Chemistry - Tripple Flashcards
How did John Dalton arrange the table?
Arranged elements in order of their atomic mass
Who created the first periodic table in 1808?
John Dalton
Who created the periodic table in 1864?
John Newlands
How did John Newlands arrange his periodic table?
Built on John Daltons idea and came up with the idea of the “law of octaves” every eighth element had similar properties so he arranged them into rows of 7
Why was John Newlands table criticised?
Left no gaps- elements were still being discovered
Only worked up till calcium
His groups didn’t contain similar properties
He mixed metals and non-metals
Who came up with the periodic table in 1869?
Dmitri Mendeleev
How did Dimitri arrange the table?
Put elements in order of their atomic mass but left gaps this predicted new elements
Put the elements in vertical columns (groups) these were the similar properties
How is the modern periodic table arranged?
Arranged in order of their atomic proton number, the group number tells us the number of electrons in the outermost shell and therefore how it reacts
How does shielding work?
The further away from the nucleus the lest attracted the electron is to the nucleus
The more electrons in the inner shells the more shielded it is so the attraction is even less
Why do group 1 metals get more reactive as they go down the group?
As you go down the group the larger the atom is therefore the less attracted the electron is in the outermost shell due to distance and shielding this means the electron is more easily lost
Why do group 7 elements get less reactive going down the group?
The atoms get larger as you go down the group therefore there is increased distance and shielding this means that the outer shell is less likely to gain and electron
Name the properties of the group 1 alkali metals
Go down more reactive and have a lower melting and boiling point
Low density
Have 1 electron in outer shell making it very reactive
Form ionic compounds with non-metals as they are keen to lose an electron
Squeaky pop
Produces hydrogen and hydroxide
Name the properties of the group 7 halogens
As they go down they are Less reactive Higher melting points Higher boiling points - more reactive halogens will displace less reactive halogens
What is the properties of fluorine?
Very reactive and has a yellow gas
What is the properties of chlorine?
Fairly reactive and a dense green gas
What are the properties of bromine?
Dense and poisonous and red/brown volatile liquid
What are the properties of iodine?
Dark grey crystalline solid with purple vapour
What do halogens form with metals?
They form ionic bonds 1- ions called halides they gain an electron
Why can’t fluorine react in a aqueous solution?
Because it reacts strongly with water
What are the properties of transition metals?
good conductor Dense strong and shiny Less reactive than group 1 metals Much denser stronger and harder than group 1 metals Higher melting points that group 1
Why do transition elements have different colours?
Different ions form different colour compounds
What colour is potassium chromate?
Yellow
What colour is potassium manganate?
Purple
What colour is copper sulfate?
Blue
What colour is Fe 2+?
Green
What colour is Fe3+?
Red/brown
How do you test for soft water and how do you test for hard water?
Soft > produces lather with soap
Hard> nasty scum
Why does hard water produce a nasty scum?
Dissolved calcium and magnesium ion react with soap to make scum which is insoluble to get a descent lather you should use more soap
What does heating do to hard water?
Produces scale
This reduces the efficiency of the heating system which will need to be replaced
Also acts as a thermal insulator which means it takes longer to heat up e.g. A kettle
How is hard water formed?
Hard water contains mg2+ ions and ca2+ ions
When rain falls on types of rocks like limestone the ions react with it and dissolve to magnesium sulfate and calcium sulfate these are both soluble. This then goes into rivers and then reservoirs and into the water supply
What is temporary hard water caused by
The hydrocarbonate ion HCO3- in Ca(HCO3)2
What is permanent hard water caused by?
Dissolved calcium sulfate
How do you remove temporary hardness?
Boiling
The calcium hydrocarbonate decomposes to form calcium carbonate which is insoluble this is solid limescale
And the two permanent ways
How do you make permanent hard water soft?
Washing soda - adding washing soda (sodium carbonate) to it, the carbonate ions react with calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The ions are no longer dissolved in the water so cannot make it hard
- ion exchange column - removes hardness by replacing the calcium and magnesium ions with sodium and hydrogen ions
Why do water softeners have to be topped up with salt?
Resin is washed with sodium chloride solution this puts the sodium ions back in
Why is hard water good for you?
Calcium ions are good for teeth and bones
Less risk of developing heart disease due to minerals in hard water
Why must water be treated?
It must be free of harmful poisonous salts like nitrates and phosphates
No harmful microbes as these could cause disease like cholera
How is water in a reservoir treated?
- Water passed through a mesh to get rid of twigs and leaves
- Chemicals like aluminium sulfate and lime added this causes the dirt and impurities to clump together and microbes to stick together and sink
- Water is passed through a gravel bed usually made of fine sand to remove and solids left
- Water is chlorinated to kill of any microbes
- Ph of water checked and corrected if not neutral
- Pumped to homes
What does filtering do?
Carbon > Reduces level of chlorine, pesticides and other impurities
Silver > discourages growth of bacteria
Ion exchange > removes calcium magnesium aluminium and lead
What is distilling?
Boiling water to make steam and then condensing it
Pure water
To expansive
Only in labs as they dint want ions reacting
What are the pros and cons of fluorine in water?
\+ reduces tooth decay \+ been used for 50 years \+ reduce amount of tooth decay \+ only added in tiny amounts - high dosages can cause cancer and bone problems like flouris - ethical not right as theres no choice - cant control intake - benefit not significant
What are the benefits and costs of adding chlorine to water?
+ prevent disease
- increase in certain cancers ad it reacts with other natural substances in the water to produce toxic by products
- ozone is alternative
