Unit 1- Chemical Changes And Structure

Question 1

activated complex

Answer 1

The activated complex is a very unstable arrangement of atoms formed at the maximum of the potential energy barrier during a chemical reaction.

Question 2

activation energy

Answer 2

Activation energy is the minimum kinetic energy required by colliding particles before a reaction will occur.

Question 3

adsorption

Answer 3

Adsorption occurs when molecules become bonded to the surface of a catalyst.

Question 4

allotropes

Answer 4

Allotropes are one of two or more existing forms of an element.

For example, graphite and diamond are allotropes of carbon.

Question 5

bonding electrons

Answer 5

Bonding electrons are shared pairs of electrons from both atoms forming the covalent bond.

Question 6

chemical bonding

Answer 6

Chemical bonding is the term used to describe the mechanism by which atoms are held together.

Question 7

chemical structure

Answer 7

Chemical structure describes the way in which atoms, ions or molecules are arranged.

Question 8

collision theory

Answer 8

Collision theory suggests that, for a chemical reaction to occur, particles must collide.

Question 9

covalent bond

Answer 9

A covalent bond is formed when two atoms share electrons in their outer shell to complete the filling of that shell.

Question 10

covalent radius

Answer 10

Covalent radius is half the distance between the nuclei of two bonded atoms of an element.

Question 11

delocalised

Answer 11

In metallic bonding, delocalised electrons are free from attachment to any one metal ion and are shared amongst the entire structure.

Question 12

desorption

Answer 12

Desorption occurs when the bonds between the molecules and the surface break and the molecules leave the surface of the catalyst.

Question 13

diatomic

Answer 13

Molecules with only two atoms are described as diatomic (e.g. oxygen, O2, and carbon monoxide, CO).

Question 14

dipole

Answer 14

A dipole is an atom or molecule in which a concentration of positive charges is separated from a concentration of negative charge.

Question 15

electronegativity

Answer 15

Electronegativity is a measure of the attraction that an atom involved in a bond has for the electrons of the bond.

Question 16

enthalpy change

Answer 16

Enthalpy change for a reaction is defined as the change in heat energy when 1 mole of reactant is converted to products at constant pressure.

It has the symbol ΔH and units of kJ/mol.

Question 17

fullerenes

Answer 17

Molecules of pure carbon constructed from 5- and 6-membered rings combined into hollow structures; the most stable contains 60 carbon atoms in a shape resembling a football.

Question 18

hydrogen bonds

Answer 18

Electrostatic forces of attraction between molecules containing a hydrogen atom bonded to an atom of a strongly electronegative element, such as fluorine, oxygen or nitrogen, and a highly electronegative atom on a neighbouring molecule.

Question 19

intermolecular forces

Answer 19

Forces of attraction which exist between molecules; they are weaker than chemical bonds.

Question 20

intramolecular forces

Answer 20

Forces of attraction which exist within a molecule.

Question 21

ion-electron equations

Answer 21

A half-equation, either an oxidation or a reduction, which in combination of the opposite type can be part of a complete redox equation.

Question 22

ionisation energy

Answer 22

The energy required to remove one mole of electrons from one mole of atoms in the gaseous state.

Question 23

isoelectronic

Answer 23

Particles which have the same arrangement of electrons, e.g. the noble gas neon, a sodium ion (Na +) and a magnesium ion (Mg²+).

Question 24

lattice

Answer 24

A regular 3D arrangement of particles in space; the term is applied to metal ions in a solid, and to positive and negative ions in an ionic solid.

Question 25

London dispersion forces

Answer 25

The forces of attraction which result from the electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

Question 26

What does miscible mean?

Answer 26

Fluids which mix with or dissolve in each other in all proportions.

Question 27

non-polar molecule

Answer 27

A molecule where the electronegativities are such that no permanent dipole is formed.

Question 28

periodicity

Answer 28

The regular recurrence of similar properties when the elements are arranged in order of increasing atomic number.

Question 29

Physical properties

Answer 29

Properties that can be measured without changing the chemical identity of a substance e.g melting/boiling point

Question 30

Polar

Answer 30

A molecule containing covalent bonds between atoms of different electronegativity, which results in an uneven distribution of electrons and a partial charge along the bond

Question 31

Polar covalent

Answer 31

A molecule containing covalent bonds between atoms of different electronegativity, which results in an uneven distribution of electrons and a partial charge along the bond

Question 32

Polar covalent bond

Answer 32

A covalent bond between atoms of different electronegativity which results in an uneven distribution of electrons and a partial charge along the bond

Question 33

Potential energy diagram

Answer 33

Shows the enthalpy of reactants and products and the enthalpy change during a chemical reaction

Question 34

Properties

Answer 34

Physical and chemical characteristics of a substance; these are often a reflection of the chemical bonding and structure of the material

Question 35

Viscosity

Answer 35

The resistance to flow that is exhibited by all liquids.