THEORY kerboodle

Question 1

(a) the term electronegativity; qualitative electronegativity trends in the periodic table; use of relative electronegativity values to predict bond polarity in a covalent bond; relation of overall polarity of a molecule to its shape and the polarity of its individual bonds

Answer 1

• Electronegativity: A measure of the ability of an atom in a molecule to attract electrons in a chemical bond towards itself
• Increases across a period + Decreases down a group
• In a covalent bond, the atom of higher electronegativity is partially negative (𝛿-) and difference in electronegativity = polarity in bond
• Bond may be polar - but if molecule = symmetrical

Question 2

(g) the role of catalysts in providing alternative routes of lower activation enthalpy

Answer 2

• Catalysts speed up a reaction, by providing an alternative pathway of lower activation enthalpy, E_a
• Catalysts take part in the reaction but are unchanged at the end
• enthalpy change, ΔH for catalysed and uncatalysed reactions is the same

Question 3

(j) (ii) the recognition of and formulae for examples of members of the following homologous series:
amines

Answer 3

• primary amine

Question 4

(l) the terms substitution and nucleophile

Answer 4

• Substitution: A reaction which one atom or group in a molecule is replaced by another atom or group
• Nucleophile: A nucleophile is a molecule or negatively charged ion with a lone pair of electrons that it can donate to a positively charged atom to form a covalent bond

Question 5

(i) calculations, from given data, of values for composition by volume of a component in a gas mixture measured in percentage concentration and in parts per million (ppm)

Answer 5

• Converting ppm (parts per million) of a gas to a percentage:
  
  • Divide by 10,000
• Converting percentage of gas to ppm:
  
  • Multiply by 10,000

Question 6

(j) (i) the recognition of and formulae for examples of members of the following homologous series:
haloalkanes, including systematic nomenclature

Question 7

(u) calculation of values for frequency, wavelength and energy of electromagnetic radiation from given data.

Answer 7

• speed of light c (ms^-1) = wavelength λ (m) x frequency v (s^-1)
• energy of a photon E (J) = planck constant h (Js) x frequency v (s^-1)

Question 8

(c) intermolecular bonds: the formation of hydrogen bonds and description of hydrogen bonding, including in water and ice

Answer 8

• Hydrogen bonding = strongest intermolecular bond