Bonding and Structure

Question 0

Covalent bond definition

Answer 0

A bond formed by a shared pair of electrons

Question 1

Ionic bonding definition

Answer 1

An electrostatic attraction between oppositely-charged ions

Question 2

Dative covalent bond definition

Answer 2

A shared pair of electrons which has been provided by one of the bonding atoms only

Question 3

What is the shape of a simple molecule determined by?

Answer 3

Repulsion between electron pairs surrounding a central atom

Question 4

Give the shape and bond angle of a molecule with 2 bonding pairs of electrons and no lone pairs

Answer 4

Linear

180

Question 5

Give the shape and bond angle of a molecule with 3 bonding pairs of electrons and no lone pairs

Answer 5

Trigonal planar

120

Question 6

Give the shape and bond angle of a molecule with 4 bonding pairs of electrons and no lone pairs

Answer 6

Tetrahedral

109.5

Question 7

Give the shape and bond angle of a molecule with 3 bonding pairs of electrons and 1 lone pair

Answer 7

Triangular pyramidal

107

Question 8

Give the shape and bond angle of a molecule with 2 bonding pairs of electrons and 2 lone pairs

Answer 8

V-shaped

104.5

Question 9

Give the shape and bond angle of a molecule with 6 bonding pairs of electrons and no lone pairs

Answer 9

Octahedral

90

Question 10

Electronegativity definition

Answer 10

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

Question 11

How may a permanent dipole arise?

Answer 11

A permanent dipole is something with a δ+ and a δ- at all times (ie a polar bond)
They occur when covalently-bonded atoms have different electronegativities

Question 12

What are the 4 most electronegative elements?

Answer 12

Fluorine, oxygen, nitrogen, chlorine

These elements can form polar bonds

Question 13

What intermolecular force do all molecules have?

Answer 13

Van der Waals’

These are the only forces that act between non-polar molecules

Question 14

What groups must a molecule contain to form hydrogen bonds?

Answer 14

OH or NH

Question 15

How do hydrogen bonds arise?

Answer 15

The O-H or N-H bond is polar because of the difference in negativity between hydrogen and oxygen
If 2 molecules were approach each other, the δ+ end of one molecules would be attracted to the δ- end of the other molecule
One of the lone pairs of electrons from one molecule can form a partial dative covalent bond with the δ+ H on the other molecule

Question 16

How do Van der Waals’ forces arise?

Answer 16

Electrons in molecules are constantly moving. At any instant, the distribution may not be symmetrical. This results in an instantaneous temporary dipole. This dipole induces dipoles in neighbouring molecules and leads to an attraction between the opposite charges in the dipoles. These attractions between molecules are Van der Waals’

Question 17

Describe and explain the 2 factors affecting the strength of Van der Waals’ forces

Answer 17

The more electrons there are in the molecule, the greater the fluctuations in the electron cloud, and the stronger the Van der Waals’ forces
The greater the contact area between molecules, the stronger the induced dipoles that develop. Long, thin molecules can line up beside each other more closely than short, spherical ones. So unbranched molecules have stronger Van der Waals’ forces than branched molecules

Question 18

Describe and explain the anomalous properties of water

Answer 18

Relatively high boiling point - hydrogen bonds and Van der Waals’ forces must be broken, which requires more energy than just overcoming Van der Waals’
More dense than ice - ice has an open lattice with hydrogen bonds holding the water molecules apart. When ice melts, the hydrogen bonds collapse, allowing water molecules to move closer together

Question 19

Metallic bonding definition

Answer 19

The attraction of positive ions to delocalised electrons

Question 20

Describe and explain the structure of a giant metallic lattice

Answer 20

A giant metallic lattice consists of a regular array of positive ions surrounded by a sea of delocalised electrons. The metal is held together by the attraction between positive ions and delocalised electrons

Question 21

Describe and explain the properties of a giant metallic lattice

Answer 21

High melting and boiling point - there is a very strong attraction between the positive ions and the delocalised electrons, and a lot of energy is required to break the bonds
Conduct electricity - the delocalised electrons are free to move around and carry charge throughout the structure
Malleable & ductile - the layers of atoms can slide over each other

Question 22

Explain how alloys affect the structure of a metal

Answer 22

Alloying a metal involves introducing atoms of different sizes into the structure, which disrupts the regularity of the layers. This means the layers cannot slide over each other as easily, and are therefore harder

Question 23

Describe the structure of a giant ionic lattice

Answer 23

Each ion is surrounded by oppositely charged ions, which attract each other to form a giant ionic lattice

Question 24

Describe and explain the properties of a giant ionic lattice

Answer 24

High melting and boiling point - all compounds are solid at room temperature. A large amount of energy is needed to break the strong electrostatic forces that hold the oppositely charged ions together
Conduct electricity - only when melted or dissolves in water, because the solid lattice breaks down and the ions are free to move and conduct electricity. In a solid, the ions are fixed and the lattice cannot conduct electricity
Soluble in polar solvents (eg water) - water molecules attract the positive and negative ions, this breaks down the ionic lattice and the water molecules surround the ions. The positive ion attracts δ- charges in the O atoms of the water molecules, the negative ion attracts δ+ charges on the H atoms if the water molecules

Question 25

Describe the structure of a simple molecular lattice

Answer 25

Atoms within each molecule are held together by strong covalent bonds
Molecules are held together by weak intermolecular forces (Van der Waals)

Question 26

Describe and explain the properties of simple molecular structures

Answer 26

Low melting and boiling point - not much energy is needed to break the weak Van der Waals’ forces between the molecules
Don’t conduct electricity - there are no mobile charge carriers
Soluble in non-polar solvents (eg hexane) - Van der Waals’ forces form between the simple molecular structure and the non-polar substance, which weakens the lattice structure

Question 27

Describe the structure of diamond

Answer 27

Diamond is a giant covalent structure

It is a tetrahedral structure held together by strong covalent bonds throughout the lattice

Question 28

Describe and explain the properties of diamond

Answer 28

High melting and boiling point - a lot of energy is needed to break the strong covalent bonds in the lattice
Poor conductivity - there are no delocalised electrons as all outer-shell electrons are used for covalent bonds
Insoluble in polar and non-polar solvents - the covalent bonds in the lattice are too strong to be broken by either type of solvent
Hard - the tetrahedral shape allows external forces to be spread throughout the lattice

Question 29

Describe the structure of graphite

Answer 29

Graphite is a giant covalent structure

Is has a strong hexagonal layer structure, but with weak Van der Waals’ forces between layers

Question 30

Describe and explain the properties of graphite

Answer 30

High melting and boiling point - a lot of energy is needed to break the strong covalent bonds in the lattice
Good conductivity - there are delocalised electrons between layers & electrons are free to move parallel to the layers when voltage is applied
Insoluble in polar and non-polar solvents - the covalent bonds in the lattice are too strong to be broken by either type of solvent
Soft - bonding within each layer is strong but weak forces between layers allow layers to slide easily

Question 31

What is a permanent dipole-dipole force?

Answer 31

A weak attractive force between permanent dipoles in neighbouring polar molecules

Question 32

What are the 4 most electronegative elements?

Answer 32

F, O, N, Cl

Question 33

What is a permanent dipole-dipole force?

Answer 33

A weak attractive force between permanent dipoles in neighbouring polar molecules

Question 34

What is a permanent dipole-dipole force?

Answer 34

A weak attractive force between permanent dipoles in neighbouring polar molecules