Chemical Changes & Structure

Question 1

activated complex

Answer 1

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

the minimum kinetic energy required by colliding particles before reaction will occur (since a high energy activiated complex must be formed)

Question 3

adsorption

Answer 3

occurs when molecules become bonded to the surface of a catalyst

Question 4

allotrope

Answer 4

one of two or more existing forms of an element

e.g. graphite and carbon are allotropes of carbon

Question 5

bonding electrons

Answer 5

shared pairs of electrons from both atoms forming a covalent bond

Question 6

chemical bonding

Answer 6

term used to describe the mechanism by which atoms are held together

Question 7

chemical structure

Answer 7

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

Question 8

collision theory

Answer 8

collision theory of reactions suggests that, for a chemical reaction to occur, particles must collide

Question 9

covalent bond

Answer 9

electrostatic forces of attraction between positively charged nuclei and negatively charged shared pairs of electrons

Question 10

covalent radius

Answer 10

half the distance between the nuclei of two bonded atoms of an element

Question 11

delocalised

Answer 11

outer electrons, in metallic bonding, are free from attatchment to any one metal ion and shared amongst the entire structure

allows the metal to conduct

Question 12

desorption

Answer 12

occurs when the bonds between the molecules on the surface of a catalyst break and the molecules leave the surface of the catalyst

Question 13

diatomic

Answer 13

molecules with only two atoms

Question 14

dipole

Answer 14

an atom or molecule in which a concentration of positive charges is separated from a concentration of negative charges

Question 15

electronegativity

Answer 15

a measure of the attraction that an atom in a bond has for the electrons of the bond

Question 16

enthalpy change

Answer 16

the change in heat energy when 1 mole of reactant(s) is converted to product(s) at constant pressure

symbol: ∆H units: kJ mol^-1

Question 17

fullerenes

Answer 17

• molecules of pure carbon which form a spherical shape
• it is a discrete covalent molecular substance

Question 18

hydrogen bonding

Answer 18

type of intermolecular bond which arises when hydrogen bonds with a small, highly electronegative atom like fluorine, nitrogen and oxygen

Question 19

intermolecular

bonds

Answer 19

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

Question 20

intramolecular

bonds

Answer 20

forces of attraction which exist within a molecule

Question 21

ion

Answer 21

formed when atoms lose or gain electrons to obtain the stable electron arrangement; in general, metal atoms form positive ions and non-metals form negative ions

Question 22

ionisation energy

Answer 22

the energy required to remove one electron from each atom in one mole of atoms in the gaseous state

Question 23

isoelectric

Answer 23

atoms/ions which have the same arrangement of electrons are isoelectric

e.g. Na⁺ and Mg²⁺

Question 24

lattice

Answer 24

a regular 3D arrangement of particles in space

metallic lattice, ionic lattice

Question 25

london dispersion forces

LDFs

Answer 25

the electrostatic force attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules

Question 26

miscible

Answer 26

fluids which mix with or dissolve in each other in all proportions

Question 27

non-polar

Answer 27

a molecule where the electronegativities are such that no permanant dipole is formed

O=C=O
<-+ +->

Question 28

periodicity

Answer 28

the regular recurrance of similar properties when the elements are arranged in order of increasing atomic number

Question 29

permanant dipole to permanent dipole

Answer 29

• when a molecule has an uneven distribution of electrons due to a difference in electronegativites a permanent dipole is formed
• opposite dipoles attract to form permanent dipole to permanent dipole bonds

Question 30

physical properties

Answer 30

properties that can be measured without changing the chemical identity of a substance

e.g. melting point, boiling point

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

properties

Answer 32

physical and chemical characteristics of a substance

often reflection on bonding and sturcture

Question 33

viscosity

Answer 33

the resistance to flow that is shown by all liquids