LC Chemistry

Dalton's Atomic Theory

A theory that states that all matter is made up of small particles called atoms. All atoms are indivisible. Atoms cannot be created or destroyed.

Cathode Rays

Streams of negatively charged particles called electrons.

Energy Level

The fixed energy value that an electron in an atom may have.

Orbital

A region in space within which there is a high probability of finding an electron.

Sublevel

A subdivision of a main energy level and consists of one or more orbitals of the same energy.

Ground State

The state of an atom when all of its electrons are in their lowest available energy levels.

Excited State

The state of an atom when one or more of its electrons have been promoted to higher energy levels.

Heisenberg's Uncertainty Principle

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

Aufbau Principle

When building up the electronic configuration of an atom in its ground state, the electrons occupy the lowest available energy level.

Hund's Rule of Maximum Multiplicity

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

Pauli Exclusion Principle

No more than 2 electrons may occupy an orbital and they must have opposite spin.

Dobereiner Triad

A group of 3 elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.

Newlands' Octaves

Groups of elements arranged in order of increasing atomic weight, in which the first and eighth element of each group have similar properties.

Mendeleev's Periodic Law

When elements are arranged in order of increasing atomic weight (relative atomic mass) the properties of the elements vary periodically.

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 of the same element that have different mass numbers due to a different number of neutrons in the nucleus.

Relative Atomic Mass

The average of the mass numbers of the naturally occurring isotopes of an element (taking their abundances into account) expressed on a scale in which in which the atoms of the carbon-12 isotope have a mass of exactly 12 units.

Alloy

A mixture of metals.

Amphoteric Oxide

An oxide that shows both acidic and basic properties.

Amphoteric Substance

A substance that can act both as an acid and as a base.

The Octet Rule

When bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.

Element

A substance that cannot be split into simpler substances by chemical means.

Compound

A substance that is made up of two or more different elements combined together chemically.

Molecule

A group of atoms joined together.

Ion

A charged atom or group of atoms.

Ionic Bond

The force of attraction between oppositely charged ions in a compound.

Transition Metal

A metal that forms at least one ion with a partially filled d sublevel.

Covalent Bond

A bond that involves the sharing of electrons.

Polar Covalent Bond

A covalent bond in which the electrons are shared unequally.

Valency

The number of atoms of hydrogen or any other monovalent element with which each atom of an element combines.

VSEPR

The Valence Shell Electron Pair Repulsion theory states that the shape of a molecule depends on the number of pairs of electrons in the valence shell of the central atom. Since electrons are negatively charged, the electron pairs repel each other and arrange themselves in space so as to be as far apart as possible.

Electronegativity

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

Van Der Waals Forces

Weak attractive forces between molecules resulting from the formation of temporary dipoles.

Dipole-Dipole Forces

Forces of attraction between the negative pole of one molecule and the positive pole of another.

Hydrogen Bonds

Particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen, or fluorine.(small, highly electronegative elements)

Intermolecular Forces

Forces of attraction between molecules.

Intramolecular Forces

Bonding within a molecule (e.g., covalent or ionic bonding).

Immiscible Liquids

Liquids that do not mix.

The Law of Conservation of Mass

The total mass of the products of a chemical reaction is the same as the total mass of the reactants.

The Law of Conservation of Matter

In any chemical reaction, matter is neither created nor destroyed, but merely changes from one form to another.

Atomic Radius (Covalent Radius)

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

First Ionization Energy

The minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state.

Second Ionization Energy

The energy required to remove an electron from an ion with one positive charge in the gaseous state.

Radioactivity

The spontaneous decay of unstable nuclei with the emission of one or more types of radiation.

Radioisotope

A radioactive isotope.

Half-Life

The time taken for half of the nuclei in any given sample to decay.

Mole

One mole of a substance is the amount of that substance which contains 6 x 10^23 particles of that substance.

Boyle's Law

At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.

Charles' Law

At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured on the Kelvin scale.

Gay-Lussac's Law of Combining Volumes

In a reaction between gases, the volume of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers, provided the volumes are measured at the same temperature and pressure.

Avogadro's Law

Equal volumes of gases contain equal numbers of molecules, under the same conditions of temperature and pressure.

Ideal Gas

A gas that obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.

Volatile Liquid

A liquid with a low boiling point that is easily vaporized.

Arrhenius' Definition of an Acid

An acid is a substance that dissociates in water to produce H+ ions.

Arrhenius' Definition of a Strong Acid

A strong acid is an acid that dissociates fully in water to produce H+ ions.

Arrhenius' Definition of a Weak Acid

A weak acid is an acid that partially dissociates in water to produce H+ ions.

Arrhenius' Definition of a Base

A base is a substance that dissociates in water to produce OH- ions.

Arrhenius' Definition of a Strong Base

A strong base is a base that dissociates fully in water to produce OH- ions.

Arrhenius' Definition of a Weak Base

A weak base is a base that partially dissociates in water to produce OH- ions.

Bronsted-Lowry Definition of an Acid

An acid is a proton donor.

Bronsted-Lowry Definition of a Strong Acid

A strong acid is a good proton donor.

Bronsted-Lowry Definition of a Weak Acid

A weak acid is a poor proton donor.

Bronsted-Lowry Definition of a Base

A base is a proton acceptor.

Bronsted-Lowry Definition of a Strong Base

A strong base is a good proton acceptor.

Bronsted-Lowry Definition of a Weak Base

A weak base is a poor proton acceptor.

Conjugate Acid-Base Pair

Any pair consisting of an acid and a base which differ by one proton. A strong acid has a weak conjugate base and vice versa. A weak acid has a strong conjugate base and vice versa.

Neutralisation

A reaction between an acid and a base to form a salt and water.

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 known concentration.

Standard Solution

A solution of known concentration.

Oxidation Number

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

Oxidation

(i) Oxidation is the loss of electrons (ii) Oxidation is an increase in oxidation number

Reduction

(i) Reduction is the gain of electrons (ii) Reduction is a reduction in oxidation number

Rate of Reaction

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

Instantaneous rate of reaction

The rate of reaction at any one particular time during the reaction

Catalyst

A substance that alters the rate of reaction but is not consumed in the reaction.

Enzyme

A substance produced by a living cell and acts as a biological catalyst

Autocatalysis

The catalysis of a reaction by one of the products of that reaction.

Heterogeneous Catalysis

Reactant and catalyst in different phases

Homogeneous Catalysis

Reactant and Catalyst in the same phase

Catalyst poison

A substance which destroys the activity of a catalyst.

Activation Energy

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

Reversible reaction

A reaction in which the products react to give back the reactants (reaction is going in both directions)

Chemical Equilibrium

A state of dynamic balance where the rate of the forward reaction equals the rate of the reverse direction.

Dynamic Equilibrium

Reactants are continually reacting to form products and products are continually decomposing to form reactants. The reaction is always moving.

Le Chatalier’s Principle

If stress is applied to a system at equilibrium, the system readjusts to relieve the stress applied.

Equilibrium constant, Kc

For a reversible system, a constant that tells how far the reaction has gone to the right-hand side, by the time equilibrium has been established.

pH

pH = -log10[H+] where the square brackets indicate concentration in moles per litre

Ionic product of water

Kw = [H+][OH-] = [H3O+][OH-]

Self-ionisation of water

2H2O -> H3O+ + OH-

Hard Water

Water that will not easily form a lather with soap. Hardness in water caused by the presence of Calcium(Ca2+) or Magnesium(Mg2+) ions.

Temporary Hardness

Hardness that can be removed by boiling the water.

Permanent Hardness

Hardness that cannot be removed by boiling and is caused by the presence of calcium sulfate(CaSO4) or magnesium sulfate(MgSO4).

Biological Oxygen Demand (B.O.D.)

The amount of dissolved oxygen consumed by biological action when a sample of water is kept at 20 degrees Celsius in the dark for 5 days.

Eutrophication

The enrichment of water with nutrients leading to excessive growth of algae.

Flocculation

The process in which small particles in water are made to coagulate (clump together) and form a precipitate. It is done by adding a FLOCCULATING AGENT such as aluminium sulphate.

Electrolysis

The use of electricity to bring about a chemical reaction.

Electroplating

A process where electrolysis is used to put a layer of one metal on the surface of another.

Electrochemical Series

A list of elements in order of their standard electrode potential.

Homologous Series

A series or family of compounds in which the molecular formula of each member differs from that of the previous member by a definite number of carbon and Hydrogen atoms.