chemistry spec

• Elements are arranged in the periodic table in order of increasing atomic number
• Periodic table

  • Allows chemists to make accurate predictions of physical properties and chemical behaviour for any element, based on its position
• Features of the periodic table

  • Groups: vertical columns within the table contain elements with similar chemical properties resulting from a common number of electrons in the outer shell
  • Periods: rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from metallic to non-metallic characteristics
• Trends in covalent radius across periods and down groups can be explained in terms of the number of occupied shells, and the nuclear charge
• The second and subsequent ionisation energies refer to the energies required to remove further moles of electrons
• Trends in ionisation energies across periods and down groups can be explained in terms of the atomic size, nuclear charge and the screening effect due to inner shell electrons
• Trends in electronegativity across periods and down groups can be rationalised in terms of covalent radius, nuclear charge and the screening effect due to inner shell electrons
• Compounds formed between metals and non-metals are often, but not always, ionic
• Physical properties of a compound, such as its state at room temperature, melting point, boiling point, solubility, electrical conductivity, should be used to deduce the type of bonding and structure in the compound
• The anomalous boiling points of ammonia, water and hydrogen fluoride are a result of hydrogen bonding
• Hydrogen bonding between molecules in ice results in an expanded structure that causes the density of ice to be less than that of water at low temperatures
• To predict the solubility of a compound, key features to be considered are the presence in molecules of O-H or N-H bonds, which implies hydrogen bonding, and the spatial arrangement of polar covalent bonds, which could result in a molecule possessing a permanent dipole
• The solubility, boiling point and volatility of a compound can be predicted by considering the presence of O-H or N-H bonds, the spatial arrangement of polar covalent bonds, molecular size, and the polarities of solute and solvent
• Alcohols can be classified as primary, secondary or tertiary
• Alcohols containing two hydroxyl groups are called diols, and those containing three hydroxyl groups are called triols
• Hydroxyl groups make alcohols polar and this gives rise to hydrogen bonding, which can be used to explain the properties of alcohols
• Carboxylic acid

  A molecule containing the carboxyl functional group, -COOH
• Carboxylic acids can react with bases to form salts and water, and the name of the salt produced depends on the acid and base used
• Ester

  A molecule containing an ester link, -COO-
• Esters can be named given the names of their parent alcohol and carboxylic acid, or the structural formulae of esters formed from primary, straight-chain alcohols and straight-chain carboxylic acids
• Molecular formula

  Can be written or a structural formula drawn from the systematic name of a straight-chain or branched-chain carboxylic acid that contains no more than eight carbon atoms in its longest chain
• Carboxylic acids reacting with bases

  1. Metal oxide + carboxylic acid → salt + water

  2. Metal hydroxide + carboxylic acid → salt + water

  3. Metal carbonate + carboxylic acid → salt + water + carbon dioxide
• Ester

  A molecule containing an ester link: ─COO─
• Naming esters

  1. Given the names of their parent alcohol and carboxylic acid

  2. Given the structural formulae of esters formed from primary, straight-chain alcohols containing no more than eight carbons and straight-chain carboxylic acids containing no more than eight carbons
• Writing molecular and structural formulae for esters

  1. Given the systematic names of esters formed from primary, straight-chain alcohols containing no more than eight carbons and straight-chain carboxylic acids containing no more than eight carbons

  2. Given the structural formulae of their parent alcohol and carboxylic acid
• Esters

  • Used as flavourings and fragrances as many have pleasant, fruity smells
  • Used as solvents for non-polar compounds that do not dissolve in water
• Formation of esters

  1. Condensation reaction between an alcohol and a carboxylic acid

  2. Elimination of water
• Hydrolysis of esters

  1. Ester reacts with water to break down into smaller molecules

  2. Produce an alcohol and a carboxylic acid
• Naming products of ester hydrolysis

  1. Given the name of the ester

  2. Given the structural formula of an ester formed from a straight-chain or branched alcohol and a straight-chain or branched carboxylic acid, each containing no more than eight carbons in their longest chain
• Writing molecular and structural formulae for ester hydrolysis products

  1. Given the systematic names of esters formed from primary, straight-chain alcohols containing no more than eight carbons and straight-chain carboxylic acids containing no more than eight carbons

  2. Given the structural formula of the ester
• Edible fats and edible oils

  Esters formed from the condensation of glycerol (propane-1,2,3-triol) and three carboxylic acid molecules (fatty acids)
• Edible oils

  • Have lower melting points than edible fats
  • Double bonds in fatty acid chains prevent oil molecules from packing closely together, so the greater the number of double bonds present, the weaker the van der Waals forces of attraction
  • The greater the degree of unsaturation, the lower the melting point
• Bromine addition reaction

  Bromine molecules add across the carbon–carbon double bonds
• Number of double bonds

  The more bromine solution can be decolourised
• Fats and oils

  • A concentrated source of energy
  • Essential for the transport and storage of fat-soluble vitamins in the body
• Soap production

  1. Alkaline hydrolysis of edible fats and edible oils

  2. Produces three fatty acid molecules and one glycerol molecule

  3. Fatty acid molecules are neutralised by the alkali, forming water-soluble, ionic salts called soaps
• Soap ions

  Have long non-polar tails, readily soluble in non-polar compounds (hydrophobic), and ionic heads that are water-soluble (hydrophilic)
• Soap action

  1. The hydrophobic tails dissolve in the oil or grease

  2. The negatively-charged hydrophilic heads remain in the surrounding water

  3. Agitation causes ball-like structures to form

  4. The negatively-charged ball-like structures repel each other and the oil or grease is kept suspended in the water
• Hard water

  Water containing high levels of dissolved metal ions
• Soapless detergents

  • Substances with non-polar hydrophobic tails and ionic hydrophilic heads
  • Remove oil and grease in the same way as soap
  • Do not form scum with hard water