Key Definitions Flashcards
(28 cards)
Element
A substance that cannot be broken down into simpler substances by chemical means.
(Robert Boyle)
Element
A substance whose atoms all have the same atomic number.
Law of Conservation of Mass
States that matter cannot be created or destroyed in the course of a chemical reaction.
Atomic Number
The number of PROTONS in the nucleus of an atom.
Mass Number
The sum of the number of protons AND neutrons in the nucleus of an atom.
Isotopes
Atoms with the same number of protons but different numbers of neutrons.
Relative Atomic Mass
The average mass of an atom relative to 1/12 of the mass of an atom of Carbon-12
Radioactivity
The spontaneous breaking up of unstable nuclei, accompanied by the emission of radiation.
Alpha Particles
Have 2 protons + 2 neutrons (helium nuclei)
Have a POSITIVE charge and little penetrating ability.
Americium-241
Beta Particles
Neutrons disintegrate into protons and electrons. The electrons are emitted in a fast-moving stream - negative charge.
Carbon-14
Gamma Rays
Emitted by radioactive isotopes. No mass or charge, move very quickly.
High-energy electromagnetic radiation.
Cobalt-60
Half-Life
The half-life of a radioactive isotope is the time taken for half of the atoms in the isotope to decay.
Energy Level
A region of definite energy within the atom that electrons can occupy.
Line Spectrum
A seriös of coloured lines against a dark background .
Absorption Spectrum
The spectrum that is observed after white light had been passed through the element.
Heisenberg Uncertainty Principle
States that is it not possible to determine the position and velocity of an electron at the same time.
Atomic Orbital
A region in space where the probability of finding an electron is relatively high.
Energy Sublevel
A group of atomic orbitals that all have the same energy.
Aufbau Principle
States that electrons will occupy the lowest energy sublevel available.
Atomic Radius
Half the distance between the nuclei of two atoms that are joined together by a single covalent bond.
First Ionisation Energy
The minimum energy in kJ required to remove the most loosely bound electron from each isolated atom of the element in its ground state.
Second Ionisation Energy
The energy required to remove the most loosely bound electron from each singly charged positive ion in a mole of these ions.
Oxidation
The loss of electrons.
(Occurs at anode)
Reduction
The gain of electrons.
(Occurs at cathode)
