crystallisation

  • Impure solid from dissolved solvent

• Chromatography

  • Separates coloured chemicals

• Filtration

  • Insoluble solid from solution

• Fractional distillation

  • Mixture

  • Similar BP

When to use: centrifugation, evaporation, dissolving and separating funnel

• Separating funnel

  • Two immiscible liquids that can be separated based on their densities

• Centrifugation

  • Based on density of centrifugal forces

  • Less dense stay in the middle

• Evaporation

  • Separate soluble solid from liquid

• Dissolving

  • Used when soluble solid is present in mixture

  • Solute can then be filtered out

Chromatography

• Separation of mixtures of soluble substances by running a solvent through the mixture on paper - one spot if pure

• Mobile phase:

  • Solvent

• Stationary phase

  • Paper

Rf value

distance travelled by spot/ solvent front