Definitions

Definitions of key words needed for AS Chemistry

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Key Words and Definitions
~ Unit 1 and Unit 2 ~
Atomic Structure
Relative Atomic Mass (Ar) ­ Average mass of an atom/element
1
/
mass of one atom of C12
12
Relative Molecular Mass (Mr) ­ Average mass of a molecule
1
/
mass of one atom of C12
12
Mass Number ­ The number of protons and neutrons in the nucleus of an atom
Atomic Number ­ The number of protons in one atom or nucleus
Isotopes ­ An element with the same number of protons and a different number or neutrons. This changes
...............the mass but does not change the chemical properties of an element
Ionisation Energy
First Ionisation Energy ­ The enthalpy change when an electron is removed from a gaseous ion to form
.....................................a uni-positive gaseous ion.
E.g. Na(g) -e
Na+ (g)
Second Ionisation Energy ­ The enthalpy change when an electron is removed from a uni-positive
........................................gaseous ion to form a gaseous ion with a 2+ charge
+ 2+
E.g. Na (g) - e Na (g)
Third Ionisation Energy ­ The enthalpy change when an electron is removed from a gaseous ion with a
+
......................................2 charge
to form a gaseous ion with a 3+ charge
3+
E.g. Na2+ (g) - e Na (g)
Electron Arrangement
S-Block ­ Outer Electrons are in the S sub-level (Group 1 and Group 2 are s-block)
P-Block ­ Outer Electrons are in the P sub-level (Group 3 ­ Group 7)
D-Block ­ Outer Electrons are in the D sub-level (Transition Metals)
Amount of Substance
Mole ­ The amount of a substance that has the same number of particles as there are atoms in 12g of ...........Carbon-12
Avogadro's Constant ­
The number of particles in one mole of a substance is 6.02 x 1023 (The number of
..................................atoms in 12g of Carbon-12)
Empirical Formula ­ The simplest whole number ratio of elements that are present in the compound
Molecular Formula ­ The actual number of atoms of each element in each molecule of a substance
Atom Economy ­ The proportion of the products of a reaction compared to the desired products

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Bonding Definitions
Ionic Bond ­ The electrostatic attraction between positive and negative ions held in a crystal lattice
Single Covalent Bond ­ When 2 electrons are shared in a covalent bond between two non-metals
Double Covalent Bond ­ When 4 electrons are shared in a covalent bond between two non-metals
Dative/Co-ordinate Bond ­ When one atom donates both the electrons to form the covalent bond
Metallic Bond ­ The force of attraction between a lattice of positive ions surrounded by a sea of
........................delocalised electrons.…read more

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Collision Theory ­ This states that particles must collide with enough energy and with the correct
............................orientation to break the bonds between them
Catalyst ­ A substance that speeds up the reaction but is not chemically unchanged or used up at the end ...............…read more

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Key Words and Definitions
~ Unit 3 ~
Isomerism
Structural Isomer ­ Compound with the same molecular formula but has a different structural formula
Positional Isomer ­ Structural isomers that differ by having functional group in different place
Functional Group Isomer ­ Structural isomers that differ by having a different functional group
Chain Isomer ­ Structural isomers that differ by having a different carbon chain
Stereoisomer ­ Molecules with same molecular and structural formula but a different spatial arrangement
......................…read more

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Hydrolysis ­ Reaction involving breaking of bonds with addition of water
CFCs ­ These are compounds containing carbon, chlorine and fluorine atoms, also known as
...........…read more

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