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Explain Simple and Giant Covalent Structures

Worksheet Overview

QUESTION 1 of 10

Ionic and metallic bonding each only make one type of structure. Covalent bonding is a bit harder, because there are two types of structure that form. Don't panic, because you will soon understand both of them.

Most covalent compounds form simple structures, also called simple molecules, or simple molecular structures. Simple molecules are tiny; many of them only contain two or three atoms. The forces between the atoms in each molecule are made by covalent bonds, so they are very strong. Scientists call these "intramolecular forces" ("intra" at the beginning of a word means "inside").

 

The forces between separate molecules are very very weak. Scientists call these forces "intermolecular forces" ("inter" at the beginning of
a word means "between"- think of international, or internet). That means that the molecules in oxygen gas look like this:

The properties of simple covalent structures depend on the weak intermolecular forces; it doesn't really matter that the forces within the molecule are strong. Simple covalent molecules:
have very low melting and boiling points (oxygen turns from a solid to a liquid at -219 C, and from a liquid to a gas at -183 C). Larger molecules have higher boiling points, but still lower than for ionic or metallic bonding.
are usually gases or liquids at room temperature.
dissolve easily  in water
do not conduct electricity, because there are no mobile electrons or ions.

Although most covalent substances make simple molecules, a few make giant structures- more like the structures formed by metallic or ionic bonding. The important point about covalent giant structures is that all the bonds linking atoms are covalent, so all the bonds are very strong indeed. Giant covalent structures are usually based on carbon or silicon. The reason for this is that they can make four covalent bonds per atom, which is more than most other elements. You need four covalent bonds to make a giant structure with bonds in three dimensions. Diamond is a giant covalent structure made of carbon atoms:

This means that covalent giant structures:
are very hard, because the covalent bonds are very strong.
have very high melting temperatures, because huge amounts of energy are needed to break covalent bonds.
do not dissolve in water, because water cannot weaken covalent bonds.
do not conduct electricity, because there are no mobile electrons or ions.

The key difference between molecules and giant structures is that giant structures only have covalent bonds. To make a liquid or solid from molecules, we need other (very weak) forces to hold the molecules together.

Which of these phrases describe simple molecules?

many atoms

few atoms

strong intermolecular forces

strong intramolecular forces

Which of these phrases describe intramolecular forces?

within molecules

between molecules

strong

weak

ionic

covalent

Which of these phrases describe intermolecular forces?

strong

weak

within molecules

between molecules

covalent

ionic

Match the properties with their reasons

Column A

Column B

Electrical insulator
because there are weak forces between molecules
Low melting temperature
is not true.
High melting temperature
because there are no mobile charged particles.
These compounds all have simple molecular structures
compound formula melting temperature (ºC)
propane C3H8 -190
butane C4H10 -138
pentane C5H12  
hexane C6H14 -95

Pick the best estimate of the melting temperature of pentane from the list.

-150 ºC

-125 ºC

-100 ºC

These compounds all have simple molecular structures
compound formula melting temperature (ºC)
propane C3H8 -190
butane C4H10 -138
pentane C5H12 -130
hexane C6H14 -95

Complete this paragraph; each of the gaps is increases or decreases.

-150 ºC

-125 ºC

-100 ºC

Which of these phrases describe giant covalent structures?

many atoms

a few atoms

joined by ionic bonding

joined by covalent bonding

Which common elements tend to form giant covalent structures?

silicon (Si)

nitrogen (N)

oxygen (O)

carbon (C)

Which of these phrases describe neither simple molecular nor giant covalent materials?

electrical conductor

hard

high melting point

dissolve in water

Mark the sentences in this paragraph about giant covalent structures by ticking the correct ones.

In giant covalent structures, all the bonds are strong covalent bonds.

There are no weak bonds in the structure at all.

This allows the structure to break easily.

  • Question 1

Which of these phrases describe simple molecules?

CORRECT ANSWER
few atoms
strong intramolecular forces
EDDIE SAYS
Simple molecules are small. Many are only 2 or 3 atoms. A few very large ones are about 100 atoms. The forces holding the molecule together are very strong- unlike the forces between different molecules.
  • Question 2

Which of these phrases describe intramolecular forces?

CORRECT ANSWER
within molecules
strong
covalent
EDDIE SAYS
People often get intra and inter mixed up. "Intra" means within or inside, so intramolecular is inside the molecule. These forces are strong, covalent forces.
  • Question 3

Which of these phrases describe intermolecular forces?

CORRECT ANSWER
weak
between molecules
EDDIE SAYS
"Inter" means between, so intermolecular is between molecules. These forces are very weak. There are various ways that they can happen, but they are too weak to be ionic or covalent.
  • Question 4

Match the properties with their reasons

CORRECT ANSWER

Column A

Column B

Electrical insulator
because there are no mobile charg...
Low melting temperature
because there are weak forces bet...
High melting temperature
is not true.
EDDIE SAYS
The melting temperature of materials is linked to how strong the bonds are. Electrical conductivity depends on how easily it is for charged particles(electrons or ions) to move.
  • Question 5
These compounds all have simple molecular structures
compound formula melting temperature (ºC)
propane C3H8 -190
butane C4H10 -138
pentane C5H12  
hexane C6H14 -95

Pick the best estimate of the melting temperature of pentane from the list.

CORRECT ANSWER
-125 ºC
EDDIE SAYS
As the molecules get larger, the melting temperature increases. This is because the forces between the molecules get a bit less weak. The pattern isn't smooth; the actual melting temperature of pentane is -130 ºC. But -150 ºC is definitely too low, and -100 ºC is probably too high.
  • Question 6
These compounds all have simple molecular structures
compound formula melting temperature (ºC)
propane C3H8 -190
butane C4H10 -138
pentane C5H12 -130
hexane C6H14 -95

Complete this paragraph; each of the gaps is increases or decreases.

CORRECT ANSWER
EDDIE SAYS
Larger molecules have stronger intermolecular forces. The structure of this paragraph is worth learning; a lot of science answers are about patterns where one thing increases, and another thing either increases or decreases as a result.
  • Question 7

Which of these phrases describe giant covalent structures?

CORRECT ANSWER
many atoms
joined by covalent bonding
EDDIE SAYS
We're still thinking about covalent bonding. The difference is that giant structures are giant- they have many many atoms in them.
  • Question 8

Which common elements tend to form giant covalent structures?

CORRECT ANSWER
silicon (Si)
carbon (C)
EDDIE SAYS
Silicon and carbon both make 4 covalent bonds, which is needed to have an endless network, like a giant structure. Not every carbon compound is a giant structure; carbon dioxide is molecular.
  • Question 9

Which of these phrases describe neither simple molecular nor giant covalent materials?

CORRECT ANSWER
electrical conductor
EDDIE SAYS
Giant covalent structures are hard and have a high melting point. Covalent molecules dissolve in water. Both types of covalent structure are insulators, so neither is an electrical conductor.
  • Question 10

Mark the sentences in this paragraph about giant covalent structures by ticking the correct ones.

CORRECT ANSWER
In giant covalent structures, all the bonds are strong covalent bonds.
There are no weak bonds in the structure at all.
EDDIE SAYS
The important point about giant covalent structures is that they have no weak parts at all. This explains their strength; diamond is one of the hardest and strongest materials that exist.
---- OR ----

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