Topic 9 - Groups Of The Periodic Table Flashcards
Inert
The noble gasses have full outer shell so are unreactive.
Main properties of noble gasses.
1) Low boiling points
2) Monatomic (full outer shell)
3) Low densities
4) Inert, not flammable
Helium
Use and why
Used as a lifting gas in party balloons and airships.
Less dense than air, so balloons and airships rise.
Non-flammable so the helium cannot set on fire.
Argon
Use and why
Used instead of air in lightbulbs.
Inert stops the metal filament from reacting with oxygen and burning out the metal filament
Neon
Use and why
Red neon signs, lasers
Conductor of electricity at high voltage and gives out red light.
Krypton
Use and why
Used in photography flash bulbs.
Produces very white light.
Stops the flash filament from burning up during the high temperature flashes.
What else can helium and argon be used for?
Welding
Inert so stops hot metals reacting with oxygen - reduces brittle oxide formation reducing the weld quality.
Why are the alkali metals in group 1?
They all have 1 electron in their outer shell.
What happens to reactivity as you go down group 1?
Elements get more reactive.
The more shells an atom has, the further the outer shell electron is from the nucleus. This decreases the attraction between the nucleus and the outer shell electron. This makes it easier to remove the outer shell electron and so the more reactive the alkali metal is.
What is the word equation for alkali metal reactions with water?
Alkali metal + water —> Metal hydroxide + Hydrogen
Example
Lithium + water —> Lithium hydroxide + hydrogen
Alkaline Bubbles
2Li + 2H2O —> 2LiOH + H2
Properties of alkali metals?
• Low melting and boiling point
• Soft
• Low density
• Shiny when cut but goes dull quickly
Lithium physical properties
• Grey
• Soft
• Shiny but goes dull when cut
Lithium reaction with water
Move around the surface fizzing furiously.
Lithium colour and Ph of solution
• Blue
• 13-14
Sodium physical properties
• Lighter grey
• Softer
• Goes dull quickly when cut
Sodium reaction with water
Float around the surface, fizzing furiously.
Melt in the heat of the reaction.
Sodium colour and PH of solution
• Dark blue
• 13-14
Potassium physical properties
• Really soft
• Light grey
Potassium reaction with water
Floats around the surface fizzing furiously
Melt in heat of reaction
Lilac flame gets hit enough to ignite the hydrogen gas being produced.
Potassium colour and PH of solution
• Dark blue
• 14
Fluorine
State and colour at room temperature
Pale yellow gas.
Chlorine
State and colour at room temperature
Pale green gas
Bromine
State and colour at room temperature
Red/orange liquid
Iodine
State and colour at room temperature
Grey solid
Astatine
State and colour at room temperature
Black solid
What happens to reactivity going down group 7?
The halogens become less reactive
When an element in group 7 takes part in a reaction, its atoms outer shells gain an electron and form negatively charged ions, called anions. The less easily these anions form, the less reactive the halogen.
• The atoms become larger.
• The outer shell becomes further from the nucleus
• The force of attraction between the nucleus and the outer shell decrease
• An outer electron is gained less easily
• The halogen becomes less reactive
What happens to the melting and boiling point down group 7?
They increase because going down group 7 the molecules become larger, the intermolecular forces become stronger.
What do the group 7 molecules consist of and what does it mean?
Diatomic molecules, they contain 2 atoms that are chemically bonded.
How to test for chlorine gas?
Damp blue litmus paper goes red then bleaches white.
Halogens reaction with metal
Lithium + Chlorine
Lithium Chloride
2Li + Cl2 —> LiCl
Halogens reaction with hydrogen
Hydrogen and fluorine
Hydrogen fluoride
H2 + 2F —> 2HF
How does the colour of the halogens change as you go down the group?
They become darker.
What do halogens have in common?
• They are fairly toxic
• Have low melting points
• All form acids when combined with hydrogen
Displacement reactions
A displacement reactions happens when a more reactive element displaces the less reactive element from it compound.
Chlorine + potassium bromide —> Bromine + potassium chloride
Cl2 + 2KBr —> Br2 + 2KCl
The chlorine is reduced to chloride ions so the salt solution becomes potassium chloride. The bro Jed ions are oxidised to bromine, which turns the solution orange.
What type of reactions are halogen displacement reactions?
Redox reactions. The halogens gain electrons (reduction) whilst halide ions loose electrons (Oxidation).
What colour are the halide salt solutions?
Colourless
What controls the colour of the product?
The less reactive halogen.
Core practical: reactivity trends method
1) Start by measuring out a small amount of halide solution to each dot on your laminated sheet.
2) Add a few drops of halogen solution to it.
3) If you see a colour change then, then a reaction has happened - the halogen has displaced the halide ions from the salt. If no reaction happens, there wont be a colour change - the halogen is less reactive than the halide and so can’t displace it.
Chlorine water colour
Pale yellow-green to colourless
Bromine water colour
Orange
Iodine water colour
Brown
Chlorine water + bromide solution
Reaction colour
Orange solution (Br2)
Chlorine water + potassium iodide
Reaction colour
Brown solution (I2)
Bromine water + potassium iodide
Reaction colour
Brown solution (I2)
What are spectator ions?
Ions that don’t change in a reaction.
