DALTON'S THEORY: all matter is made up of tiny indivisible particles which can neither be created nor destroyed
ENERGY LEVELS : fixed energy value that an electron in an atom may have
HEISENBERG UNCERTAINTY PRINCIPLE: it is impossible to measure at the same time both the velocity and position of an electron
AN ORBITAL: a region in space within which there is a high probability of finding an electron
THE PERIODIC LAW: when elements are arranged in order of increasing atomic number, the properties of the elements vary periodically
ATOMIC NUMBER: number of protons in the nucleus of that atom
MASS NUMBER: of an element is the sum of the number of protons and neutrons in the nucleus of an atom of that element
ISOTOPE: are atoms of the same element (i.e. same atomic number) that have different mass numbers due to the different number of neutrons in the nucleus
RELATIVE ATOMIC MASS: is the average of the mass numbers of the isotopes of the element, as they occur naturally, taking their abundances into account and compared with 1/12th of the mass of the carbon-12 isotope
THE AUFBAU PRINCIPLE: when building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level
PAULI EXCLUSION PRINCIPLE: no more than two electrons can occupy an orbital and they must have opposite spin
HUND'S RULE: when two or more orbitals of equal energy are available, electrons occupy them singly before filling them n pairs
COMPOUND: is a substance that is made up of two or more different elements chemically combined
OCTET RULE: states when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in outermost shell
IONIC BOND: force of attraction between oppositely charged ions in a compound
TRANSITION METAL: is one that forms at least one ion with a partially filled d sub-level
COVALENT BOND: formed when two atoms share a pair of electrons
VALENCY: the number of atoms of hydrogen or any other monovalent element with which each atom of that element combines
ELECTRONEGATIVITY: the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
LAW OF CONSERVATION OF MASS: total mass of products of a chemical reaction is the same as total mass of reactants
LAW OF CONSERVATION OF MATTER: in any chemical reaction, matter is neither created nor destroyed, but merely changed from one form to another
ATOMIC RADIUS: half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond
FIRST IONISATION ENERGY: of an element is the energy required to remove the most loosely bound electron from a neutral gaseous atom in its ground state
RADIOACTIVITY: is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation
HALF-LIFE: time taken for half of the nucleus in any given sample to decay
RELATIVE MOLECULAR MASS: of a substance is the mass of one molecule of that substance compared with 1/12th of the mass of the carbon-12 isotope
ONE MOLE: is the amount of that substance which contains 6 x 1023 particles of that substance
BOYLE'S LAW: states that at constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure
CHARLE'S LAW: states that at a constant pressure the volume of a fixed mass of gas is directly proportional to its temperature measured on the kelvin scale
GAY-LUSSAC'S LAW: states that in a reaction between gases the volume of the reacting gases and the volume of any gaseous products are in the ratio of small whole number provided that the volumes are measured at the same temperature and pressure
AVOGADRO'S LAW: states that equal volumes of gases contain equal number of molecules under the same conditions of temperature and pressure
IDEAL GAS: is one that obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure
EMPERICAL FORMULA OF A COMPOUND: formula which gives the simplest whole number ratio of the elements in the compound
MOLECULAR FORMULA OF A COMPOUND: formula that gives the actual number of each atom in the molecule