Period Table & Atomic Theory

Atomic Orbital

Region (with no definite boundary) in space around nucleus in which there is high probability of finding an electron

Relative Atomic Mass

Average mass of atoms of element compared (relative) to 1/12 mass of carbon-12 isotope

First Ionisation Energy

Minimum energy to remove most loosely-bound electron from an isolated gaseous atom in its ground state

Oxidation

Loss of electrons or Increase in oxidation number (may be asked for one or both specifically)

Isotopes

Atoms of same element with different mass numbers due to different number of neutrons or atoms with same atomic number (Z) but different mass numbers (A)

(Atomic) Energy Level

Fixed amount of energy of an electron in an atom

Radioactivity

Spontaneous breaking up of a nucleus to release α, β or γ radiation

Atomic Radius

Half the distance between the nuclei of two identical atoms (of the same element) joined by a single covalent bond

Heisenberg’s Uncertainty Principle

It is not possible to measure the exact position and momentum of electron in atom simultaneously (at the same time)

Alpha particle

Helium (He) nucleus or particle consisting of 2 protons + 2 neutrons

Principle of Mass Spectrometry

Positively charged ions are separated by mass when moving in a magnetic field

Ground State

In lowest energy state or in n = 1 level (shell)

Excited State

Higher energy state or in n > 1 level (shell)

Atomic Number

Number of protons in nucleus of an atom

Radioisotope

Radioactive isotope or isotope (atom) with unstable nucleus

(Energy) Sub-Level

Sub-division of a main energy level consisting of one or more orbitals of the same energy

Mass Number

Number of nucleons (protons + neutrons) in the atoms of an isotope

Half Life

Time taken for half of the nuclei in a sample to decay or Time taken for activity to reduce by (to) a half

Oxidation number

Charge on atom if electrons distributed by rules (if bonds assumed ionic)

Second ionisation energy

Electron removed from monopositive ion or X+ → X2+ + e-

Reduction

Gain of electrons or decrease in oxidation number (may be asked for one or both specifically)

Cathode Rays

Streams of negatively charged electrons which travel from the cathode to anode, are deflected by magnetic and electric fields, and have sufficient energy to move a small object e.g. paddle wheel

(Bohr) Orbit

2-D pathway at fixed distance from nucleus where electron is definitely located

Element

An element cannot be broken down into anything simpler

Mendeleev’s Periodic Law/System

When elements are listed according to relative atomic mass, their chemical properties repeat periodically

Modern Periodic Law/System

When elements are listed according to atomic number, their chemical properties repeat periodically

Aufbau Principle

Electrons occupy the lowest available energy levels

Dalton’s Atomic Theory

All matter is made of indivisible small particles called atoms

Empirical Formula

Shows simplest whole number ratio of the different atoms in a molecule

Molecular Formula

Shows the number and type of each atom in a molecule of a compound

Hund’s Rule

When two or more orbitals of equal energy are available, electrons occupy them singly before filling them in pairs

Law of Conservation of Matter/Mass

During chemical reaction matter is neither created nor destroyed or Total mass of reactants = total mass of products

Newland’s Octaves

Arrangement of elements in which the first and the eighth have similar properties

Nuclear Reaction

Process that alters the composition, structure, or energy of a nucleus

Pauli Exclusion Principle

No more than two electrons may occupy an orbital and they must have opposite spin

(Radio)Carbon Dating

Dates an object containing carbon based on C-14 to C-12 ratio

Triad

Group of 3 elements with similar chemical properties where the atomic weight of the middle one is approx. equal to the average of the other two

Oxidising Agent

Substance that brings about oxidation in other substances (is reduced)

Reducing Agent

Substance that brings about reduction in other substances (is oxidised)

Electrolysis

Use of electricity to bring about chemical reaction in an electrolyte

Electrolyte

Compound which conducts electricity when molten or dissolved in water