Every key word

1.1 Substances, states of matter and the particle model

matter define it

anything that has mass and volume; all matter is made of atoms

E.G.air, water, this desk, you

NOTlight, heat, sound, an idea — no mass, no volume

particle model define it

the idea that matter is made of tiny moving particles with forces between them

E.G.explaining why a gas fills its container and a solid holds its shape

NOTthe idea that the particles themselves melt or expand — their spacing and energy change, not their size

elemental substance (element) define it

a substance made of only one type of atom

E.G.Fe (iron), He (helium), O₂ (oxygen)

NOTH₂O or CO₂ — more than one type of atom

compound substance (compound) define it

two or more types of atom chemically combined in fixed ratios

E.G.H₂O, NaCl, C₆H₁₂O₆

NOTair or salt water — mixed, not bonded, and no fixed ratio

mixture define it

different substances mixed but not chemically combined, in no fixed ratio

E.G.air, salt water, sea water, brass

NOTpure water or carbon dioxide — bonded in a fixed ratio

homogeneous / heterogeneous define it

uniform throughout / made of visibly separate parts

E.G.homogeneous: a salt solution, air · heterogeneous: oil and water, granite

NOTa judgement about particle size — milk looks uniform but is heterogeneous

chemically combined define it

joined by chemical bonds; separable only by another chemical reaction

E.G.the H and O in water — no filter or funnel will separate them

NOTsalt in salt water — evaporate the water and the salt returns unchanged

1.2 Atomic structure and classification of matter

chemical symbol define it

one or two letters for an element; first letter capital, second lowercase

E.G.C, Ca, Cl, Na, Fe

NOTCO — that is a formula for a compound; and NA or nA — wrong case

chemical formula define it

symbols and subscripts showing the atoms in a substance

E.G.H₂SO₄ — 2 H, 1 S, 4 O

NOT"sulphuric acid" — that is the name, not the formula

subscript define it

the small number after a symbol; counts the atoms of that element only

E.G.the 2 in H₂O counts hydrogen only → 2 H and 1 O

NOTthe 2 in 2 H₂O — that one is a coefficient and multiplies everything

coefficient define it

the large number in front of a formula; multiplies the whole formula

E.G.2 H₂O means 4 H and 2 O in total

NOTthe small 2 inside H₂O — never change that

diatomic molecule define it

a molecule of two atoms, e.g. O₂, H₂, Cl₂

E.G.H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

NOTO₃ (three atoms), He (a single atom), H₂O (two different elements)

1.3 The ‘Bohr model’: Atoms, ions and isotopes

atom define it

the smallest particle of an element that still behaves like that element

E.G.one Fe atom is still iron and behaves like iron

NOTa lone proton — that is a part of an atom

nucleus define it

the tiny, dense centre of an atom; holds the protons and neutrons

E.G.carbon's nucleus: 6 protons + 6 neutrons

NOTthe shells — those hold the electrons, outside the nucleus

proton define it

positive particle in the nucleus — relative charge +1, relative mass 1

E.G.every carbon atom has exactly 6 — that is what makes it carbon

NOTa neutron (no charge) or an electron (negative, almost no mass)

neutron define it

neutral particle in the nucleus — relative charge 0, relative mass 1

E.G.carbon-12 has 6 of them; carbon-14 has 8

NOTthe particle that decides which element it is — change the protons for that

electron define it

negative particle in the shells — relative charge #sym.minus 1, almost no mass

E.G.a neutral carbon atom has 6, arranged 2, 4

NOTcounted in the mass number — far too light to matter

shell (energy level) define it

a region around the nucleus where electrons are found

E.G.sodium fills 2, 8, 1 across three shells

NOTa solid surface or a track — nothing is physically there

Bohr model define it

a simple, useful model with electrons in fixed circular shells

E.G.drawing sodium as three rings holding 2, 8, 1

NOTa photograph of a real atom — nobody has ever seen electrons in rings

orbital define it

the more accurate idea: a region where an electron is likely to be

E.G.a fuzzy cloud, densest near the nucleus

NOTa fixed circular path like a planet's orbit

atomic number (Z) define it

the number of protons; also called the proton number — defines which element it is

E.G.Z = 6 is always carbon; Z = 7 is always nitrogen

NOTthe neutron count, and not the mass number

mass number (A) define it

the number of protons + neutrons; also called the nucleon number (protons and neutrons together are called nucleons)

E.G.sodium: 11 protons + 12 neutrons → A = 23

NOTa mass in grams — and it does not count electrons

ion define it

an atom that has lost or gained electrons, so it carries a charge

E.G.Na⁺ (lost one), Cl− (gained one), Mg²⁺ (lost two)

NOTa neutral Na atom; and never an atom that gained a proton

isotope define it

atoms of the same element (same Z) with different numbers of neutrons

E.G.carbon-12 and carbon-14 — both 6 protons, 6 vs 8 neutrons

NOTcarbon and nitrogen — different protons, so different elements

relative atomic mass define it

the average mass of an element's atoms, allowing for its isotopes

E.G.chlorine 35.45 — the average of Cl-35 and Cl-37

NOTthe mass number of any one atom — no chlorine atom weighs 35.45

electron arrangement define it

how the electrons are spread across the shells, e.g. 2, 8, 1 for sodium

E.G.sodium 2, 8, 1 · chlorine 2, 8, 7

NOT8, 2, 1 — shells fill from the nucleus outwards

1.4 The Periodic Table of the elements

group define it

a vertical column; same number of outer-shell electrons → similar properties

E.G.Li, Na and K are all Group 1 — one outer electron each

NOTa horizontal row — that is a period

period define it

a horizontal row; the period number equals the number of occupied shells

E.G.Na, Mg, Al … are all Period 3 — three occupied shells

NOTa vertical column — that is a group

metal / non-metal define it

metals (left and centre) conduct and are malleable; non-metals (right) do not and are brittle

E.G.metals Fe, Cu, Na — conduct, malleable, shiny · non-metals S, O, Cl — brittle, poor conductors

NOTa sharp dividing line — silicon sits between the two as a metalloid

noble gas define it

a Group 18 element with a complete outer shell, so very unreactive

E.G.He, Ne, Ar — balloons, lighting, welding shields

NOThydrogen — also a light gas, but very reactive and not in Group 18

proton number (atomic number) define it

the number of protons; sets each element's place in the table

E.G.the table runs 1 H, 2 He, 3 Li … in proton order

NOTordered by mass — argon (40) still comes before potassium (39)

1.5 Chemical change 1: Recognizing & describing reactions

physical change define it

particles rearrange but stay the same substance; usually reversible (e.g. melting)

E.G.melting ice, dissolving sugar, boiling water

NOTburning magnesium or rusting — new substances form

chemical change define it

particles rearrange into one or more new substances; usually hard to reverse

E.G.burning magnesium, rusting, cooking an egg

NOTmelting, dissolving or evaporating — same substance throughout

reactant / product define it

the substances that react / the new substances formed

E.G.Mg + O₂ → MgO: reactants Mg and O₂; product MgO

NOTa catalyst — present, but neither used up nor produced

state symbol define it

(s), (l), (g) or (aq), showing a substance's physical state in an equation

E.G.NaCl(aq) — sodium chloride dissolved in water

NOT(aq) for pure water itself — water is (l)

law of conservation of mass define it

total mass of products = total mass of reactants (Lavoisier; explained by Dalton)

E.G.magnesium burned in a sealed flask: mass unchanged

NOTan open dish appearing to lose mass — the gas escaped

coefficient define it

the number in front of a formula, adjusted to balance an equation

E.G.2 H₂O means 4 H and 2 O in total

NOTthe small 2 inside H₂O — never change that

1.8 Reactions of group 1 ‘alkali’ metals

reactivity define it

how readily a substance takes part in a chemical reaction

E.G.potassium reacts violently with water; gold barely reacts at all

NOThow fast something melts or dissolves — those are physical changes

alkali metal (Group 1) define it

a soft, very reactive metal with one outer electron; reacts with water to give hydrogen

E.G.Li, Na, K — soft enough to cut, stored under oil

NOTcalcium (Group 2) or aluminium — different outer-electron count

alkaline earth metal (Group 2) define it

a reactive metal with two outer electrons

E.G.Mg and Ca — two outer electrons, form 2+ ions

NOTsodium — Group 1, one outer electron, forms a 1+ ion

halogen (Group 17) define it

a reactive non-metal with seven outer electrons; reacts by gaining one electron

E.G.F₂, Cl₂, Br₂, I₂ — all gain one electron

NOTa noble gas — full outer shell, no drive to gain anything

diatomic define it

existing as molecules of two atoms, e.g. Cl₂

E.G.Cl₂, Br₂, I₂

NOTsolid iodine as "one big molecule" — the units are still I₂

1.10 Rates of reaction & the investigation

rate of reaction define it

the change in concentration of a reactant or product over time

E.G.20 cm³ of gas collected in 10 s → 2 cm³/s

NOTthe total gas produced — that is an amount, not a rate

collision theory define it

particles must collide with enough energy (a successful collision) to react

E.G.heating speeds a reaction: collisions are harder and more frequent

NOT"more collisions always means faster" — they must be successful

successful collision define it

a collision with enough energy for a reaction to occur

E.G.two particles hit hard enough that bonds break and new ones form

NOTparticles that collide and simply bounce apart unchanged

catalyst define it

a substance that speeds up a reaction without being used up

E.G.manganese(IV) oxide added to hydrogen peroxide

NOTa reactant — a catalyst comes back out unchanged at the end

surface area define it

the amount of a solid's surface exposed to react; greater for a powder than a lump

E.G.powdered marble reacts faster than one marble chip

NOTthe mass — same mass of powder and chip, very different surface area