1.
1st law of thermodynamics: states that during chemical reactions, energy is only converted from one form to another - it can either be created nor destroyed.
2.
atomic radius: actual sizes of atoms calculated from average distance between neighbouring atoms.
e.g. atomic radius of hydrogen atom is one half of the shortest inter-atomic distance.
3.
bond energy: the minimum energy required to break one mole of a specified bond in a gaeous molecule.
4.
bond polarity: when 2 atoms have different electronegativities, an uneven sharing of bond pair or pairs of electrons.
5.
catalysts: are substances which change the rate of a chemical reaction without themselves being used up.
6.
change in enthalpy: chemical reactions involve changes in energy.
7.
chemical bonds: forces that holds atoms together in compounds. An electrostatic force of attractin between -ve and +ve charged species.
8.
covalent bonds: involves sharing of at least one pair of electrons between 2 atoms. If 2 atoms are different, they will have different attraction for the bonded pair of electrons(electronegativities).
9.
electronegativity: the measure of attraction between a nucleus and a bonded pair of electrons. This attraction that an atom has for its bonded electrons depend on nuclear charge, distance between nucleus and bonded electrons(atomic radius), and the shielding effect of inner electrons.
10.
endothermic: breaking bonds requires energy. as reactants form individual atoms.
11.
exothermic: forming bonds releases energy. between atom to form products.
12.
Hess's law: states that the energy change (heat evolved or absorbed) due to a chemical reaction is independent of the route (pathway) taken.
13.
ionic bonds: forms between atoms that lose or gain electrons. +ve and -ve ions are attracted to each other.
14.
ionic radius: mono-atomic ions, calculated using measurements of ionic crystals.
15.
ionisation energies: the minimum energy needed to move one electron from each atom in a mole of atoms in the gaseous state.
16.
latent heat of fusion/enthalpy of fusion: energy needed to break enough of the weakest forces of particles in 1mol of a solid at its melting point to form a liquid.
17.
latent heat of sublimation/enthalpy of sublimation: energy needed to break enough of the forces between the particles to convert 1mol of a solid to gas.
18.
latent heat of vapourisation/enthalpy of vapourisation: energy needed to break enough of the weakest forces between the particles in 1mol of a liquid at its boiling point to form a gas.
19.
non-polar diatomic molecules: if 2 atoms have the same electronegativity and the bonded pair of electron is shared equally.
e.g. oxygen
20.
non-polar polyatomic molecules: contains more than 2 atoms, and polar bonds, the molecule is non-polar if it is arranged symmetrically around the central atom so that the dipoles cancels out.
e.g. carbon dioxide
21.
permanent dipole: the more electronegative atom has a stronger pull on the electrons so becomes slightly -ve. the less electronegative atom has the weaker pull on the electrons so it becomes slightly +ve.
22.
permanent dipole-dipole attractions: adding to temporary dipoles, polar molecules have permanent dipole-dipole forces of attraction.
23.
phase: of a substance is a recognisable form in which that substance exists.
24.
polar diatomic molecules: if 2 atoms have different electronegativities and the bond joining the atoms is a polar covalent bond. Overall molecule is dipole.
e.g. hydrochloric acid
25.
polar polyatomic molecules: contains more than 2 atoms, and polar bonds arranged asymmetrically around the central atom so that the dipoles don't cancel out. Overall it is polar molecule- acts as a dipole.
e.g. carbon dioxide
26.
temporary dipole-dipole attractions: changing molecular polarities through uneven distribution of electrons as electrons move randomly in their orbitals. Influenced by shape of the molecule.
27.
transition metals: an element whose atoms form at least one ion with apartially filled 'd' subshell. Found within the 'd' block of the periodic table. (Sc and Zn don't form an ion with a partially filled 'd' subshell, so dn't have all the properties of transition metals.)
