AQA chemistry unit 1 definitions

defintions of key words fro unit 1

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Alkaline earth metals

The metals in group 2 of the periodic table. 

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Pure elements which can exsist in different physical forms in which their atoms are arranged differently 

e.g. Diamond, Graphite and buckminsterfullerene are all allotropes of carbon.  

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atom economy

Describes the efficency of a chamical reaction by compairing the total number of atoms in the starting materials. it is defined by: 

mass of desired product product/ total mass of reactants    x100

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atomic orbital

a region of space around an atomic nucleus where there is a high probablilty of finding an electron. 

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co-ordinate bonding

covalent bonding in which both the electrons in the bond come from one of the atoms in the bond. (also known as dative covalent bonding.)

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Describes electrons that are spread over several atoms and help to bond them together. 

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Dipole-dipole force

An intermolecular force that resu.ts from the attraction between molecules with permanate dipoles. 

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Electron density

The probablity of and electron being found in a particular volume of space.

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Electron pair repulsion theory

A theory that explains the shapes of simple molecules by assuming that pairs of electrons around a central atom repel each other and therefore take up positions as far away as possible from each other in space.

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The power of an atom to attract electrons in a covalent bond. 

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Electrostatic forces

The forces of attraction and repulsion between electrically charged particles. 

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A vertical column of elements in the periodic table. the elements have similar properties because they have the same outer electron arrangement. 

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Hydrogen bonding

A type of intermolecular force in which a hydrogen atom covalently bonded to an electronegative atom, interacts with another electronegative atom.

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Ionic bonding

Chemical bond in which an electron or electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions with electrostatic forces of attraction between them. 

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Ionisation energy

The energy required to remove a mole of electrons from one mole of gaseous atoms or ions to produce one mole of postive ions. 

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A regular three dimensional arrangement of atoms, ions or molecules. 

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Lone pair

A pair of electrons in the outer shell of an atom that is not involved in bonding. Also called an unshared pair. 

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metallic bonding

Chemical bond in which outer electrons are spread over a lattice of metal ions in a delocalised system.   

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Molecular ion

in mass spectometery this is a molecule of the sample which has been ionised but which has not broken up during its flight through the instrument.  

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Protons and neutrons- the subatomic particles found in the nulcei of atoms. 

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The tiny postively charged centre of an atom composed of protons and neutrons.

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A horisontal row of elements in the periodic table. There are trends in the properties of the elements as we cross a period. 

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The regular recurrance of the properties of elements when they are arranged in atomic number order as in the periodic table. 

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Describes a molecule in which the charge is not symmetrically distributed so that on area is slightly positively charged and the other slightly negatively charged. 

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Proton number

The number of protons in the nucleus of an atom, the same as the atomic number.  

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Relative atomic mass

Ar= average mass of an atom/ 1/12th mass of 1 atom of 12C 

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Relative formula mass

Mr= average mass of entity  /  1/12th the mass of 1 atom of 12C

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Relative molecular mass

Average mass of a molecule  /   1/12th mass of 1 atom of 12C

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van der Waals

Intermolecular force of attraction that is caused by instantaneous dipoles and acts between all atoms and molecules. 

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a quantity of substance that contains the Avogadro number ( 6.022 x 10-23 ) of particles (e.g. atoms molecules or ions) 

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Molecular formula

A formula that tell us the number of atoms of each different element that make up a molecule of a compound. 

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Empirical formula

The simplest whole number ratio in which the atoms in a compound combine together. 

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A hydrocarbon with C-C and C-H single bonds only, with the general formular CnH2n+2 

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Homologous series

A set of organic compounds with the same funtional group. the compunds differ in length of their hydrocarbon chain. 

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a reaction in which an atom or a group of atoms loses electrons. 

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Percentage yield

In a chemical reaction this is the actual amount of product produced divided by the theoretical amount (predicted from the chemical equation) expresssed as a percentage.  

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spectator ions

ions tha6t are unchanged during a chemical reaction i.e, they take no part in the reaction 

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structural formula

Bonds are not shown but each carbon atom is written seperately with atoms or groups of atooms attached to it. 

e.g, butan-2-ol 


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saturated hydrocarbon

a compound containing only hydrogen and carbon withonly C-C and C-H single bonds

i.e. one to which no more hydrogen can be added.  

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displayed formula

show every bond.

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one of two (or more) compounds with the same molecular formula but different structural formular 

i.e. the same atoms are arranged differently in space. 

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strong nuclear force

the force that hold protons and neutrons together within the nucleus of the atom. 

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