topic 3

Question 1

why do atoms bond?

Answer 1

so that they have a full outer shell

Question 2

what does each covalent bond provide?

Answer 2

one extra shared electron for each atom

Question 3

what is formed when atoms make covalent bonds with one or more other atoms?p

Answer 3

a molecule

Question 4

what sheep do you need to draw in a covalent bond diagram?

Answer 4

the outer shell

Question 5

what are the two kinds of covalent substances?

Answer 5

simple molecular and giant molecular

Question 6

what kind of bonds do simple molecular covalent substances have?

Answer 6

very strong covalent bonds to form small molecules of two or more atoms

Question 7

the forces between molecules in simple molecular covalent substances are …

Answer 7

very weak

Question 8

do simple molecular covalent substances have low or high melting and boiling points?

Answer 8

low

Question 9

why do simple molecular substances have low melting points?

Answer 9

because they have weak inter-molecular forces so the molecules are easily parted from each other

Question 10

what is covalent bonding?

Answer 10

the sharing of a pair of electrons between two atoms

Question 11

do simple molecular covalent substances conduct electricity?

Answer 11

no

Question 12

why don’t simple molecular covalent substances conduct electricity?

Answer 12

because there are no ions

Question 13

what are giant molecular covalent substances structure similar to?

Answer 13

ionic lattices but there is no charged ions

Question 14

what kind of bonds do giant molecular covalent substances have?

Answer 14

all atoms are bonded to each to whe by strong covalent bonds

Question 15

do giant molecular covalent substances have high or low boiling points?

Answer 15

high

Question 16

why do giant molecular covalent substances have high melting and boiling points?

Answer 16

because they have strong covalent bonds between the atoms

Question 17

do giant molecular covalent substances conduct electricity?

Answer 17

no not even when molten apart from graphite

Question 18

are giant molecular covalent substances soluble in water?

Answer 18

no they are usually insoluble in water

Question 19

what are the main examples of giant molecular covalent substances?

Answer 19

graphite and diamond

Question 20

why so diamond really hard?

Answer 20

because each carbon atom forms four covalent bonds in a rigid giant covalent structure

Question 21

does diamond conduct electricity and why?

Answer 21

no because there are no free electrons

Question 22

why is graphite useful as a lubricant?

Answer 22

because each carbon atom only forms three covalent t bonds creating sheets of carbon atoms which are free to slide over each other

Question 23

in graphite are the layers of carbon atoms help together loosely or strongly?

Answer 23

loosely so they can be rubbed off easily - this is how a pencil works

Question 24

is graphite a good conductor of electricity? why?

Answer 24

yes because there are lots of spare (delocalised) electrons so they can move and Cary an electrical current

Question 25

how do you identify the bonding in a substance?

Answer 25

by its properties

Question 26

what does miscible mean?

Answer 26

liquids will mix together

Question 27

immiscible

Answer 27

liquids won’t mix together

Question 28

how do you separate miscible liquids?

Answer 28

fractional distillation

Question 29

how do you desperate immiscible liquids?

Answer 29

separating funnel

Question 30

when separating a immiscible liquid how do a separating funnel work?

Answer 30

the denser layer sinks to the bottom and the less dense one forms a layer on top. they are then separated using a funnel with a tap. the tap can be opened to drain off the denser liquid into a beaker

Question 31

how does fractional distillation separate miscible liquids?

Answer 31

air is filtered to remove dust
cooked to -200c and becomes a miscible mixture of liquid
during cooking water vapour condenses and it is removed
carbon dioxide freezes and is removed
the liquified air then enters the fractional distillation column and is slowly heated
the remaining gases are separated by fractional distillation - oxygen and argon come out together so another column is used to separate them

Question 32

during fractional distillation why do the two liquids need to have different boiling points?

Answer 32

so that when the mixture is heated the different liquids will condense at different temperatures and can be collected separately

Question 33

chromatography can be used to identify what?

Answer 33

substances

Question 34

what are the steps of chromatography?

Answer 34

1) put spots of each mixture being tested on a baseline on filter paper
2) roll up the paper and put it in a beaker containing a solvent
3) the solvent seeps up the paper taking the samples with it
4) the different chemicals in the sample form separate spots on the paper

Question 35

in chromatography what do the amount of different sports show?

Answer 35

the amount of stub stances in the sample mixture

Question 36

why does chromatography work?

Answer 36

different substances wash through wet filter paper at different rates

Question 37

how do you work out the rf value in chromatography?

Answer 37

distance travelled by substance % distance travelled by solvent