C13- Transition Metals Flashcards
What’s a transition metal
They are elements in the central block of periodic table between groups 2 and 3 - include most metals used for construction, vehicles, jewellery and other everyday uses
Tell me the TYPICAL physical properties
Malleable
Ductile - can be stretched out to make thin wires
Good conducters of electricity
Shiny when polished
When compared to aluminium and the metals in groups one and two: they typically have high melting points and high densities
Tell me some exceptions of the properties
Mercury is a transition metal and has a high density but is liquid at room temp
Tell me about the chemical properties of transition metals
Form coloured compounds
The metals and compounds typically show catalytic activity
Catalysts increase the rate of a reaction without being changed chemically or in mass at the end of a reaction
Eg iron is used as a catalyst to manufacture ammonia in the Haber process
When do metal oxides form
When metals react with oxygen in in air and oxidise
More reactive metals oxidise quickly
When metals lose electrons
What’s tarnish
Some metals may form a layer of tarnish when they oxidise - this stops oxygen reaching the metals preventing further oxidation
What’s corrosion
Happens when a metal continues to oxidise so a metal becomes weaker over time
What’s rusting
It’s the corrosion of iron or steel with reacts with oxygen and water
Iron + oxygen + wager = hydrated iron (III) oxide - it looks like dust - flakes fall off to expose more metal to air and continues to weaken the iron
How can rusting be prevented
Keeping metal in an unreactive atmosphere of nitrogen or argon
Or if water Is kept away using a desiccant powder that absorbs water vapour
Or painting , coating with plastic, oiling and greasing
Tell me about sacrificial protection
Method of rust prevention that doesn’t rely of keeping air or water away
A piece of magnesium or zinc or since is attached to an iron or steel object which oxidises more easily so oxygen reacts with them instead and protection continues until the sacrificial metal corrodes away
The more reactive a metal - the more reactive a metal loses its electrons and more easily oxidised
What’s electroplating
It coasts the surface of one metal with a thin layer of another - less reactive or corrosion resistant
What do you need to carry out an electroplating
An anode made from the plating material
An electrolyte - solution containing ions of the plating metals
Cathode which is the metal object itself
What’s a d.c
Direct current which flows through the electrodes and the electrolyte
How does the electroplating of a copper ring with silver work
A d.c flows through electrodes and electrolytes - silver jons in electrolyte move to cathode (copper ring) and gain electro jons and are deposited as silver ions, at the silver anode, silver atoms lose electrons to become silver ions, which go into the electrolyte, the longer the current flows, the thicker the silver layer on the ring becomes
What’s galvanising
Coating iron and steel objects with since - improves corrosion resistance by stopping water reaching the iron or steel and acting as a sacrificial metal - and sacrificial protection can continue even if zone layer is damaged
How is galvanising carried out
Using electroplating or dipping the object In molten zinc
Tell me about tin plating
Food cans inner surface is protected from rusting by electroplating with Tin which doesn’t react with air or water at room temp - so it can reach the steal but of its damaged the steel can rust faster because iron is more reactive than tin - so iron acts as a sacrificial metal
What’s an alloy
A mixture of a metal element with one or more other elements, usually metals
What are alloy steels
They are made by deliberately adding other elements to iron to add properties by varying their composition
Tell me about stainless steel
Resists rusting and contains chromium which reacts with oxygen in the air and water reaching the metal below - but thing enough to be transparent but if it’s scratched more chromium reacts to replace the layer
Add manganese for strength and maintain malleability
The greater the carbon content of steel…..
The stronger and harder it is
Why can stronger steels be bad
Can be more difficult to press into shape but used to produce strong but relatively light weight car bodies
Why are alloys often stronger than pure metals
In solid, pure metal atoms are the same size so layers can be pushed past each other if enough force
- so they are malleable and ductile
In an alloy - the atoms of other elements present may be different sizes - distort the regular structure so alloys are stronger but still are usually malleable and ductile
What does the use of a metal or alloy depend on
Chemical properties such as resistance to corrosion
Physical properties such as density
Depends on the use
Tell me about magnalium
Alloy of aluminium 95% and 5% magnesium used for aircraft parts and scientific instruments its less dense and almost 4 times stronger than aluminium alone - so it can be used to manufacture strong but light weight parts
