Untitled

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Atoms, elements and compounds

compound- make from more that one element

chemical symbols represent atoms

element- made from one type of atom

all substances are made from atoms

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Atomic structure

atomic number is equal to the number of protons

mass number is sum of protons and neutrons

mass number - atomic number = number of neutrons

nucleus made up of protons and neutrons

elements arranged a periodic table in order of proton number

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Charge

atoms have a overall charge of 0

protons- positive

neutrons- neutral

electrons negative

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Arrangement of electrons in atoms

noble gases (group 0) are very nonreactive

elements in the same group have the same number of electrons in their outer shell

electrons are arranged in shells around the nucleus

shell 1 holds 2 electrons

shell 2 and 3 holds 8 electrons

shell 1 is closest to the nucleus

electrons fill from shell 1 first

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Forming bonds

formula of ionic compounds shows the ratio of ions

nonmetals bond covalently to form molecules

metals bond with nonmetals ionically

ion- charged particle

formula of a molecule shows atoms in a molecule

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Chemical equations

during reactions, atoms get rearranged

but never created destroyed or charged

Mass of reactants + mass of products

word equations state the name of reactants and products,

where as symbol equations give formulas

symbol equations should always be balanced

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Concrete

cement aggregate, sand and water

used to make calcium oxide

used to make building material

used to make cement

Cement and concrete

concrete is made by mixing (small stones) into mortar

mortar is made by mixing cement, sand and water

cement is made by heating clay and limestone in a kiln

product is then ground to a powder

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Limestone

limestone is calcium carbonate (CaCo2)

limestone decomposes when heated

thermal decomposition- the temperature when a substance chemically decomposes

Limestone issues

Quarrying and processing limestone

Advantages

improved roads

more employment and local job opportunities

increased trade

Disadvantages

dust and noise

loss of habitat

more traffic

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Limestone reaction cycle

Thermal decomposition of calcium carbonate to form calcium oxide and carbon dioxide (CaCo3s = CaOs + CO2g)

Hydration of calcium oxide to form calcium hydroxide (CaO + H2O = Ca(OH)2 ) calcium hydroxide is an alkali used to neutralize acids such as acidic soil

Dissolving of calcium hydroxide to form calcium hydroxide solution (CaO +H2O = Ca(HO)2 )

Carbonate dioxide added to form calcium carbonate precipitate (Ca(HO)2 + CO2 = CaCO2 + H2O

metal carbonates decompose when heated to produce metal oxide and carbon dioxide

carbon dioxide turns calcium hydroxide (lime water) cloudy, by forming insoluble calcium carbonate

(Carbonate + acid = salt + water + carbon dioxide

Reaction of carbonates

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Extracting metals

nonreactive metals can be found in the earth as metal

metals are usually found in the earths crust, often as compounds with other elements such as oxygen

metal oxides, where the metal is less reactive than carbon, can be reduced by carbon

ore- metal compounds containing enough metal to make extracting it worth while

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Metallic issues

Using metals in construction

Advantages

Malleable

Ductile

good conductors of heat and electricity

strong

Disadvantages

can rust

more expensive than other materials

uses limited resources

Useful metals

most metals we use are alloys

Central block of the periodic table are the transition metals

transition metals have useful properties such as being strong yet malleable

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Iron and steels

blast furnace is too brittle to use

most iron is converted into alloy, steels

steel contains calculated quantities of carbon and other elements

Aluminium and titanium

resist corrosion

have to be extracted by electrolysis

extraction is expensive due to the large amount of energy needed

lower densities than other strong materials

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Extracting copper

copper can be extracted from solutions by displacement or electrolysis

most copper is extracted from ores by smelting

copper is then purified by electrolysis

copper rich ores and are a limited resource so scientists are finding new ways or sourcing copper

bio-leaching uses bacteria to produce copper compound solutions

phytomining using plants to absorb copper compound, which are collected from from the plants ashes

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Crude oils and fuels

alternative fuels

cleaner fuels

fractional distillation

fuels from crude oil

burning fuels

Fuels from crude oil

crude oil is a mixture of many compounds

most of the compounds in crude oil are hydrocarbons- only contain hydrogen and carbon

distillation separates a mixture of liquids

alkanes are saturated hydrocarbons meaning there as many hydrocarbons as possible in the molecule

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Crude oil is mostly alkanes

methane: formula: CH4

ethane: formula: C2H6

propane: formula: C3H8

butane: formula: C4H10

alkanes all have the general formula CnH2n+2

e.g if an alkali has 5 carbons, its got to have (2*5)+2 = 12 hydrocarbons

the shorter the molecule, the more runny the hydrocarbon is - that is, less gloopy

the shorter the molecules, the more volatile they turn into a gas a lower temperature, so the shorter the molecules, the lower temperature

at which the fraction vaporizes or condenses and the lower its boiling point

shorter the molecules, then more flammable the hydrocarbon is

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Fractional distillation

crude oil can be separated into fractions by fractional distillation

properties of these fractions depend on molecule size

fractions with lower boiling points are less viscous and more flammable

Burning fuels

burning hydrocarbons produces carbon dioxide and water

when burnt sulfur compounds produce sulfur dioxide and nitrogen compounds from nitrogen oxides

both can cause acid rain

burning hydrocarbons in a limited air supply causes incomplete combustion and may produce carbon monoxide and soot.

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Products from oil

ethanol

cracking hydrocarbons

new and useful polymers

making polymers from alkenes

plastic waste

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Plant oils

food issues

everyday emulsions

cooking with vegetable oil

extracting vegetable oil

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Our changing planet

gases in the atmosphere

carbon dioxide in the atmosphere

structure of the earth

restless earth

earths atmosphere in the past

life on earth

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Increasing carbon dioxide causes climate change

the level of carbon dioxide in the atmosphere is increasing

because of the fossil fuel humans burn

extra carbon dioxide has caused the average temperature of the earth to increase- global warming

global warming is a type of climate change and causes other types of climate change

e.g changing in rainfall patterns, its could also cause severe flooding due to polar ice caps melting

Particles cause global dimming

25% less sunlight has been reaching the surface compared to 50 years ago. They have called it global dimming

this is caused by particles of soot an ash are produced when fossil fuels are burnt

these particles reflect sunlight back into space, or they can help to produce more clouds that reflect the sunlight back into space

Alternative fuels are being developed

Ethanol: can be produced from plant material so is known as bio fuel. Its made by fermentation of plants and is used to power cars in some places. Its often mixed with petrol to make a better fuel.

pros:

CO2 released when burnt was taken in by the plant as it grew. so if its carbon neutral. the only other product is water

cons:

engines need to be converted before they'll work with ethanol fuels. And ethanol fuel isn't widely available. There are worries that as demand for it farmers will switch from growing food crops to growing crops to make ethanol- this will increase food prices

Bio diesel: is another type of bio fuel. It can be produced from vegetable oils such as rapseed oil and soybean oil. Bio diesel can be mixed with ordinary diesel fuel and used to run a diesel engine.

pros:

bio diesel is carbon neutral. Engines don't need to be converted. It produces much less sulfur dioxide and particulates that ordinary diesel or petrol

cons:

we make enough to completely replace diesel. Its expensive to make. It could increase food prices like using more ethanol could.

Hydrogen gas: can also be used to power vehicles. You get the hydrogen from the electrolysis of water, it takes electrical energy to split it up. This energy can come from a renewable source e.g solar

pros:

hydrogen combines with oxygen in the air to form just water- so its clean

cons:

you need a special, expensive engine and hydrogen isn't widely available. you still need to use energy from another source to make it. Also, hydrogen is hard to

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Environmental problems

burning fuels releases gases and particles

power stations burn huge amounts of fossil fuels to make electricity

most fuels, such as crude oil and coal, contain carbon and hydrogen

during combustion, the carbon and hydrogen are oxidized so that carbon dioxide and water vapor are released into the atmosphere

e.g hydrocarbon+oxygen - carbon dioxide+water vapor

if the fuel contains sulfur, the sulfur will be released into the atmosphere as sulfur dioxide when the fuel is burnt

oxides of nitrogen will also form if the fuel burns - this is called complete combustion

if there isn't enough oxygen, some of the fuel doesn't burn - this is called partial combustion

when this happens, solid particles of soot (carbon) and non burnt fuel are released

carbon monoxide ( a poisonous gas ) is also released

Sulfur dioxide

sulfur dioxide is one of the gases that caused acid rain

when the sulfur dioxide mixes with clouds it forms dilute sulfuric acid. this then falls as acid rain

in the same way, oxides of nitrogen cause acid rain by forming dilute nitric acid in clouds

acid rain can cause lakes to become acidic and many plan ts and animals die as a result to it

acid rain kills trees and damages limestone buildings and ruins stone statues

the benefits of electricity and travel have to be balanced against the environmental impacts

governments have reduced emissions of air pollutants such as sulfur dioxide

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Cracking crude oil

Cracking means splitting up long-chain hydrocarbons

longer molecules produced from fractional distillation are turned into smaller ones, by a process called cracking

products of cracking are useful as fuels e.g petrol for cars, and paraffin for jet fuel

cracking also produces substances like ethene, which are needed

for making plastics

By passing over a hot catalyst

cracking is a thermal decomposition reaction- breaking molecules down by heating them

the first step is to heat the long-chain hydrocarbons to vaporize it (turn into gas)

then the vapor is passed over a powdered catalyst at a temperature of about 400c - 700c

aluminium oxide is the catalyst used

the long-chain molecules split apart or crack on the surface of the specks of catalyst

vaporized kerosene - aluminium oxide - octane + ethane

most if the products of cracking are alkanes and unsaturated hydrocarbons called alkenes

long - chain hydrocarbon molecule - shorter alkane molecule + alkene

e.g kerosene (ten c atoms) - octane (eight c atoms) + ethene (two c atoms)

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Alkenes have a c=c double bond

alkenes are hydrocarbons that have a double bond between two of the carbon atoms in their chain

they are also known as unsaturated because they can make more bonds- the double bond can open up

allowing the two carbons atoms to bond with other atoms

the first two alkenes are ethene (with two carbons) and propene (three c's)

all alkenes have the general formula CnH2n they have twice as many hydrogen's as carbon

Ethene: formula: C2H4

Propene: formula: C3H6

you can test for an alkene by adding the substance to bromine water.

an alkene will decolorize the bromine water, turning it form orange to colorless

this is because the double bond has opened up and formed bonds with the bromine

Ethene can be reacted with steam to produce ethanol

ethene (C2H4) can be hydrated with steam (H20) in the presence of a catalyst to make ethanol

at the moment thus us a cheap process, because ethene's a fairly cheap and not much of it is wasted

ethene's produces from crude oil, which is a non-renewable resource that could start running out fairly soon.

This means that using ethene to make ethanol will become very expensive

Ethanol can be produced by non-renewable resources

the raw material for fermentation is sugar. This is converted into ethanol using yeast

the word equation for this is: sugar - carbon dioxide + ethanol

this process needs a lower temperature and simpler equipment than when using ethene

another advantage is that raw material is a renewable resource

sugar is grown as a major crop in parts of the world, including poor countries

the ethanol produced this way can also be used as quite a cheap fuel in countries which don't have oil reserves for making countries

there are disadvantages, the ethanol you get from this process isn't very concentrated

so if you want to increase it's strength you have to distil it (as in whiskey distilleries) it also needs to be purified

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Polymers

Alkenes can be used to make polymers

polymerization is the process of joining small alkene molecules (monomers) to form large- chain molecules called polymers

many ethene molecules can be joined up to produce poly(ethene)

many monomers - pressure + catalyst - polymers

Different polymers have different physical properties

the physical properties of a polymer depend on what it's made from

polyamides are usually stronger than poly(ethene)

e.g a polymers physical properties are also affected by the temperatures and pressure of polymerization

poly(ethene) made at 200c and 2000 atmospheres pressure is flexible, and has low density.

but poly(ethene) made at 60c and a few atmospheres pressure with a catalyst is rigid and dense

Polymers are suitable for different uses

light, stretchable polymers such as low density poly(ethene) are used to make plastic bags

elastic polymer fibres are used to make super-stretchy Lycra fibre for tights

new uses are developed all the time. Waterproof coatings for fabrics are made of polymers

dental polymers are used in resin tooth-fillings. Polymer hydro-gel wound dressing keep wounds

new biodegradable packaging materials made from polymers and cornstarch are being produced

memory foam is an example of a smart material. It's a polymer that gets softer as it gets warmer

mattresses can be made of memory foam- they mould your body shape when you lie on them

polymers are cheap and don't rot

most polymers aren't biodegradable they're not broken by microorganisms, so they don't rot

it's difficult to get rid of them- if you bury them in a landfill site, they'll still be there years later

the best things is to re-use them as many times as possible and then recycle them of you can

things made from polymers are usually cheaper than things made from metal

however, as crude oil resources get used up, the price of crude oil will rise.

crude oil products like polymer will get dearer

there won't be enough oil for fuel and plastics and all other uses, choosing how to use the oil that's left

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Plant oils

Extract oils from plants

some fruits and seeds contain a lot of oil. e.g avocados and olives are really oily fruits.

Brazil nuts, peanuts and sesame seeds are oily seeds

these oils can be extracted and used for food or fuel

to get the oil out, the plant material is crushed

the next step is to press the crushed plant material between metal plates and squash the oil out

this is the traditional method of producing olive oil

oil can be separated from crushed plant material by a centrifuge - rather like a spin dryer to get water out of wet clothes

or solvents can be used to get oil from plant material

distillation refines oil, and removes water, solvents and impurities

Vegetable oils are used in food

vegetable oils provide a lot of energy- they have a very high energy content

there are other nutrients in vegetable oils. .e.g oils from seeds contain vitamin E

vegetables oils contain essential fatty acids, which the body needs for many metabolic processes

Vegetable oils have benefits for cooking

vegetable oils have higher boiling points than water

this means they can be used to cook foods at a higher temperature and faster speeds

cooking with vegetable oil gives a food a different flavor

this is because of the oil's own flavor

but it's also down to the fact that many flavors come from chemicals that are soluble in oil.

this means that the oil carries the flavor, making it seem more intense

using oil to cook increases the energy we get from eating

Vegetable oils can be used to produce fuels

vegetable oils such as rapseed oil and soy bean oil can be processed and turned in to fuels

because vegetable oils provide a lot of energy they're really suitable for use as fuels

a particularly useful fuel made from vegetable oils is called bio-diesel

bio-diesel has similar properties to ordinary diesel fuel- it burns in the same way, so you can use it to fuel a diesel engine

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More plant oils

Unsaturated oils contain c=c double bonds

oils and fats contain long-chain molecules with lots of carbon atoms

oils and fats are either saturated or unsaturated

unsaturated oils contain double bonds between some of the carbon atoms in their carbon chains

so, and unsaturated oil will decolorize bromine water

monounsaturated fats contain one c=c double bond in their carbon chains

polyunsaturated fats contain more than on c=c double bond

Unsaturated oils can be hydrogenated

unsaturated vegetable oils are liquid at room temperature

they can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60c

this is called hydrogenation, the hydrogen reacts with the double-bonded carbons and opens out the double bonds

hydrogenate oils have higher melting points than unsaturated oils, so they're more solid at room temperature

this makes them useful as spreads and for baking cakes and pastries

margarine is usually made from partially hydrogenated vegetable oil

turning all the double bonds in vegetable oils to single bonds would make margarine to hard and difficult to spread

hydrogenating most of them gives margarine a nice, buttery, spreadable consistency

partially hydrogenated vegetable oils are often used instead of butter in processed foods

e.g biscuits. These oils are cheaper than butter and they keep longer

this makes biscuits cheaper and gives them a long shelf life

but partially hydrogenated vegetable oils means you end up with a lot of trans fats

there's evidence to suggest that trans fats are very bad for you

Vegetable oils in foods can affect health

vegetable oils tend to be unsaturated, while animal fats tend to be saturated

saturated fats are less healthy than saturated fats as saturated fats increase the amount of cholesterol in the blood

which can block up the arteries and increase the risk of heart disease

natural unsaturated fats such as olive oil and sunflower oil reduce the amount of blood cholesterol

because of the trans fats, partially hydrogenated vegetable oils increases the amount of cholesterol in the blood

eating a lot of foods made with partially hydrogenated vegetable oils can actually increase the risk of heart disease

cooking food in oil, whether saturated, unsaturated or partially hydrogenated, makes it more fattening

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Emulsions

Emulsions can be made from oil and water

oils don't dissolve in water

however, you can mix an oil with water to make and emulsion

emulsions are made up of lots of droplets of one liquid suspended in another liquid.

you can have an oil-in-water emulsion (oil droplets suspended in water)

or a water-in-oil emulsion (water droplets suspended in oil

emulsions are thicker than either oil or water

e.g mayonnaise is an emulsion of sunflower oil or olive oil and vinegar- it's thicker than either

the physical properties of emulsions make them suited to lots of uses in food

e.g salad dressings and in sauces

a salad dressing made by shaking olive oil and vinegar together forms an emulsion that coats salad better than plain oil or vinegar

the more oil you've got in an oil-in-water emulsion the thicker it is

milk is and oil-in-water emulsion with not much oil and a lot of water- there's just about 3% oil in full-fat milk

single cream has a bit more oil - about 18%

double cream has a lot of oil- nearly 50%

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Plate tectonics

Alfred Wegner came across some work listing the fossils of a similar

planet and animals which had been found on opposite sides of the Atlantic ocean

and found other cases of very similar fossils on opposite sides of oceans

there have been land bridges linking the continents so animals had been able to cross

the bridges had sunk or been covered since then

the coastlines of Africa an south america seemed to match like the pieces of a jigsaw

he thought that these two continents had previously been one continent split

there were matching layers in the rocks

fossils have been found in wrong places

in 1915 Wegner had found enough evidence

300 million years ago there, was just on super continent

this landmass, Pangaea broke into smaller chunks and which moved moved apart

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The earths structure

the crust is very thin and is surrounded by the atmosphere

below that is the mantle

the mantle has all the properties of a solid

in the mantle radioactive decay take place this produces a lot of heat

which can cause the mantle to flow in convection currents

at the center of the earth is the core

which is said to be made of nickel

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The earths surface is made up of tectonic plates

the crust and upper part of the mantle are cracked

in to a number of large pieces called tectonic plates

the plates don't stay in one place though, they move around

because of convection currents in the mantle which causes the plates to drift

most of the planets move at speeds of a few cm a year

occasionally the plates move suddenly causing an earthquake

volcanoes and earthquakes often occur at boundaries between two tectonic plates

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Evolution of atmosphere

Phase 1- volcanoes gave out gases

the earths surface was molten for many years

things cooled down and a thin crust formed, but volcanoes kept erupting

the volcanoes gave out a lot of gas because of how the oceans and atmosphere were formed #

the early atmosphere was mostly CO2 with no oxygen

was may have been water vapor and small amounts of methane and ammonia

oceans were formed when the water vapor condensed

Phase 2- Green plants evolved and produced oxygen

green plants and algae evolved over most of the earth

they liked the CO2 atmosphere

the early CO2 dissolved into the oceans

the green plants and algae absorbed the CO2 and produced O2 by photosynthesis

plants and algae died and were buried under layers of sediment

along with skeletons and shells of marine organisms that had slowly evolved

the carbon and hydrogen inside them became locked up in sedimentary rocks

as insoluble carbonates e.g limestone and fossil fuels

when fossil fuel is burnt this locked up carbon is released

and the concentration of CO2 in the atmosphere rises

Phase 3- Ozone layer allows evolution of complex animals

the build up of oxygen in the atmosphere

killed off some early organisms that couldn't handle it

more organisms evolved and flourished

the oxygen also created the ozone layer (O3)

which blocked harmful rays from the sun and enabled us more complex organisms to evolve

there is no CO2 left now

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Life, resources and atmospheric changes

primordial soup theory states that billions of years ago the earths atmosphere was rich in nitrogen, ammonia and methane

lightning struck causing a chemical reaction between the gases, resulting in the formation of amino acids

the amino acids collected a primordial soup- a body of water of which life gradually crawled

the amino acids gradually combined to form organic matter which evolved in to living organisms

in the 1950's miller and Urey carried out an experiment to prove this theory

they sealed the gases, heated them and applied an electrical charge for a week

they found that amino acids were made, but not as many as there are on earth

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The earth has all the resources humans need

earths crust, oceans and atmosphere are the ultimate source of minerals and resources

e.g we fractionally distill air to get a variety of products (e.g nitrogen and oxygen)

for use in industry:

air is filtered to remove dust

its then cooled to around -200c and becomes a liquid

during cooling water vapor condenses ans is removed

carbon dioxide freezes and is removed

the liquefied air then enters the fractionating column and is slowly heated

the remained gases are separated by fractional distillation

oxygen and argon come out together so another column is used to separate them