C3- Periodic table Flashcards
What were the two ways scientists in the 19th century organised elements?
- by their physical and chemical properties
- by their atomic weight
What did Newland do?
Put elements in the order of their atomic massive
And said that every 8th element had similar properties (law of octaves)
What were the criticisms of newland’s ideas?
- some groups had a mix of metals and non metals
- elements in some groups didn’t have similar properties
- he didn’t leave gaps for elements to be discovered
- his law only worked for the first few elements
What did Mendeleev do ?
He arranged the elements in a periodic way (regular occurring pattern)
- left gaps for undiscovered elements to show otherwise, elements would not have similar properties to others in the group
- predicted the atomic masses and properties of undiscovered elements
Why did some scientists disapprove of Mendeleevs work?
-not much evidence to suggest the elements fit together in that way
What is the modern periodic table based on?
Electronic structure
- table arranged in order of atomic number
- all elements put into groups
What happens to the electrostatic attraction when the electron gets further away from the nucleus?
The attraction becomes weaker
What is shielding?
When the electrostatic attraction of the nucleus is less because of a lot of inner electrons that ‘shield’ the nuclear charge
Why are group one metals more reactive as you go down the group?
There’s less attraction from the nucleus holding the electron in place due to increased distance and shielding
What are the features of group 1?
- low density
- react with non metals to form ionic compounds
- release hydrogen when reacting with water
- form hydroxides that dissolve in water to give alkaline solutions (colourless)
What happens when lithium is put in water?
It fizzes and moves around the water
What happens when sodium is put into water?
Produces a flame and moves around the surface of the water
What happens when potassium reacts with water?
It spits sparks , has a flame and moves around the surface of the water
What kind of ion do the alkali metals want to form?
A 1+ ion
What are the properties of transition metals compared to group 1?
- higher melting points and boiling points (except mercury)
- harder and stronger
- less reactive with water and oxygen
What are transition metals good for in the industry?
- conductors of heat and electricity
- used in structural materials
What can transition metals do?
- Form ions with different charges
- Form coloured compounds (copper sulphate)
- Useful as catalysts (iron in haber process etc)
What coloured compound does Fe2+ form?
Green compounds
What coloured compound does Fe3+ form?
Reddish brown
What are the properties of group 7?
- poor conductors
- poisonous
- produce coloured vapours
What happens as you move down group 7?
They become less reactive because it’s harder to gain an extra electron
Higher melting and boiling point
What compound is formed when halogens react with metals?
Ionic compound
What is the ion produced by group 7?
A halide ion (-1 charge)
What is the colour and properties of fluorine?
- very reactive
- poisonous yellow gas
What are the properties and colour of chlorine?
- fairly reactive
- poisonous dense green gas
What is the property and colour of bromine ?
- dense
- poisonous, red-brown volatile liquid
What is the property and colour of iodine?
-dark grey crystalline solid or purple vapour
What does hard water make?
Scum and scale
How is scum made?
Dissolved calcium ions and magnesium ions in the water reacting with soap is insoluble
How is scale formed?
When heated, hard water forms scale
What problems can scale cause?
- reduce the efficiency of heating systems which may need to be replaced
- blocks pipes
- thermal insulator
What is hardness caused by?
Ca2+ and Mg2+ ions
What are the benefits of the ions in hard water?
- good for bone and teeth development
- less risk of heart disease
What is temporary hard water?
Can be softened by heating or boiling
-caused by hydrogenate ion
What is permanent hard water?
Remains hard even when heated or boiled
Caused by dissolved calcium sulfate
How can washing soda (sodium carbonate) soften water?
The added carbonate ions react with the Ca and Mg ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate
How can hardness be removed through an ion exchange column ?
The Columns contain resins that have lots of sodium ions and exchange them for calcium or magnesium ions in the water
