Chemistry LC definitions

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

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+ à 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 or 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

Electronegativity

Measure of attraction of an atom for shared electrons in a covalent bond

Pi Bond

Sideways overlap of p-orbitals

Sigma Bond

Head-on (end-on) overlap of orbitals (any type of orbitals)

Intermolecular

Forces between molecules

Ionic bonding

Bond between oppositely-charged ions

Polar Covalent Bonding

Unequal sharing of bonding electrons or bond has slight positive and slight negative ends

Intramolecular

Forces between atoms (with)in a molecule

Covalent Bond

Involving the sharing of one or more pair(s) of electrons

Compound

Single substance made of two or more different elements (types of atoms)

Dipole-Dipole Forces

Attraction between polar molecules (d+ of one and d- of the other)

Hydrogen Bonds

Particular dip-dip for molecules where H is bonded to N, O, or F

Ion

Charged atom or group of atoms

Octet Rule (of thumb)

When bonding, atoms tend to reach an electron configuration with eight electrons in the outermost energy level

Van der Waals Forces

Weak attraction between non-polar molecules due to temporary dipoles

Valency

Number of H atoms with which each atom of the element combines

Transition Metal

Forms at least one ion with a partially filled d sub-level

Molecule

Group of covalently bonded atoms which is the smallest particle of an element or compound that can exist independently

Avogadro's Law

Equal volumes of gases at the same temperature and pressure have equal numbers of particles (not all conditions or at STP)

Mole

Contains the Avogadro number (6 x 1023) of particles or relative molecular mass in grams (g) or amount containing as many particles as the no. of atoms in 12g of carbon-12

Charles' Law

Volume varies directly with Kelvin temperature for definite mass of gas at constant pressure or V/T* = k for definite mass of gas at constant pressure *Capital letter.

Ideal Gas

A gas that obeys the gas laws under all conditions of temperature and pressure

Gay Lussac's Law

Volumes of reacting gases and their gaseous products are in small whole number ratios provided they are measured at the same temperature and pressure (not all conditions or STP)

Boyles' Law

Pressure inversely proportional to volume for definite mass of gas at constant temp or PV = k

Acid (Brønsted-Lowry)

Proton (H+) donor

Base (Brønsted-Lowry)

Proton (H+) acceptor

Conjugate Pair

Acid-Base differing by a proton (H+)

Primary Standard

Pure, stable, water soluble, high molecular mass substance from which solutions of known concentration can be made

Base (Arrhenius)

Produces OH- ions in aqueous solution or dissociates into OH- in water

Conjugate Acid (B-L)

Produced by gain of one proton (H+) or Base + H+

Standard Solution

Solution of known concentration (molarity)

Standardised

Concentration known by another titration (or by colorimetry or by u.v. spectroscopy)

Acid (Arrhenius)

Produces H+ (hydrogen ion) by dissociation in water (aqueous solution)

Concentration (Molarity)

Amount of solute dissolved in given volume of solution (moles/L)

Titration

Measured vol of one solution added to known vol of another until reaction is complete

Salt

When the H in an acid is replaced by a metal or ammonium ion

Neutralisation

Reaction where Acid + Base → Salt + Water

Solution

Homogeneous mixture of solute and solvent

Heat of Combustion

Heat change when one mole of a substance is burned completely in excess oxygen

Octane Number

Measure of the tendency of a fuel to auto-ignite

Structural Isomers

Compounds having the same molecular formula but different structural formulas (different arrangement of atoms)

Unsaturated

Having at least one carbon to carbon double or triple bond present or undergoes addition reactions

Homologous Series

Group of organic chemicals which have the same general formula or differ by CH2 or same functional group

Bond Energy

Average energy required to break 1 mole of a particular bond into separate atoms in the gaseous state

Catalytic Cracking

Splitting of long chain molecules by heat and catalyst(s)

Heat of Formation

Heat change when 1 mole of compound formed from its elements in their standard states

Heat of Reaction

Heat change when the number of moles of reactants in the balanced equation react completely

Hydrocarbon

Compounds composed of carbon (C) and hydrogen (H) only

Auto-ignition

Tendency to premature ignition (explosion/knocking)

Isomerisation

Different structure or different arrangement of atoms or changing straight to branched and vice versa

Saturated

All single (no double or triple) carbon-carbon bonds or have maximum number of H (monovalent) atoms attached to carbon skeleton

Fractionation

Separation into components according to size (mass, boiling pt) or splitting into components by distillation

Rate of a Chemical Reaction

Change in concentration per unit time of any one reactant or product

Activation Energy

Minimum combined energy of particles for effective collisions or minimum combined energy of colliding particles for reaction to take place between them

Heterogeneous Catalysis

Catalyst in different phase (not state) from reactants (not products)

Catalyst

Substance that alters the rate of a reaction and is not used up (consumed) in reaction

Effective Collision

One that results in a reaction (product formation) or reaches activation energy

Delocalised electron

Shared between more than two atoms or moving between one pair of bonded atoms and another

Primary Alcohol

One carbon atom attached to the carbon to which the OH group is attached

Secondary Alcohol

Two carbon atoms attached to the carbon to which the OH group is attached

Emulsion

Oil droplets in water or dispersion of one liquid in a second liquid in which it is insoluble