2.3 The metallic model

Question 1

What is a metallic bond?

Answer 1

Electrostatic attraction between a lattice of cations and delocalised electrons

Question 2

What is the ionisation energy of metals usually?

Answer 2

Low

Question 3

What occurs in the metallic bonding model?

Answer 3

Valence electrons become delocalised
Resulting metal cations are densely packed in a lattice
Delocalised valence electrons spread tehemselves out throughout metallic lattice (sea of delocalised electrons)

Question 4

What are the properties of metals?

Answer 4

lustruous
malleable
ductie
high boiling point (often high melting point)
dense
good head nad electricity conductors

Question 5

Why are metals good conductors of electricity when solid and molten?

Answer 5

Delocalised electrons are free to move if source of electric current is attached.
Can flow from negative to positive electrode

Question 6

Why are metals good conductors of heat?

Answer 6

When heated, the kinetic energy of delocalised electrons is increased and rapidly distributed through the lattice. Increased lattice vibrations also pass energy on from one densely packed metal cation to the next

Question 7

Why are metals malleable and ductile?

Answer 7

Layers of cations can be forced across each other. Delocalised electrons can move to compensate for this and re-establish electrostatic forces

Question 8

What does malleable mean?

Answer 8

Able to be bent into a sheet

Question 9

What does ductile mean?

Answer 9

Able to be bent into a wire

Question 10

Why do metals have high boiling points?

Answer 10

Large amounts of heat energy are required to overcome the strong electrostatic forces of attraction between cations and delocalised electrons

Question 11

Why are metals lustruous?

Answer 11

delocalised electrons reflect light

Question 12

Why do metals have high densities usually?

Answer 12

Closely packed in lattice -> high mass per unit volume

Question 13

What does more crystals mean for the brittleness of the metal?

Answer 13

More brittle

Question 14

What does the strength of the metallic bonding depend on?

Answer 14

Radius of a metal ion
Charge of a metal ion

Question 15

What happens to the metallic bonding strenght as it goes down Group 1?

Answer 15

Decreases

Question 16

Why does a small ionic radius lead to strong metallic bonding?

Answer 16

The smaller the ionic radius, the stronger the electrostatic attraction between lattice of positive cations and sea of negative delocalised electrons, and thus stronger metallic bonding

Question 17

What is charge density?

Answer 17

Ratio of charge to volume of an ion

Question 18

Why does the strenght of metallic bonding increase with increasing charge on the metal ion?

Answer 18

For ions of similar radius, greater charge leads to greater charge density, leads to stronger electrostatic attraction between lattice of positive cations and sea of delocalised negative electrons, thus stronger metallic bonding

Question 19

What are alloys?

Answer 19

Mixture of a metal with one or more elements, that retain the characteristics of a metal

Question 20

Why are alloys made?

Answer 20

To enhance properties of the metal, such as

Increased hardness
Improved corrosion resistance
Variation in colour
Lower melting point

Question 21

How are alloys generally prepared?

Answer 21

Mixing molten liquid metals or dissolving a solid in a molten metal

Question 22

What is a substitutional alloy?

Answer 22

Alloy where the atoms have similar ionic radii so they can be substituted for each other in a lattice

Question 23

What is an interstitial alloy?

Answer 23

Alloy where atoms are of different sizes, thus fitting in between each other.

Question 24

What is a homogeneous alloy?

Answer 24

Atoms of different elements distributed uniformly

Question 25

What is a heterogeneous alloy?

Answer 25

Contains crystalline phases with different compositions

Question 26

How are atoms arranged in a substitutional alloy?

Answer 26

Ionic radii are similar so they can be substituted for each other in the lattice. Delocalised electrons are shared by both types of atoms, As ions have slightly different radii, layers within lattice are restricted so the alloy is harder and less malleable

Question 27

What elements are involved in steel?

Answer 27

Iron and carbon

Question 28

How are atoms arranged in the interstitial alloy of steel?

Answer 28

Smaller carbon atoms fit in spaces between iron atoms. Carbon forms strong carbon-iron directional bonds which results in the alloy being harder, stronger and less malleable

Question 29

Why are alloys less malleable?

Answer 29

Presence of different atoms in the lattice restrict movement of layers within the lattice