Chemical Bonding 1

Question 1

Define ionic bonding.

Answer 1

The electrostatic forces of attraction between oppositely charged ions in an ionic compound.

Question 2

Describe how an ionic bond is formed.

Answer 2

Electrons are transferred from metal atoms to non-metal atoms to form ions. The atom that transferred electrons gets positive charges and becomes a cation. The atom that gained electrons gets negative charges and becomes an anion. The oppositely charged ions attract each other, forming a giant ionic lattice.

Question 3

Sodium forms the oxide Na₂O. Explain why the oxide of sodium has this fomula.

Answer 3

Each Na atom has one valence electron. To attain noble gas electronic configuration, each Na atom loses its one valence electron to form a Na+ cation. Each O atom has six valence electrons. To attain noble gas electronic configuration, each O atom gains two electrons from two Na atoms to form an O2- anion. Since the ratio of Na+ : O2- is 2:1 such that the lattice is electrically neutral, the formula is Na₂O.

Question 4

State the relationship between the charge of the ions and the strength of the ionic bonds

Answer 4

The greater the charge of the ions, the stronger the ionic bonds.

Question 5

State the relationship between the ionic radii and the strength of the ionic bonds.

Answer 5

The greater the sum of the ionic radii, the bigger the ions and thus the weaker the ionic bonds.

Question 6

State the physical properties of ionic compounds.

Answer 6

1) high melting and boiling points
2) soluble in water
3) conducts electricity in molten and aqueous state
4) hard (do not dent), rigid (do not bend) and brittle (crack without deforming)

Question 7

Why do ionic compounds have high melting and boiling points?

Answer 7

Ionic compounds have a giant ionic lattice. Thus, large amounts of energy is required to overcome the strong electrostatic forces of attraction between the oppositely charged ions to break the giant ionic lattice and form free ions.

Question 8

Explain whether NaCl or MgO has a higher melting point.

Answer 8

Mg^2+ and O^2- have higher charge and smaller ionic radius than Na+ and Cl-, thus the strength of the ionic bonds in MgO is larger than that of NaCl. More energy is required to overcome the stronger electrostatic forces of attraction between the oppositely charged ions in MgO, hence it has a higher melting point.

Question 9

What happens when an ionic salt dissolves in water?

Answer 9

When an ionic salt dissolves, each ion on the crystal’s surface attracts the oppositely charged poles of the water molecules and the ions become hydrated. This process releases energy, causing the ionic crystal structure to break down and the solid dissolves.

Question 10

Why do ionic compounds not conduct electricity in the solid state but conducts electricity in the molten and aqueous solutions?

Answer 10

In the solid state, ions in the ionic compounds are fixed in positions and unable to move freely. In the molten and aqueous solutions, the ions are mobile. They are thus free to move and flow towards the oppositely charged electrodes and act as mobile charge carriers, carrying a current.

Question 11

Why are ionic solids hard, rigid, and brittle?

Answer 11

In an ionic lattice, oppositely charged ions are held in fixed positions by strong ionic bonding. Moving the ions require large amounts of energy to break these bonds, thus they are hard and rigid.
If enough pressure is applied, ions of like charge are brought together and the repulsion between them causes the lattice to shatter, thus it is brittle.

Question 12

Define metallic bonding.

Answer 12

The electrostatic forces of attraction between a lattice of metal cations and the sea of delocalised electrons in the metallic lattice.

Question 13

State the relationship between the number of delocalised valence electrons and the strength of the metallic bond.

Answer 13

The greater the number of valence electrons contributed per atom, the stronger the metallic bonding.

Question 14

State the relationship between the charge and radius of the metal cation and the strength of the metallic bond.

Answer 14

The higher the charge and the smaller the radius of the metal cation, the greater the electrostatic forces of attraction between the cation and the sea of delocalised electrons.

Question 15

Describe the structure and bonding in calcium metal.

Answer 15

The structure of calcium is a giant ionic lattice containing an array of Ca^2+ ions, with the valence electrons of calcium removed and free to flow throughout the lattice.
Metallic bonding exists between the Ca^2+ ions and the sea of delocalised electrons.

Question 16

State the physical properties of metals.

Answer 16

1) high melting and boiling points
2) conducts electricity
3) good conductor of heat
4) malleable (can be beaten and flattened into sheets) and ductile (can be pulled into wires)
5) shiny surface
6) hard

Question 17

Explain what is meant by the term “malleable”.

Answer 17

Being able to be beatened and flattened into sheets.

Question 18

Explain what is meant by the term “ductile”.

Answer 18

Being able to be pulled into wires.

Question 19

Why do most solid metals have high melting points and boiling points?

Answer 19

Metals have a giant metallic lattice structure which consists of a lattice of metal cations with a sea of delocalised electrons, and the electrostatic forces of attraction between the cations and the delocalised electrons constitute the metallic bond. A large amount of energy is required to overcome the strong electrostatic forces of attraction between the cations and delocalised electrons.

Question 20

Why are metals good electrical conductors?

Answer 20

The sea of delocalised electrons which act as mobile charge carriers are free to move about in the solid structure.

Question 21

Why are metals good heat conductors?

Answer 21

They have mobile delocalised electrons which disperse heat quickly from a region of higher temperature to a region of lower temperature.

Question 22

Why are metals malleable and ductile?

Answer 22

The ions in metals are held in an orderly array in the giant metallic structure. When an external force is applied to the metal, the layers of metal ions in the solid structure slide past each other and end up in new positions. The overall shape changes but the metal does not break because the sea of
delocalised electrons prevents the repulsion among the cations as they move past one another. The metallic bond strength still remains the same, hence its malleability and ductility.

Question 23

Define alloys.

Answer 23

Alloys are a mixture of metals involving incorporation of small quantities of other elements into the pure metal.

Question 24

State the parent and alloying elements of the metals:
1) bronze
2) brass
3) steel
4) stainless steel
5) pewter

Answer 24

1)
Parent element: copper
Alloying element: tin
2)
Parent element: copper
Alloying element: zinc
3)
Parent element: iron
Alloying element: carbon
4)
Parent element: iron
Alloying element: chromium, nickel
5)
Parent element: tin
Alloying element: copper, antimony

Question 25

Why are alloys less malleable than pure metals?

Answer 25

Alloying makes metals harder. This is because atoms of the added metal have of different size. This disrupts the orderly arrangement of the main metal cations, and the layers of the metal cations can no longer slide over each other easily when a force is applied.