Chemistry Definitions (Full Course)

Dalton’s Atomic Theory

All matter is made up of indivisible atoms which cannot be created or destroyed.

Plum Pudding Model

Solid positive sphere with negative electrons embedded

Energy Level

The fixed energy value an atom in an electron may have

Hiesenberg’s Uncertainty Principle

It is impossible to measure at the same time both the velocity and the position of an electron

Orbital

The region of space around the nucleus of an atom where you are highly likely to fimd and electron

Element

A substance that cannot be split into smaller parts by chemical means

Mendeleev’s Periodic Table arrangement

Elements are arranged in order of increasing atomic weight

Atomic Number

The number of protons in the nucleus of that atom

Mass Number

The sum of the number of protons and neutrons in the nucleus of an atom of that element

Isotope

Atoms of the same element, with the same atomic number, but different mass numbers due to the different number of neutrons in the nucleus

Relative Atomic Mass

The average if the mass numbers of thhe isotopes of an element, as they occur naturally, taking their abundances into account, compared to the Carbon-12 isotope

Aufbau Principle

When an atom is in ground state, electrons occupy the lowest available energy levels first

Hund’s Rule of Maximum Multiplicity

Electrons will fill orbitals singly before they fill in pairs

Pauli Exclusion Principle

No more than 2 electrons may fill and orbital and when they do they have opposite spin

Atomic Radius

Half the distance between the nuclei of 2 atoms of the same element that are joined together by a single covalent bond

First Ionisation Energy

The minimum energy required to remove the most loosely bound electron from a nuetral gaseous atom in ground state

Compound

A substance in which 2 or more elements are chemically combined

Octet Rule

When bonding occurs atoms tend to reach an arrangement with 8 electrons present in their outer shell

Ion

A charged group of atoms

Ionic Bond

The force of attraction between oppositely charged ions in a compound

Valency

The number of atoms of hydrogen or any monovalent with which each atom of the element combines

Electronegativity

The relative attraction an atom in a molecule has for the shared pair of electrons in a covalent bond

London Dispersion Forces

Weak attractive forces between molecules resultingbin the formation of temporary dipoles

Dipole Dipole Bonds

The forces of attraction between the negative pole and positive pole of any molecule

Hydrogen Bonds

A type of Dipole Dipole Bond between in which hydrogen is bonded to other small molecules such as nitrogen, oxygen or fluorine. Resulting in a strong bond

Law of Conservation of Mass

The total mass of the products in a chemical reaction is equal to the total mass of the reactants

Law of Conservation of Matter

In a chemical reaction matter can neither be created or destroyed merely change form

A mole

The amount of a substance that contains 6x10 23 particles of that substance

Relative Molecular Mass

The sum of the relative atomic masses of all the atoms in a molecule of compound

Arrhenius Acid

Substance that dissociates in water to produce H + ions

Arrhenius Base

Substance that dissociates in water or produce OH - ions

Brønsted Lowry Acid

A good proton donor

Brønsted Lowry Base

A good proton acceptor

Conjugate Acid

Will change to a conjugate base when it accepts a proton

Conjugate Base

Will change to a conjugate acid when it accepts a proton

Neutralisation

A reaction between and acid and a base that forms salt and water

Conjugate Acid-Base Pair

Any pair consisting of and acid and a base that differ by one proton

Concentration

The amount of solute that is dissolved in a given volume of solution

Primary Standard

A 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 know concentration

Oxidation

The loss of electrons

Reduction

The gain of electrons

Reducing agent

A substance that brings about reduction in other substances

Oxidising Agent

A substance that brings about oxidation in other substances

Oxidation Number

The charge an atom has or appears to have when electrons are distributed according to certain rules

Reduction (Ox Num)

A decrease in oxidation number

Oxidation (Ox Num)

An increase in oxidation number

Rate of Reaction

The change in concentration per unit time of any one product or reactant

Catalyst

A substance that alters the rate of a chemical reaction but is not used up in it

Activation Energy

The minimum energy required which colliding particles must have for a reaction to occur

Chemical Equilibrium

The state of dynamic balance when ther forward and reverse rate are both equal

Le Chatelier’s Principle

If stress is applied to a system in equilibrium the equilibrium will move to oppose that stress

Electrolysis

The use of electricity to bring about a chemical reaction

The Electrochemical Series

A list of elements in order of their standard electrode potentials

Hydrocarbon

A compound that contains only hydrogen and carbon

Structural isomers

Compounds with the same molecular formula but different structural formulae

Heat of Reaction

The heat change when the number of moles of reactants, indicated in the balanced equation for the reaction, react completely

Heat of Combustion

The heat change when one mole of the substance is burned completely in excess oxygen

Heat of Neutralisation

The heat change when one mole of H + ions from an acid reacts with one mole of OH - ions from a base

Hess’s Law

States that if a chemical reaction take splace in a number of stages, the sum of the heat changes in the seperate stages is equal to the heat change if the reaction was carried out in 1 stage