Sqa Higher Chem

• what are saturated compounds?


  compounds containing only single carbon-carbon bonds
• what are unsaturated compounds?


  compounds containing at least one carbon-carbon double bond
• what can happen to compounds containing carbon-carbon double bonds?


  they can take part in addition reactions
• what happens in an addition reaction?


  2 molecules combine to form a single molecule
• how can you distinguish an unsaturated compounds from a saturated compound?


  using bromine solution as unsaturated compounds quickly decolourise bromine solution
• what are isomers?


  compounds with the same molecular formula but different structural formulae
• How are the elements in the periodic table arranged?


  in order of increasing atomic number
• What are groups?


  Vertical columns within the table contain elements with similar chemical properties resulting from a common number of elements in the outer shell
• What are 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
• What is the covalent radius?


  measure of the size of an atom
• what happens to covalent radius across a period?

  the covalent radius decreases as the number of protons increases. this results in an increased nuclear charge and so the electrons are held more tightly
• what happens to covalent radius down a group?


  the covalent radius increases as the number of electron shells increases so there is increased shielding and the attraction of the nucleus for the outer electrons decreases.
• What is the first ionisation energy?

  the energy required to remove one mole of electrons from one mole of gaseous atoms.
• what happens to the ionisation energy across a period?


  it increases as the number of protons increase which results in an increased nuclear charge meaning the electrons are held more tightly and so more energy is required to remove them
• what happens to ionisation energy down a group?


  it decreases because the number of electron shells increases so there is increased shielding. the attraction of the nucleus for the outer electrons decreases
• What is electronegativity?


  a measure of the attraction an atom involved in a bond has for the electrons of the bond
• what happens to electronegativity across a period?


  the electronegativity increases as the number of protons increases which results in an increased nuclear charge and so the electrons are held more tightly
• What happens to electronegativity down a group?


  The electronegativity decreases because the number of electrons increases as there is increased shielding and the attraction of the nucleus for the outer electrons decreases
• what is a covalent bond?

  a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.
• How are polar covalent bonds formed?


  when the attraction of the atoms for the pair of bonding electrons is different.
• what are ionic bonds?

  the electrostatic attraction between positive and negative ions.
• what do ionic compounds form?


  lattice structures of oppositely charged ions
• how is the bonding continuum arranged?


  Pure covalent bonding and ionic bonding can be considered as opposite ends with polar covalent bonding lying between these two extremes.
• what does a difference in electronegativity between bonded atoms mean?


  An indication of the ionic character
• What does a greater difference of electronegativity mean?


  The more polar the bond is
• how are ions formed?

  The movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions.
• how does all molecular elements and compounds and monatomic elements condense and freeze at sufficiently low temperatures?


  some attractive forces must exist between the molecules or discrete atoms.
• What are Van der Waals forces?


  Intermolecular forces acting between molecules
• What are the types of van der Waals forces?

  - London dispersion forces

  - permanent dipole-permanent dipole interactions

  - hydrogen bonding
• How are London dispersion forces formed?

  They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.
• What is the strength of London dispersion forces related to?


  The number of electrons within an atom or molecule
• How is a molecule described if it has a permanent dipole?


  Polar
• What can result in a molecule being polar?


  The spatial arrangement of polar covalent bonds
• What are permanent dipole-permanent dipole interactions?

  additional electrostatic forces of attraction between polar molecules
• what are hydrogen bonds?


  electrostatic forces of attraction between molecules that contain highly polar bonds such as fluorine, oxygen or nitrogen
• what is viscosity?


  a measure of the thickness of a liquid
• what does stronger intermolecular forces mean in terms of visocity?


  the liquid will move more slowly when poured or stirred and so the greater the viscosity
• what is the general rule for solubility?


  like dissolves like
• what is the anomalous boiling points of ammonia, water and hydrogen fluride a result of?


  hydrogen bonding
• why is the density of ice less than that of water at low temperatures?


  hydrogen bonding between molecules in ice results in an expanded structure