Ch.6-Ionic And Covalent Bonding

Question 1

What is water of crystallisation?

Answer 1

Water of crystallisation is water chemically combined in definite proportions in a crystalline compound.

Question 2

What is a chemical bond?

Answer 2

A chemical bond holds atoms together in a molecule or compound.

Question 3

State the octet rule.

Answer 3

The octet rule states that atoms on reaction tend to reach an electron arrangement with 8 electrons in the outer shell. This is true for sodium chloride.

Question 4

What are the exceptions to the octet rule?

Answer 4

Beryllium and boron have too few electrons on their outer level to reach 8 electrons. Usually, the d-block elements don’t obey the rule. The rule is inconsistent with sulphur and phosphorus. Hydrogen and lithium tend to reach the outer electronic configuration of helium rather than that of the other noble gases. Transition elements do not obey this rule.

Question 5

What is the valency of an element?

Answer 5

The valency of an element is the number of bonds an atom of the element forms when it reacts.

Question 6

What are the valences of each group in the periodic table?

Answer 6

Group I have a valency of one. Group II have one of 2. Group III have one of 3. Group IV have one of 4. Group V have one of 3. Group VI have one of 2. Group VII have one of 1. The noble gases don’t typically form compounds, so their valency is 0.

Question 7

What are the transition elements and what are their valences?

Answer 7

Transition elements are elements that have partially filled 3d orbitals, they have variable valences. Examples include chromium, manganese, iron and copper.

Question 8

What are ionic bonds?

Answer 8

An ionic bond is the electrostatic force of attraction between pairs of oppositely charged ions in a compound.

Question 9

What are ions, anions and cations?

Answer 9

Ions are charged atoms. Anions are negatively charged ions. Cations are positively charged ions.

Question 10

What structure is made as a result of ionic bonding?

Answer 10

Ionic bonding doesn’t result in the formation of molecules. Instead, oppositely charged ions attract each other to form a rigid 3D lattice.

Question 11

What are the characteristics of ionic substances?

Answer 11

Ionic substances create a network of ions in a crystal. They are usually hard and brittle, they have high melting and boiling points. They are usually solid at room temperature. They conduct electricity when molten or in aqueous solution due to the freeing of ions.

Question 12

What are examples of ionic materials in everyday life?

Answer 12

Salt tablets are taken to replace salt lost from the body by sweating. Brine, a solution of sodium chloride, is used as preservation for bacon.

Question 13

What is a covalent bond?

Answer 13

A covalent bond is formed when 2 atoms share pair(s) of electrons.

Question 14

What are bonding pairs?
What are lone pairs?

Answer 14

Bonding pairs are shared electron pairs that form covalent bonds. Lone pairs (or non-bonding pairs) are pairs of electrons that aren’t involved in bonding.

Question 15

What is a single covalent bond?

Answer 15

A single bond occurs when there is one shared pair of electrons in a covalent bond.

Question 16

What is a double and triple covalent bond?

Answer 16

A double covalent bond is formed when 2 atoms share 2 pairs of electrons. A triple covalent bond is formed when 2 atoms share 3 pairs of electrons.

Question 17

What is a sigma bond?

Answer 17

All single bonds are sigma bonds. A sigma bond is a molecular orbital formed by the head-on overlap between atomic orbitals of different atoms.

Question 18

What is a pi bond?

Answer 18

A pi bond is formed in double or triple bonds where sideways overlap is possible between 2 p atomic orbitals, each containing one electron.

Question 19

What is a non-polar bond?

Answer 19

A non-polar covalent bond is one where the nuclei of the 2 atoms involved attract the shared electrons in the covalent bond equally.

Question 20

What factors dictate the extent to which the shared electrons are attracted by different nuclei?

Answer 20

The size of the atom because smaller atoms have a stronger attraction than larger ones because they can get closer to the shared pair of electrons. And nuclear charge because atoms of a similar size will have greater attraction for shared electrons if there is a bigger charge in the nucleus.

Question 21

What are polar covalent bonds?

Answer 21

Polar covalent bonds share electrons unequally.

Question 22

What are the characteristics of covalent substances?

Answer 22

Covalent substances contain individual molecules. In covalent substances, the intramolecular forces are strong, but the intermolecular forces are weak. Most solid covalent substances have low melting and boiling points. In general, they do not conduct electricity even in a liquid state or aqueous solution. Most covalent substances do not dissolve readily in water. They are usually soft, and are liquids or gases at room temperature.

Question 23

What is electronegativity?

Answer 23

Electronegativity is the relative attraction of an atom for shared pairs of electrons in a covalent bond.

Question 24

How does electronegativity change going across a period?

Answer 24

Electronegativity increases across a period as the atomic number and nuclear charge increases. Across a period, there is no change in the screening effect, and so there is no reduction of the nuclear charge’s force of attraction. Larger nuclear charge means smaller atomic radius, resulting in increased electronegativity.

Question 25

How does electronegativity change going down a group?

Answer 25

Extra levels of electrons increases the screening effect, the size of the atomic radius, resulting in decreased electronegativity. Even though nuclear charge is increasing, electrons aren’t attracted strongly enough.

Question 26

How can differences in electronegativity be used to predict the nature of a bond between 2 atoms?

Answer 26

If the difference in electronegativity is less than about 0.4, then the bond can be regarded as being non-polar covalent. The bond is predicted to be polar covalent if the electronegativity difference is less than 1.7 but greater than 0.4. When electronegativity difference is greater than 1.7, the degree of ionic character is greater than the degree of covalent character, so the bond is predicted to be ionic.

Question 27

What is a compound?

Answer 27

A compound is a substance that is made of 2 or more elements combined together chemically.

Question 28

What is a molecule?

Answer 28

A molecule is a group of atoms which are chemically joined.

Question 29

Why don’t noble gases form compounds. Give examples of the uses of noble gases.

Answer 29

The noble gases do not tend to form compounds and so their electronic configurations are taken to be particularly stable. Argon is used in light bulbs to prevent the filament from burning and helium is used in balloons.

Question 30

What happens during an ionic bond formation?

Answer 30

An ionic bond is formed when electrons are transferred from one atom to another resulting in ion formation. Each ion achieves the electronic configuration of the nearest noble gas.

Question 31

Why don’t the noble gases have electronegativity values?

Answer 31

The noble gases don’t have electronegativity values because they are very unreactive and they dont typically form compounds.

Question 32

What are characteristics of transition metals?

Answer 32

Transition metals exhibit variable valency, they form coloured compounds and can behave as catalysts. When transition metals react, the first electron is lost from the 4s sublevel as this is a part of the outer shell. (scandium and zinc can more properly be classified as d-block elements).

Question 33

What is intermolecular bonding?

Answer 33

Intermolecular bonding are the forces of attraction between molecules. These include Van der Waals’ forces, dipole-dipole forces and hydrogen bonding.

Question 34

What is a dipole?

Answer 34

A dipole is a bond or molecule whose ends have opposite charges.

Question 35

What is intramolecular bonding?

Answer 35

Intramolecular bonding is bonding that takes place within a molecule. Examples of this are ionic, polar covalent and non-polar covalent bonding.

Question 36

What is bond energy?

Answer 36

Bond energy is the average amount of energy required to break or form a bond of the same type in the gaseous state.