Bonding and Structure

Question 1

What structure does a metallic bond form?

Answer 1

A giant metallic lattice

Question 2

What structure does an ionic bond form?

Answer 2

Giant ionic lattice

Question 3

What structure does a covalent bond form?

Answer 3

• Giant molecular - covalent bonding throughout the structure
• Simple molecular - weak intermolecular forces.

Question 4

Give the definition of an ionic bond

Answer 4

Strong electrostatic force of attraction between the oppositely charged ions

Question 5

How does a giant ionic lattice form?

Answer 5

• Metal transfers its electrons to the non-metal to increase stability of each atom
• However, the positive and negative charges do not just point in one direction, they span out to create a giant 3D structure
• There is a constant state of repulsion between same charged ions and attraction between oppositely charged ions
• All of the forces find a balance as ions form a giant ionic lattice

Question 6

How do you draw a dot and cross diagram for an ionic bond?

Answer 6

1. Determine charge of metal
2. Draw metal without its outer electrons
3. Determine charge of non-metal
4. Work out formula of ionic compound
5. Draw the electrons on outer shell as dots on the non metal
6. Draw crosses on non metal as electrons gained from the metal
7. Add charges

Question 7

Give three physical properties of ionic compounds

Answer 7

1. High melting points and boiling points, giant ionic lattice structure, many strong electrostatic forces of attraction between ions, requires a lot of energy to overcome - greater ionic charge, stronger ionic bond - smaller atomic radius, stronger ionic bond.
2. Electrical conductivity - will not conduct electricity in the solid state, ions are in a fixed position. Will conduct electricity in the molten (or aqueous) state, ions are free to move
3. Dissolve in water, ions make attractions to the different atoms in water and are pulled apart

Question 8

Give the definition of a covalent bond

Answer 8

• A shared pair of electrons between atoms

Question 9

How does a double covalent bond form?

Answer 9

• When two pairs of electrons are shared between atoms.

Question 10

Can the central atom be stable with fewer than 8 electrons in a covalent molecule in some cases? Give two examples.

Answer 10

Yes
BF3 and AlCl3

Question 11

Can the central atom a covalent molecule fit more than 8 electrons in its outer shell if its in period 3 or higher?

Answer 11

Yes

Question 12

What are lone pairs?

Answer 12

If an atom does not use all of its outer electrons, these spare electrons are called lone pairs

Question 13

Explain coordinate/dative covalent bonding

Answer 13

• Occurs when one atom provides both the electrons needed to form a covalent bond
• Atom donating must have a lone pair, atom receiving must have a vacant orbital
• The bond is represented as an arrow pointing to the direction in which the electrons are being given

Question 14

Explain the electron repulsion theory

Answer 14

• Electron pairs repel one another and cause the molecule to adopt a shape which causes for the least amount of repulsion, the electron pairs need to be as far apart as possible
• Lone pairs repel more than bonding pairs, they reduce the bonding angle by 2.5 degrees

Question 15

How would you work out the 3D shape of a molecule?

Answer 15

• Work out a dot and cross diagram and find out how many bonding pairs there are lone pairs and then go from there
• If there is a double bond it will repel the same amount as a single bond would

Question 16

Give the number of bonding pairs and lone pairs, angle and name of shape of the six 3D molecular shapes you need to know

Answer 16

• Linear, 180 degrees, 2 bonding pairs
• Trigonal planar, 120 degrees, 3 bonding pairs
• Tetrahedral, 109.5 degrees, 4 bonding pairs
• Trigonal pyramid, 107 degrees, 3 bonding pairs, one lone pair
• Non linear, 104.5 degrees, 2 bonding pairs, 2 lone pairs
• Octahedral, 90 degrees, 6 bonding pairs

Question 17

Define electronegativity

Answer 17

The ability of an atom to attract a pair of electrons in a covalent bond

Question 18

What happens if two atoms of the same element form a covalent bond in terms of electronegativity?

Answer 18

• The nuclei are identical and so the attraction to the electrons is equal. the electron density is distributed equally - bond is non-polar

Question 19

What does the value of electronegativity depend on?

Answer 19

• Nuclear charge of atom (number of protons); higher=greater
• Atomic radius of atom; smaller=greater
• Number of principle energy levels; fewer=greater

Question 20

Does electronegativity increase as you go up and right of the Periodic Table?

Answer 20

Yes

Question 21

What is the most electronegative element? Explain why.

Answer 21

Fluorine
- Small atomic radius and a high nuclear charge

Question 22

Do noble gases have electronegativity? Explain why.

Answer 22

No ability to attract a pair of electrons

Question 23

What happens when two atoms of different electronegativities bond together?

Answer 23

• The electron density is distributed unequally resulting in a polar bond
• If there is a very large difference, ionic bonding will occur

Question 24

What is the definition of a polar bond?

Answer 24

A covalent bond in which there is an unequal share of the electrons due to the differing electronegativities of the atoms involved

Question 25

Why do some molecules have polar bond but overall are non-polar molecules?

Answer 25

They are symmetrical and the dipoles cancel out

Question 26

Why are C-H bonds classed as non-polar?

Answer 26

Electronegativities are very similar

Question 27

What are the five symmetrical molecule shapes?

Answer 27

Linear, trigonal planar, octahedral and tetrahedral

Question 28

What are intermolecular forces?

Answer 28

Forces between molecules, only applies to simple covalent molecules

Question 29

Give the three types of intermolecular forces in order of increasing strength

Answer 29

London forces, permanent dipole-dipole and hydrogen bonding

Question 30

Explain London forces in terms of; what their strength depends on, how they form and what types of molecules they apply to

Answer 30

• Applies to all molecules
• Strength depends on size of molecule, and therefore number of electrons and surface area contact e.g. spherical molecules have less surface area contact
• Form because: electrons are constantly moving and so the charge can change distribution at any time, causing a temporary dipole which occurs when there is an uneven distribution of electrons

Question 31

Explain permanent dipole-dipole forces in terms of; what their strength depends on, how they form and what types of molecule they apply to

Answer 31

• Strength depends on size of molecule and therefore number of electrons
• They form due to a difference in electronegativity
• Only forms between two polar molecules, which then forms a polar bond due to the difference in electronegativity

Question 32

Explain hydrogen bonding in terms of; how they form and what types of molecules do they form between

Answer 32

• Only occurs if molecule contains a N-H, O-H or F-H bond. This is because N, O and F have the biggest electronegativity
• This leaves the nucleus very delta positive meaning a lone pair of electrons on a neighbouring molecule containing O,F or N will be attracted

Question 33

Give the three features of a H bonding diagram

Answer 33

1. Partial charges on all atoms
2. All lone pairs shown clearly
3. H bond is shown as a dotted line

Question 34

What are the two anomalous properties of water and explain them

Answer 34

1. Ice is less dense than liquid water, this is because water molecules will spread out more to form H bonds
2. Has a relatively high melting/boiling point as H bonds are the strongest intermolecular force

Question 35

What are the three physical properties of simple molecules? Explain why

Answer 35

1. Low melting/boiling points - weak intermolecular forces require little energy to overcome
2. No electrical conductivity - no charges particles free to move in any state
3. Won’t generally dissolve in water unless they are able to form H bonds