Bonding

What are positive and negative ions called?

What are positive and negative ions called?

Cations and anions respectfully

Why are ionic substances brittle?

They form a lattice of alternating positive and negative ions. A blow from a single direction may mean like-charged ions line up and repel each other, then the sample shatters.

Why do ionic substances dissolve in water?

Because when moving water molecules hit an ionic lattice they can knock off ions and then the water molecules surround the ions

What is the formula for the hydroxide ion?

(OH)-

What is the formula for the nitrate ion?

(NO3)-

What is the formula for the sulfate ion?

(SO4)2-

What is the formula for the carbonate ion?

(CO3)2-

What is the formula for the phosphate ion?

(PO4)3-

What is the formula for the ammonium ion?

NH4+

What is a covalent bond?

A shared pair of electrons

What is a dative/coordinate bond?

A type of bond where one atom provides both electrons to form a covalent bond

How do you represent a coordinate bond?

With an arrow

What are the 4 types fo crystal structure?

1. Ionic

2. Metallic

3. Macromolecular (giant covalent)

4. Molecular (simple covalent)

2 examples of a macromolecular crystal structure

Diamond, graphite

An exmaple of an ionic crystal structure

Sodium chloride

An example of a metallic crystal structure

Magnesium

2 examples of a molecular crystal structure

Ice, iodine

What are the 3 things the shape of a molecule or ion depends on?

1. Total number of electron pairs around the central atom

2. The number of bonding pairs of electrons

3. The number of lone pairs of electrons

What do pairs fo electrons do to minimise repulsion?

They arrange themselves as far apart as possible

Rank the 3 repulsion stength between different pairs of electrons

1. Lone pair - lone pair

2. Lone pair - bonding pair

3. Bodning pair - bonding pair

By how many degrees does adding a lone pair of electrons decrease a bond angle by?

2.5 degrees

What is the shape and bond angle for a molecule with 2 total pairs and 0 lone pairs?

Linear, 180

What is the shape and bond angle for a molecule with 3 total pairs and 0 lone pairs?

Trigonal planar, 120

What is the shape and bond angle for a molecule with 4 total pairs and 0 lone pairs?

Tetrahedral, 109.5

What is the shape and bond angle for a molecule with 4 total pairs and 1 lone pair?

Pyramidal, 107

What is the shape and bond angle for a molecule with 4 total pairs and 2 lone pairs?

Bent, 104.5

What is the shape and bond angle for a molecule with 5 total pairs and 0 lone pairs?

Trigonal bipyramidal, 90 and 120

What is the shape and bond angle for a molecule with 5 total pairs and 2 lone pairs?

T-Shaped, 86

What is the shape and bond angle for a molecule with 5 total pairs and 3 lone pairs

Linear, 180

What is the shape and bond angle for a molecule with 6 total pairs and 0 lone pairs?

Octahedral, 90

What is the shape and bond angle for a molecule with 6 total pairs and 2 lone pairs?

Square planar, 90

Define the term electronegativity

The power/ability of an atom to attract the electron density in a covalent bond towards itself

What scale is used for electronegativity and what are the most and least electronegative elements?

The Pauling scale, the most electronegative atom is F (4.0) and the least Cs (0.7)

What 3 factors do electronegativity depend on?

1. The distance between the bonding electrons and the attractive power of the nucleus

2. The size of the nuclear charge

3. Shielding of the outer bonding electrons by inner electrons

Why does electronegativity increase across a period? (two points)

1. Atomic radius decreases

2. Nuclear charge increases

Why does electronegativity decrease down a group? (two points)

1. Atomic radius increases down a group

2. Shielding of nuclear charges increase down a group

Why is CO2 non-polar despite the C=O bond being polar?

As the molecule is symmetrical so the polarities of the two bonds cancel out

Rank the 3 types of intermolecular forces from strongest to weakest

1. Hydrogen bonding

2. Permanent dipole-dipole forces

3. Van der Waal’s forces

Which substances have VDW’s forces?

All substances

How are temporary dipoles induced to bring about VDW’s forces?

The random movement of electrons causes an imbalance in charge, inducing a dipole in a neighboring molecule as the electrons are repelled from the delta- charge

What 2 things affect the strength of VDW’s forces?

1. Number of electrons in the molecule (more and bigger temporary dipoles)

2. Surface area of the molecule - bigger the molecule the stronger the forces

What two conditions are needed for hydrogen bonding to occur?

1. A “H” atom bonded to a O, N, or F atom

2. An electronegative atom on an adjacent molecule

Why is the boiling point of water much higher than that of the other group 6 hydrides?

As there is hydrogen bonding between water molecules as O and H are present in the molecule.

Give 4 common substances containing hydrogen bonds

1. Water

2. Alcohols

3. Carboxylic acids

4. Amines

Why is ice less dense than water?

As when water freezes the hydrogen bonds hold the molecules in a fixed position which are more spread out than in water

Why is ethanol soluble in water?

As water can form hydrogen bonds with ethanol