chem defs

• Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction
• Atomic Number (Z): Number of protons in the nucleus of an atom
• Mass Number (A): Sum of the number of protons and neutrons in the nucleus
• Isotopes: Atoms with the same number of protons but different numbers of neutrons
• Relative Atomic Mass (Ar): Average mass of an atom of an element relative to one-twelfth of the mass of a carbon-12 atom
• Radioactivity: Spontaneous disintegration of certain unstable nuclei and the emission of radiation
• Half-Life of a radioactive isotope: Time taken for half the atoms in a sample of the isotope to decay
• Energy Level: Region of definite energy within the atom that electrons can occupy
• Absorption Spectrum of an Element: Spectrum observed after light has passed through the element
• Heisenberg Uncertainty Principle: It is impossible to determine at the same time the exact position and velocity of an atomic particle
• Atomic Orbital: Region in space within an atom where the probability of finding an electron is relatively high
• Energy Sublevel: Group of atomic orbitals within an atom, all of which have the same energy
• Aufbau Principle: Electrons will occupy the lowest available sublevel available to them
• Atomic Radii: Half the distance between the nuclei of two atoms of the element that are joined together by a single covalent bond
• First Ionisation Energy: Minimum energy needed to remove the loosely held electron from an isolated atom of the element in its ground state
• Oxidation: Loss of electrons, increase in oxidation number
• Reduction: Gain of electrons, decrease in oxidation number
• Oxidising Agent: Substance that allows oxidation to happen by gaining electrons itself
• Reducing Agent: Substance that allows reduction to happen by losing electrons itself
• Electrolyte: Substance that conducts electricity when dissolved in water or molten
• Electrolysis: Splitting up of a substance due to the passage of an electric current through it in an aqueous solution or when molten
• Valency: Number of bonds an atom of the element forms when it reacts
• Ionic Bond: Electrostatic force between oppositely charged ions
• Covalent Bond: Formed when two atoms share a pair of electrons
• Polar Covalent Bond: Bond where electrons are shared unequally between two atoms
• Electronegativity: Relative attraction of an atom for the shared pair of electrons in a covalent bond
• Electron Pair Repulsion Theory: Electron pairs in the valence shell of the central atom repel each other and end up as far apart as geometrically possible
• Diffusion: Spontaneous spreading out of a substance, natural movement of its particles
• Boyle's Law: At a constant temperature, the volume of a gas is inversely proportional to the pressure of the gas
• Charles's Law: At constant pressure, the volume of a gas is directly proportional to the temperature in Kelvins
• Gay-Lussac's Law of Volumes: When gases react, the volumes consumed in the reaction are simple whole number ratios to one another, under the same conditions of temperature and pressure
• Avogadro's Law: Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules
• Mole: Amount of a substance that contains as many particles (atoms or molecules or ions) as there are atoms of 12C in 12g of 12C
• Relative Molecular Mass (Mr): Average mass of a molecule of the substance relative to one twelfth of the mass of an atom of 12C
• Molar Mass: Mass in grams of a mole of the substance
• Ideal Gas: Gas that obeys all the assumptions of the kinetic theory under all conditions of temperature and pressure (PV = nRT)
• Empirical Formula: Indicates what elements are present and the simplest whole number ratio in which the atoms of these elements are present
• Molecular Formula: Actual number of atoms of each element present in a molecule of the compound
• Structural Formula: Arrangement of the atoms within a molecule of the compound
• Arrhenius Acid: Substance that dissolves forming hydrogen ions