OCR Chemistry Unit 1 Definitions

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Atoms of an element with different numbers of neutrons and different masses.

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The mass of an atom of an isotope

compared with 1/12th the mass of an atom of C-12.

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The weighted mean mass of an atom of an element

compared with 1/12 the mass of an atom of C-12.

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The weighted mean mass of a molecule

compared with 1/12th the mass of a C-12 atom.

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The weighted mean mass of a formula unit

compared with 1/12th the mass of a C-12 atom.

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The quantity whose unit is the mole.

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The amount of any substance that contains the same number of particles

as there are carbon atoms in 12g of C-12.

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The number of particles per mole- 6.02 x 10^23 mol^-1

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The mass per mole of a substance- g mol^-1

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The simplest whole number ratio of atoms of each element present in a compound.

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The actual number of atoms of each element in a molecule.

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Substance containing no water molecules.

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A crystalline compound containing water molecules.

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Water molecules that form an essential part of the crystalline structure of a compound.

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Loss of electrons.

Increase in oxidation number.

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Gain of electrons.

Decrease in oxidation number.

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The amount of energy required to remove 1 mol of electrons

from 1 mole of gaseous atoms

to produce 1 mol of gaseous uni positive ions.

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A measure of how much energy is required to remove each electron in turn.

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A region that can hold up to 2 electrons

with opposite spins.

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Electrostatic attraction

between oppositely charged ions.

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A shared pair of electrons.

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The ability of an atom to attract the bonding electrons in a covalent bond.

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A strong dipole-dipole attraction between

an electron deficient hydrogen atom on one molecule

and a lone pair of electrons on a highly electronegative atom of a different molecule.

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The attraction of positive ions

to delocalised electrons.

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A regular periodic variation of elements' properties

with their atomic number

and position in the periodic table.

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A reaction in which an element is

simultaneously oxidised and reduced.