Monday 14 April 2014

GCSE biology unit 1 - the nervous system

The nervous system

Its job is to detect stimuli so we can coordinate our behaviour. Stimuli are changes in the environment.
Receptors sense these changes:

  • eyes contain light receptors that detect light
  • noses contain chemical receptors that detect smells
  • mouths contain chemical receptors that detect tastes
  • skin has various receptors that are sensitive to touch, temperature, pressure and pain
  • ears contain sound receptors and also receptors that detect position (balance)
once the receptor has detected the stimulus, the sensory neurone passes an electrical impulse to the central nervous system (brain + spinal chord), where relay neurones pass the signals from one nerve cell to another. The CNS then passes an impulse through the motor neurone to the effectors  and a response happens.

e.g. sound stimulus - sound receptors - sensory neurone - CNS - motor neurone - effector - response.

The CNS contains synapses which are junctions between the three neurones. that pass the electrical impulses through gaps by using chemical signals.

Reflexes miss out the CNS and go straight through the three neurones. This way they are quicker so protect you. If the brain was involved, there would be a delay.

GCSE biology unit 1 - growing microbes

Growing Microbes

Also referred to as "culturing" microbes. We grow microbes to investigate what medicines can kill it. we do this under ASEPTIC CONDITIONS (make sure nothing gets contaminated that might effect the results)

STEP 1: sterilise the agar jelly inside the Petri dish
STEP 2: transfer microbes to the agar jelly using a inoculating hoop and place in neat, straight lines. The inoculating hoop should be heated first to kill any bacteria then left to cool before transferring the microbes.
STEP 3: quickly place lid on Petri dish and seal the container with tape to prevent any further contamination.
STEP 4: incubate at 25 degrees if in a school or 37 degrees if in a safe lab with scientists incase a pathogen is grown at the higher temperatures.

testing for disinfectants or antibiotics

use the microbes grown and place different sorts of disinfectants or antibiotics on the patch of microbes. once the microbes die, the agar jelly turns clear so the most effective disinfectant of antibiotic will have the largest clear area.

GCSE biology unit 1 - antibiotic resistance

Antibiotic Resistance

Medicines and Antibiotics

Pathogens infect the body and, after a while, cause symptoms. people's options are to wait for the white blood cells kick in or they can take medicines (pain killers) to relieve the symptoms. Medicines such as painkillers only relieve the symptoms - they don't effect the pathogens.

Antibiotics are medicines that relieve symptoms, have an effect on bacteria and can actually kill pathogens. These are good but...

If a doctor prescribes too many and too often the bacteria get a lot of exposure to the antibiotics and a mutation occurs (a random, spontaneous change in tis DNA) that causes the bacteria to become antibiotic resistant. This mutation is caused by natural selection. as this new bacteria multiplies, the person ends up with a population of antibiotic resistant bacteria.

scientists are developing new antibiotics that will actually kill that bacteria as opposed to just having an effect on them. These, again should not be prescribed too much.

Saturday 12 April 2014

GCSE biology unit 1 - vaccinations

vaccinations

protecting against future diseases
  • vaccines contain dead pathogens that still have antigens (codes or shapes on the cell wall)
  • the white blood cells will produce antibodies to attack the antigens
  • in the future, if these pathogens enter the body, the white blood cells will be able to produce antibodies quicker as it will recognise the antigens
The more people that are vaccinated, the harder it is for the disease to spread as there are fewer people who can catch it.

MMR
  • measles, mumps and rubella
  • linked to autism (condition that effects people's communication and social interaction skills)
Ignas Semmelweis (1850s) noticed that there were fewer cases child bed fever (a common birth disease) in the wards where only the midwives worked and the were more cases of child bed fever in the wards where the medical students dealt with child birth. 
He noted that the medical students were also working on dead bodies whereas the midwifes only dealt with child birth. He also noted that the medical students didn't wash their hands after carrying out investigations on dead bodies.

He recorded results and there were indeed many more cases of the disease on the medical student wards. Semmelweis predicted that something from the dead bodies was passing on causing child bed fever. He asked the medical students to wash their hands and the number of deaths reduced but his ideas were rejected because he could not explain what was passing on. Nowadays we know this is bacteria and it is normal procedure for doctor and nurses to wash their hands continually.



Wednesday 9 April 2014

GCSE CHEMISTRY - unit 1 - compounds and bonding

REACTIONS AND COMPOUNDS

New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bonds.

Ionic bonds

Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons:
  • metal atoms lose electrons to form positively charged ion
  • non-metal atoms gain electrons to form negatively charged ions
The ionic bond is the force of attraction between the oppositely charged ions. 

Covalent bonds

Two non-metals share an electron to form covalent bonds that hold the atoms together to form molecules.

Chemical formulas

The chemical formula of a compound shows how many of each type of atom join together to make the units which make up the compound. For example, in iron sulfide every iron atom is joined to one sulfur atom, so we show its formula asFeS. In sodium oxide, there are two sodium atoms for every oxygen atom, so we show its formula as Na2O. Notice that the 2 is written as a subscript, so Na2O would be wrong.


GCSE biology unit 1 - infectious diseases

Infectious diseases

Microorganisms
  • E.g bacteria, viruses, fungi
  • Not all cause diseases
  • Ones that cause diseases are called pathogens 
Pathogens
Microorganisms that cause disease

Bacteria
Produce toxins (poisons)

Viruses
Much smaller
Infect body cells by getting inside and reproducing so many times that the cell explodes/breaks so is permanently damaged

DEFENCE - white blood cells
They ingest bacteria and release enzymes to digest pathogens
They produce antibodies to latch onto the antigens (small shapes on cell walls) of the pathogen and start destroying them. Different diseases have different antigens.
They produce antitoxins which neutralise bacteria toxins, making them harmless.

GCSE biology unit 1 - balanced diets

Balanced diet

Proteins
  • Meat, fish, eggs, pulse veg. Etc.
  • Build new tissue (important if still growing)
  • Repairs damaged tissues
  • Made up of amino acids
Carbohydrates
  • Potatoes, breat, rice, sugars, etc.
  • Provide energy
  • Can lead to obesity if not balanced with exercise 
Fats
  • Butter, oil, etc.
  • Provides stored energy to be used later when needed
  • Can lead to obesity if not balanced with exersise
Fibre
  • Veg, fruit, etc.
  • Not absorbed by body/ blood so not a nutrient
  • Helps prevent constipation
Vitamins and minerals
  • For general health
  • Can't get energy from them
  • A lack of them leads to deficiency disease
If you take in more energy compared with what you release, you will put on weight.

MALNUTRITION is caused by a non-balanced diet.
You can either be underweight or overweight.

Metabolism
Total of the chemical reactions that are going on in your body

Affected by
  • Amount of exersise you do
  • Genetics
  • Muscle to fat ratio (muscle requires energy)
  • Gender (females tend to have lower)
Cholesterol 
Required in the body to make cell membranes
Too much can lead to blocked arteries (especially around the heart), restricting the blood flow
This can lead to a heart attack.

Type 2 diabetes
Linked to being overweight
Means you cannot control blood sugar levels
Insulin is not recognised by body cells so cells don't take sugar out of the blood.


GCSE chemistry unit 1 - fractional distilation of air

Fractional distillation of the air

Today the air is a mixture of:
  • 78% nitrogen
  • 21% oxygen
  • And 1% other gases (including 0.04% carbon dioxide and 0.8% argon - a noble gas)
Fractional distillation

The air is cooled to -200 degrees so all the gases in the air are condensed into a liquid. Carbon dioxide and water are then removed so we are left with the other gases including nitrogen, argon and oxygen, which all have different boiling points. Heating it to a hoc her temperature each time, nitrogen evaporates first, then argon, then oxygen which can be collected as three different substances.

Uses of argon
  • Unreactive so used inside filament bulb and fluorescent tubes
  • Preserving old document because they are so unreactive.
Uses of nitrogen
  • Food packaging to stop food decomposing (unreactive)
  • In liquid form it can preserve living cells
  • Fertilisers
Uses of oxygen
  • Part of fuels for rockets
  • Oxygen masks etc.

GCES chemistry unit 1 - Miller-Urey experiment

Miller-Urey experiment

Miller and Urey were two scientists who set up apparatus that recreated the conditions that were in the atmosphere 4.5 billion years ago to try and work out how organisms could have been created. 

Water was heated to create water vapour which travelled to a flask containing ammonia, hydrogen and methane. They used a series of different electric shocks on the flask and then condensed the gasses. Within a week, they found they had produced the organic chemicals needed for life such as amino acids. But how these organic chemicals turned into life, still remains unanswered, they won a Nobel Prize for their discoveries.

GCES chemistry unit 1 - the development of the Earth's atmosphere

The development of the Earth's atmosphere

Volcanic eruptions 4.5 billion years ago gave off carbon dioxide, water vapour, ammonia and methane. The earth was continually cooling so, over time, the water vapour condensed into water and created the oceans . The ocean then gradually removed some of the CO2 in the air by absorbing it.

3.5 billion years ago, the first signs of life occurred somehow and they could carry out photosynthesis which removed CO2 from the air and replaced it with oxygen. Oxygen levels continued to rise and Co2 levels fell.

More complex organisms evolved and CO2 from the ocean became CO3 (carbonate) in the shells and skeletons of these animals. These shells and skeletons, along with plant waste, all contained CO2 and over millions of years formed sedimentary rocks containing locked away carbon - a carbon sink. These are the fossil fuels we use today but they are running out.

GCSE chemistry unit 1 - plate tectonics

Plate tectonics

The Earth's structure
  • The atmosphere - 10km thick (mostly)
  • The crust - 5-70km thick)
  • The mantle - 3500km thick 
  • The core (inner and outer) - 3500km thick
Plate tectonics

1915, Alfred Wegener proposed continental drift. He noted that continents fit together like a jigsaw and found that, where they supposedly met, the rocks and fossils are identical. He could not explain, however, how this happened so his proposal was rejected.

Nowadays we accept the theory because we have found that the plates moved, and continue to move, due to radioactive processes in the core that produce heat which leads to convection currents in the mantle. The convection currents move the plates by about a centimetre a year.

Volcanoes can form where the plates move away from each other or one subsides (goes under the other).
Mountains are formed when plates move towards each other and buckle upwards.
Earthquakes occur when plates slide past each other.

It is difficult to predict exactly when earthquakes and volcanic eruptions will occur.

GCSE chemistry unit 1 - plant oils

Plant oils

Oils from plants are useful:
  • They contain nutrients and energy
  • Give a much higher energy content to food
  • Give different flavours to food
  • Are used in cosmetics
  • Can be used in biofuels (more renewable fuels)
They can be made in two ways:
  • STEAM DISTILLATION
  • OR PULPING THE FRUIT

Steam distillation



















As the plant material and water is heated, the plant oils and steam is evaporated but then condenses when it reaches the cooling jacket. The products are two separate liquids: water and plant oil. It is simple to separate them because they are not mixed.


Pulping the fruit

Plant or fruit is crushed to a pulp and then squeezed. The squeezed oils are purified, removing water and impurities and is now pure oil. The pulp or seed left over are dissolved in a solvent to create oil. The solvent and oil are then separated to create even more pure oil. There is little waste.

GCES chemistry unit 1 - saturated and unsaturated fats/oils

Saturated and unsaturated fats(solid) and oils(liquid)

Saturated
  • Solid at room temperature
  • Higher melting point
  • Come from animals (e.g butter)
  • Less healthy (build up cholesterol)
  • NEVER HAS A DOUBLE BOND
  • E.g alkane
Unsaturated
  • Liquids at room temperature
  • Lower melting point (due to double bond)
  • From plants (e.g olive oil)
  • More healthy
  • ALWAYS HAS ONE OR MORE DOUBLE BONDS
  • E.g alkene
Test for unsaturated fats
In bromine water, an unsaturated fat will turn the bromine water colourless and if it's a saturated fat, the solution will stay browny, orange.

Turning an unsaturated fat into an almost saturated fat

React the unsaturated fat (containing hydrocarbon chains) with hydrogen at 60 degrees. The double bonds break as the hydrogens join the hydrocarbons. 
Add a nickel catalyst to speed up the reaction.
It creates an almost saturated molecule
DOSEN'T GET RID OF ALL THE DOUBLE BONDS BUT MOST OF THEM (it's still healthier than fully saturated)

This almost saturated product can be turned into low fat butters as they now have a higher boiling point so are solid at room temperature. They are also great for making cakes. They are a healthier than fully-saturated products.

GCSE chemistry unit 1 - emulsions

Emulsions

An emulsifier helps water and oil mix by suspending oil droplets throughout the water. They create EMULSIONS.

Emulsions are:
  • More viscous (thicker)
  • Better at coating things
  • Have a better texture
  • Because of this, emulsifiers are added to make products such as paint, mayonnaise, salad dressing, ice cream, milk and cosmetics.
  • Egg yolk is an example of a good emulsifier
Molecules of an emulsifier look like this:


The hydroPHOBIC tail repels water (just remember phobia means you're scared of something).

The hydroPHILIC head is attracted to water.

So when added to a substance contains oil and water the molecules surround the oil droplets, the tails in the oil droplet, repelling the water and the heads in the water.

This suspends the oil droplets throughout the water so they appear to be mixed, like below:




GCSE chemistry unit 1 - ETHANOL (alcohol)

Ethanol

Uses
  • Used in alcoholic drinks
  • Disinfectants (kills microbes)
  • Perfumes
  • Fuels (because it as originally part of a cracked hydrocarbon that came from crude oil)
Can be made in 2 ways:
  1. FERMENTATION
  2. REACTING ETHENE (alkene) WITH STEAM (water)

Fermentation

Sugar (glucose), yeast (microorganism) are placed in a container and water is added to help them mix easily. The yeast converts the glucose into ethanol, shown in the equation below:

GLUCOSE --------- ETHANOL + CARBON DIOXIDE

(the CO2 comes from the yeast respiring)

This can be carried out on a huge scale and the ethanol can then be purified.

Hydration (reacting ethene with water)

ETHENE + WATER (in the form of steam) ------(300 degrees)------- MAKES JUST ETHANOL

The hot temperature is a catalyst and speeds up the reaction.

Comparison

Fermentation
  • Much cheaper
  • Happens at low temperatures (no cost of heating)
  • Produces carbon dioxide which adds to the greenhouse effect
  • Lots of land is needed to grow crops that produce glucose (land that could be used for something else)
Hydration
  • No carbon dioxide produced
  • Quicker
  • Less people needed to complete the process
  • Expensive - equipment, high temperatures + energy used
  • Uses ethene (part of crude oil) which is running out ( non-renewable)

Wednesday 19 February 2014

GCSE chemistry - unit 1 - making polymers and polymerisation

Making Polymers and Polymerisation

ALKENES
  • Double bond
  • Gas
  • Very flammable so could be used as a fuel BUT...
  • They can join their individual molecules (MONOMERS) together to make POLYMERS
  • This makes plastic which is much more useful

The bracket and n just means that depending on how many monomers you get, the size of the polymer will vary. YOU WILL ALWAYS GET THE SAME NUMBER OF CARBONS AND HYDROGENS THEY WILL JUST BE JOINED WHEN THE DOUBLE BOND BREAKS.

Polymers (plastics)
  • Very useful
  • Lots and lots of uses (packaging etc.)
  • Taken to landfill and can't decompose because they're very unreactive (this is bad)
  • Scientists are working on biodegradable polymers by adding corn starch which bacteria can feed off and break down
  • These new cornstarch polymers will reduce that amount of pollution caused by polymers
  • Polymers can also be re-used to cause less harm to the environment
Uses for polymers
  • Food packaging - can let carbon dioxide out and oxygen in
  • Fabric coating (protective layer)
  • Breathable fabrics like vortex with let's out sweat and keeps out rain
  • HYDROGELS - absorbs a lot of moisture so good for wounds
  • SHAPE MEMORY POLYMERS, when heated, go back to their original shapes (good for glasses, car bumper etc.)

GCSE chemistry - unit 1 - cracking alkanes to make alkenes

Cracking alkanes to make alkenes

Short chain hydrocarbons (alkanes) are very useful. Especially for fuels.
Long chain hydrocarbons (alkanes) aren't as useful.

WE CRACK A LONG ALKANE TO MAKE A SHORTER ALKANE AND AN ALKENE


The wool is soaked in paraffin (made up of long hydrocarbons/alkanes). This evaporates at the start and when it meets the porcelain bits (the catalyst) it THERMALLY DECOMPOSES (breaks down chemically because of heat). The product is a gas made up of a shorter ALKANE and an ALKENE, seen below:


The shorter hydrocarbon is much more useful as it has a higher flammability and can now be added to petrol.
The ALKENE contains a double bond therefore it's UNSATURATED

The test for unsaturated (ALKENE) hydrocarbons

Bromine water turns colourless when it meets unsaturated hydrocarbons but stays orange when it meets saturated hydrocarbons (without double bonds - alkanes)


GCSE chemistry - unit 1 - burning hydrocarbon fuels

Burning Hydrocarbon Fuels

NEEDED FOR: 
  • Transport
  • Electricity
  • Heating
BAD BECAUSE:
  • Sulfur dioxide is created and contributes to acid rain
  • Nitrogen from the air reacts and also causes acid rain
  • Soot are tiny fragments of carbon that reduce the amount of light that reaches earth (GLOBAL DIMMING)
  • When burnt, carbon becomes oxidised to make carbon dioxide which leads to global warming
  • INCOMPLETE COMBUSTION (not enough oxygen) leads to carbon monoxide (poisonous gas)
  • Crude oil is running out
  • not CARBON NEUTRAL (see below)
There is a solution however...

Biofuels (biodiesel and ethanol)

Biodiesel and ethanol are made from plant material. They are both CARBON NEUTRAL because plant pull in the carbon dioxide through photosynthesis and, when burnt, put the same amount into the air again (no more carbon is put into the air).
  • Labour intensive process so provides lots of jobs
  • Low technology and energy use so a lot cheaper
  • Carbon neutral, renewable and sustainable
  • Using a lot of land that could be used for growing food crops
  • What would we do if there were massive crop failures?
  • A very slow process 
  • Habitat destruction to grow crops so reduction in biodiversity
ETHANOL is produced by the fermentation of sugared cane and is a fuel suitable for cars.




Tuesday 18 February 2014

GCES chemistry - unit 1 - crude oil

Crude Oil

Crude oil is made up of remains of sea creatures, decomposing under the sea bed with no exposure to air and is deeply buried in rock under the sea. In the sea, pipelines supply crude oil to oil rigs which is then pumped into oil tankers which take it to be processed.

Crude oil is a thick, black and stickler liquid and is a mixture of lots of different compounds. Because it is a mixture, it is easily separated because the compounds are not chemically bonded.

Separating these compounds - FRACTIONAL DISTILATION
  • The different compounds in the crude oil have different boiling points
  • The compounds are called hydrocarbon molecules (made of hydrogen and carbon)
  • The smallest hydrocarbons have the lowest boiling and cooling points
  • The smallest are also highly flammable so are good for fuels
  • The longest have low flammability and a high boiling and cooling point
In a fractionating column, crude oil vapour is pumped into the bottom where the temperature is the hottest and the larger molecules feed off as they cool at the higher temperatures. The temperature at the top is the lowest so this is where the smaller hydrocarbons condense and feed off (the thinner fuels)



Alkanes

These hydrocarbons are called ALKANES which contain NO double bonds and have a general rule for the number of carbon to hydrogen ratio... Cn H2n+2 so if you have 2 carbons you will have double that, add two = 6 hydrogens. They are SATURATED because they have no double bonds.

The first four shortest alkanes are METHANE, ETHANE, PROPANE, BUTANE.




GCSE chemistry - unit 1 - alloys

Alloys

An alloy is a mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain.
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder than the pure metal.

ALLOYS ARE NOT CHEMICALLY BONDED THEY ARE JUST MIXED 

Example
Iron is produced in a blast furnace with coke, limestone and iron oxide (from iron ore) in it. The coke contains carbon which takes the oxygen away from the iron oxide to leave just iron. This is called REDUCTION (loss of oxygen)
The iron produced is called impure pig iron and has to be purified to make it stronger.
Scientist can also control the amount of carbon they put in it to form STEEL.
LOW CARBON STEEL has 0.4% carbon and is easy to shape and not as brittle (easily broken) 
HIGH CARBON STEEL has 1.5% carbon and is resistant to corrosion, is harder but is more brittle

If we mix chromium with iron however we get stainless steel which does not corrode, rust or react.

Most metals are really soft in pure form and have limited use. We add copper to gold and aluminium to make them. Iron is the exception where you can add carbon to form steel.


GCSE chemistry - unit 1 - extracting metals

Extracting Metals

Metals are very useful as so many thing are made out of it. Metals are found in metal ores (rock with large amounts of the metal of interest; enough metal to make it worth while)

The metal ore contains impurities  and the actual metal is chemically combined with substances (usually oxygen).

First we CONCENTRATE the metal ore (basically get rid of any impurities) by SMELTING (heating) it.

The metal ore without impurities then under goes either DISPLACEMENT or ELECTROLYSIS to remove what it is chemically combined with; mostly oxygen)

All of this will happen only if the metal that is produced is worth more than the cost of getting it out if the ore (A HIGH GRADE ORE). If it is not worth while, they need to find a cheaper way of extraction or one that gets more of the metal out. If not, it's not worth it.

The reactivity series

Potassium              MOST REACTIVE
Sodium
Calcium
Magnesium
Aluminium
-----------------
*carbon*
-----------------
Zinc
Iron
Tin
Lead
Copper
Silver
Gold                      LEAST REACTIVE

If the metal is LESS reactive than carbon they undergo DISPLACEMENT. This means they are reacted with carbon and because the carbon is more reactive than them, it will take away the oxygen the the metal is bonded with to leave the metal and carbon dioxide. This is the cheaper of the two.

If the metal is MORE reactive than carbon they undergo ELECTROLYSIS because carbon is less reactive than theses metal so won't be able to steal the oxygen from them. Electrolysis uses electricity to separate the metal away from the oxygen.

IT IS IMPORTANT TO NOTE THAT GOLD IS SO UNREACTIVE THAT IT IS FOUND NATIVE IN THE GROUND (DOES NOT NEED TO BE EXTRACTED)

E.g. COPPER EXTRACTION

ELECTROLYSIS - a negative and positive electrode are placed in the melted ore solution (IN COPPER'S CASE IT IS CHEMICALLY BONDED WITH SULFUR NOT OXYGEN). The sulfur and copper have bonded ionically so the copper is made up of positive ions and the sulfur, negative ions. The positive copper ions are attracted to the negative electrode so is now separated and can be purified. Salt is left at the positive electrode.

DISPLACEMENT - scrap iron (more reactive than copper) removes the sulfate from the copper sulfate and the copper coats itself around the iron which can be easily removed and purified. This is a lot cheaper

The problem is, there's a shortage of high grade copper ores. We can use PHYTOMINING and BIOLEACHING  to extract copper from low grade ores (containing less than 1% copper) and then use electrolysis and displacement as usual after.

Phytomining

  • Grow certain type of plant on land with low grade copper ore in it
  • Plants take copper compounds into their body tissue
  • Burn plants to leave ash that contains copper which can be extracted by electrolysis or displacement
Bioleaching
  • Use certain bacteria to grow on the low grade copper ore to use it as a source of nutrition
  • The bacteria produce a byproduct solution containing copper
  • The solution goes through electrolysis or displacement to extract the copper






GCSE chemistry - unit 1 - calcium carbonate (limestone)

Calcium Carbonate (Limestone)

Uses of limestone

  • Building and statues (strong and durable rock with a nice colour)
  • Can be crushed, mixed with clay and heated to make cement
  • Can add sand to cement to make mortar (like cement, hard and strong once set and lasts for a long time)
  • If you add aggregate (small pebbles) to mortar you get concrete
  • So LOTS of uses as BUILDING MATERIALS
Quarrying
  • Limestone is a rock so is found in the ground and has to be quarried
  • This involves using explosives and heavy mechanical equipment which creates noise dust and pollution
  • It spoils the landscape + habitats
  • The land is ruined so much that it can't be used again
  • It produces a valuable material (limestone)
  • Positive economic impact in the area
  • Creates employment in the local area
Limestone cycle



Thermal decomposition (seen above)

HAPPENS TO OTHER CARBONATES (CO3)

We see above that Calcium carbonate, when heated, makes calcium oxide and it also makes carbon dioxide.

Other carbonates do exactly the same thing:
  • Copper carbonate, when heated, makes copper oxide and carbon dioxide
  • Zinc carbonate, when heated, make zinc oxide and carbon dioxide 
  • Magnesium carbonate, when heated, makes magnesium oxide and carbon dioxide
  • Etc.

GCSE chemistry - unit 1 - covalent bonding

Covalent Bonding

A chemical bond between two or more non-metal atoms (these can be from the same element or from different elements as long as they are both non-metals.)

It involves the sharing of an electron. If both atoms need on electron to get a full outer shell they share an electron and become joined. They share a pair of electrons and now both have a full outer shell.




More than one other atom can join to one atom; if an atom need two electrons, two other atoms will join to share two pairs of electrons. In this case the two atoms will be different to the atom needing two electrons. See above right.

These are all now SIMPLE MOLECULAR COMPOUNDS with strong bonds. However covalent bonding can also form giant covalent structures such as diamonds or graphite.

Chemistry AQA - unit 1 - ionic bonding

Ionic Bonding

A chemical reaction between a metal and a non-metal.

Atoms from group 7 in the periodic table are very reactive because they have 7 electrons in their outer shell and need just one more to become stable; because all atoms want to become stable. Similarly atoms in group one and two are very reactive because they are so close to a full outer shell they just need to loose one electron.

Therefore if one needs and electron and the other wants to get rid of an electron a transfer of electron happens. The non-metal (e.g halogen) always gains the electron because it it so close to a full shell and the metal always looses because it needs to get rid of one to show the full shell underneath.

METAL ALWAYS LOOSES THE ELECTRON
NON-METAL ALWAYS GAINS THE ELECTRON

Because the metal has lost an electron, it overall charge is now positive because it has more protons than electrons. And because the non-metal has gained an electron it has an overall negative charge. We say they've formed negative/positive ions. An ion is an atom that's lost or gained an electron.

METAL BECOMES POSITIVE ION
NON-METAL BECOMES NEGATIVE ION

This can happen with one or more electron. If the metal looses one electron it has a charge of +1 and if it looses two it has a charge of +2. And the same for the non-metal but with a minus charge.

The positive and negative ions then attract (opposites attract) and this creates strong bonds into a ionic lattice and structure formed by strong attraction.

The new structure is stable as there is no need for it to react because both of its substances have full outer shells.

Monday 17 February 2014

CHEMISTRY - unit 1 - the periodic table

CHEMISTRY - UNIT 1

The periodic table - shows the elements in order of increasing atomic number

Elements in the same group in the periodic table have similar chemical properties. This is because their atoms have the same number of electrons in their outer shells.




GROUP 1 - alkali metals

  • Low melting and boiling points
  • Low densities
  • React quickly with water and oxygen to produce hydroxides and oxides
  • Their hydroxides and oxides dissolve in water to form strong alkali solutions.

GROUP 0 - noble gasses
  • Very unreactive because they have full outer shells

All atoms want complete outer shells. Atoms in group 1 are very reactive because they want to get rid of their single outer electron (this would be easier than trying to get seven more). They are more reactive than transitional metals because they are closer to a full shell. Halogens are equally very reactive because they only need one electron to get a full outer shell. Noble gasses are very unreactive because they have a full outer shell so don't need to react. They are stable.

CHEMISTRY - unit 1 - basic ideas of chemistry


CHEMISTRY - UNIT 1 ATOMS


Atoms consist of ELECTRONS surrounding a nucleus containing PROTONS and NEUTRONS.

  • NEUTRONS are neutral
  • PROTONS have a charge of +1
  • ELECTRONS have a charge of -1


The number of electrons is equal to the number of protons so atoms have no overall charge.

All substances are made up of these tiny particles called atoms.
  • An element is made up of only one type of atom.
Structure of atoms

ATOMIC NUMBER is the number of protons an atom contains (therefore the number of electrons)
MASS NUMBER is the total number of protons and neutrons in the nucleus (usually the bigger no.)


E.g          35
                   Cl    has 17 protons and 35 protons                    ...............................and neutrons.
                17
    
      Chlorine therefore has 18 neutrons (35-17)



Periodic table - shows the elements in order

(part of the periodic table)

  • The horizontal rows are periods and show the number of shells an atom has
  • The vertical columns are groups and show how many electrons an atom has in its outer shell
Therefore all elements in period 4 have atoms that have 4 occupied shells and all elements in group 3 have atoms that have 3 electrons in their outer shell.



Electronic structure

The shells around atoms are energy levels.
The innermost shell can hold 2 electrons and the rest can hold 8, so we write 2,8,8,8 etc. depending on how many electrons an atom has (shown by the atomic number)

If sodium (Na) has an atomic number of 11, it has 11 electrons. We show it's electronic structure as 2,8,1 
  • 2 electrons in the first shell (can only hold 2)
  • 8 electrons in the second shell (can only hold 8)
  • And 1 electron in the third shell (only 1 electron left)
Sodium will be found in group 1 because it has 1 electron in its outer shell.


The electronic structure diagram for sodium will be:



Use the periodic table to work out electronic structures:
  1. Work out the period (rows) and draw that many circles (shells)
  2. Look at the atomic number (bottom one) and draw on dots.  2 in the first and 8 from then on.