C3 Flashcards
1) Before 1800 how were elements classified?
2) Why?
1) By physical and chemical properties and atomic mass
2) They had no understanding of atomic structure; protons/electrons weren’t discovered until the 20th century
What was Newland’s table of Octaves?
Give 3 reasons why it was criticized by the chemical society in 1865.
Newland noticed every 8th element had similar properties so listed elements in rows of 7
1) Groups contained elements that didn’t have similar properties (carbon & titanium)
2) He mixed up metals and non metals (oxygen and iron)
3) There were no gaps left for elements that hadn’t yet been discovered
How was Dmitri Mendeleev’s periodic table different?
Mendeleev also arranged the elements in order of atomic mass but left gaps so that ones with similar chemical properties fell into vertical columns.
These gaps were found to predict the properties of undiscovered elements.
What is the modern periodic table based?
The electronic structure of atoms.
Arranged in order of atomic number which means elements with similar properties are in the same column
How is the group number and the number of electrons in the outer shell linked?
Apart from in transition metals, the group number (column) is the same as the number of electrons in the highest occupied energy level (outer shell)
Why is the periodic table so useful?
It can help predict the properties of elements
It is a useful summary of atomic structure
What is shielding?
The positive charge of the nucleus attracts the electrons and keeps them in place.
Shielding is when inner electrons block the positive charge attractive from the nucleus on outer electrons
Why do alkali metals become more reactive as your go down the group?
The further down the table, the more shells the alkali metal has.
So increased distance and shielding mean there is less attraction from the nucleus securing the outer electrons, so it is easily lost and the element is more reactive.
Alkali metals only need to lose one electron to have a complete outer shell.
Name 3 alkali metals.
Name the trends shown by alkali metals as you go down the table.
Any other points?
1) lithium, sodium, potassium #1 lower melting and boiling points #2 more reactive - increased shielding/distance
What type of bounds do alkali metals form?
They form ionic compounds with non-metals (metal ion carries a 1+ charge) producing white compounds that dissolve in water to form colourless solutions.
Describe the qualities of an alkali metal.
1) Silvery solids
2) Very reactive; stored in oil and handled with forceps
3) They react with water producing hydrogen.
4) They form hydroxides (OH-) making substances alkaline
5) They have a low density
6) Form ionic compounds
How do you test for hydrogen?
What color will universal indicator turn in a hydroxide solution?
1) Lit splint goes ‘pOp’
2) Purple
What happens to Halogen metals as you go down the table?
And why?
The Halogens become less reactive.
Group 7 elements need one more electron for an full outer shell, but the further down the group the more shells there are - so there’s increased distance and shielding. This means there’s less attraction from the nucleus to pull in electron
Name the trends shown by Halogens as you go down the table
1) Higher melting and boiling points
2) less reactive
1) What type of bounds do halogens form?
2) What is a halide?
1) Ionic bonds with metal ions
2) a halide, is a 1- ion formed when halogens and metals react
Name the qualities of the halogens.
Non metals
Have coloured vapors
Form ionic bonds
More reactive halogens displace less reactive halogens from an aqueous solution of it’s salt
1) What types of halides can other halides displace?
2) Work out the displacement reaction for the displacement of potassium bromine by chlorine
1) More reactive halogens displace less reactive halogens from an aqueous solution of it’s salt
2) KBr + Cl –> KCl + Br
How do halogens travel around?
In pairs! F2, Cl2, Br2, I2
Lots of other gases not just halogens do this to; O2 and H2
Describe the properties of transition metals.
1) Good conductors of heat and electricity
2) Dense, strong and shiny
3) Less reactive than group 1 metals (don’t react vigorously with water/oxygen)
4) Have higher densities and melting points (except mercury) than group 1
5) Have different ions (different charges)
6) Form coloured compounds (cause colours in gemstones)
Transition metals makes good catalysts, name three metals and there uses.
#1 Iron is the catalyst in the Haber process--> ammonia #2 Manganese oxide is a good catalyst for decomposition of hydrogen peroxide #3 Nickel turns oils --> fats (making margarine)
What causes hard water?
Calcium (Ca2+) and magnesium (Mg2+) ions, these usually enter water when it passes over rocks like gypusm, liestone and chalk which have soluble compounds
Name the positives (2) and negatives (4) of hard water.
+ Ca2+ ions are good for teeth and bones
+ Minerals in hard water decrease the risk of heart disease
- Ions react with soap; lathering to make scum
- When heated hard water forms limescale clogging up kettles/boilers/dishwasher
- Limescale is a thermal insulator so kettles with scale take longer to boil
- People in hard water areas have to spend more on soap, limescale removers and plumbers
-/+ has a distinctive taste some people like and others don’t
What is temporary hardness caused by?
Temporary hardness is caused by hydrogencarbonate ion. The rain dissoves CO2 from the air forming carbonic acid which reacts with calcium carbonate (in limestone) producing calcium hydogencarbonate.
What happens when you heat temporary hard water?
When heated the calcium carbonate decomposes to form calcium carbonate which is insoluble
Calcium hydrogencarbonate –> calcium carbonate + water + carbon dioxide
Ca(HCO3)2 –> CaCO3 + H2O + CO2
1) What is permanent hardness caused by?
2) What happens when you boil permanent hard water?
1) Dissolved calcium sulfate.
2) Nothing
Why does washing soda soften all types of hard water?
Advantages?
Disadvantages?
Washing soda (sodium cabronate) reacts with Ca2+ & Mg2+ ions forming a precipitate of calcium carbonate & magnesium carbonate.
+ Cheap
+ Works for both types of hardness
- Cause limescale
1) What’s an ion exchange column?
2) What type of hard water does it soften
3) Advantages?
4) Disadvantages?
1) A column filled with resin beads coated with salt (Na+) as the hard water is passed through, the sodium ions are displaced by the magnesium and calcium ions in the water
2) Both types; temporary and permanent
+ Works for both types of water
- Expensive; has to be replenished when resin becomes too saturated
How might you compare the hardness of two different waters?
Fill a flask with a water sample and add a drop of soap at a time.
Shake the sample after each soap drop until a lasting lather (bubbles for 30+s) is formed.
Repeat with other samples.
The more drops of soap needed the harder the water
Water is essential for life, why do people need to purify it?
To ensure it is free/has low levels of poisonous salts and harmful microbes (cholera)
When choosing water from an source (lakes, reservoirs an rivers) what should you check
That the water is fresh and free from chemicals (heavy metals) monitor pollution
Name 3 filtering processes and what they do…
1 Screening (mesh) removes debris like twigs/branches/leaves that would clog up water pipes
Why would you add chlorine?
Advantages of adding chlorine to water?
Disadvantages?
To sterilise water, killing harmful microbes (dysentery, typhoid, and cholera)
Adding chlorine
+ Prevents disease
- Reacts with natural substances in water to produce toxic by products
Naturally low levels of fluroride are present in areas of England, but some health authorities add additional fluoride. Why would you add fluorine?
Advantages of adding chlorine to water?
Disadvantages?
To reduce tooth decay
+ Improves dental health
+ reduces tooth decay
- Linked to teeth discoloration
- High levels of fluoride can cause bone cancer/problems
- Public can’t agree to have fluoridated water
Equation for removing temporary hardness by boiling?
Ca(HCO3)2 –> CaCO3 + CO2 +H2O
Why do some people use carbon or silver filters on water?
Because they are said to…
Carbon; remove taste/smell
Silver; ‘kill’ bugs
What is a reversible reaction?
One where the products of the reaction can themselves react to form the original reactants
What is equilibrium?
The point when the backwards and forwards rate of the reaction is equal. It is only reached in a closed system (so none of the reactants / products can escape)
Why would the position of equilibrium shift?
To cancel out any changes in the conditions (heat / pressure)
this means if you deliberately alter the conditions you can increase / decrease the amount of product / reactants formed.
What can change the point of equilibrium?
1) Temperature
2) Pressure and concentration
What is a endothermic reaction?
One that takes heat in from the surroundings (temperature falls)
What is a exothermic reaction?
One that gives out heat to the surroundings (temperature rise)
If a reaction is endothermic one way it what the other?
Exothermic.
What happens if you increase the temperature of a reaction?
If the temperature is raised, the endothermic reaction increases. This is because the endothermic reaction increases to remove the heat by producing more products.
The yield from the exothermic reaction decreases.
What happens if you lower the temperature of a reaction?
If the temperature is lowered, the exothermic reaction increases. This is because exothermic reaction will increase to give out more heat by producing more products.
The endothermic reaction decreases.
What does greater volume mean and what does less volume mean?
Greater volume; side with more gas molecules on
Less volume; side with fewer gas molecules on
What happens if you increase the pressure of a reaction?
An increase in pressure favors (encourages) the reaction that produces less volume (less molecules)
