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Chemistry Leaving Cert Definitions
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- 1Dalton's Atomic Theory1. All matter is made up of small particles called atoms
2. All atoms are indivisible. They cannot be broken down into simpler particles.
3. Atoms cannot be created or destroyed - 2Cathode RaysCathode rays are streams of negatively charged particles called electrons.
- 3An OrbitalAn orbital is a region in space within which there is a high probability of finding an electron.
- 4An ElementAn element is a substance that cannot be split up into simpler substances by chemical means.
- 5A TriadA Triad is a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.
- 6Newlands' OctavesNewlands Octaves are groups of elements arranged in order of increasing atomic weight, in which the first and eight element of each group have similar properties.
- 7Mendeleev's Periodic LawWhen elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the elements vary periodically.
- 8Atomic NumberThe number of protons in the nucleus of that atom.
- 9Modern Period TableAn arrangement of elements in order of increasing atomic number.
- 10Modern Periodic LawWhen elements are arranged in order of increasing atomic number, the properties of the elements vary periodically.
- 11The Mass Number of an ElementThe sum of the number of protons and neutrons in the nucleus of an atom of that element.
- 12IsotopesAtoms of the same element (same atomic number) that have a different mass numbers due to the different number of neutrons in the nucleus.
- 13Relative Atomic Mass- The average of the mass numbers of the isotopes of the element,
- As they occur naturally,
- Taking their abundances into account and,
- Expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units. - 14The Aufbau PrincipleWhen building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level.
- 15Hund's Rule of Maximum MultiplicityWhen two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.
- 16The Pauli Exclusion PrincipleNo more than two electrons may occupy an orbital and they must have opposite spin.
- 17A CompundA substance that is made up of two or more different elements combined together chemically.
- 18The Octet RuleWhen bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
- 19An IonA charged atom or group of atoms.
- 20An Ionic BondThe force of attraction between oppositely charged ions in a compound.
- 21A Transition MetalA transition metal is one that forms at least one ion with a partially filled d sublevel.
- 22A MoleculeA group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.
- 23The Valency of an ElementThe number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.
- 24ElectronegativityThe relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.
- 25Van der Waals ForcesVan der Waal forces are weak attractive forces between molecules resulting from the formation of temporary dipoles.
- 26Dipole-Dipole ForcesDipole-Dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another.
- 27Hydrogen BondsHydrogen bonds are particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule. Thus, it acts as a bridge between two electronegative atoms.
- 28The Law of Conservation of MassThe total mass of the products of a chemical reaction is the same as the total mass of the reactants.
- 29The Law of Conservation of MatterIn any chemical reaction, matter is neither created nor destroyed but merely changed from one form into another.
- 30The Atomic/Covalent Radius of an AtomHalf the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond.
- 31RadioactivityThe spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation.
- 32The Half-Life of an ElementThe time taken for half the nuclei in any given sample to decay.
- 33One Mole of a SubstanceThe amount of that substance which contains 6x10^23 particles of that substance.
- 34Mass of One Mole of an ElementThe relative atomic mass in grams.
- 35The Relative Molecular Mass of a Compound- The sum of the relative atomic masses of all the atoms in a molecule of a compound.
- The mass of one molecule of that compound compared with one twelfth of the mass of the carbon-12 isotope. - 36A GasA substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed.
- 37Boyle's LawAt constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.
- 38Charles' LawAt constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale.
- 39Gay-Lussac's Law of Combining VolumesIn a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided that the volumes are measured at the same temperature and pressure.
- 40Avogadro's LawEqual volumes of gases contain equal numbers of molecules, under the same conditions of temperature and pressure.
- 41Molar VolumeAt s.t.p one mole of any gas occupies a volume of 22.4 litres.
- 42Kinetic Theory of Gases1. Gases are made up of particle that are in continuous motion,
2. There are no attractive/repulsive forces between the molecules of a gas,
3. Their molecules are so small and widely separated that the actual volume is negligible compared with the space that they occupy,
4. When molecules collide, there is no loss of kinetic energy but there may be a transfer of energy between the colliding particles,
5. The average kinetic energy is proportional to the temperature (Kelvin). - 43An Ideal GasAn ideal gas is one that obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.
- 44Real Gases differ from Ideal Gases because..(i) Forces of attraction and repulsion between the molecules and,
(ii) The volume of the molecules is not negligible (especially at high pressure). - 45The Empirical Formula of a compoundThe formula showing the simplest whole number ratio of the numbers of different atoms present in the molecule.
- 46Molecular FormulaIs equal to Empirical Formula x n, (where n is a whole number)
- 47Arrhenius' definition of an AcidAn acid is a substance that dissociates in water to produce H+ ions.
- 48Arrhenius' definition of a BaseA base is a substance that dissociates in water to produce OH- ions.
- 49Brønsted–Lowry definition of an AcidAn acid of a proton donor.
- 50Brønsted–Lowry definition of a BaseA base is a proton acceptor.
- 51Acid to Conjugate BaseAn acid changes into a conjugate base when it donates a proton.
- 52Base to Conjugate AcidA base changes into a conjugate acid when it accepts a proton.
- 53A Conjugate Acid-Base PairAny pair consisting of an acid and a base which differ by one proton.
- 54NeutralisationThe reaction between an acid and a base to form salt and water.
- 55The Concentration of a SolutionThe amount of solute that is dissolved in a given volume of solution.
- 56A 1 Molar SolutionA solution that contains one mole of the solute dissolved in one litre of solution
- 57A Primary StandardA substance which can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration.
- 58A TitrationA laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete.
- 59Oxidation of an ElementOxidation of an element takes place when it loses electrons.
- 60Reduction of an ElementReduction of an element takes place when it gains electrons.
- 61An Oxidising AgentA substance that brings about oxidation in other substances.
- 62A Reducing AgentA substance that brings about reduction in other substances.
- 63Oxidation NumberThe charge that atom has or appears to have when electrons are distributed according to certain rules.
- 64The Rate of ReactionThe change in concentration per unit time of the reactant/product
- 65A CatalystA substance that alters the rate of a chemical reaction but is not consumed in the reaction.
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- Secondary Chemistry Fichas sobre Chemistry Leaving Cert Definitions, creado por AislingK el 06/12/2014.
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