Chapter 7 Molecular compounds

Question 1

Why do simple covalent structures have low Melting point and boiling point?

Answer 1

The covalent bonds within these molecules are strong (covalent) but the bonds between molecules weak (intermolecular forces) and easy to break

Question 2

Properties of simple covalent structures

Answer 2

1. Usually gases or liquids at room temperature (if solid,
   they are soft solids)
2. Low melting points and boiling points
3. Do not conduct electricity

Question 3

Why are Molecular compounds unable to conduct electricity?

Answer 3

There are no Free electrons due to the strong electrostatic forces between the positive nuclei and the negative electrons keeping them in place.

Question 4

What is a Monomer?

Answer 4

Small molecules that join together
by covalent bonds

Question 5

Which has a higher melting/boiling point , Polymer or Monomer? why?

Answer 5

Polymer due to the longer chains which contain more intermolecular forces

Long chains get tangled meaning they will need more energy to be broken

Question 5

What is a polymer?

Answer 5

A long chain molecule made from many monomers joining together.

Question 6

What are allotropes?

Answer 6

Different structural forms of the same element are called allotropes

Question 7

What are molecules?

Answer 7

Molecules are atoms joined by covalent bonds

Question 7

Can molecules be compounds or elements?

Answer 7

Both! Molecules can be compound ( such as water , H2O ) or element (Such as oxygen, O2)

Question 8

What are some properties of fullerenes?

Answer 8

Fullerenes have weak intermolecular forces between molecules and so have low melting point these weak forces also make the soft and slippery.

Question 8

What are the 4 types of carbon allotropes?

Answer 8

Fullerenes , Graphene , Graphite , Diamond

Question 8

Is Fullerene simple of or complex molecules?

Answer 8

Simple

Question 9

What Shape is Buckminsterfullerene?

Answer 9

Football

Question 10

What are some properties of graphene?

Answer 10

Graphene has high melting point due to thew strong covalent bonds and can conduct electricity due to the delocalized electrons that carry electricity.

Question 10

Is graphene simple or complex and why?

Answer 10

graphene is complex because it consists of a sheet of carbon atoms with no fixed formula

Question 10

How many carbon atoms is Buckminsterfullerene?

Answer 10

60 carbon atoms

Question 11

What is a Giant molecular structure?

Answer 11

Giant molecular structures have huge three-dimensional networks of carbon atoms linked by covalent bonds,

Question 12

Tell me all the properties of Graphite? (5)

Answer 12

Graphite has a high melting point because of many strong covalent bonds that need a lot of energy to be broken. Graphite has three covalent bonds for each carbon atom. This gives graphite a layered structure and means that not all of its electrons are held in covalent bonds. This means it is a good electrical conductor due to the delocalized electrons. weak force’s of attraction allow the sheets of carbon to slide past each other which makes quite soft and useful as a lubricant

Question 13

Tell me all the properties of Diamond? (5)

Answer 13

diamond has a high melting point because of many strong covalent bonds that need a lot of energy to be broken. Diamonds has four covalent bonds for each carbon atom. The carbon atoms are in a tetrahedral arrangement , joined by strong covalent bonds that gives diamond its extreme hardness and this is why it is used to make cutting tools. Graphite has a high melting point because of many strong covalent bonds that need a lot of energy to be broken.

Question 14

What are the common properties of metals? (5)

Answer 14

• solids with high melting points
• shiny (when polished)
• malleable
• high density
• good conductors of electricity.

Question 15

Why are metals malleable?

Answer 15

When you hit a metal, the layers of ions slide over
each other. The ‘sea’ of electrons holds the ions
together and so the metal changes shape instead of
breaking.

Question 16

What is Metallic bonding?

Answer 16

Metallic bonding is the electrostatic forces of attraction between the positive metal ions and the negative sea of delocalized electron.

Question 17

Which of the following has a higher electrical conductivity and why? Mg+2 and Na+

Answer 17

Mg+2 because is contributes 2 electrons to the sea of electrons while Na+ only contributes 1

Question 18

What are the properties of Metallic bonding?

Answer 18

Hight Melting/boiling point
Solid at room temperature
Malleable
Conduct electricity when Solid or liquid

Question 19

What are the properties of Giant Covalent bonds?

Answer 19

Hight Melting/boiling point
Most do not conduct electricit

Question 20

What are the properties of Simple Covalent bonds?

Answer 20

Low Melting/boiling points
do not conduct electricity

Question 21

Describe the structure of Metallic bonding.

Answer 21

Positive ions surrounded by a ‘sea’ of delocalized electrons

Question 22

Describe the structure of Giant ionic.

Answer 22

Regular 3D arrangement of positive and negative ions

Question 23

Describe the structure of Simple covalent.

Answer 23

Isolated molecules with weak forces between molecules

Question 24

Describe the structure of Giant Covalent?

Answer 24

Repeating 3D structure with strong bonds between atoms

Question 25

What are the advantages of bonding models

Answer 25

Bonding models help explain some properties such as substances with high melting point have many strong bonds that need to be broken during melting. substances with low melting point only have weak forces that need to be overcome between molecules

Also substances that conduct electricity have charged particles that can freely move substances that do not conduct electricty have charged particles that cannot move or particles that are not charged

Question 26

What are the problems with the dot and cross diagram?

Question 27

What are the problems of the metallic bonding model?