chem

• label the molar volume triangle

  A) v

  B) volume

  C) n

  D) number of moles

  E) vm

  F) molar volume (24)

  
• when an atom gains an electron to become an ion, it increases in size due to the addition of an extra electron
• in an equation of enthalpy of combustion, the reactant (carbohydrate) cant have more than one mole or it would become a different carbohydrate, its products must always be CO2 and H2O
• why there is an increase in first ionisation energy from elements?

  increasing number of protons increases nuclear charge, therefore holds electrons closer
• Explain fully the large increase between the first and second ionisation energies of sodium?

  involves the removal of an electron from an electron shell more closer to the nucleus
• State what is meant by the term electronegativity?

  electronegativity is the measure of attraction the nucleus has for the electrons in a bond
• Explain fully why electronegativity decreases going down a group?

  increased number of electron shells, therefore more screening, covalent radius increases so attraction of nucleus of shared electrons decreases
• Why do boiling points increase going down a group?

  intermolecular forces increase going down a group

  LDF are the forces broken between molecules

  the more electrons the stronger the LDFs
• Explain fully why silicon oxide has a much higher melting point than silicon hydride?

  covalent bonds are broken

  intermolecular forces are broken

  covalent bonding are stronger than LDFs
• in exothermic reactions, the reactants have more potential energy than the prodcuts
• in endothermic reactions the reactants have less potential energy than the products
• ionisation energy is the energy required to remove one mole of electrons from one mole of atoms in a gaseous state
• ionisation decreases down a group as the outer electrons are further from the nucleus and are more shielded from the nucleus's pull making them easier to remove from their energy level
• as we go across a group, ionisation energy increases as the number of protons and nuclear charge increases, pulling electrons closer
• noble gases have the highest ionisation energy as they all have stable electron shells meaning the removal of an electron requires more energy, greater attraction between nucleus and outer electrons
• covalent radius increases down a group as the number of electron shells increases
• covalent radius decreases going across a period due to increased nuclear charge, causing electron shells to be pulled closer
• covalent radius is half the distance between two bonded atoms
• electronegativity is the attraction an atom has for the shared electrons in a bond
• the higher the electronegativity the more ionic
• electronegativity increases across a period as the number of protons and nuclear charge increases, pulling electrons closer to the nucleus and increasing attraction
• electronegativity for noble gases can't be measured as they have a stable electron arrangement
• the higher the electronegativity the higher attraction for bonding electrons
• positive ions decrease the covalent radius, while negative ions increase the covalent radius
• why do melting and boiling points increase going down a group? (include intermolecular forces)

  • intermolecular forces increase going down a group
  • LDFs are broken
  • the more electrons the stronger the LDFs
• ionisation energy INCREASES across a period, and DECREASES down a group
• the mole ratio of glycerol molecules to fatty acid molecules is 1:3
• First 20 elements in the periodic table categorised by bonding and structure

  • Metallic (Li, Be, Na, Mg, Al, K, Ca)
  • Covalent molecular — H2, N2, O2, F2, Cl2, P4, S8 and fullerenes (eg C60)
  • Covalent network — B, C (diamond, graphite), Si
  • Monatomic (noble gases)
• Covalent radius

  A measure of the size of an atom
• First ionisation energy

  The energy required to remove one mole of electrons from one mole of gaseous atoms
• Electronegativity

  A measure of the attraction an atom involved in a bond has for the electrons of the bond
• Covalent bond

  Atoms share pairs of electrons
• Polar covalent bond

  Formed when the attraction of the atoms for the pair of bonding electrons is different, resulting in partial charges (delta+ and delta-)
• Ionic bond

  Electrostatic attraction between positive and negative ions
• Pure covalent bonding and ionic bonding can be considered as opposite ends of a bonding continuum, with polar covalent bonding lying between these two extremes
• The difference in electronegativities between bonded atoms gives an indication of the ionic character. The larger the difference, the more polar the bond will be
• Intermolecular forces

  Attractive forces that exist between molecules or discrete atoms
• Types of intermolecular forces

  • London dispersion forces
  • Permanent dipole-permanent dipole interactions (including hydrogen bonding)
• London dispersion forces

  Forces of attraction that can operate between all atoms and molecules, formed as a result of electrostatic attraction between temporary dipoles and induced dipoles
• The strength of London dispersion forces is related to the number of electrons within an atom or molecule