key concepts 2

Question 1

explain how ionic bonds are formed

Answer 1

• transfer of electrons
• when metal and non-metal react together the metal loses electrons to form a cation and the non-metal gains these electrons to form an anion

Question 2

what is a cation and an anion

Answer 2

cation - positive ion
anion - negative ion

Question 3

what are oppositely charged ions attracted to one another by

Answer 3

• electrostatic forces of attraction
• this attraction is called an ionic bond

Question 4

what is an ion

Answer 4

an atom or group of atoms with a positive or negative charge

Question 5

explain the formation of ions in ionic compounds from their atoms in groups 1 and 2

Answer 5

• group 1 and 2 are metals
• lose electrons to form positive ions

Question 6

explain the formation of ions in ionic compounds from their atoms in groups 6 and 7

Answer 6

• non-metals
• gain electrons to form negative ions

Question 7

why do elements in the groups form ions with the same charges

Answer 7

because elements in a group have the same number of outer electrons
so have to lose or gain the same number to get a full outer shell

Question 8

when do anions and cations form

Answer 8

• anions form when atoms gain electrons (they have more electrons than protons)
• cations form when atoms lose electrons (they have more protons than electrons

Question 9

how to know when to use -ide or -ate in the names of compounds

Answer 9

-ide = just contains 2 elements
-ate = contains 3 or more elements, one of which is oxygen

Question 10

how to work out the formula of an ionic compound

Answer 10

• ionic compounds are made up of a positively charged part and a negatively charged part
• overall charge of any ionic compound is 0 so all the negative charges in the compound must balance all the positive charges
  1. write out the formulas of the ions
  2. the overall charge must be 0 so work out the ratio of the ions that gives an overall neutral charge
  ex - 1.Ca 2+, NO3 -
  2. to balance 2+ charge you need to NO3 - ions
• the formula is Ca(NO3)2

Question 11

what is the structure of an ionic compound

Answer 11

lattice structure
a) consisting of a regular arrangement of ions
b) held together by strong electrostatic forces (ionic bonds) between oppositely - charged ions

Question 12

explain how a covalent bond is formed

Answer 12

• when a pair of electrons is shared between two atoms

Question 13

what does covalent bonding result in the formation of

Answer 13

molecules

Question 14

recall the typical size (order of magnitude) of atoms and small molecules

Answer 14

about 10 to the power of negative 10 m

Question 15

explain the formation of hydrogen using a dot and cross diagram

Answer 15

• hydrogen atoms have one electron so need one more to complete the first shell
• can form a single covalent bond with another hydrogen atom to do this (h2)

Question 16

explain the formation of hydrogen chloride using a dot and cross diagram

Answer 16

• both atoms only need one more electron to complete their outer shells

Question 17

explain how water is formed using a dot and cross diagram

Answer 17

• in water molecules an oxygen atom shares a pair of electrons with two H atoms to form
• two single covalent bonds

Question 18

explain how methane is formed using a dot and cross diagram

Answer 18

• carbon has four outer electrons
• it can form four covalent bonds with hydrogen atoms to fill up its outer shell

Question 19

explain how oxygen is formed using a dot and cross diagram

Answer 19

• an oxygen atom need two more electrons co complete its outer shell
• in oxygen gas each oxygen atom forms a double covalent bond
  ( bond made of two shared electron pairs) with another oxygen atom

Question 20

explain the formation of carbon dioxide using a dot and cross diagram

Answer 20

• carbon atom shares two pairs of electrons
• with two oxygen atoms
• to form two double covalent bonds

Question 21

explain the properties of ionic compounds

Answer 21

a) high melting and boiling points due to strong attraction between ions
b) solid ionic compounds don’t conduct electricity as the ions can’t move however when an ionic compounds melts, the ions are free to move and will carry an electrical charge

Question 22

explain why typical covalent, simple molecular compounds have low melting and boiling points

Answer 22

• only need to break the feeble intermolecular forces and not the covalent bonds
• so its low because the molecules are easily parted from each other

Question 23

explain why typical covalent, simple molecular compounds are poor conductors of electricity

Answer 23

• don’t contain any free electrons or ions

Question 24

what are graphite and diamond

Answer 24

• different forms of carbon
• examples of giant covalent substances

Question 25

describe the structures of graphite

Answer 25

- 3 covalent bonds, creating sheets of carbon atoms arranged in hexagons

Question 26

describe the structures of diamond

Answer 26

- four covalent bonds - rigid lattice structure

Question 27

why is graphite used to make electrodes and as a lubricant

Answer 27

- no covalent bonds between layers - held together weakly so free to move over each other - so its soft and slippery

Question 28

why is diamond used in cutting tools

Answer 28

- rigid lattice structure making diamond really hard

Question 29

why does diamond have a high melting point

Answer 29

strong covalent bonds take a lot of energy to break

Question 30

explain the properties of fullerenes

Answer 30

- huge surface area = good catalyst - can cage other molecules = can deliver drugs directly to cells in the body - made up of carbon atoms in closed tubes or hollow balls

Question 31

explain the properties of fullerenes like C60

Answer 31

- buckminsterfullerene = C60 - forms a hollow sphere - made of hexagons and pentagons - stable molecule that forms soft brownish-black crystals

Question 32

explain the properties of the fullerene graphene

Answer 32

- one layer of graphite - a sheet of carbon atoms joined in hexagons - one atom thick so it's two dimensional

Question 33

what properties do giant covalent structures have

Answer 33

- high melting and boiling points as lots of energy is needed to break covalent bonds - generally don't conduct electricity - no soluble in water

Question 34

describe simple polymers using poly(ethane) as an example

Answer 34

- large molecules containing chains of carbon atoms - formed when monomers join together

Question 35

what are the properties of metals

Answer 35

- malleable - can conduct electricity

Question 36

explain why metals are malleable

Answer 36

- layers of atoms can slide over each other

Question 37

explain why metals contain an electrical charge

Answer 37

- delocalised electrons carry electrical charge and thermal energy through the material - so metals are good conductors of electricity and heat

Question 38

describe the limitations of models - dot and cross

Answer 38

- don't show size of atoms or ions or how they are arranged

Question 39

describe the limitations of the ball and stick models

Answer 39

- no correct scales make it looks like there are gaps between atoms

Question 40

describe the limitations to two and three dimensional shapes

Answer 40

2D - shape of substance or size of atoms 3D - only show outer layer of substance

Question 41

describe metals

Answer 41

- shiny solids - high melting points - high density - good conductors of electricity

Question 42

describe non-metals

Answer 42

- low boiling points - poor conductors of electricity

Question 43

During ionic bonding do the non metals gain or lose electrons

Answer 43

Non metals GAIN electrons

Question 44

During ionic bonding do metals gain or lose electrons

Answer 44

Metals LOSE electrons