Chapter 3- Structure and Bonding

Question 1

What is an ionic bond?

Answer 1

An electrostatic attraction between oppositely charged ions.
+ and - ions are formed due to transfer of electrons (usually) between metal atoms and non-metal atoms.

Question 2

What is the structure of ionic compounds?

Answer 2

Giant ionic lattice

Question 3

What are some properties of ionic compounds?

Answer 3

Conduct electricity when molten or dissolved as ions are free to move.
High melting point as bonds are strong and there are lots of bonds.
Brittle as like charges repel, causing the lattice to shatter.

Question 4

What is a covalent bond?

Answer 4

A shared pair of electrons (usually) between two non-metal atoms (2 atoms of similar electronegativities).
The attraction between the nuclei and shared electrons hold the atoms together.
Multiple covalent bonds contain multiple shared pairs of electrons.

Question 5

What are the properties of substances with molecular structures?

Answer 5

Low melting points due to weak intermolecular forces between the molecules which require little energy to break.
Poor conductors of electricity as the molecules are neutral overall (no delocalised electrons/ free charged particles to carry charge)

Question 6

What is a dative covalent bond (coordinate bond) ?

Answer 6

A shared pair of electrons (covalent bond) but both electrons are supplied by one atom.
The atom with a lone pair of electrons donates them and the electron-deficient atom accepts the electrons.
It is represented by an arrow rather than a line.

Question 7

What is a metallic bond?
What structure do metals have?

Answer 7

An electrostatic attraction between the delocalised electrons and positive metal ions arranged in a lattice.
Metals have giant structures.

Question 8

What are some properties of metals and why are these the properites?

Answer 8

Good conductors of electricity and heat due to delocalised electrons that can move throughout and carry charge.
Malleable (molded) and ductile (pulled) as when there is a change, each ion is in the same environment so it retains new shape.
High melting points due to strong attraction between metal ions and delocalised sea of electrons.

Question 9

What do molecular crystals consist of?

Answer 9

Molecules held in a regular array by intermolecular forces.
There are strong covalent bonds within the molecules but weak IMFs between the molecules, hence a low melting point.

Question 10

What is the structure and properties of diamond?

Answer 10

Macromolecular (giant covalent): lots of atoms covalently bonded to form regular 3D arrangement.
Pure carbon, carbon atoms covalently bonded to 4 other carbon atoms.
Properties: very hard, very high melting point, poor conductor.

Question 11

What is the structure of graphite?

Answer 11

Pure carbon, each carbon atom covalently bonded to 3 other carbon atoms, causing 2D layers of linked hexagons.
Weak Van der Waals’ forces between which are easily broken.
One remaining outer electron from each atom because delocalised to form cloud of delocalised electrons which moves freely throughout the material

Question 12

What are the properties of graphite?

Answer 12

Soft, slippery material as VdWs forces between layers are weak (lubricant).
High melting point due to strong network of covalent bonds.
Conducts electricity (and heat) along planes of hexagons due to delocalised electrons.

Question 13

What shape is a molecule with two pairs of electrons around the central atom?

Answer 13

Linear, 180°

Question 14

What shape is a molecule with three pairs of electrons around the central atom?

Answer 14

Trigonal planar, 120°

Question 15

What shape is a molecule with four pairs of electrons around the central atom?

Answer 15

Tetrahedral, 109.5°

Question 16

What shape is a molecule with five pairs of electrons around the central atom?

Answer 16

Trigonal bipyramidal, 90° and 120°

Question 17

What shape is a molecule with six pairs of electrons around the central atom?

Answer 17

Octahedral, 90°

Question 18

What is the electron pair repulsion theory?

Answer 18

Bonding pairs and lone pairs of electrons repel each other and so pairs of electrons in the outer shells of atoms are arranged as far apart as possible to minimise repulsion.

Question 19

How do lone pairs repelling compare to other pairs repelling?

Answer 19

Lone pair-lone pair repulsion greater than lone pair-bonding pair repulsion greater than bond pair-bond pair repulsion.

Question 20

How do lone pairs affect the bond angles in a tetrahedral?

Answer 20

Decrease bond angles by 2.5°

Question 21

What shape is a molecule with three bonding pairs and one lone pair of electrons around the central atom, eg ammonia?

Answer 21

Trigonal pyramidal, 107°

Question 22

What shape is a molecule with two bonding and two lone pairs of electrons around the central atom?

Answer 22

Bent or V-shaped, 104.5°

Question 23

What shape is a molecule with four bonding pairs and two lone pairs of electrons around the central atom?

Answer 23

Square planar, 90°

Question 24

What do you do to electrons when drawing ions?

Answer 24

Positive ions: remove an electron.
Negative ions: add an electron (drawn as a triangle).

Question 25

What is electronegativity?

Answer 25

The power of an atom to attract the pair of electrons in a covalent bond towards itself.

Question 26

What three factors affect electronegativity?

Answer 26

Nuclear charge
Distance between nucleus and outer shell electrons
Shielding of the nuclear charge by electrons in inner shells

Question 27

What is a polar covalent bond?

Answer 27

A covalent bond between two atoms with different electronegativity.
The shared pair of electrons are attracted towards the more electronegative atom.
This causes asymmetrical electron distribution causing the more electronegative side to be δ- (partially negative) and the other to be δ+ (partially positive).

Question 28

How does difference in electronegativity affect a polar bond?

Answer 28

The greater the difference in electronegativity, the more polar the covalent bond.

Question 29

Why don’t all molecules with polar bonds have a permanent dipole?

Answer 29

In molecules in which the electron distribution is symmetrical, the dipoles cancel out and so overall the molecules does not have a permanent dipole.

Question 30

What are the three types of IMF?

Answer 30

Van der Waals forces
Dipole-dipole forces
Hydrogen bonds (not actually bonds)

Question 31

How do Van der Waals forces work?

Answer 31

There is electron fluctuation in all molecules, even those without polar bonds. This causes there to be temporary dipoles due to uneven electron distribution.
This then induces a temporary dipole in a neighbouring molecule, producing a temporary induced dipole-dipole attraction.
Large the molecule, stronger the VdW forces.

Question 32

How do permanent dipole-dipole attractions work?

Answer 32

Occurs between molecules with polar bonds that have an overall dipole. Uneven electron distribution in the molecule causes there to be two poles.
There are attractions between the δ+ pole of one dipole and the δ- pole of a neighbouring molecule.
They are usually stronger than VdWs forces unless the non-polar molecules are very large.

Question 33

How do hydrogen bonds work?

Answer 33

Occurs when a H atom is bonded to a very electronegative atom (N, O, F).
This polar bond produces a strong partial positive charge on the hydrogen atom.
Strong attraction between the lone pair on the N, O, F of one molecule to the positive hydrogen of another molecule.
Stronger than other IMFs (weaker than covalent bond).

Question 34

Why is ice less dense than water?

Answer 34

When it’s a liquid, H bonds break and reform as the molecules move about.
When solid, the water molecules no longer move and the H bonds hold the molecules in fixed positions.
The molecules are less closely packed to fit this structure, hence its lower density.