Electrons, bonding and structure

Question 1

How many electrons are there in each of the first 4 electron shells when full?

Answer 1

1st shell: 2 electrons
2nd shell: 8 electrons
3rd shell: 18 electrons
4th shell: 32 electrons

Question 2

What is an orbital?

Answer 2

The region of space in which an electron orbits the nucleus in an atom.

Question 3

How many electrons can each orbital hold?

Answer 3

2

Question 4

What shape does an s orbital have?

Answer 4

A spherical shape

Question 5

What shape does a p orbital have?

Answer 5

A dumbbell shape, like a figure of eight.

Question 6

At any one energy level it is possible to have up to ______ absolutely equivalent p orbitals pointing mutually at right angles to each other

Answer 6

3

Question 7

What is the Aufbau principle? (the order of filling of orbitals) and Hund’s rule?

Answer 7

Electrons fill low energy orbitals first and progress. For orbitals with the same energy, the electrons fill singly first before the second electrons are added to orbitals.

Question 8

What is the point of Hund’s rule?

Answer 8

It helps to minimise the repulsions between electrons, therefore making the atom more stable

Question 9

Why does 4s fill before 3d?

Answer 9

3d has a slightly higher energy level than 4s

Question 10

How many orbitals are there in s, p, d and f?

Answer 10

s: 1
p: 3
d: 5
f: 7

Question 11

Define ionic bonding

Answer 11

Electrostatic attraction between positively and negatively charged ions.

Question 12

Why is NaCl referred to as 6:6 coordinated?

Answer 12

Each chloride ion is touching 6 sodium ions and vice versa, which is the maximum number of ions that can fit around a sodium ion. This gives the ionic compound energetic stability. If more ions are introduced, chloride ions will start touching each other, causing repulsion.

Question 13

Why do ionic compounds have high melting and boiling points?

Answer 13

The electrostatic forces of attraction between oppositely charged ions is strong, so a lot of heat energy is required to overcome them.

Question 14

Why is the mp and bp of MgO higher than that of NaCl?

Answer 14

Mg and O have charges of 2+ and 2- respectively, which have stronger electrostatic forces of attraction than the 1+ and 1- charges on Na and Cl.

Question 15

How does the size of ions affect mp and bp?

Answer 15

Smaller ions have stronger electrostatic forces of attraction as they can be closer together, and so have higher mp and bp

Question 16

Why are ionic compounds often brittle?

Answer 16

If layers of an ionic compound shift slightly, ions of the same charge are brought next to each other and repel each other, causing the compound to break apart.

Question 17

Why are many ionic compounds soluble in water?

Answer 17

Positive ions are attracted to the lone pairs on water molecules, and if this attraction outweighs that to the negative ions in the ionic compound, dative (coordinate) covalent bonds can form between the positive ions and water. Water molecules form hydrogen bonds with the negative ions.

Question 18

Why are ionic compounds often insoluble in organic solvents?

Answer 18

The attractions between the ions and the solvent molecules are not strong enough to outweigh the ionic bonds.

Question 19

Why don’t ionic compounds conduct electricity when solid?

Answer 19

The ionic compounds have no free ions or delocalised electrons in their giant ionic lattice, so there are no mobile ions to carry charge.

Question 20

Why do molten ionic compounds conduct electricity?

Answer 20

In a liquid state, the ions are mobile and therefore free to move and carry charge through the compound

Question 21

What is a covalent bond?

Answer 21

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Question 22

What is a dative covalent bond?

Answer 22

A covalent bond in which both electrons in the shared pair of electrons are derived from the same atom

Question 23

What is average bond enthalpy?

Answer 23

The average enthalpy change when one mole of gaseous bonds are broken

Question 24

Define bond dissociation enthalpy

Answer 24

The enthalpy required to break one mole of bonds to give separate atoms.

Question 25

2bonding pairs 0lone pairs

Answer 25

Linear, 180º

Question 26

3bonding pairs, 0lone pairs

Answer 26

Trigonal planar, 120º

Question 27

4bonding pairs, 0lone pairs

Answer 27

Tetrahedral, 109.5

Question 28

5bonding pairs, 0lone pairs

Answer 28

Trigonal bipyramidal, 90º and 120º

Question 29

6bonding pairs, 0lone pairs

Answer 29

Octahedral, 90º

Question 30

2bonding pairs, 1lone pair

Answer 30

Bent/ Non-linear, less than 120º

Question 31

3bonding pairs, 1lone pair

Answer 31

Trigonal Pyramidal, 107º

Question 32

4bonding pairs, 1lone pair

Answer 32

See-saw, 90º and 120º

Question 33

5bonding pairs, 1lone pair

Answer 33

Square Pyramidal, 90º and 180º

Question 34

2bonding pairs, 2lone pairs

Answer 34

Bent, 104º

Question 35

3bonding pairs, 2lone pairs

Answer 35

T-shaped, 90º and 120º

Question 36

4bonding pairs, 2lone pairs

Answer 36

Square Planar, 90º and 180º

Question 37

What is VSEPR?

Answer 37

Valence Shell Electron Pair Repulsion: The valence electron pairs surrounding an atom tend to repel each other, so they adopt an arrangement that minimises the repulsion.

Question 38

Define electronegativity

Answer 38

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

Question 39

What makes a polar molecule polar?

Answer 39

The molecule must contain a polar bond- a covalent bond in which there’s a difference in electronegativity between the two atoms and therefore one atom is slightly positive and the other negative. The molecule must not be symmetrical in its charge or else the charges cancel each other out.

Question 40

What are van der Waal’s forces?

Answer 40

Temporary intermolecular forces caused by shifts in electron density in an atom which cause temporary dipoles that result in induced dipoles in nearby atoms.

Question 41

What affects van der Waal’s force strength?

Answer 41

Molecular mass. Greater molecular mass gives stronger VDW forces as there are more electrons.

Question 42

Why are hydrogen bonds the strongest intermolecular force?

Answer 42

There’s a large difference in electronegativity between oxygen and hydrogen, (which makes water very polar) and this gives a very strong permanent dipole interaction.

Question 43

Why is ice less dense than water?

Answer 43

The molecules in ice are held apart by hydrogen bonds and ice has an open lattice structure.

Question 44

Why is the melting point of ice relatively high?

Answer 44

The hydrogen bonds are strong, so more energy is required to break them.

Question 45

Why does water have a cohesive property?

Answer 45

Cohesiveness is a result of the hydrogen bonds

Question 46

Why is water a good solvent?

Answer 46

The polarity of water molecules makes them a good solvent as solutes can interact with the charged regions. Water can form hydrogen bonds with solutes.

Question 47

Why does water have a relatively high specific heat capacity?

Answer 47

The hydrogen bonds make water relatively stable

Question 48

Define a dipole

Answer 48

A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond. The greater the difference in electronegativity, the more polar the bond.

Question 49

Why are the covalent bonds in diatomic gases non polar?

Answer 49

The two atoms have equal electronegativity and so the electrons are equally attracted to both nuclei.

Question 50

What makes a bond purely covalent?

Answer 50

To be purely covalent, a bond must be between two atoms of the same element, such as in diatomic gases. This is because there is 0 difference in electronegativity between the two.

Question 51

How do induced dipole-dipole forces form?

Answer 51

Electrons in charge clouds are constantly moving. At any particular moment the electrons are likely to be more to one side than the other, which gives the atom a temporary dipole.
This dipole causes other temporary dipoles in neighbouring atoms, which attracts the atoms to each other. This begins a domino effect of induced dipoles. As the electrons are constantly moving, the dipoles are created and destroyed all the time, but the overall effect is attraction.

Question 52

What gives molecules stronger induced dipole-dipole forces?

Answer 52

Larger molecules will have larger electron clouds and this gives stronger induced dipole forces. Molecules with larger surface areas have a more exposed electron cloud and so their induced dipole forces are stronger.

Question 53

What are permanent dipole-dipole interactions?

Answer 53

Where the delta+ and delta- charges on polar molecules cause weak electrostatic forces of attraction between molecules.

Question 54

What are the three elements that hydrogen can covalently bond to?

Answer 54

Oxygen, nitrogen or fluorine.

Question 55

How do you melt or boil a simple covalent compound in terms of the bonds?

Answer 55

To melt or boil a simple covalent compound you do not have to break the covalent bonds, it is the intermolecular forces that hold molecules together that must be overcome. This is why simple covalent molecules have relatively low melting and boiling points.