Chemistry Definitions Flashcards
chemical bond
a mutual attraction between two atoms resulting from the
simultaneous attraction between their nuclei and the outer electrons.
Valence electrons
the electrons in the highest energy level of an atom in which there are electrons.
covalent bond
the sharing of electrons between two non-metal atoms to form a molecule.
molecule
A group of two or more atoms covalently bonded and that function as a unit.
bonding pair
a pair of electrons that is shared between two atoms in a covalent bond.
lone pair
a pair of electrons in the valence shell of an atom that is not shared with another atom.
electronegativity
a measure of the tendency of an atom in a molecule to attract bonding electrons.
non-polar covalent bond
a bond in which the electron density is shared equally between the two atoms.
polar covalent bond
a bond in which the electron density is shared unequally between the two atoms.
bond energy of a compound
the energy needed to break one mole of a substance’s molecules into separate atoms.
bond length
the average distance between the nuclei of two bonded atoms.
Mutually induced dipole forces or London forces:
Forces between non-polar
molecules
Dipole-dipole forces:
Forces between two polar molecules
Dipole-induced dipole forces:
Forces between polar and non-polar molecules
Hydrogen bonding:
Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or fluorine – a special case of dipole-dipole forces
Ion-dipole forces:
Forces between ions and polar molecules
Ion-induced dipole forces
forces between ions and non-polar molecules
Boiling point:
The temperature at which the vapour pressure of a substance equals atmospheric pressure.
Melting point:
The temperature at which the solid and liquid phases of a substance are at equilibrium.
Vapour pressure:
The pressure exerted by a vapour at equilibrium with its liquid in a closed system.
Solubility:
The property of a solid, liquid, or gaseous chemical substance (solute) to
dissolve in a solid, liquid, or gaseous solvent (solvent) to form a homogeneous solution.
Thermal expansion
the change in volume of a substance as the temperature increases.
thermal conductivity
the ability of a substance to conduct heat
surface tension
the force between particles on the surface of a liquid that tends to minimise the surface area of a liquid
viscosity
a measure of how easily a liquid flows as particles move past each other
capillarity
the tendency of a liquid to rise against gravity in a narrow tube
specific heat
the amount of energy required to increase the temperature of a unit mass of a substance by 1 degree C
(latent) heat of vaporisation
energy needed to change a given quantity of a substance into a gas
Brownian motion
the random movement of particles in a liquid or gas caused by collisions between these particles and the motion of the liquid/gas.
ideal gas
a gas with identical particles of zero volume with no IMFs all moving at the same speed
real gas
gases that behave like ideal gases except at high pressures and/or low temperatures
temperature
a measure of the average kinetic energy of a gas
pressure
the force applied per unit area by a gas when the gas particles collide
Boyle’s law:
The pressure of an enclosed gas is inversely proportional to the volume it occupies at constant temperature.
Charles’ law:
The volume of an enclosed gas is directly proportional to its kelvin temperature provided the pressure is kept constant.
Gay-Lussac’s Law
the pressure of a gas is directly proportional to its temperature in kelvin at
constant volume
Avagadro’s Law
one mole of any gas occupies the same volume at the same
temperature and the same pressure
one mole
the amount of substance having the same number of particles as
there are atoms in 12 g carbon-12.
molar mass
the mass of one mole of a substance measured in g·mol-1
concentration
the amount of solute per litre of solution.
molecular formula
the total number of atoms of each element present in a molecule
limiting reagent
a reagent that is completely used up in a chemical reaction
heat of reaction (ΔH)
the energy absorbed or released per mole in a chemical reaction.
exothermic reactions
reactions that release energy.
endothermic reactions
chemical reaction that absorbs energy
activation energy
the minimum energy needed for a reaction to take place.
activated complex
the unstable transition state from reactants to products.
Arrhenius theory:
Acids and Bases
An acid is a substance that produces hydrogen ions (H+)/hydronium ions (H3O+) when it dissolves in water.
A base is a substance that produces hydroxide ions (OH-) when it dissolves in water.
Lowry-Brønsted theory:
Acid and Base
An acid is a proton/H+ ion donor.
A base is a proton/H+ ion
acceptor.
Ampholyte
a substance that can act as either acid or base,
acid-base indicator
a weak acid, or a weak base, which colour changes
as the H+ ion concentration or the OH- ion concentration in a solution changes.
Redox reaction
a reaction involving an electron transfer. It always involves changes in oxidation numbers
Oxidation:
A loss of electrons./An increase in oxidation number.
Reduction:
A gain of electrons./A decrease in oxidation number.
Reducing agent:
A substance that is oxidised/that loses electrons/whose oxidation
number increases.
Oxidising agent:
A substance that is reduced/that gains electrons/whose oxidation
number decreases.
synthesis reaction
a reaction in which 2 or more substances combine to form a new product
decomposition reaction
a reaction in which a substance breaks up into two or more products
displacement reaction
a reaction in which an ion of a less reactive element is replaced with an ion of a more reactive element.
