Bonding

Question 1

Why do chemical bonds form?

Answer 1

So that the atoms can achieve a more stable electron arrangement, often a full outer energy level, like noble gases.

Question 2

What is ionic bonding?

Answer 2

A chemical bond in which electron(s) are transferred from one atom to another, resulting in the formation of oppositely charge ions with electrostatic forces of attraction between them.

Question 2

What is metallic bonding?

Answer 2

A chemical bond in which outer electrons are delocalised within the lattice of metal ions.

Question 4

What is covalent bonding?

Answer 4

A chemical bond in which a pair of electrons are shared between two atoms.

Question 5

Properties of ionic substances

Answer 5

Always solid at room temperature, have giant structures so high melting points, conduct electricity when molten or dissolved in water, are brittle.

Question 6

Why are ionic compounds brittle?

Answer 6

When they receive a sharp blow, the ions may move and contact with another ion of a like charge which repels it and the structure shatters.

Question 7

Properties of covalent substances

Answer 7

At room temperature they are gases, liquids or solids with low melting points. Poor conductors of electricity.

Question 8

Properties of metals

Answer 8

Good conductors of electricity. Good conductors of heat. Malleable and ductile. High melting point.

Question 9

What is dative covalent bonding?

Answer 9

Where both the electron in the covalent bond come from one of the atoms in the bond.

Question 10

Electron pair repulsion theory

Answer 10

Each pair of electrons will repel all other electron pairs and will therefore take up positions as far apart as possible to minimise repulsion

Question 11

2 electron pairs and 2 bonding pairs shape and angle

Answer 11

Linear, 180

Question 12

3 electron pairs and 3 bonding pairs shape and angle

Answer 12

Trigonal planar, 120

Question 13

3 electron pairs and 2 bonding pairs shape and angle

Answer 13

Bent (still planar), 118

Question 14

4 electron pairs and 4 bonding pairs shape and angle

Answer 14

Tetrahedral, 109.5

Question 15

4 electron pairs and 3 bonding pairs shape and angle

Answer 15

Trigonal pyramid (lone pair at top), 107

Question 16

4 electron pairs and 2 bonding pairs shape and angle

Answer 16

V-shaped (on plane), 104.5

Question 17

5 electron pairs and 5 bonding pairs shape and angle

Answer 17

Trigonal bipyramid (trigonal planar with one atom above and below), 90 and 120

Question 18

5 electron pairs and 3 bonding pairs shape and angle

Answer 18

Trigonal planar (with one lone pair above and below), 120.
Or t-shape (lone pairs on same plane), 89

Question 19

6 electron pairs and 6 bonding pairs shape and angle

Answer 19

Octahedral, 90

Question 20

6 electron pairs and 5 bonding pairs shape and angle

Answer 20

Square pyramid (with one lone pair below), 89

Question 21

6 electron pairs and 4 bonding pairs shape and angle

Answer 21

Square planar (with one lone pair above and below), 90

Question 22

Electronegativity

Answer 22

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

Question 23

What does electronegativity depend on?

Answer 23

The nuclear charge, the atomic radius, the shielding

Question 24

What happens to electronegativity down a group?

Answer 24

It decreases as the atoms get bigger and there are more electron shells for shielding.

Question 25

What happens toe the electronegativity going across a period?

Answer 25

Increases because the atoms get smaller, the nuclear charge increases for the same amount of shielding (same number of shells)

Question 26

What are the most electronegative elements?

Answer 26

Fluorine, Oxygen, Nitrogen

Question 27

What does polar mean?

Answer 27

Describes a molecule in which the charge is not symmetrically distributed so that one area is slightly positively charged and another slightly negatively charged.

Question 28

Why are bonds between the same elements (e.g H2) non polar?

Answer 28

Because the electronegativity of the atoms is equal so the electrons will be equally shared between the atoms.

Question 29

What happens in a covalent bond with two atoms of different electronegativity?

Answer 29

The bond is polar because the electrons in it will be attracted to the more electronegative atom making it delta negative and leaving the other atom delta positive.

Question 30

Van der Waal forces

Answer 30

Happens in all atoms. Electrons are always moving. At any moment that could be unevenly distributed. This creates a temporary negative dipole but it is almost certain that there will be a dipole somewhere in the atom at any moment in time. The dipole affects the electron distribution in nearby atoms so that they are attracted to the original atom for an instant. They are very weak forces.

Question 31

Why do smaller atoms have weaker and less van der waals?

Answer 31

Because they have less electrons (so a weaker negative dipole) and a smaller surface area so can’t have an effect on many other atoms.

Question 32

Permanent dipole-dipole forces

Answer 32

Permanent dipoles are in all polar molecules. Two of the same polar molecule are attracted to each other as the delta+ atom attracts to the delta- atom in the other molecule and vice versa. They are stronger than van der waals but still weak.

Question 33

What type of molecules dissolve well in water?

Answer 33

Polar ones because water is also polar.

Question 34

Hydrogen bonds

Answer 34

They occur when H is bonded to F,O or N. The H atoms only have the two electrons that are in the covalent bond and these are attracted to the other very electronegative atom leaving the H nucleus exposed. The electronegative element in another of the same molecule has a lone pair which is strongly attracted to the hydrogen nucleus. This is the bond. They are much stronger than permanent dipole forces but still weaker than covalent bonds.

Question 35

Why is ice less dense than water?

Answer 35

In water, the hydrogen bonds break and reform easily as the molecules move about. In ice, the molecules are no longer free to move and the hydrogen bonds hold them in fixed positions. The resulting 3D structure is like diamond. In order to fit in this structure, the molecules are slightly less closely packed than in water meaning there are less molecules in a given area. The ice floats on water.