Bonding

Question 1

Key Phrases about Giant covalent lattices and the 4 common giant covalent lattices.

Answer 1

Diamond, Graphite, silicon and silicon dioxide are the 4 common giant covalent lattices.

Key phrases - Giant covalent lattice contain many strong covalent bonds which causes their properties. Covalent bonds have a shared pair of electrons.

graphite has delocalised electrons and van der Waals forces between layers

Question 2

Coordinate/Dative bond

Answer 2

Special type of covalent bond where both electrons come from one atom called a coordinate bond or dative bond

Question 3

Key phrases around giant ionic lattices and how to spot them.

Answer 3

How to spot them: They’re either containing ammonium (NH4+) or a metal and at least one non-metal.

Giant ionic lattices/(ionic bonds) have strong electrostatic attraction between oppositely charged ions. Larger ions and lower charges have weaker attraction.

Question 4

Key phrases around giant metallic lattices and how to spot them

Answer 4

How to spot them - These compounds are just metals on their own.

The atoms lose their outer electrons causing the molecule to have delocalised electrons (forming metal cations)

Key phrase - Giant metallic lattices have strong electrostatic attraction between delocalised electrons and positively charged ions. Larger ions and lower charges have weaker attraction.

Question 5

Giant ionic lattices - Properties

Answer 5

Properties
Ionic compounds conduct electricity when melted or in solution, have high melting points and are the second strongest structure and second strongest bond.

Question 6

Giant Metallic lattice - Properties

Answer 6

Properties
Metallic compounds conduct electricity, have high melting points, are ductile, malleable and are the third strongest structure and third strongest bond.

Question 7

Define electronegativity

Answer 7

Electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond.

Question 8

What effects electronegativity? How to spot electronegative elements at a level?

Answer 8

Electronegativity is affected by having a smaller atomic radius and larger number of protons.

The most electronegative element is F. N, O and then Cl and the next most electronegative. This can be used to help compare electronegativity.

Question 9

Simple molecular compounds -description

Answer 9

Simple molecular compounds are the most common crystal structure for covalent molecules. They have bonds holding atoms together to make molecules. The molecules are held together as solids and liquids by forces between the molecules.

Question 10

Define polar bonds and what causes them/cancels them out

Answer 10

Polar bonds are bonds that have a permanent uneven distribution of electron density caused by a large difference in electronegativity. Symmetrical molecules the electronegative elements pull in equal and opposite directions so cancel.

Question 11

Hydrogen bonding - What is it? Key phrases around it? Where is it between? How is it represented in diagrams?

Answer 11

Misnamed – this is not a bond but is the strongest intermolecular force
Key Phrases:
The electrostatic attraction in a hydrogen bond is between the lone pair on the N/O/F and the ∂+ hydrogen on a different molecule attached to a N/O/F. This attraction is between molecules

This is represented as a dotted line.

Question 12

Permanent Dipole-Dipole forces key phrases and what cases them.

Answer 12

This kind of intermolecular force is caused by the large difference in electronegativity between two elements in a covalent bond. It is the second strongest intermolecular force.

This creates a polar bond where one of the elements is usually one of N/O/F/Cl. This, more electronegative, element is ∂-. The other element is less electronegative, such as C, H or other elements further to the left of the periodic table. This less electronegative element is ∂+.

The attraction is between molecules, this time between the ∂+ atom in one molecule and the ∂- in the other molecule. This is shown with a dotted line.

Question 13

van der Waals’ forces key phrases/description

Answer 13

Key description
It is caused by a random movement of electrons causing a temporary dipole in that molecule (with a small d+ and d-). This partial charge then causes electron density to be attracted/repelled in other nearby molecules which induces a dipole in them.

Van Der Waals’ forces are the weakest intermolecular force, but the larger the surface area of the electron cloud (or the larger the molecule) the stronger this intermolecular force is as the size of the partial charge will increase. This can mean for large molecules van der waal’s forces are stronger between molecules than other intermolecular forces

Question 14

Scaffold for doing melting point comparisons

Answer 14

When asked questions about melting points it’s essential to identify the crystal structure of the materials being compared. You need to discuss the forces/bonds that hold them together. The list below is in order of melting point from highest to lowest.
Diamond, graphite, silicon and silicon dioxide are giant covalent lattices (macromolecular). Bonds break to melt this.
metal and a non-metal is a giant ionic lattice, Forces of attraction are overcome.
Metals (usually alone) are giant metallic lattices. Forces of attraction are overcome.
2 or more non-metals bonded together tend to be simple molecular. Forces of attraction are overcome between molecules (chose most relevant of the three intermolecular forces)

Question 15

Define Enthalpy of vaporisation

Answer 15

Enthalpy change when one mole of a liquid is turned into a gas

Question 16

What is the perfect ionic model?

Answer 16

The perfect ionic model suggests that all ions are perfectly spherical and the charge is found in the centre (point charges)
Larger anions bonded to small cations tend to have more covalent character as smaller cations distorts (polarises) the electron density of the larger anion
The bigger the difference between the lattice enthalpy and the theoretical value the more covalent character. More covalent character the stronger the ionic bond.

Question 17

What does the size of the lattice enthalpy of formation/dissociation tell you about the compound?

Answer 17

The larger in magnitude the value then the stronger the ionic bond is.

Question 18

Key phrase - Why are symmetrical molecules not polar (even if there’s a large difference in electronegativity?)

Answer 18

Key phraseidea that dipole moments (or dipoles) cancel out due to symmetry

Question 20

Shape and bond angles of a compound with 2 bonding pairs and 0 lone pairs

BeCl2 is being used as the example in diagram

Answer 20

Linear, angles 180 degrees

Question 21

Shape and bond angles of a compound with 3 bonding pairs and 0 lone pairs

BCl3 is being used as the example for structure

Answer 21

Trigonal Planar, 120 degrees

Question 22

Shape and bond angles of a compound with 4 bonding pairs and 0 lone pairs

CH4 is being used as the example for structure

Answer 22

Tetrahedral, 109.5 degrees

Question 23

Shape and bond angles of a compound with 3 bonding pairs and 1 lone pairs

NH3 is being used as the example for structure

Answer 23

Trigonal Pyramidal, 107 degrees

Question 24

Shape and bond angles of a compound with 2 bonding pairs and 2 lone pairs

H2O is being used as the example for structure

Answer 24

Bent/V-shaped 104.5 degrees

Question 25

Shape and bond angles of a compound with 5 bonding pairs and 0 lone pairs

PF5 is being used as the example for structure

Answer 25

Trigonal Bipyramidal, 120 degrees and 90 degrees

Question 26

Shape and bond angles of a compound with 6 bonding pairs and 0 lone pairs

SF6 is being used as the example for structure

Answer 26

Octahedral, bond angles 90 degrees