c3 - structure and bonding

Question 1

give the limitations of the particle model

Answer 1

• assumes particles are solid spheres with no forces between them
• but particles can be atoms, molcules or ions
• contain many atoms
• vary in size
• are not solid or spherical

Question 2

define covalent bonding

Answer 2

when atoms of non-metallic elements join together by sharing electrons

Question 3

define ionic bonding

Answer 3

when metallic elements react with non-metallic elements to produce ionic compounds

Question 4

why do we use dot and cross diagrams?

Answer 4

to show electrons in the outer shell of the atoms and ions involved in forming ionic bonds

Question 5

how are giant structures/ giant lattices formed?

Answer 5

oppositely charges ions formed are help together by strong forces of attraction, which acts in all directions

Question 6

how can you predict what ions will form?

Answer 6

group 1, 2 and 3: 1 + 2+ 3+
group 6, 7: 2 -, 1-
8 - (6/7/8)

Question 7

why are ionic compounds solids at room temperature?

Answer 7

• ionic compounds have giant structures in which many strong electrostatic forces, operating in all directions, hold the oppositely charged ions together

Question 8

why do ionic compounds have high melting points and high boiling points?

Answer 8

it takes a lot of energy to overcome the ionic bonds to melt the solids

Question 8

what happens when an ionic compound melts?

Answer 8

• ions are free to move
• allows them to carry electrical charge, so liquids can conduct electricity

Question 8

why do some ionic compounds dissolve in water?

Answer 8

• water molecules can be split up the lattice
• the ions are free to move in the solutions and so they can also conduct electricity

Question 9

how do atoms of non-metals gain electrons to achieve stable electronic structures?

Answer 9

• by sharing electrons with other atoms
• each shared pair of electrons strongly attracts the two atoms, forming a covalent bond
• substances that have atoms held together by covalent bonds are called molecules

Question 10

what are the limitations of using models to represent molecules?

Answer 10

• most do not show the actual shape of the molecule
• all electrons are identical but dot and cross diagrams show electrons from different atoms differently
• in giant structures, the models only represent a very tiny fraction of the millions of atoms (or ions) bonded together

Question 11

what is attraction like in covalent bonds?

Answer 11

• covalent bonds are very strong so they hold the atoms with a molecule very tightly
• however each molecule is separate from the neighbouring molecules and so simple molecules have little attraction for eachother
• weak intermolecular forces

Question 12

what are intermolecular forces?

Answer 12

• forces of attraction between molecules
• they increase with the size of the molecules, so larger molecules have higher melting and boiling points

Question 13

what are polymers?

Answer 13

• have very large molecules
• made up of many small molecules that covenlently bond to each other to form long chains
• e.g polyethene is made up from thousands of ethene molecules

Question 14

why are polymers solids at room temperature?

Answer 14

their intermolecular forces are relatively strong

Question 15

why do simple molecules not conduct electricity?

Answer 15

there is no overall charge on the simple molecules in a compound like sucrose