definitions Flashcards
periodicity
the occurrence of patterns in the periodic table.
atomic size
the covalent radius is half the distance between the nuclei of two bonded atoms of the element.
first ionisation
the energy required to remove one electron from each atom of one mole of gaseous atoms.
second ionisation
the energy required to remove one electron from each singly positive ion of one mole of the gaseous ions.
electronegativity
a measure of the attraction an atom involved in a bond has for the electrons of the bond
metallic bond
the electrostatic force of attraction between the positively charged ions and the delocalised electrons.
covalent bond
a single covalent bond consists of one shared pair of electrons.
non-polar covalent bond
when atoms of the same element form a covalent bond, the electrons are shared equally. these atoms have the same electronegativity.
polar covalent
when atoms of different elements share electrons, atoms with different electronegativity values will share the pair of bonding electrons unequally, forming partial charges of a permanent dipole.
ionic bond
due to periodic trends in electronegativity, elements far apart in the periodic table are more likely to form ionic rather than covalent bonds.
van der waals
the forces of attraction that hold discrete atoms (noble gases) and discrete molecules (diatomics) together in the liquid state.
london dispersion forces in monatomic elements
london dispersion forces are very weak, resulting in the noble gases having very low melting and boiling points.
temporary or instantaneous (induced) dipoles
one side of the atom has a slight negative charge and the other side has a slightly positive charge.
london dispersion forces in discrete molecules
london dispersion forces are formed as a result of electrostatic attractions between temporary and induced dipoles caused by the movement of electrons.
permanent dipole - permanent dipole
a covalent bond in which the atoms have a ifference in electronegativity is a polar covalent bond.
hydrogen bonds
electrostatic forces of attraction between molecules that contain highly polar bonds ( N, O, F)
behaviour in an electric field
if a charged rod is held up to a stream of liquid, the permanent dipoles of polar liquids become attracted to the charged rod.
viscosity
the resistance to flow
solubility/miscibility
very polar molecules such as water do not mix with non-polar molecules such as oil and form two layers.
oxidation (structure and bonding)
loss of electrons by a reactant in any reaction.
reduction
gain of electrons by a reactant in any reaction.
redox reaction
one in which both oxidation and reduction steps occur.
oxidising agent
a substance which accepts/gains electrons during a chemical reaction. (itself reduced)
reducing agent
a substance which donates/loses electrons during a chemical reaction. (itself oxidised)
standard solution
a solution of which the concentration is accurately known.
self-indicating reaction
a colour change involving one of the reactants indicating the end point of the reaction.
chromatography
allows chemists to separate substances in complex mixtures.
disclosing agent
a spray which causes the amino acids to show up as coloured spots.
gas-liquid chromatography
mobile phase is an inert gas
stationary phase
a very thin layer of a high boiling point, inert liquid absorbed onto an inert solid support.
retention time
the amount of time that a substance takes to pass through the column.
activation energy
the minimum kinetic energy with which particles have to collide in order to react.
activated complex
an unstable arrangement of atoms, intermediate between reactants and products, formed at the maximum of the potential energy barrier during a reaction.
temperature
a measure of the average kinetic energy of all the particles in a substance.
Use of a Catalyst
A catalyst provides an alternative reaction pathway with a lower activation energy.
enthalpy change
the energy difference between the products and the reactants and is the overall enthalpy change for a reaction.
enthalpy of combustion
the energy released when one mole of a substance is burned completely in oxygen.
Hess’s Law
Hess’s law states that the enthalpy change for a chemical reaction is independent of route.
bond enthalpy
the energy required to break one mole of a particular bond between a pair of atoms in the gaseous state.
equilibria
a reaction is at equilibrium when the rate of the forward and reverse reaction are equal and the concentration of reactants and products remain constant.
position of equilibrium
if the concentration of reactants is greater than the products at equilibrium, we say the position of equilibrium lies to the left.
condensation reaction (esterification)
a reaction where a molecule of water is eliminated as two molecules join.
hydrolysis
the splitting of a molecule by reaction with water.
heating under reflux
involves heating the mixture in a flask with a condenser attached.
acid hydrolysis
when esters are heated under reflux with an acid catalyst the hydrolysis reaction is reversible.
alkaline hydrolysis
when esters are heated under reflux with an alkali, the hydrolysis reaction goes to completion. this is thought of in 2 stages, reversible and non-reversible.
fats
- saturated
- pack closely together
- allows many/stronger LDFs to be set up
- results in a solid at room temp
oils
- unsaturated
- distorts long fatty acid chains
- cant pack closely together
- allows fewer/weaker LDFs to be set up
- results in a liquid at room temp
hydrogenation / hardening
this means the addition of H across a carbon to carbon double bond. this is carried using a nickel catalyst.
hard water
water containing calcium and magnesium ions
emulsion
an emulsion contains small droplets of one immiscible liquid dispersed in another.
emulsifier
an emulsifier makes an emulsion more stable by holding the oil water droplets in water for longer.
essential amino acids
amino acids that are not made in the body, so must be found in the diet.
hydrolysis
addition of water molecules to break down large molecules into smaller molecules.
optimum temperature or pH
the rate of reaction or enzyme activity is greatest.
oxidation (natures chemistry)
when carbon compounds are oxidised, the oxygen to hydrogen ratio increases, so either oxygen atoms are being added to the compound, or hydrogen atoms removed.
antioxidants
antioxidants are molecules which will prevent oxidation reactions taking place, antioxidants are reducing agents.
reducing agents
cause reduction to take place but they are oxidised themselves.
free radicals
reactive atoms or molecules with unpaired electrons.
essential oils
concentrated extracts of the volatile, non-water soluble aroma compounds from various parts of plants.
terpenes
unsaturated compounds based on an isoprene unit.
uv light
can cause the covalent bond to break so that molecules split up into atoms or groups of atoms with unpaired electrons.
heterolytic fission
polar bonds, both shared electrons end up with the atom with the greatest electronegativity.
homolytic fission
non-polar bonds, each atom represents an unpaired electron.
sunblock
contains compounds such as titanium dioxide that reflect all the uv so that it doesnt reach the skin at all.
sunscreen
contains organic compounds that absorb/filter the uv so less reaches the skin.
free radical scavengers
produced to react with the free radicals and make stable compounds.
