LC Chemistry Definitions

Relative atomic mass

The average mass of an atom, relative to 1/12 mass of the carbon 12 isotope, with its abundance taken into account.

What are isotopes?

Atoms of the same element with different numbers of neutrons.

Define a mole of a substance

An amount containing Avogadro's number of particles*

State Avogadro's Law

Equal volumes of gases contain equal numbers of molecules under the same conditions

State Charles' Law

Volume of a gas varies directly with temperature

State Boyle's Law

The volume of a gas is inversely proportional to pressure at constant temperature

Define mass number

The sum of the number of protons and neutrons in an atom of an isotope

State Gay-Lussac's Law of Combining Gases

The volumes of reacting gases at the same temperature and pressure, can be represented by whole number ratios

Define electronegativity

The measure of the ability of an atom to attract a shared pair of electrons in a covalent bond

State Le Chatelier's principle

A system at equilibrium will move to oppose stress

Define atomic orbital

A region of space surrounding the nucleus where there is a 99% probability of finding an electron

Define first ionisation energy

The minimum energy needed to remove the most loosely-bound electron from a gaseous atom in its ground state

Define (atomic) Energy level

Discrete energy of an electron

Define radioactivity

Spontaneous emission of alpha, beta, or gamma radiation from an unstable decaying nuclei.

Define atomic radius

Half the distance between the centres of two single-bonded atoms of the same element

What is the series of coloured lines in a line emission spectrum known as?

The Balmer series

What is an ideal gas?

A gas that obeys the gas laws under all conditions

Define bond energy

Average energy required to break one mole of a bond and to separate the atoms

State the Heisenberg uncertainty principle

It is not possible to measure both the position and momentum of an electron simultaneously

Who discovered Cathode rays?

JJ Thompson

Explain the term "Intermolecular forces"

Attractive or repulsive forces between molecules

What is meant by ground state?

An electron in its lowest energy state

Hydrogen "bonding"

the intermolecular force in which a hydrogen atom that is bonded to an atom of NOF is attracted to a lone pair of another electronegative molecule

Dipole-dipole interaction

an attraction between regions of polar molecules that have partial charges of opposite sign

Van der Waals Forces

a slight, brief attraction that develops between the oppositely charged regions of nearby molecules

Define second ionisation energy

The energy required to remove an electron from a monopositive atom in its ground state

State Aufbau principle

An electron occupies the lowest-energy orbital first in its ground state

State the Pauli exclusion principle

Maximum of 2 electrons may occupy an orbital and they must be of opposite spin

State Hund's rule of maximum multiplicity

states that when two or more orbitals of
equal energy are available, they fill them single before fully.

Define octane number

A measure of the tendency of a fuel to resist knocking

activation energy

minimum energy required for colliding particles to react

aliphatic compound

organic compound that consists of open chains of carbon atoms and ring compounds that resemble them in chemical properties

Alkane

a hydrocarbon containing only single covalent bonds

Alkenes

hydrocarbons that contain only one double carbon-carbon bond

alkynes

hydrocarbons which contain only one carbon-carbon triple bond

amphoteric substance

substance which can act as either an acid or a base e.g water

Anion

A negatively charged ion attracted to the anode

anode

Positive electrode

cation

A positively charged ion attracted to the cathode

cathode

Negative electrode

aromatic compounds

substances containing a benzene ring

Atomic number

the number of protons in an atom

Atomic orbit

fixed path of an electron around the nucleus of an atom

Sublevel

subdivision of an atomic orbit (main energy level) and consists of one or more orbitals of the same energy

Autocatalysis

catalysis of a reaction by one of the products of that reaction

Biochemical Oxygen Demand (BOD)

the amount of oxygen consumed when a sample of water is kept in the dark at 20°C for five days

Bronsted-Lowry acid

proton donor

Bronsted-Lowry base

proton acceptor

Bronsted-Lowry strong acid

good proton donor

Bronsted-Lowry weak acid

poor proton donor

Arrhenius acid

substance that dissociates in water to produce H+ ions

Arrhenius base

substance that dissociates in water to produce OH- ions

Esterification

The reaction of an alcohol with a carboxylic acid to produce an ester and water.

Eutrophication

nutrient enrichment in lakes caused by heavy metal ions in polluted water leading to algal bloom (algae overgrowth)

Excited state

electrons at higher energy levels than ground state

Exothermic reaction

Reaction that releases heat

Endothermic Reaction

Reaction that absorbs heat

Saponification (Base Hydrolysis)

A variation on esterification where a long chain Organic Acid reacts with a base to produce a Soap molecule (metal salts of fatty acids)

hydrolysis reaction

A chemical reaction that breaks apart a larger molecule by adding a molecule of water

addition reaction

A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule

elimination reaction

The removal of a molecule from a saturated molecule to make an unsaturated molecule

substitution reaction

a reaction in which one or more atoms replace another atom or group of atoms in a molecule

Screening (of drinking water)

water passed through a wire mesh to remove floating debris

flocculation

addition of a flocculating agent to water to cause clumping (coagulation) of suspended solids

sedimentation

water passed into bottom of settlement tanks, rises up slowly and clear water decants into channels, solids remain at base

Chlorination

chlorine added to water to sterilise it (kill micro-organisms)

fluoridation

adding flourine to drinking water to reduce tooth decay and strengthen enamel

Primary treatment of sewage

large solids removed by screened and suspended solids removed by sedimentation

secondary treatment of sewage

decomposition of sewage pollutants by micro-organisms

tertiary treatment of sewage

removal of phosphorus compounds by precipitation and removal of nitrogen compounds by ion-exchange or denitrifying bacteria

principle of colorimetry

amount of absorbance of light by a coloured solution is proportional to the concentration of the solution

feedstock

Raw materials needed for a chemical manufacturing process.

fractional distillation

separation of crude oil into different compounds by boiling point differences

octane number

measure of the ability of a fuel to resist auto-ignition

EDTA

ethylenediaminetetraacetic acid

MTBE

Methyl Tertiary Butyl Ether

ways to increase octane number

Dehydrocyclisation, isomerisation, catalytic cracking, addition of oxygenates

Heterogenous catalysis

catalysis where reactants and catalyst are in different phases

functional group

group of atoms within a molecule that allows that molecule to be identified

ground state

electrons at lowest energy state

hard water

water that contains calcium or magnesium ions in it that does not easily form a lather with soap and forms scum

heat of combustion

energy released when one mole of a substance is burned completely in excess oxygen

heat of formation

energy change when one mole of a substance is formed from its reactants in their ground states

heat of reaction

energy change in a chemical reaction according to the equation

heat of neutralisation

The heat change when one mole of H+ ions from an acid reacts with one mole of OH- ions from a base.

Hess's law equation

∆Hr = Σ∆HfP - Σ∆HfR

Oxidising agent

Substance that causes oxidation and it itself is reduced

Oxidation

loss of electrons, increase in oxidation number, increase in oxygen

Reducing agent

substance that causes reduction and it itself is oxidised

reduction

gain of electrons, decrease in oxidation number, decrease in oxygen

temporary hardness

water hardness that can be removed by boiling the water

permanent hardness

water hardness that cannot be removed through boiling

methods of removing hardness

boiling, distillation, Washing soda (Na2CO3), ion-exchange resin

complexometric titration

titration involving formation of complex between metal ions and a reagent e.g edta

buffer solution

solution that resists changes in pH

carbonium ion

Unstable positive carbon intermediate

Primary standard

substance that is pure, stable, does not sublime, can be used to make up a standard solution, does not effervesce

how is hydrogen gas produced industrially

electrolysis of water, steam reforming

Volatile liquid

a liquid that evaporates readily or at a low temperature

Dalton's atomic theory

All matter is made up of very small particles.
Atoms are individible