2.10

Question 1

What are metallic crystals?

Answer 1

Solids with closely packed metal cations held together by electrostatic interactions and a sea of free moving electrons

Examples include Zn, Au, and Al.

Question 2

What are metallic bonds?

Answer 2

The bonds that hold the nuclei and electrons together in metallic crystals

These bonds are responsible for the unique properties of metals.

Question 3

What is the Electron Sea Theory?

Answer 3

A theory stating that electrons in metallic crystals move freely around positively charged nuclei

This theory helps explain the conductivity and malleability of metals.

Question 4

Do all metallic crystals have the same properties?

Answer 4

No, different metallic crystals have varying properties

For example, gold is soft, while aluminum is strong.

Question 5

Can metallic crystals conduct electricity in solid form?

Answer 5

Yes, all metallic crystals can conduct electricity in solid form

This property is due to the free-moving electrons.

Question 6

What are covalent-network crystals?

Answer 6

Solids in which atoms form an interwoven network of covalent bonds

Examples include diamond (C), silicon dioxide (SiO2), and silicon carbide (SiC).

Question 7

What properties do covalent-network crystals have due to their strong covalent bonds?

Answer 7

High melting points and boiling points, and extreme hardness

Their structure prevents atoms from moving easily.

Question 8

Are covalent-network crystals good conductors?

Answer 8

No, covalent-network crystals are not very good conductors

Their structure limits the movement of electrons.

Question 9

Match the solid to the property: NaBr(s), P2O5(s), SiO2(s) - High melting point, conducts electricity.

Answer 9

NaBr

This solid is known for its high melting point and electrical conductivity.

Question 10

Match the solid to the property: P2O5(s) - Low melting point, soft.

Answer 10

P2O5

This solid has a low melting point and is considered soft.

Question 11

Match the solid to the property: SiO2(s) - Very high melting point, non-conductor.

Answer 11

SiO2

Silicon dioxide is known for its very high melting point and lack of electrical conductivity.

Question 12

What is the melting point characteristic of diamond?

Answer 12

Very high melting point

Diamond has a significantly higher melting point than octane due to its covalent-network structure.

Question 13

Why does diamond have a higher melting point than octane?

Answer 13

Because it is a covalent-network structure

Octane is a molecular structure, which contributes to its lower melting point.

Question 14

What are the different forms that solid carbon can take?

Answer 14

• Tetrahedral arrangements (diamonds)
• Layers of sheets (graphite)
• Large spherical molecules (Bucky balls)
• Long thin tubes (carbon nanotubes)

Carbon’s versatility allows it to form various structures.

Question 15

What property does graphite have that is unique among carbon structures?

Answer 15

Conducts electricity

Graphite is hard and has a high melting point, yet it can conduct electricity.

Question 16

What are semiconductors made of?

Answer 16

Valence crystals of metalloid elements

Common examples include silicon and germanium.

Question 17

How do semiconductors behave at room temperature?

Answer 17

They conduct a small amount of electric current

Conductivity increases at higher temperatures due to energy gaps in their structure.

Question 18

What is the process called that modifies semiconductors to enhance their conductivity?

Answer 18

Doping

This involves adding elements like arsenic or boron to introduce extra valence electrons.

Question 19

What happens during the doping process in semiconductors?

Answer 19

Extra valence electrons are added

This modification allows for the creation of semiconductors with specific conductive properties.

Question 20

What is a characteristic of semiconductors regarding energy gaps?

Answer 20

There is a small energy gap between valence orbitals and empty orbitals

Thermal energy can promote electrons into these empty orbitals, enhancing conductivity.

Question 21

What is an example of an ionic crystal?

Answer 21

NaOH (sodium hydroxide)

Other examples include Na3PO4 (sodium phosphate) and MgO (magnesium oxide).

Question 22

What are the four categories of solids?

Answer 22

• Ionic crystal
• Molecular crystal
• Metallic crystal
• Covalent-network crystal

Each category has distinct structures and properties.

Question 23

What holds ionic crystals together?

Answer 23

Very strong ionic bonds

Ionic bonds form from the interaction of metal and non-metal ions.

Question 24

What property of ionic crystals leads to high boiling and melting points?

Answer 24

Strong ionic bonds

These bonds require significant energy to break.

Question 25

Do ionic crystals conduct electricity in solid form?

Answer 25

No ## Footnote Ionic crystals conduct electricity only when dissolved in water.

Question 26

What are molecular crystals composed of?

Answer 26

Individual molecules ## Footnote These molecules are held together by intermolecular forces of attraction.

Question 27

How do the boiling and melting points of molecular crystals compare to ionic crystals?

Answer 27

Lower ## Footnote This is due to weaker intermolecular forces compared to ionic forces.

Question 28

Do molecular crystals conduct electricity in their pure form?

Answer 28

No ## Footnote Molecular crystals contain neutral molecules that do not conduct electricity well.

Question 29

Fill in the blank: Salt is an example of an _______ crystal.

Answer 29

ionic ## Footnote Sugar, in contrast, is an example of a molecular crystal.

Question 30

Fill in the blank: Sugar is an example of a _______ crystal.

Answer 30

molecular ## Footnote This highlights the differences between sugar and salt in structure and properties.