Chap 5 Chem

Question 1

Ionic substances properties

Answer 1

-giant ionic crystal lattice structures
-strong electrostatic forces of attraction
-hard but brittle
-high melting and boiling point (solids at room temp)
-conduct electricity in molten state
-soluble in water, insoluble in organic solvents

Question 2

Properties of simple covalent molecules

Answer 2

-strong covalent bonds
-weak intermolecular forces of attraction (between molecules)
-change of state in substance during boiling or melting
(breaks weak intermolecular forces of attraction NOT strong covalent bonds)
-low melting and boiling point (affected by size)
-volatile
-insoluble in water, soluble in organic solvent
-cannot conduct electricity (all states)

Question 3

Allotropes

Answer 3

Different forms of the same element with different structural arrangement of atoms

Question 4

Giant covalent substances

Answer 4

-hardness (diamond)
very hard (diamond and silicon dioxide)
graphite: layers slide, soft and slippery
-high melting and boiling point
-insoluble in water & organic substances
- cannot conduct electricity: diamond, graphite
can conduct electricity: graphite

Question 5

Macromolecules physical properties

Answer 5

Most are solids @ room temp (large size)
No fixed bp and mp
Usually soften over range of temp
Insoluble in water, soluble in organic solvents
Do not conduct electricity

Question 6

Why ionic compounds are hard but brittle (not so impt?)

Answer 6

Hard- attractive forces cause ions to resist motion

Brittle- when force is applied, ions of same charge approach each other, Repulsive forces between ions of the same charge becomes larger than attractive forces -> shatters lattice

Question 7

Why ionic substances cannot conduct electricity in solid state but can in liquid/aqueous/molten state

Answer 7

Solid- ions not free to move abt, vibrate about fixed positions cannot conduct
Liquid- ions mobile, can conduct

Question 8

Diff structures of covalent substances

Answer 8

Simple molecular
Giant molecular
Macromolecular

Question 9

Relationship between Mr/size and intermolecular forces of attraction and mp bp

Answer 9

Larger Mr -> stronger … attraction -> higher mp, bp

Question 10

Can simple covalent molecules conduct electricity and why

Answer 10

No
Absence of mobile charge carriers/ no free moving ions/electrons

(exception, HCL which dissociates in water and has mobile ions)

Question 11

Why are allotropes usually in solid state

Answer 11

Many atoms connected by strong covalent bonds

Question 12

Why giant covalent structures have high mp and bp

Answer 12

Large amt of energy needed to break strong covalent bonds within molecule

Question 13

Electrical conductivity in giant covalent substances

Answer 13

No - diamond, silicon dioxide (no mobile electrons)
Yes- graphite (free and mobile electrons (delocalised electrons in each layer of carbon atoms))

Question 14

Why are macromolecules usually in solid state at room temp

Answer 14

Large size of polymers-> strong intermolecular forces of attraction

Question 15

Why do macromolecules usually soften over range of temp

Answer 15

Weaker intermolecular forces of attraction overcome by molecular vibrations with higher KE

Question 16

Why do polymers melt and boil over a range of temp

Answer 16

Diff sizes of molecules/monomers

Question 17

What are alloys

Answer 17

Mixture of metal with one/more elements

Question 18

Properties of pure metals

Answer 18

-malleable
-ductile
-high mp and bp
-good electrical conductor (sea of delocalised electrons)
-layers of atoms slide over one another easily

Question 19

Properties of alloys

Answer 19

-less malleable
-less ductile
-harder and stronger than pure metals
-melt over a range of temp (mixture, irregular lattice arrangement)
-good electrical conductor
-larger force needed to make layers slide over one another

Question 20

Malleable

Answer 20

Ability to be hammered into different shapes

Question 21

Ductile

Answer 21

Ability to be pulled into wires without breaking

Question 22

Explain why alloys are harder than pure metals

Answer 22

Alloys contain atoms of diff sizes
Disrupts the regular and orderly arrangement of pure metals
Layers of atoms cannot slide over one another easily
Thus Alloys are harder and stronger than pure metals

Question 23

Explain mp and bp of ionic compounds

Answer 23

High mp and bp, solids at room temp

Strong electrostatic forces of attraction between oppositely charged ions -> large amt of energy needed to overcome these forces