Key term
Edexcel GCSE Chemistry 1CH0
Key Concepts in Chemistry
Topic overviewFormulae, word equations and balanced equationsHazard symbols and assessing riskThe changing model of the atomProtons, neutrons and electronsThe nucleus, mass number and atomic massElements and isotopesCalculating particle numbers and relative atomic massMendeleev's periodic tableHow the modern periodic table is arrangedElectronic configuration and the periodic tableHow ionic bonds formIons in ionic compoundsFormulae of ionic compoundsNaming compounds and the ionic latticeCovalent bonds and moleculesDot and cross diagrams for simple moleculesClassifying substances and the properties of ionic compoundsProperties of simple molecular substances, and forms of carbonGraphite and diamondFullerenes and graphenePolymers and models of bondingThe properties of metalsRelative formula mass and percentage compositionEmpirical and molecular formulaeConservation of mass in closed and open systemsReacting masses from balanced equationsConcentration in grams per cubic decimetre
States of Matter and Mixtures
Topic overviewThe three states of matter and changes of stateEnergy changes during changes of state, and predicting statePure substances and melting point dataChoosing a separation techniqueSeparating a mixture in practicePaper chromatography and interpreting a chromatogramInvestigating inks by distillation and chromatographyMaking water potable
Chemical Changes
Topic overviewAcids, alkalis and the pH scaleIndicators: litmus, methyl orange and phenolphthaleinInvestigating pH change when neutralising an acidBases and alkalisReactions of acids, and testing for hydrogen and carbon dioxideNeutralisation and its ionic equationPreparing soluble salts from insoluble and soluble reactantsPreparing pure, dry copper sulfate crystalsCarrying out an acid-alkali titrationSolubility rulesPredicting precipitates and preparing an insoluble saltElectrolytes and what electrolysis isMovement of ions and predicting the products of molten electrolysisElectrolysis with inert electrodesElectrolysis of copper sulfate solutionInvestigating the electrolysis of copper sulfate
Extracting Metals and Equilibria
Transition Metals, Quantitative Chemistry and Industrial Processes
Topic overviewTransition metals and their propertiesCorrosion and electroplatingPreventing rustingAlloys and alloy steelsHow the uses of metals relate to their propertiesCarrying out an accurate titrationPercentage yieldAtom economyThe Haber processFertilisers and ammonium saltsPreparing ammonium sulfate in the lab and in industryChemical cells and fuel cellsEvaluating fuel cells
Groups in the Periodic Table
Topic overviewThe groups of the periodic table, and the alkali metalsReactions of the alkali metals with waterThe pattern in alkali metal reactivity and why it happensPhysical properties of the halogensThe test for chlorine, and halogens reacting with metalsHydrogen halides, and explaining halogen reactivityDisplacement reactions of the halogensGroup 0: the noble gases
Rates of Reaction and Energy Changes
Fuels and Earth Science
Topic overviewHydrocarbons and crude oilFractional distillation and the fractionsProperties of the fractions and homologous seriesComplete and incomplete combustionCarbon monoxide and sootPollutants and acid rainHydrogen and fossil fuels comparedCracking and why it is necessaryThe Earth's early atmosphereHow the oceans formed and how oxygen appearedThe test for oxygen and the greenhouse gasesToday's atmosphere and evidence for climate change
Chemical Analysis, Organic Chemistry and Materials
Topic overviewWhy an ion test must be unique, and flame testsTests for metal ions and for ammoniaTests for carbonate, sulfate and halide ionsIdentifying the ions in an unknown saltInstrumental methods and flame photometryAlkanes and why they are saturatedAlkenes and why they are unsaturatedReactions of alkenes, and combustionWhat a polymer is, and how poly(ethene) formsOther addition polymers, and monomers from polymersUses of polymers, and natural polymers including DNAProblems with polymers and recyclingAlcohols and the -OH functional groupComparing the energy released by alcohol fuelsMaking ethanol by fermentation and distillationCarboxylic acids and the -COOH functional groupOxidising alcohols to carboxylic acids, and homologous seriesThe size of nanoparticlesUses and risks of nanoparticlesChoosing a material for a use
Key Concepts in Chemistry
- 27 subtopics
- 45 things to know
- Papers 1 and 2
What Key Concepts in Chemistry covers
Key Concepts in Chemistry is examined in both papers, as the key concepts that run through the whole course. It covers formulae, word equations and balanced equations, hazard symbols and assessing risk, the changing model of the atom, protons, neutrons and electrons, the nucleus, mass number and atomic mass, elements and isotopes, calculating particle numbers and relative atomic mass, Mendeleev's periodic table, how the modern periodic table is arranged, electronic configuration and the periodic table, how ionic bonds form, ions in ionic compounds, formulae of ionic compounds, naming compounds and the ionic lattice, covalent bonds and molecules, dot and cross diagrams for simple molecules, classifying substances and the properties of ionic compounds, properties of simple molecular substances, and forms of carbon, graphite and diamond, fullerenes and graphene, polymers and models of bonding, the properties of metals, relative formula mass and percentage composition, empirical and molecular formulae, conservation of mass in closed and open systems, reacting masses from balanced equations and concentration in grams per cubic decimetre.
Where it is assessed
Papers 1 and 2
Key concepts, examined on both chemistry papers.
Check the Pearson Edexcel specification ↗The 27 subtopics
Each one has its own page.
- Formulae, word equations and balanced equationsFormulae of oxygen, the diatomic elements, ammonia, methane, common acids and ions such as sulfate, carbonate, hydroxide and ammonium, writing word equations, and balancing equations with state symbols without changing any formula.Open →
- Hazard symbols and assessing riskThe purposes of hazard symbols and what the corrosive, flammable, oxidising, toxic, harmful and environmental symbols warn of, hazard and risk in practical work, suitable precautions, and how the likelihood, severity and perception of a risk are judged.Open →
- The changing model of the atomDalton's solid spheres, the discovery of the electron and the plum pudding model, alpha scattering and the nucleus, the neutron and electron shells, why models change, the structure of the atom, and peer review and how scientific results are communicated.Open →
- Protons, neutrons and electronsThe relative mass and charge of the proton, neutron and electron, why an atom has equal numbers of protons and electrons and no overall charge, and what happens to its charge when it loses an electron.Open →
- The nucleus, mass number and atomic massThe sizes of the atom and the nucleus, why most of an atom is empty space yet nearly all its mass is in the nucleus, what mass number means and how neutrons are found from it, and the symbols <, ≪ and ~ for comparing sizes and masses.Open →
- Elements and isotopesWhat every atom of one element shares, why the proton number identifies an element, what isotopes are, how their mass numbers differ and why they react identically.Open →
- Calculating particle numbers and relative atomic massWorking out protons, neutrons and electrons from atomic and mass numbers, what relative atomic mass means, why chlorine's is 35.5 while fluorine's is almost exactly 19, and the isotope masses and abundances that decide it.Open →
- Mendeleev's periodic tableHow Mendeleev ordered the elements by relative atomic mass and grouped them by properties, why he left gaps and how his predictions were confirmed, what periodic means, why some pairs fell out of order and were swapped, and ordering by atomic number today.Open →
- How the modern periodic table is arrangedHow atomic number fixes an element's place in the table, periods and groups and why elements in a group behave alike, where the metals, non-metals and transition metals sit, and the metal and non-metal divide explained in terms of electrons.Open →
- Electronic configuration and the periodic tableHow many electrons each shell holds, the configurations of sodium, chlorine, calcium and oxygen, the order shells fill, and how group and period follow from the configuration.Open →
- How ionic bonds formElectron transfer between a metal and a non-metal, cations and anions, what dot and cross diagrams show, what an ion is and why a chloride ion is negative.Open →
- Ions in ionic compoundsProtons, neutrons and electrons in magnesium, chloride, oxide and aluminium ions, the ions formed by groups 1, 2, 6 and 7, and why atoms gain or lose electrons.Open →
- Formulae of ionic compoundsDeducing the formulae of ionic compounds such as calcium chloride, sodium sulfate, aluminium oxide and magnesium hydroxide from their ions, the rule that the charges must cancel, and why brackets are placed around a whole ion.Open →
- Naming compounds and the ionic latticeWhat the –ide and –ate endings show about the elements in a compound, naming compounds such as calcium chloride and calcium carbonate, and the giant ionic lattice held together by strong electrostatic forces acting in all directions.Open →
- Covalent bonds and moleculesHow covalent bonds form when non-metal atoms share electron pairs and why they are strong, single, double and triple bonds, what a molecule is, and the size of a small molecule in powers of ten and nanometres.Open →
- Dot and cross diagrams for simple moleculesThe bonding in molecules of hydrogen, hydrogen chloride, water, methane, oxygen and carbon dioxide, the single and double bonds each contains, and the bonding and non-bonding electron pairs shown in dot and cross diagrams.Open →
- Classifying substances and the properties of ionic compoundsThe four structure types, telling them apart by melting point, conductivity and solubility, and why ionic compounds melt high and conduct only when molten or dissolved.Open →
- Properties of simple molecular substances, and forms of carbonWhy simple molecular substances melt low and do not conduct, how molecule size affects boiling point, intermolecular forces, and why diamond and graphite are giant covalent forms of carbon.Open →
- Graphite and diamondThe bonding and arrangement of carbon atoms in diamond and graphite, the delocalised electrons in graphite, and how structure explains graphite's use for electrodes and as a lubricant, diamond's use in cutting tools, and graphite's softness yet high melting point.Open →
- Fullerenes and grapheneThe size, shape and bonding of the C₆₀ fullerene, why it melts low and feels slippery, and what graphene is and why it conducts and is so strong.Open →
- Polymers and models of bondingPoly(ethene) as a polymer of ethene with a covalently bonded carbon backbone and chains of varying length, why it is solid, and the limitations of dot and cross diagrams, ball and stick models, two-dimensional drawings and ionic lattice diagrams.Open →
- The properties of metalsThe metallic lattice of positive ions and delocalised electrons, why metals conduct electricity and heat, are malleable and melt at high temperatures, the typical properties of metals and non-metals, and exceptions such as mercury and graphite.Open →
- Relative formula mass and percentage compositionAdding up relative formula masses for CO₂, CaCO₃, Ca(OH)₂ and H₂SO₄, finding the percentage by mass of an element, and working out empirical formulae from reacting masses.Open →
- Empirical and molecular formulaeEmpirical formulae of glucose, hydrogen peroxide and butane, going from empirical formula and relative molecular mass to molecular formula, and the crucible experiment that finds the formula of magnesium oxide.Open →
- Conservation of mass in closed and open systemsThe law of conservation of mass and why it holds, how mass changes in closed and open systems when a precipitate forms, a carbonate decomposes, magnesium burns or a candle burns, and calculating the mass of gas released.Open →
- Reacting masses from balanced equationsWhat a reacting mass calculation needs, why the equation must be balanced, and worked masses for calcium carbonate decomposing, magnesium burning, iron(III) oxide reduced and hydrogen burning.Open →
- Concentration in grams per cubic decimetreWhat g dm⁻³ means, converting cm³ to dm³, calculating the concentration, mass or volume of a solution, what adding water does to concentration, and giving answers to an appropriate number of significant figures.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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Describe an atom's nucleus in terms of what it contains, its size and mass, and what its mass number counts.
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Explain how an ionic bond forms and how the two kinds of ion involved are made.
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What is the chemical formula of a molecule of oxygen gas?
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What does the corrosive hazard symbol tell you about a substance?
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How did John Dalton describe atoms in his model?
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State the relative mass and relative charge of a proton.
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Why is the number of protons used to identify an element?
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How is the number of neutrons in an atom calculated?
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Why did Mendeleev leave gaps in his table?
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How does atomic number fix an element's position in the periodic table?
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What is the maximum number of electrons the first shell of an atom can hold?
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How is the number of electrons in a positive ion worked out from the atomic number?
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Deduce the formula of calcium chloride from the ions Ca²⁺ and Cl⁻.
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Which elements are present in magnesium sulfide?
Process
How is a covalent bond formed?
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Describe the bonding in a molecule of hydrogen.
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Why do simple molecular substances have low melting and boiling points?
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Describe the arrangement of the carbon atoms in diamond.
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What is the shape of a C₆₀ fullerene molecule?
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What forms the backbone of a poly(ethene) molecule?
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Describe the structure of a metal.
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How is the relative formula mass of a compound worked out?
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How is a molecular formula obtained from an empirical formula and a relative molecular mass?
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State the law of conservation of mass.
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What information is needed before the mass of a product can be calculated from the mass of a reactant?
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What does a concentration measured in g dm⁻³ tell you?
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Which seven elements exist as diatomic molecules, and what does diatomic mean?
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What hazard is shown by a flame symbol on a bottle?
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Which discovery first showed that the idea of an indivisible atom was wrong?
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State the relative mass and relative charge of a neutron.
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Compare the size of the nucleus with the size of the whole atom.
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What would happen if the number of protons in a nucleus were changed?
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Why is the relative atomic mass of chlorine 35.5 rather than a whole number?
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How did Mendeleev use his table to predict elements that had not been discovered?
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Why does every element have a different atomic number?
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For the first twenty elements, how many electrons fill the second shell?
Process
How is an ionic bond formed?
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Explain what happens to the electrons when magnesium reacts with oxygen.
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Deduce the formula of sodium sulfate from the ions Na⁺ and SO₄²⁻.
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Which elements are present in magnesium sulfate?
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Why is a covalent bond strong?
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Describe the bonding in a molecule of hydrogen chloride.
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What are the four main types of structure used to classify elements and compounds?
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How does the size of a molecule affect the boiling point of a simple molecular substance?
Take Key Concepts in Chemistry further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Mass number vs Atomic number
Mass number: total of protons and neutrons in the nucleus. Atomic number: count of protons in the nucleus, which identifies the element.
Cation vs Anion
Cation: positive ion formed when an atom loses one or more electrons. Anion: negative ion formed when an atom gains one or more electrons.
Empirical formula vs Molecular formula
Empirical formula: simplest whole number ratio of the atoms of each element. Molecular formula: actual number of atoms of each element in one molecule.
Questions from this topic
Each one with the model answer underneath.
- 1
What is the chemical formula of a molecule of oxygen gas?
Model answer
Oxygen gas has the formula O₂.
- 2
Which seven elements exist as diatomic molecules, and what does diatomic mean?
Model answer
Hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine are diatomic, meaning each molecule contains two atoms joined together.
- 3
State the formulae of ammonia and methane.
Model answer
Ammonia is NH₃ and methane is CH₄.
- 4
Give the formulae of sulfuric acid, nitric acid and hydrochloric acid.
Model answer
They are H₂SO₄, HNO₃ and HCl.
- 5
State the formula and charge of the sulfate ion and of the carbonate ion.
Model answer
Sulfate is SO₄²⁻ and carbonate is CO₃²⁻.
- 6
What are the formulae of the hydroxide ion and the ammonium ion?
Model answer
Hydroxide is OH⁻ and ammonium is NH₄⁺.
What is inside Levo
Six ways to work the same material.
Key Concepts in Chemistry revision questions
- What does Key Concepts in Chemistry cover in Edexcel GCSE Chemistry?
- 27 subtopics: formulae, word equations and balanced equations, hazard symbols and assessing risk, the changing model of the atom, protons, neutrons and electrons, the nucleus, mass number and atomic mass, elements and isotopes, calculating particle numbers and relative atomic mass, mendeleev's periodic table, how the modern periodic table is arranged, electronic configuration and the periodic table, how ionic bonds form, ions in ionic compounds, formulae of ionic compounds, naming compounds and the ionic lattice, covalent bonds and molecules, dot and cross diagrams for simple molecules, classifying substances and the properties of ionic compounds, properties of simple molecular substances, and forms of carbon, graphite and diamond, fullerenes and graphene, polymers and models of bonding, the properties of metals, relative formula mass and percentage composition, empirical and molecular formulae, conservation of mass in closed and open systems, reacting masses from balanced equations and concentration in grams per cubic decimetre. Each one has its own page with questions and model answers.
- How is Key Concepts in Chemistry organised?
- By the Edexcel 1CH0 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Key Concepts in Chemistry, on a schedule.
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