Topic 9 - Structure and bonding

Question 1

how is a covalent bond formed

Answer 1

when a pair of electrons is shared between two non-metal atoms to achieve a full shell

Question 2

how is a ionic bond formed

Answer 2

when electrons are transferred from metal to non metals to produce metal cations and non metal anions

Question 3

why do covalent bonds have strong forces of attraction

Answer 3

the pair of negatively charged electrons are attracted to the two positive nuclei through electrostatic forces

Question 4

properties of simple covalent structures

Answer 4

• don’t conduct electricity
• low melting/ boiling points

Question 5

why don’t simple covalent structures conduct electricity?

Answer 5

they have no ions or free electrons so there’s nothing to carry the electrical charge

Question 6

why do simple covalent structures have low MP/BP?

Answer 6

• although the covalent bonds within the small molecules are strong
• molecules have weak intermolecular forces of attraction
• only intermolecular forces need to be broken down to melt/boil
• takes small amount of energy to overcome the intermolecular forces

Question 7

what are giant covalent structures

Answer 7

made up of lots of atoms all bonded together by strong covalent bonds

Question 8

properties of giant covalent structures

Answer 8

• high melting and boiling point
• doesn’t conduct electricity ( apart from graphite
• aren’t soluble in water

Question 9

why do giant covalent structures have a high MP/BP

Answer 9

lots of energy needed to overcome the many covalent bonds holding the atoms together
- covalent bonds have strong forces of attraction

Question 10

why don’t MOST giant covalent structures conduct electricity

Answer 10

they have no ions or free electrons so there’s nothing to carry the electrical charge

Question 11

allotropes ( of carbon )

Answer 11

different structural forms of the same element

Question 12

why is diamond hard and tough?

Answer 12

• each carbon atom forms 4 covalent bonds with other carbon atoms
• this forms a very rigid structure and the ions can’t slide over each other

Question 13

why can’t diamond conduct electricity?

Answer 13

they have no ions or free electrons so there’s nothing to carry the electrical charge

Question 14

why is graphite soft ?

Answer 14

-each carbon atom only forms 3 covalent bonds
- creates layers of carbon atoms arranged in hexagons
- no covalent bonds between layers so they easily slide over each other

Question 15

why does graphite conduct electricity?

Answer 15

-only 3 of 4 outer electrons of carbon atoms are used in covalent bonding
-this leaves one electron that’s delocalised and can move
-these carries electricity

Question 16

graphene

Answer 16

single layer of graphite
- very strong and light

Question 17

uses of diamond

Answer 17

strengthen cutting tools, such as drill bits

Question 18

uses of graphite

Answer 18

lubricating material, in pencils

Question 19

uses of fullerenes

Answer 19

in medicine, catalysts, strengthening materials

Question 20

properties of ionic substances

Answer 20

• high melting/boiling points
• dissolves in water easily
• only conducts electricity when molten or in solution

Question 21

why do ionic substances have high MP/BP

Answer 21

• oppositely charged ions are strongly attracted to each other and
• this holds the ions in an ionic lattice
• it takes a large amount of energy to overcome the many strong bonds which have this attraction

Question 22

why do ionic substances only conduct electricity when molten or dissolved ?

Answer 22

• when solid the ions are all held in fixed positions and can’t move
• when molten/dissolved the ions are free to move and carry electrical charge

Question 23

properties of metals

Answer 23

• high melting and boiling points
• conduct electricity
  -malleable
• don’t dissolve in water
• high density

Question 24

why do metals have high MP/BP?

Answer 24

• the electrostatic forces between the
  positive metal ions and delocalised sea of electrons are very strong
• lots of energy needed to overcome these forces

Question 25

why do metals have conduct electrictiy?

Answer 25

• delocalised electrons which are free to move through whole metal
• much better at conducting electricity than most non-metals

Question 26

why are metals mallaeble?

Answer 26

• consists of atoms held together in a regular structure
• form layers which are able to slide over each other
• they can be rolled in flat sheets

Question 27

nanoparticles

Answer 27

really tiny particles that have diameter between 1nm to 100nm
10-1000 time bigger than atoms