Chemistry 5070 — chapter handouts

Three states, one difference

In a solid, particles are packed close and vibrate in fixed positions — fixed shape, fixed volume. In a liquid, they still touch but can slide past each other — fixed volume, takes the shape of the container. In a gas, they are far apart and move fast in all directions — no fixed shape or volume.

Changing state is about energy, not about becoming a new substance

Melting, boiling, freezing and condensing are all physical changes. Ice, water and steam are all H₂O. Heating gives particles enough energy to break free of their neighbours; cooling lets the forces pull them back together.

Diffusion happens by itself

Particles move randomly, so they spread from where there are many to where there are few. Lighter particles diffuse faster because they move faster at the same temperature — which is why ammonia (lighter) travels further than hydrogen chloride in the classic tube experiment.

Pure substances have sharp melting points

A pure substance melts at one exact temperature. An impure one melts over a range, and at a lower temperature. That is why melting point is used as a purity test, and why salt is put on icy roads.

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What is inside an atom

A tiny central nucleus of protons (positive) and neutrons (neutral), with electrons (negative) in shells around it. Proton number decides which element it is. Mass number is protons plus neutrons. Atoms are neutral because protons and electrons balance.

Electron shells explain the Periodic Table

Electrons fill shells: 2, then 8, then 8. The number of electrons in the outer shell is the group number, and it decides the chemistry. That is why all Group 1 metals behave alike — they all have one outer electron to lose.

Ionic bonding: giving and taking

A metal atom hands its outer electrons to a non-metal atom. Both end up with full outer shells. Now one is positive and one is negative, and they stick together by electrostatic attraction in a giant lattice. That gives high melting points and conduction only when molten or dissolved.

Covalent bonding: sharing

Two non-metals share electrons instead. Simple molecules like water or carbon dioxide have strong bonds inside the molecule but weak forces between molecules, so they melt and boil easily and do not conduct.

Giant covalent structures are the exception

Diamond and silicon dioxide are covalent but giant — millions of atoms in one network. Breaking them means breaking strong covalent bonds, so they are extremely hard with very high melting points. Graphite is the odd one: layers that slide, plus a spare delocalised electron per carbon, so it is soft and conducts.

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Equations must balance because atoms are not destroyed

Whatever atoms go in must come out. Balancing is just bookkeeping: adjust the big numbers in front until each element has the same count on both sides. Never change the small subscript numbers — that would change the substances themselves.

The mole is just a counting word

'Dozen' means 12. 'Mole' means 6.02 × 10²³. One mole of any substance has a mass in grams equal to its relative formula mass. So one mole of water is 18 g, and one mole of carbon dioxide is 44 g.

Three formulas do nearly everything

moles = mass ÷ relative formula mass · moles = concentration × volume (in dm³) · moles = gas volume ÷ 24 dm³ at room conditions. Almost every calculation is: convert to moles, use the balanced equation ratio, convert back.

Empirical and molecular formulas

The empirical formula is the simplest whole-number ratio; the molecular formula is what is really there. Glucose is CH₂O empirically but C₆H₁₂O₆ actually. Find the empirical formula by dividing masses or percentages by relative atomic masses, then dividing through by the smallest result.

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Electrolysis needs ions that can move

A solid ionic compound will not work — its ions are locked in place. Melt it or dissolve it in water and the ions become free to travel. That is why the electrolyte must be molten or aqueous.

Opposites attract, and that decides everything

Positive ions (metals and hydrogen) go to the negative electrode, the cathode, and gain electrons. Negative ions (non-metals) go to the positive anode and lose electrons. Remembering that positive goes to negative gets you most of the marks.

In solution, water competes

With aqueous solutions you are not just electrolysing the salt — water provides H⁺ and OH⁻ too. As a rule, the less reactive species wins. So with copper sulfate you get copper at the cathode, but with sodium chloride solution you get hydrogen instead of sodium, because sodium is far too reactive.

Simple cells turn chemistry into electricity

Put two different metals in an electrolyte and electrons flow from the more reactive one to the less reactive one through the wire. The bigger the gap between them in the reactivity series, the bigger the voltage.

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Breaking bonds costs energy, making bonds releases it

Always. Pulling atoms apart takes energy in; letting them snap together gives energy out. Whether the whole reaction heats up or cools down depends on which total is bigger.

Exothermic: more out than in

If the energy released making new bonds exceeds the energy needed to break the old ones, the surplus escapes as heat and the surroundings get warmer. Combustion, neutralisation and most displacement reactions are exothermic. ΔH is negative.

Endothermic: more in than out

If breaking costs more than making returns, the reaction draws energy in from the surroundings and they get colder. Thermal decomposition and photosynthesis are endothermic. ΔH is positive.

Energy level diagrams show the journey, not just the endpoints

Draw reactants on one side, products on the other, and a hump in between. That hump is the activation energy — the energy needed to get the reaction started, even for a reaction that gives energy out overall. That is why petrol needs a spark despite burning exothermically.

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Reactions need collisions with enough energy

Particles must actually hit each other, hard enough to react. Anything that makes collisions more frequent or more energetic speeds the reaction up. That single idea explains every rate factor in the syllabus.

Four ways to speed things up

Concentration or pressure: more particles in the same space, so more collisions. Surface area: powder reacts faster than a lump because more particles are exposed. Temperature: particles move faster and hit harder, so far more collisions exceed the activation energy. Catalyst: provides an easier route with lower activation energy.

A catalyst is not used up

It takes part but is regenerated, so a tiny amount works on a huge quantity. It speeds the reaction without changing how much product you finally get.

Some reactions go both ways

In a reversible reaction the products can re-form the reactants. In a closed container the forward and backward reactions eventually run at the same rate — equilibrium. Nothing has stopped; the two directions simply balance. Change the conditions and the balance shifts.

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What makes something an acid

An acid produces H⁺ ions in solution — that is the definition, and every acidic property follows from it. Acids turn litmus red, have pH below 7, and react with metals, bases and carbonates.

Strong and concentrated are different words

Strong means fully split into ions — hydrochloric, sulfuric, nitric. Weak means only partly split — ethanoic, citric. Concentrated just means a lot of acid per litre. You can have dilute strong acid and concentrated weak acid, and mixing the words up is a classic lost mark.

Three reactions to memorise cold

acid + metal → salt + hydrogen · acid + base → salt + water · acid + carbonate → salt + water + carbon dioxide. The salt's name comes from the acid: hydrochloric gives chlorides, sulfuric gives sulfates, nitric gives nitrates.

Making a salt depends on solubility

If the salt is soluble, react acid with an excess of an insoluble base, filter off the leftover, then crystallise. If it is insoluble, mix two solutions so it precipitates, then filter, wash and dry. Choosing the right method is a standard exam question.

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Groups and periods mean something

The group number is the number of outer-shell electrons, and outer electrons decide chemistry — so a group is a family with similar behaviour. The period number is how many shells there are.

Group 1: reactivity increases going down

The alkali metals all have one outer electron to lose. Going down, that electron is further from the nucleus and better shielded, so it is lost more easily and the metal is more reactive. Lithium fizzes, sodium darts about, potassium bursts into lilac flame.

Group 7: reactivity decreases going down

The halogens need to gain one electron. Going down, the outer shell is further away, so it attracts an incoming electron less strongly and reactivity falls. A more reactive halogen displaces a less reactive one from its salt — that is the displacement test.

Group 0 and the transition metals

Group 0 gases have full outer shells, so they have no reason to react — they are inert and used where you need chemical silence. Transition metals sit in the middle block: hard, dense, high melting points, coloured compounds, variable oxidation states, and useful as catalysts.

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Why metals behave like metals

A metal is a lattice of positive ions in a sea of delocalised electrons. Those free electrons carry charge and heat, which is why metals conduct. The layers can slide without breaking the bonding, which is why metals bend rather than shatter.

The reactivity series is a ranking of electron-giving

Potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold. A more reactive metal displaces a less reactive one from its compound, reacts more vigorously with water and acid, and holds on to its oxide more tightly.

Extraction follows reactivity

Very reactive metals hold their oxides so firmly that only electrolysis will separate them — that is how aluminium is extracted, and it is expensive. Metals below carbon can be reduced with carbon in a blast furnace, which is how iron is made cheaply. Gold is so unreactive it is found as the metal itself.

Rusting needs two things and can be stopped

Iron rusts only when both water and oxygen are present — remove either and it does not. Prevent it by barrier methods (paint, oil, plastic) or by sacrificial protection: attach a more reactive metal like zinc, which corrodes instead.

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Air is mostly nitrogen

About 78% nitrogen, 21% oxygen, roughly 1% argon, and 0.04% carbon dioxide. The carbon dioxide fraction is tiny and still matters enormously — which tells you something about how sensitive the climate system is.

Where the pollutants come from

Carbon monoxide: incomplete combustion when oxygen is short — poisonous because it binds to haemoglobin better than oxygen does. Sulfur dioxide: sulfur impurities in fuel — causes acid rain. Nitrogen oxides: nitrogen and oxygen combining in the heat of an engine — acid rain and smog.

Fixes match the cause

Catalytic converters turn carbon monoxide and nitrogen oxides into carbon dioxide and nitrogen. Flue-gas desulfurisation removes sulfur dioxide from power-station chimneys using calcium oxide or carbonate. Removing sulfur from fuel before burning stops the problem at source.

Water treatment and fertilisers

Water is treated by filtration and chlorination — filtering removes solids, chlorine kills bacteria. Fertilisers supply nitrogen, phosphorus and potassium and raise crop yields, but when they wash into rivers they cause eutrophication: algae bloom, block light, then decompose and strip the water of oxygen, killing fish.

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Families behave alike

A homologous series is a family with the same general formula and the same functional group. Members differ by CH₂ each step. Because they share the functional group, they share the chemistry — so you learn the family once, not every member.

Alkanes are the unreactive ones

Single bonds only — saturated. They burn well and undergo substitution with halogens in UV light, but otherwise they are dull. That dullness is why they make good fuels and poor building blocks.

Alkenes have a double bond and that changes everything

The C=C double bond makes them unsaturated and far more reactive. They undergo addition reactions: the double bond opens and atoms join on. The test is bromine water — orange to colourless with an alkene, unchanged with an alkane.

Alcohols and acids

Alcohols have an –OH group; ethanol is made either by fermenting sugar with yeast or by adding steam to ethene. Oxidise an alcohol and you get a carboxylic acid — which is why wine left open turns to vinegar. React an acid with an alcohol and you get an ester, which is where fruity smells come from.

Polymers are long chains of small units

Alkenes join end to end, double bonds opening, to make addition polymers like poly(ethene). Because the backbone is inert carbon–carbon bonds, these plastics do not rot — useful in a bottle, a serious problem in a landfill.

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Pick the separation method to match the mixture

Filtration: insoluble solid from liquid. Crystallisation: dissolved solid from its solution. Simple distillation: the liquid from a solution, when you want the liquid. Fractional distillation: two liquids with different boiling points. Chromatography: dissolved substances with different solubilities.

Chromatography separates by how much things stick

Substances that dissolve well in the solvent travel far up the paper; those that cling to the paper stay put. The Rf value — distance moved by the spot ÷ distance moved by the solvent — is a fixed number for a given substance and solvent, so it identifies it.

Testing for gases

Hydrogen pops with a lighted splint. Oxygen relights a glowing splint. Carbon dioxide turns limewater milky. Ammonia turns damp red litmus blue. Chlorine bleaches damp litmus. Five tests, and they come up constantly.

Identifying ions

Flame tests identify metal ions by colour — lithium red, sodium yellow, potassium lilac, copper blue-green. Adding sodium hydroxide gives coloured precipitates that identify others. For negative ions: carbonates fizz with acid, halides give coloured precipitates with silver nitrate, and sulfates give a white precipitate with barium.

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