chemical changes and structure

Question 1

how are elements arranged on the periodic table?

Answer 1

by increasing atomic number

Question 2

which elements in the first 20 exist as a metallic lattice?

Answer 2

Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, and Calcium

Question 3

Which elements in the first 20 are covalent molecules?

Answer 3

Hydrogen, Oxygen, Fluorine, Chlorine, Bromine, Nitrogen, Phosphorus, Sulfur and fullerenes.

Question 4

which elements in the first 20 are covalent networks?

Answer 4

Boron, Silicon, and Carbon (as graphite or diamond)

Question 5

which elements in the first 20 are monatomic?

Answer 5

noble gases

Question 6

covalent radius + trends

Answer 6

covalent radius is the measure of the size of an atom.
across a period it decreases as nuclear charges increases.
going down a group it increases as the number of occupied shells increases.

Question 7

first ionisation energy + trends

Answer 7

it’s the energy required to remove one mole of electrons from one mole of gaseous atoms.
it increases across a period as the nuclear charge increases.
it decreases down a group as screening effect increases.

Question 8

second ionisation energy definition

Answer 8

energy required to remove the second mole of electrons from one mole of gaseous atoms

Question 9

electronegativity + trends

Answer 9

it’s the measure of the attraction an atom in a bond has for the electrons in that bond.
it increases across a period as nuclear charge increases.
it decreases down a group due to increased screening effect

Question 10

polar covalent bonds

Answer 10

form between atoms which have a difference in electronegativity. one atom will become slightly positive and the other slightly negative (atom with higher EN is negative as it pulls the electrons closer).

Question 11

why aren’t all substances with polar covalent bonds polar molecules?

Answer 11

if they have a symmetrical arrangement of polar and non-polar bonds, as the polarity will cancel out. e.g carbon dioxide

Question 12

states at room temperature

Answer 12

covalent molecules - gas/liquid
covalent networks - solid
ionic substances - solid

Question 13

melting points

Answer 13

covalent molecules - low
covalent networks - high
ionic substances - high

Question 14

solubility

Answer 14

decreases as size of molecule increases.
polar substances will dissolve in other polar substances etc (like dissolves like)

Question 15

electrical conductivity

Answer 15

covalent bonds don’t conduct (except carbon as graphite)
ionic bonds can conduct when molten or in solution

Question 16

intermolecular forces + three types

Answer 16

definition: forces that act between molecules
- london dispersion forces (weakest)
- permanent dipole-permanent dipole forces
- hydrogen bonding (strongest)

Question 17

how are LDFs formed?

Answer 17

formed between a temporary and induced dipole, which are caused by the movement of electrons in atoms and molecules.

Question 18

what affects the strength of LDFs?

Answer 18

they get stronger when an atom/molecule has more electrons (bigger molecules have more LDFs, and therefore higher mp/bp)

Question 19

when are molecules described as polar?

Answer 19

when they have a permanent dipole

Question 20

p.d-p.d interactions

Answer 20

form between oppositely charged ends of polar molecules, are in addition to LDFs and will increase a substance’s melting and boiling points.

Question 21

hydrogen bonding

Answer 21

form between hydrogen and either nitrogen, oxygen, or fluorine.
they make melting and boiling points much higher than other compounds of a similar size.

Question 22

why do ammonia and water have high boiling points?

Answer 22

they contain hydrogen bonding

Question 23

oxidation and reduction definitions

Answer 23

oxidation: loss of electrons
reduction: gain of electrons

Question 24

oxidising and reducing agents definitions

Answer 24

oxidising agent: substance that accepts electrons (is reduced itself)
reducing agent: substance that donates electrons (is oxidised itself)

Question 25

where are oxidising and reducing agents found?

Answer 25

reducing: group 1, top right of electrochemical series
oxidising: group 7, bottom left of electrochemical series

Question 26

uses of oxidising agents

Answer 26

oxidising: kill fungi and bacteria, bleach

Question 27

balancing ion-electron equations

Answer 27

1. balance non hydrogen/oxygen molecules
2. balance oxygen by adding water
3. balance hydrogen by adding hydrogen ions
4. balance the charge