Useful Definitions

Question 1

What is an element?

Answer 1

A substance that is only made up from one type of atom

Question 2

What is an atom?

Answer 2

The smallest part of an element that can take part in a chemical reaction

Question 3

What is a molecule?

Answer 3

The smallest particle of a compound/elements that are diatomic

Question 4

What is an ion?

Answer 4

The name given to any electrically charged atom or molecule

• positively charged ions are called cations
• negatively charged ions are called anions

Question 5

What is accuracy?

Answer 5

How CLOSE values are to the ACCEPTED VALUE

Question 6

What is activation energy?

Answer 6

The minimum amount of energy that colliding particles need for a reaction to occur

Question 7

What is atomic number?

Answer 7

The number of protons in the nucleus of an element

Question 8

Avogadro’s law

Answer 8

Equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules

Question 9

What are basic oxides?

Answer 9

Oxides of metals that react with water to form metal hydroxides and with acids to form salts and water

Question 10

What is bond enthalpy?

Answer 10

The enthalpy change when one mole of a bond in the gaseous state is broken

Question 11

What is bond length?

Answer 11

The distance between nuclei of two atoms that are covalently bonded together

Question 12

What is a catalyst?

Answer 12

A substance that increases the rate of a chemical reaction but is chemically unchanged at the end of the reaction

Question 13

What is cracking?

Answer 13

The breakdown of molecules into shorter ones by heating with a catalyst

Question 14

What are delocalised electrons?

Answer 14

Electrons that are not associated with any single atom or covalent bond

Question 15

What is disproportionation?

Answer 15

When an element is both oxidised and reduced in the same reaction

Question 16

What is electronegativity?

Answer 16

The ability of an atom to attract a bonding pair of electrons

Question 17

What is an electrophile?

Answer 17

• A species that is attracted to a region of high electron density
• Electron acceptor

Question 18

What is the end point?

Answer 18

The point at which the indicator just changes colour

Question 19

What does endothermic mean?

Answer 19

Heat energy is transferred from the soundings to the system

Question 20

What is the equivalence point?

Answer 20

The point at which there are exactly the right amounts of substances to complete the reaction

Question 21

What is an error?

Answer 21

The different between an experimental value and the accepted value

Question 22

What is an ethanolic solution?

Answer 22

A solution where ethanol is used as the solvent

Question 23

What does exothermic mean?

Answer 23

Heat energy is transferred from the system to the surroundings

Question 24

What is first ionisation energy?

Answer 24

The energy required to remove an electron from each atom in one mole of gaseous atoms

Question 25

What is second ionisation energy?

Answer 25

The energy required to remove a electron from each singly charged positive ion in one mole of positively charged ions in the gaseous state

Question 26

What is Hess' law?

Answer 26

The enthalpy change of a reaction is independent of the route taken

Question 27

What is a hetrogeneous catalyst?

Answer 27

A catalyst that is in a different phase to that of the reactants

Question 28

What is hetrolytic fission?

Answer 28

The breaking of a covalent bond so that both bonding electrons are taken by one atom

Question 29

What is a heterogeneous system?

Answer 29

A system where there at least two different phases are present

Question 30

What is homolytic fission?

Answer 30

The breaking of a covalent bond where each of the bonding electrons leaves with one species, forming a radical

Question 31

What does Hund's rule state?

Answer 31

Electrons will occupy the orbitals singly before electron pairing takes place

Question 32

What is a hydrogen bond?

Answer 32

- An intermolecular interaction between a hydrogen atom and an atom which is more electronegative than hydrogen - this would normally be between fluorine, oxygen and nitrogen atoms

Question 33

What is a locant?

Answer 33

A number used to indicate which carbon atom in an chain an atom or group is attached to

Question 34

What is mean bond enthalpy?

Answer 34

The average enthalpy change when one mole of a bond is broken

Question 35

What is a measurement uncertainty?

Answer 35

The potential error involved when using a piece of apparatus to make a measurement

Question 36

What is a meniscus?

Answer 36

The curving of the upper surface in a liquid in a container

Question 37

What is metallic bonding?

Answer 37

The electrostatic force of attraction between the nuclei of positively charged metal ions and delocalised electrons

Question 38

What is molar concentration?

Answer 38

The amount (in mol) of a solute divided by the volume of the solution

Question 39

What is a mole?

Answer 39

The amount of a substance that contains the same number of particles as the number of carbon atoms in exactly 12g of carbon-12

Question 40

What is the molecular ion peak?

Answer 40

The peak with the highest m/z ratio in the mass spectrum

Question 41

What are monomers?

Answer 41

Small molecules that combine to form a polymer