Metallic bonding

Question 1

What are the properties of metals?

Answer 1

• Good conductors of heat and electricity
• Ductile and malleable
• Shiny

Question 2

Explain the metallic structure.

Answer 2

• The valence electrons (delocalized) are free to move through the structure
• The delocalized electrons are called sea of delocalized electrons
• The metal atoms are ionized and form cations

Question 3

What is the metallic bond?

Answer 3

• The electrostatic attraction between the lattice of positive metal ions and the sea of delocalized electrons
• It is non-directional (the force of attraction occurs in all directions between the positive ions and delocalized electrons)

Question 4

Explain malleability.

Answer 4

• When enough force is applied to the metal, one layer of metal ions can slide over another without disrupting the metallic bond
• The bond remains intact
• This is how they can be bent into different shapes (malleable) and drawn into wires (ductile)

Question 5

Explain the high thermal and electrical conductivity in metals.

Answer 5

• When a potential difference (voltage) is applied across a metal, a direction is put into the movement of delocalised electrons
• They are repelled from the negative electrode and move towards the positive electrode (direction of an electric current)
• Electrons carry kinetic energy in the form of vibrations through a metal from the hotter to colder part of the metal
• The delocalized electrons reflect wavelengths of visible lights, hence metals appear shiny

Question 6

What does the strength of metallic bonds depend on?

Answer 6

• The charge on the metal ion AND
• The ionic radius of the metal
• The stronger the bond the higher the melting point
• The higher the ionic charge the smaller the ionic radius and the higher the melting point, hence a stronger metallic bond
• The higher the charge, the more delocalized electrons there are which increases the force of attraction between the nuclei and electrons
• The more delocalized electrons, the stronger the metallic bond
• The smaller the ionic radius (higher ionic charge) the higher the density of the metal
• Many transition metals have high melting points and have delocalized electrons which form part of the metallic structure

Question 7

What are alloys?

Answer 7

• Homogeneous mixtures composed of two or more metals or a metal and a non-metal
• They have different properties to the metals that they are made from
• There is an unlimited number of alloys that can be created
• The metals are added together in molten state, when solidified the atoms of the metals and non-metals are scattered through the lattice structure
• In alloys, the layers cannot slide over each other as easily as the different sized atoms disrupt the regular arrangement.
• Alloys are often stronger, more chemically stable and often more resistant to corrosion.
• Non-directional bonding

Question 8

Give 5 examples of alloys, their typical composition, properties and uses.

Answer 8

• Brass: 70% copper, 30% zinc, harder than pure copper, used to make musical instruments
• Bronze: 90% copper, 10% tin, harder than pure copper, used in statues
• Mild steel: 99.7% iron, 0.3% carbon, stronger and harder then pure iron, used in car manufacturing
• Stainless steel: 74% iron, 18% chromium, 8% nickle, increased resistance to corrosion, used to make cutlery
• Lead solder: 50% tin, 50% lead, lower melting point than either tin or lead, used in electrical circuit boards
• Lead-free solder (other metals included)