giant structures

Question 1

What are the physical properties of metals?

Answer 1

• High melting temperatures
• Good electrical conductivity
• Good thermal conductivity
• Malleability
• Ductility

Question 2

Describe the structure of metals

Answer 2

An array of atoms with at least some of their outer shell electrons removed and free to move through the structure. Free electrons are called delocalised electrons and they are free to move throughout the structure. There are electrostatic forces of attraction between the nuclei of the metal cations and the delocalised electrons (metallic bonding)

Question 3

Is the melting temperature of metals high or low? Why?

Answer 3

Metals have a giant lattice structure so there are many forces of attraction between the nuclei of the cations and the delocalised electrons that need to be overcome. The energy required to do this is very large

Question 4

What are the two features of metals that affect melting temperature?

Answer 4

1. Number of delocalised electrons per cation
2. Size of the cation

Question 5

How does the number of delocalised electrons per cation affect melting temperature?

Answer 5

Group 1 metals have low melting temperatures
Group 2 metals have higher melting temperatures
Metals in the d-block have high melting temperatures since they have more delocalised electrons per ion

Question 6

How does the size of the cation affect melting temperature?

Answer 6

The smaller the cation, the closer the delocalised electrons to the cation’s nucleus, resulting in an increase in the forces of attraction between the nuclei and the delocalised electrons and so an increase in melting temperature

Question 7

Do metals conduct electricity? Explain answer

Answer 7

When a potential difference is applied across the ends of a metal, delocalised electrons are attracted to and move towards the positive terminal of the cell. Movement of electrical charge constitutes an electric current

Question 8

What two factors contribute to metals thermal conductivity?

Answer 8

1. Free-moving delocalised electrons pass kinetic energy along the metal
2. Cations are closely packed and pass kinetic energy from one cation to another

Question 9

What is malleability?

Answer 9

The ability of materials to be hammered or pressed into different shapes

Question 10

What is ductility?

Answer 10

The ability of materials to be drawn into a wire

Question 11

Are metals malleable and ductile? Why?

Answer 11

Metals can be hammered or pressed into different shapes (malleability) and can be drawn into a wire (ductility). This is because when stress is applied to a metal, the layers of cations slide over one another. As the delocalised electrons are free moving, they move with the cations and prevent strong forces of repulsion between cations in one layer and cations in another layer

Question 12

Where does ionic bonding occur? Give an example

Answer 12

In solid materials consisting of a regular array of oppositely charged ions extending through a giant lattice network. For example, NaCl consists of a regular array of Na+ and Cl-

Question 13

Describe the structure and bonding in ionic solids

Answer 13

There are strong electrostatic interactions between ions. Ions are arranged so that the electrostatic attractions between oppositely charged ions are greater than the electrostatic repulsions between ions with the same charge

Question 14

How do you determine the strength of ionic bonding?

Answer 14

Calculate the amount of energy required in one mole of solid to separate the ions in the gas phase

Question 15

What factor affects the strength of ionic bonding?

Answer 15

Size of the cations as they determine how closely packed they are in the lattice

Question 16

What is the trend in ionic radii down a group?

Answer 16

As you go down the groups, the ions have more electron shells; therefore, the ions get larger

Question 17

What is the trend in ionic radii across a period?

Answer 17

The ionic radius decreases as the number of protons increases. As the positive charge of the nucleus increases, the electrons are attracted more strongly and are therefore pulled closer to the nucleus

Question 18

What are the physical properties of ionic compounds?

Answer 18

• High melting temperature
• Brittleness
• Poor electrical conductivity when solid but good when molten
• Often soluble in water

Question 19

Why do ionic solids have high melting temperatures?

Answer 19

Ionic solids are giant lattice networks of oppositely charged ions. There are many ions in the lattice and the combined electrostatic forces of attraction among all the ions is large so lots of energy is required to overcome the forces of attraction

Question 20

Why are ionic solids brittle?

Answer 20

If stress is applied to a crystal of an ionic solid, the layers of ions slide over one another. Ions of the same charge end up side by side and so repel one another, causing the crystal to break apart

Question 21

Do ionic compounds conduct electricity when solid?

Answer 21

No, because there are no delocalised electrons and the ions are not free to move under the influence of a potential difference

Question 22

Do ionic compounds conduct electricity when molten? Why?

Answer 22

Yes, because when molten, the ions are mobile and so will migrate to the electrodes of opposite sign when a potential difference is applied. If direct current is used, the compound undergoes electrolysis as the ions are discharged at the electrodes

Question 23

What ionic compound can conduct electricity when solid?

Answer 23

Lithium nitride (Li3N) so is used in batteries

Question 24

Are ionic compounds soluble? Why?

Answer 24

Many are soluble in water - because the energy required to separate ions can be supplied by the hydration of the separated ions produced

Question 25

What is the equation for the burning of sodium in chlorine?

Answer 25

2Na (s) + Cl2 (g) ---> 2NaCl (s)

Question 26

What is the equation for the formation of magnesium oxide?

Answer 26

2Mg (s) + O2 (g) ---> 2MgO (s)

Question 27

What evidence is there for the existence of ions?

Answer 27

The ability of an ionic compound to conduct electricity and undergo electrolysis when molten or in aqueous solution

Question 28

What atoms is a covalent bond formed between?

Answer 28

Formed between two atoms when an atomic orbital containing a single electron from one atom overlaps with an atomic orbital, also containing a single electron, of another atom

Question 29

What causes a sigma bond to form? What does it lead to the formation of?

Answer 29

An end-on overlap. Occurs between 2 s orbitals and 2 p orbitals (when they are horizontal). Leads to the formation of a single covalent bonds between the two atoms

Question 30

What causes a pi bond to form? What does it lead to the formation of?

Answer 30

A sideways overlap of two p-orbitals (vertical). Pi bonds cannot form until a sigma bond has formed, so pi bonds inly exist between atoms that are joined by double or triple bonds

Question 31

What happens when two hydrogen atoms bond?

Answer 31

The two s orbitals overlap to form a new molecular orbital. The two electrons then exist in this new orbital. It forms a sigma bond

Question 32

What happens when two chlorine atoms bond?

Answer 32

The two p orbitals (each containing a single electron) overlap, forming a sigma bond

Question 33

Give an example of when a pi bond is formed

Answer 33

Ethene - one of the bonds between the carbon atoms is a sigma bond, the other is a pi bond Nitrogen - the triple bond is made up of one sigma bond and two pi bonds

Question 34

What is bond length?

Answer 34

The distance between nuclei of the two atoms that are covalently bonded together

Question 35

How is the strength of a covalent bond measured?

Answer 35

The amount of energy required to break one mole of the bond in the gaseous state

Question 36

What is the relationship between bond length and bond strength in covalent molecules?

Answer 36

The shorter the bond, the greater the bond strength. This is a result of an increase in electrostatic attraction between the two nuclei and the electrons in the overlapping atomic orbitals

Question 37

What is electronegativity?

Answer 37

The ability of an atom to attract a bonding pair of electrons

Question 38

What is the trend in electronegativity down a group?

Answer 38

Decreases

Question 39

What is the trend in electronegativity across a period?

Answer 39

Increases

Question 40

What is the distribution of electron density of two atoms of the same element?

Answer 40

Symmetrical because the ability of each atom to attract the bonding pair of electrons is identical

Question 41

What is the distribution of electron density in a polar covalent bond?

Answer 41

Distribution will not be symmetrical about the two nuclei

Question 42

What is a polar covalent bond?

Answer 42

A type of covalent bond between two atoms where the bonding electrons are unequally distributed. Because of this, one atom carries a slight negative charge and the other a slight positive charge