topic 2: Metallic bonding Flashcards
(21 cards)
describe metallic bonding
The strong electrostatic attraction between the nuclei of the positive ions and a sea of the negatively charged delocalised electrons
why are metals good conductors?
in a regular lattice, the positive ions share the delocalised electrons.
these electrons can move freely meaning they can conduct electricity and thermal energy
why are metals ductile and malleable?
malleable -the ability to be bent into shape
ductile - it can be stretched into a wire without breaking
the layers of ions can slide over each other
how are alloys made? and what do they do?
- 2 or more different elements of different sizes (usually a mix if metals and non-metals) are mixed together
- this disrupts the layers of ions in the regular lattice structure preventing the layers from sliding over each other
- this makes alloys much harder and stronger than pure metals
name an example of an alloy?
Steel - mostly made of iron with 1-2% of carbon
makes it stronger than pure iron
used for cars and planes
What are the physical properties of metals?
- shiny and reflective
- solid state at room temp
- high density(heavy)
- high melting and boiling points
- good conductors
- malleable and ductile
- sonorous
What are the Chemical properties of metals?
- high reactivity
- they are easily oxidised
- can form alloys
Why do metals have a high melting/boiling point?
They have strong electrostatic attractions between the positive metal ions and the delocalised electrons
these require a high amount of energy to overcome
What is electrolysis?
The seperation of a compound into its constituent elements using electricity
What charge does the cathode have during electrolysis and which ions does it attract?
- The cathode has a negative charge (opposites attract)
- It will therefore attract cations
REMEBER: CATions are PAWsitive
The cathode has a negative charge because electrons from the power supply will flow from the annode to the cathode
What charge does the annode have during electrolysis and which ions does it attract?
- The annode has a positive charge
- It will therefore attract anions
The annode has a positive charge because electrons from the power supply will flow from the annode to the cathode
Which compounds can electrolysis be used on?
- Molten ionic
- Aqueous ionic
It only works for ionic compounds as covalent compounds do not contained charged ions, and it only works for molten or aqueous ionic compounds because only these compounds can conduct electricity
What happens in the electrolysis of a molten ionic compound (Lead Bromide(II) as an example)?
- The positive lead ions will be attracted to the cathode
- The negative bromide ions will be attracted to the anode
- Each Pb²⁺ ion will gain two electrons at the cathode, forming Pb(s)
- Each Br⁻ ion will lose an electron, and then pair up to form Br₂ (g)
- You need to heat the lead bromide first to make it molten
- The bromine gas will bubble to the top of the molten solution, and the lead will be deposited at the bottom
- Similar things will happen with any molten ionic compound, however be aware of whether the anions will form polyatomic molecules or not
- It is important to note that bromine gas only forms when doing electrolysis of a molten compound due to the presence of heat as its boiling point is only 60 degrees celcius, therefore in a solution bromine liquid will form which is red-brown in colour
What will be the two ionic half equations for the electrolysis of molten lead bromide (II) as well as the overall chemical equation?
- Pb²⁺ + 2e⁻ –> Pb
- 2Br⁻ –> Br₂ + 2e⁻
- PbBr₂ –> Pb + Br₂
what is the hierarchy for which ion is reduced at the cathode for the electrolysis of solutions?
At the cathode:
copper (Cu) is always reduced
hydrogen (H) will be reduced is no copper is present
Sodium (Na) never reduced (Think of N/a = not applicable)
general rule is that if the metal is less reactive than hydrogen it will be attracted, but if it is more reactive then hydrogen then hydrogen will be attracted to the cathode
what is the hierarchy for which ion is oxidised at the anode for the electrolysis of solutions?
At the anode
halide ions (chlorine, bromine, iodine) always be oxidised if present
Hydroxide ions (OH^-) will be oxidised if halide ions are not present
sulphate ions (SO4^2-) will never be oxidised
rule: usually if it is a complicated anion such as SO₄ it will be the OH⁻ anion
What happens in the electrolysis of an aqueous ionic compound?
- H⁺ ions and OH⁻ ions will be present compound
- Whether it is the non-metal anion or the OH⁻ anion which is attracted to the annode depends on which one is easier to break and loses electrons more readily (e.g usually if it is a complicated anion such as SO₄ it will be the OH⁻ anion)
- Whether it is the metal cation or the H⁺ cation will depend on the metal’s reactivity ( e.g if it is more reactive than hydrogen then the H⁺ ion will be attracted, if it is not then it will be the metal)
What is the ionic half equation for hydroxide ions at the annode?
4OH⁻ –> 2H₂O + O₂ + 4e⁻
Water does not always count as a product, therefore oxygen is the only product at the annode here
What will be the two ionic half equations for the electrolysis of aqueous sodium sulphate as well as the overall chemical equation?
- 2H⁺ + 2e⁻ –> H₂
- 4OH⁻ –> 2H₂O + O₂ + 4e⁻
- 2H₂O –> 2H₂ (g) + O₂ (g)
- The hydrogen is attracted to the cathode because sodium is more reactive than hydrogen
- The hydroxide is attracted to the annode because it is simpler and loses electrons more readily than the sulphate
- Water is also a product in the overall equation, but it is not written
- Sodium sulphate is there, but is not written in the equation as it remains unchanged
- Bubbling will be observed at both electrodes
What will be the two ionic half equations for the electrolysis of aqueous copper chloride as well as the overall chemical equation?
- Cu²⁺ + 2e⁻ –> Cu
- 2Cl⁻ –> Cl₂ + 2e⁻
- CuCl₂ –> Cu + Cl₂
- The copper is attracted at the cathode because it is less reactive than hydrogen
- The chloride is attracted at the annode because it is simpler and loses electrons more readily than hydroxide
- At the cathode, a red-brown metal will be deposited at the bottom, and at the annode bubbling will be observed
At which electrodes do oxidation/reduction reactions happen and why?
- Oxidation occurs at the annode because the ions lose electrons
- Reduction occurs at the cathode because the ions gain electrons
