SC7d Bonding models

Question 1

ionic bonds
1.where found?
2.how they are formed?
3.structure?
4.properties?

Answer 1

1. most compounds containing metal and non metal atoms
2. loss and gain of electrons to produce two oppositely charged ions that attract one another
3. billions of ions held together in a lattice structure
4. high melting / boiling points, many are soluble in water, conduct electricity when liquid or in solution but not when solid

Question 2

simple molecular (covalent)
1.where found?
2.how they are formed?
3.structure?
4.properties?

Answer 2

1. most non metal elements and compounds
2. when atoms share pairs of electrons
3. small distinct groups of atoms
4. low melting/ boiling point, few are soluble in water, most do not conduct electricity

Question 3

giant covalent
1.where found?
2.how they are formed?
3.structure?
4.properties?

Answer 3

1. in few non-metal elements and some compounds of non-metals
2. when atoms share pairs of electrons
3. billions of atoms held together in a lattice structure
4. high boiling / melting points, insoluble in water, most do not conduct except in carbon as graphite

Question 4

metallic
1.where found?
2.how they are formed?
3.structure?
4.properties?

Answer 4

1. in all metals
2. the electrostatic attraction between positive metal ions and negative delocalised electrons
3. billions of ions held together in a giant lattice structure of positive ions in a ‘sea’ of negative delocalised electrons
4. high melting / boiling points, insoluble in water, conduct electricity when solid or liquid

Question 5

what are the 4 different models?

Answer 5

~displayed formulae
~dot and cross diagram
~ball and stick diagrams
~space - filling models

Question 6

advantages of displayed formula?

Answer 6

Clearly shows the chemical bonds.​
Formula of compound can be worked out from the diagram.​

Question 7

disadvantages of displayed formula?

Answer 7

Does not show the relative sizes of the atoms and the bonds between them.​

Question 8

advantages of dot and cross diagrams?

Answer 8

Shows how the electrons are shared to form bonds. ​
Formula of compound can be worked out from the diagram.

Question 9

disadvantages of dot and cross diagrams? (2)

Answer 9

Only shows the outer electrons.​
Using both dots and crosses makes it looks like electrons from carbon atoms and oxygen atoms are different.​

Question 10

advantages of the ball and stick model?

Answer 10

Shows the bonds between each atom.​
Shows the three-dimensional (3D) structure clearly.

Question 11

disadvantages of ball and stick model?

Answer 11

Does not accurately show the relative sizes of the atoms and the distances between them.​
The bonds are not really like sticks.

Question 12

advantages of space filling model?

Answer 12

shows the three-dimensional (3D) structure so we can see how atoms are arranged in relation to each other.​
More accurately represents the relative sizes of each atom and the distances between them.​

Question 13

disadvantages of space filling model?

Answer 13

Does not show how the bonds are formed.​

Question 14

Suggest why the melting point of silicon dioxide (1610 °C) is so much higher than the temperature at which solid carbon dioxide changes state (-78.5 °C) although both compounds contain covalent bonds. (3 marks)​

Answer 14

The melting point of silicon dioxide is high because there are billions of atoms joined together in a giant lattice structure so billions of strong bonds need to be broken in order to melt it. (1)​
The melting point of carbon dioxide is low because it is made up of lots of small molecules (1) and only the weak forces of attraction between the molecules need to be broken in order for it to change state (1)​

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