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Chemistry Definition

Definitions in the chemistry course.

TermDefinition
A Compound A substance that is made up of two or more elements combined together chemically.
The Octet Rule The octet rule states that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
The main exceptions of the octet rule Transition metals don't follow the rule and elements near helium in the periodic table ten to have two electrons in their outer shell rather than eight.
An ion is a charged atom or group of atoms.
An ionic bond force of attraction between oppositely charged ions in a compound.
A transition metal is one that forms at least one ion with a partially filled d-sublevel
A molecule is a group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.
The valency of an element the number of atoms of hydrogen or any other monovalent element with which each atom of the element combines.
Electronegativity relative attraction that an atom in a molecule has for a shared pair of electrons in a covalent bond.
The result of different electronegativity values in bonding An electronegativity difference greater than 1.7 indicates ionic bonding in a compound. An electronegativity difference of 1.7 or less indicates covalent bonding in a compound.
Van Der Waals 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 are particular types of dipole dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. The hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule.
The names for the number of carbon atoms in a hydrocarbon Meth, Eth, Prop, But, Pent, Hex, Hept, Oct, Non, Dec
A homogulus Series Compounds of uniform chemical type Showing gradations in physical properties General formula for its members Each member has a similar method of preparation Each member differs from the previous by a CH2 unit.
Structural Isomers compounds with the same molecular formula but different structural formulas.
An aliphatic compound an organic compound that consist of open chains of carbon atoms and closed chain compounds (rings) that resemble them in chemical properties.
Aromatic compounds Compounds that contain a benzene ring structure in their molecule.
Fractional distillation a process that involves heating crude oil and seperating the various mixtures on the basis of their boiling points.
Refinery gas and a use C1- C4 used for lighter fluid
Petrol and a use C5 - C10 used as fuel for some cars
Naphtha and a use C7 - C10 used for solven
Kerosine (Parrafin)and a use C10 - C14 used as fuel for planes
Diesel oil (gas oil) C14 - C19 used for cars
Lubricating oil and a use C19 - C35 used as a lubricant to reduce the wear of engines
Fuel Oil and a use C30 - C40 used a fuel for power stations
Bitumen and a use a chain greater than C35 and used for the tar on roads
Octane Number the measure of the tendancy of the fuel to resist knocking.
Octane number of 2,2,4 trimethylpentane 100
Octane number of heptane 0
Four ways to increase the octane number of petrol 1) Isomerisation 2) Catalytic Cracking 3)Reforming (Dehydrocyclisation) 4) Adding oxygenates
Describe isomerisation changing straight chains into isomers by branching
Describe catalytic cracking breaking down of long chain hydrocarbon molecules into short chain molecules for which there is a greater demand.
Describe Reforming Using catalysts to form ring compounds.
Adding oxygenates Adding oxygen to the hydrocarbons.
Heat of reaction Heat of change when the numbers of moles of reactants indicated in the balanced equation for the reaction react completely
Heat of combustion of a substance the heat change when one mole of the substance is completely burned in excess oxygen.
The kilogram calorific value the heat energyproduced when 1kg of the fuel is completely burned in oxygen.
Bond energy the energy required to break one mole of covalent bonds and to separate the neutral atoms completely from each other.
Heat of neutalisation the heat change when one mole H+ ions from an acid reacts with one mole of OH- ions from a base.
An Element a substance that cannot be split up into simpler substances by chemical means.
A Triad a group of three elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.
Newland's Octaves groups of elements arranged in order of increasing atomic weight, in which the first and the eight 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.
Mendeleev's Table is different to Newland's table forr two reasons. State them. 1: He left gaps in his table to make the elements fit into the proper column 2:He had to reverse the order of elements in order to make them fall into groups of elements with similar properties.
The atomic number number of protons in the nucleus of that atom
Modern periodic table arrangement of elements in order of increasing atomic number.
When elements are arranged in order of increasing atomic number... the properties of the elements vary periodically.
Mass number the sum of the number of protons and neutrons in the nucleus of an atom of that element.
Isotopes atoms of the same element that have different mass numbers due to the different number of neutrons in the nucleus.
Relative Atomic Mass 1: The average of the mass numbers of the isotopes of the element 2: As they occur naturally 3: Taking their abundances into account 4:Expressed on a scale in which the atoms of the carbon-12 isotope have a mass of exactly 12 units.
The Aufbau Principle states that... 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 states that... when two or more orbitals of equal energy are available, the electrons occupy them singly before filling them in pairs.
Created by: hollylucykenny