7.3-periodic trends In Bonding and Structure

Question 1

How many metals are there in the periodic table?

Answer 1

92

Question 2

How many non metals are there in the periodic table ?

Answer 2

22

Question 3

What state are all metals at room temperature ?

Answer 3

Solids

Question 4

Define Metallic bonding

Answer 4

-The strong electrostatic attraction between cations and delocalised electrons
- the cations are fixed in position maintaining the structure and shape of the metal
- the delocalised electrons are Mobile and are able to move throughout the structure

Question 5

What are two key features of metallic bonding ?

Answer 5

• in a solid metal structure each atom has donated its negative outer shell electrons to a shared pool of electrons which are delocalised throughout the whole structure
• the cations left behind consist of the nucleus and the inner electron shells of the metal atoms

Question 6

What are some properties of metals ?

Answer 6

• strong metallic bonds - attraction between positive ions and delocalised electrons
  - high electrical conductivity
• high melting and boiling points

Question 7

What states do metals conduct electricity ?

Answer 7

Both solid and liquid states

Question 8

Explain the electrical conductivity of metals ?

Answer 8

When a voltage is applied across a metal the delocalised electrons can move through the structure carrying a charge

Question 9

Explain the melting and boiling points of metals ?

Answer 9

• the melting point depends on the strength of the metallic bonds holding together the atoms in the giant metallic lattice
• for most metals = high temps are necessary to provide a large amount of energy needed to overcome the strong electrostatic attraction between the cations and electrons

Question 10

Describe the solubility properties of metals ?

Answer 10

• Metals are insoluble
• any interactions lead to a reaction rather than dissolving

Question 11

What do non metallic elements exist as ?

Answer 11

Simple covalently bonded elements

Question 12

In solid state what do these molecules form ?

Answer 12

• form simple molecular lattice structure held together by weak intermolecular forces
• these structures thus have low melting points and boiling points

Question 13

What are the elements that form giant covalent structures

Answer 13

Boron
Carbon
Silicon

Question 14

Explain the melting and boiling points of giant covalent lattices

Answer 14

• high melting and boiling points because covalent bonds are strong
• high temperatures are necessary to provide the large quantity of energy needed to break the strong covalent bonds in the lattice structure

Question 15

Describe the solubility of giant covalent structures

Answer 15

• insoluble in almost all solvents
• As the covalent bonds are far too strong to be broken by interaction with solvents

Question 16

Describe the electrical conductivity of giant covalent structures

Answer 16

• non conductors of electricity
• only exceptions are graphene and graphite —> forms of carbon
• In diamond and silicon all 4 outer shell electrons are involved in covalent bonding = non available for conducting electricity

Question 17

What shape are graphene and graphite and what bond angles do they have ?

Answer 17

Planar hexagonal layers with bond angles of 120° by electron pair repulsion

Question 18

What is graphene ?

Answer 18

Single layer of carbon atoms that are bonded together in a repeating pattern of hexagons

Question 19

What is the shape and bond angle of diamond ?

Answer 19

Tetrahedral shape with bond angles of 109.5°

Question 20

What shape and structure does silicon ( IV ) oxide have ?

Answer 20

• Adopts the same structure as diamond
• giant covalent lattice made of tetrahedral units all bonded by strong covalent bonds

Question 21

Is graphite soft or hard ?

Answer 21

• soft
• due to the intermolecular forces between the carbon layers are weak

Question 22

Are Diamond and silicon oxide hard or soft ?

Answer 22

• hard
• it is difficult to break their 3D network of strong covalent bonds

Question 23

What happens to the melting point across period 2 and 3 ?

Answer 23

• melting point increases from group 1 to group 4
• there is a sharp decrease in melting point between group 4 and group 5
• melting points are comparatively low from group 5 to group 0

Question 24

Why does melting point increase from group 1 to group 4 ?

Answer 24

• the groups have metallic bonding which increases the strength due to increases forces of attraction between more electrons in the outer shell that are released to the sea of electrons and a smaller positive ion
• group 4 has a giant covalent structure with many strong covalent bonds requiring a lot of energy to overcome

Question 25

Explain why there is a sharp decrease in melting point from group 4 to group 5 ?

Answer 25

Group 5 to 0 gave simple molecular structures with weak London forces between molecules requiring little energy to overcome