Electrons, Bonding and Structure

Question 1

s-orbitals

Answer 1

• spherical shape
• each shell contains one s-orbital
• 2s electrons in each shell

Question 2

p-orbitals

Answer 2

• 3d dumb-bell shape
• Each shell contains 3 p-orbitals
• 6p electrons in each shells (from n=2 upwards)

Question 3

d-orbitals

Answer 3

From n=3 upwards each shell contains 5 d-orbitals (10 electrons)

Question 4

Why do the two electrons in an orbital not repel each other?

Answer 4

An electron has a property called a spin. The two electrons in an orbital must have opposite spins.

Question 5

The number of electrons in the first 4 shells

Answer 5

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

Question 6

What is an orbital?

Answer 6

A region of space where electrons can be found. It is a region around the nucleus that can hold up to two electrons with opposite spins.

Question 7

What is a sub-shell?

Answer 7

A group of the same type of orbitals within a shell. An s subshell can hold up to 2 electrons, a p subshell can hold up to 6 and a d up to 10.

Question 8

What is ionic bonding?

Answer 8

An ionic bond is the electrostatic attraction between oppositely charged ions. Electrons are transferred from a metal to a non-metal.

Question 9

Giant ionic lattices

Answer 9

Each ion is surrounded by oppositely charged ions and the ions attract each other to form a giant ionic lattice.

Question 10

Properties of ionic compounds

Answer 10

1. High melting and boiling points - large amount of energy required to break strong electrostatic bonds that hold oppositely charged ions together in a solid lattice
2. Conduct electricity when molten - ions are free to move
3. Solubility - dissolves in polar substances

Question 11

Why is the melting point of MgO higher than NaCl?

Answer 11

The charges on Mg2+ and O2- are greater than those on Na+ and Cl-. The stronger the charge, the stronger the electrostatic forces between the ions so more energy is required to break.

Question 12

Why can giant ionic lattice only conduct when molten?`

Answer 12

In a solid lattice, the ions are in fixed positions and can’t move so it can’t conduct electricity. When it is melted, the ions can move to conduct electricity.

Question 13

How does a polar substance dissolve ionic compounds?

Answer 13

The polar molecules surround the ionic lattice to form a solution. The slight charges within the polar substance are attracted to the charged ions in the giant ionic lattice. This disrupts the lattice and ions are pulled out of it.

Question 14

What is a covalent bond?

Answer 14

• Occurs between 2 non metals

- electrons are shared between atoms and are attracted to the nuclei of both bonded atoms

Question 15

Single covalent bonding

Answer 15

When atoms are bonded by one shared pair of electrons. Covalent bonds act in one direction only (unlike ionic bonds)

Question 16

What are lone pairs?

Answer 16

an outer shell pair of electrons that is not involved in chemical bonding

Question 17

What is a dative covalent bond?

Answer 17

When one of the atoms supplies both the shared electrons to the covalent bond

Question 18

Simple molecular structures

Answer 18

• atoms within each molecule are held together by strong covalent bonds
• different molecules are held together by weak intermolecular forces (London forces)

Question 19

Properties of simple molecular structures

Answer 19

1. Low melting and boiling points - little energy required to break London forces between molecules
2. Do not conduct electricity as there are no charged particles free to move
3. Generally soluble in non polar solvents as London forces can form between these solvents and covalent molecules

Question 20

Properties of giant covalent structures

Answer 20

1. High melting and boiling points as lots of energy required to break strong covalent bonds within lattice
2. Non conductors except for graphite where delocalised electrons are able to move freely between layers
3. Insoluble in polar and non polar solvents because coavalent bonds in the lattice are too strong

Question 21

What is the name of the shape of a molecule with 1 bonded electron pairs around the central atom?

Answer 21

Linear

Hydrogen

Question 22

What is the name of the shape and bond angle of a molecule with 2 bonded electron pairs around the central atom?

Answer 22

Linear
180
Carbon dioxide

Question 23

What is the name of the shape and bond angle of a molecule with 3 bonded electron pairs around the central atom?

Answer 23

Trigonal planar
120
BF3

Question 24

What is the name of the shape and bond angle of a molecule with 4 bonded electron pairs around the central atom?

Answer 24

Tetrahedral
109.5
Alkanes

Question 25

What is the name of the shape and bond angle of a molecule with 5 bonded electron pairs around the central atom?

Answer 25

Trigonal bipyramid
90 and 120
PCl5

Question 26

What is the name of the shape and bond angle of a molecule with 6 bonded electron pairs around the central atom?

Answer 26

Octahedral
90
SF6

Question 27

Why does the presence of lone pairs change the shape and how does it change the bond angle?

Answer 27

A lone pair is more electron dense so repels more than a boned pair.
Reduces bond angle by about 2.5 degrees

Question 28

What is the shape and bond angle of ammonia?

Answer 28

Pyramidal

107

Question 29

What is the shape and bond angle of water?

Answer 29

Non linear

104.5

Question 30

What is electronegativity?

Answer 30

Electronegativity measures the atttraction of a bonded atom for the pair of electrons in a covalent bond.

Question 31

What are permanent dipole-induced dipole interactions?

Answer 31

A molecule with a permanent dipole will have a slight positive end and a slight negative end. When it is near non polar molecules it can cause the electrons in its shells to shift slightly as they are repelled by the negative end or attracted to the positive end. This causes the non polar molecule to become slightly polar and an attraction occurs. This molecule with a permanent dipole has induced a dipole on the other molecule.

Question 32

What are permanent dipole-permanent dipole interactions?

Answer 32

Molecules with permanent dipoles will be attracted to other molecules with permanent dipoles. The slight positive end of one molecule is attracted to the slight negative end of the other molecule.

Question 33

What are London forces?

Answer 33

London forces occur between non polar molecules. They are caused by the constant random movement of electrons in atoms’ shells. This movement unbalances the distribution of charge. At any moment there may be an instantaneous dipole across the molecule. This instantaneous dipole will induce a dipole in neighbouring molecules. This causes a weak intermolecular force called a London force or an instantaneous dipole-induced dipole force. The more electrons, the greater the number of attractive forces between molecules.