Chemical bonding

Question 1

What affects strength of instantaneous dipole- induced dipoles forces of attraction?

Answer 1

1.Electron number
Higher number of electrons > bigger electron cloud > greater ease of distortion of electron cloud > stronger instantaneous dipole- induced dipole forces of attraction between the molecules > more energy req to overcome the stronger id-id forces of attraction > higher bp
2.Shape of molecule
Straight chains have a greater contact surface area to adjacent molecules than their branched-chain isomers that are spherical and less closely packed to one another. > Instantaneous dipoles are more easily induced in straight chain molecules. > more extensive instantaneous dipole- induced dipole forces of attraction between straight chain molecules > more energy is required to overcome these forces> higher bp

Question 2

What affects strength of permanent dipole - permanent dipole forces of attractions?

Answer 2

The more polar(electronegative) the bonds are, the stronger the id-id forces of attraction.

Question 3

What are the requirements for hydrogen bonding?

Answer 3

An electron-deficient hydrogen atom directly bonded to F , O or N.
A lone pair of electrons in F , O or N.

Question 4

What affects strength of hydrogen bonds?

Answer 4

1. Dipole moment. Larger dipole moment > stronger hydrogen bonding > more energy required to over come the forces of attraction > higher bp
2. No. of hydrogen bonds. More hydrogen bonds > stronger hydrogen bonds > more energy required to overcome forces of attraction > higher bp

Question 5

How does the electronegativity of a molecule affects its bond angle?

Answer 5

Lets say molecule X>y
X is more electronegative than Y
Bond pair electrons in X are closer to the central X atom than Y
there is more repulsion between the electrons
bigger bond angle

Question 6

What is an ionic bond?

Answer 6

Ionic bond is the electrostatic forces of attraction between two oppositely charged ions.

Question 7

How to measure strength of ionic bond?

Answer 7

Magnitudes of lattice energy which is dependent on the charge and ionic radii. Larger charge = stronger electrostatic forces of attraction. Smaller ionic radius = shorter inter-ionic distance > stronger electrostatic forces of attraction. ↑M L.E , ↑ Ionic bond.

Question 8

What are the physical properties of ionic compounds?

Answer 8

Electrical conductivity: Solid state; mobile ions are in fixed position hence there are no mobile electrical charge carriers , not able to conduct electricity.
Molten state; there are mobile ions that can act as mobile electrical charge carriers to conduct electricity.
High melting boiling point: Giant ionic lattice structure has strong electrostatic forces of attraction between anions and cations. More energy is required to overcome these forces of attraction , leading to a high bp.
Hard: Each ion is held in the closely packed crystal lattice by strong electrostatic forces of attraction between anions and cations.
Brittle: When a force is applied , the layers of ions are displaced causing ions of the same charge to repel , fracturing the ionic structure.
Soluble in water: The ions form favourable ion-dipole interactions with polar molecules. Sufficient energy is released to overcome the strong electrostatic forces of attraction between the oppositely charged ions.

Question 9

What is a metallic bond?

Answer 9

The electrostatic forces of attraction between a lattice of positive metal ions and sea of delocalised electrons.

Question 10

Factors affecting metallic bond?

Answer 10

1. No. of valence electrons delocalised in the lattice. More DE > stronger electrostatic FOA between cation and sea of DE > stronger the metallic bond.
2. Charge density. Greater the charge density > stronger electrostatic FOA btw the cations and sea of DE > stronger metallic bond

Question 11

What are the physical properties of metals.

Answer 11

Electrical and thermal conductivity: Mobile delocalised electrons act as electrical charge carriers to conduct electricity and transmit heat.

High BP MP: alot of energy is required to overcome to strong electrostatic forces of attraction between cations and sea of delocalised electrons.

Ductile and malleable: When a force is applied , layers of cations and delocalised electrons can glide over another layer easily and allows the structure to change shape without fracturing.

Question 12

Define covalent bond.

Answer 12

The strong electrostatic forces of attraction between a shared pair of electrons and the two positively charged nuclei.

Question 13

Why is a sigma bond stronger than a pi bond.

Answer 13

A pi bond is weaker than a sigma bond as a sigma bond has a greater extent of overlapping.

Question 14

What are the requirements for dative bonding?

Answer 14

1.Donor atom must possess a lone pair of electrons in its valence electron shell
2.Acceptor must have an energetically accessible vacant 1s/2s/3p/3d orbitals in its valence electron shell to accommodate the lone pair of electrons.

Question 15

What affects the strength of a covalent bond?

Answer 15

The extent of orbital overlap between two bonded atoms. The more effective the overlap of orbitals , the more electrons can experience the attraction of both nuclei hence the stronger covalent bond.

The bond length. The bond length increases with increasing size of the atom. A shorter bond length would result in a greater degree of overlap , resulting in a stronger bond.

Larger dipole moment , bigger difference in electronegativity would result in a stronger bond.

Question 16

Why is ice less dense than water?

Answer 16

At solid state , the h2o molecules are in fixed positions by hydrogen bonding in a tetrahedral arrangement. Each hydrogen atom in a molecule of h2o will form hydrogen bonds with the lone pair of electrons on an O atom of another h2o molecule. Each h2o molecule will form 2 hydrogen bonds with another molecule of h2o. This creates an open crystalline structure that occupies a larger volume for the same mass of h2o , causing a lower density.

Question 17

Why does water have high surface tension.

Answer 17

This is because at the surface of the water , h2o molecules have lesser h2o molecules to form hydrogen bonding with as it has air ontop instead. This leads to a stronger hydrogen bonding on the surface of the water hence a high surface tension.

Question 18

How does ionic bonds have a high degree of covalent character?

Answer 18

This happens when the cation has a high charge density as it has a high charge but small cationic radius. The cation will have polarising power to distort the electron cloud of the anion. Anion is big hence its electron cloud will be easily distorted by the cation.

Question 19

What are the physical properties of silicon dioxide and diamond?

Answer 19

High BP and MP: Both have a giant covalent structure held by strong covalent bonds. Large amounts of thermal energy is needed to break the covalent bonds between atoms.
Hard: Atoms are joined by strong covalent bonds throughout the three-dimensional arrangement, distorting the giant covalent structure means strong covalent bonds would have to be broken.
Non-conductor of electricity: Electrons in the covalent bonds are immobile hence there are no electrical charge carriers to conduct electricity.

Question 20

What are the physical properties of Graphite?

Answer 20

High MP: Giant covalent structure held by strong covalent structure. Large amounts of thermal energy is required to break the strong covalent bonds.
Soft (lubricant): The bonding between the layers is weak instantaneous dipole- induced dipole forces of attraction which can be easily overcome to allow layers to slide over one another.
Conductor of electricity: Within the layer , each carbon atom is only covalently-bonded to 3 other carbon atoms . Thus the fourth electron can act as electrical charge carriers and conduct electricity.