Elements, Compounds and Mixtures

What Elements, Compounds and Mixtures covers

Elements, Compounds and Mixtures is examined in Chemistry A Paper 1. It covers purity and melting point data; relative formula mass and empirical formulae; formulations and separating mixtures; paper and thin layer chromatography; interpreting chromatograms and Rf values; choosing a purification method; metals and non-metals in the Periodic Table; electron arrangement and position in the Periodic Table; ionic, covalent and metallic bonding compared; dot and cross diagrams and the limits of models; reactions, electron arrangement and Mendeleev's table; carbon's four bonds and the variety of organic compounds; diamond, graphite, fullerenes and graphene; bond strength, intermolecular forces and predicting state; bulk properties of ionic, molecular and giant structures; the size and surface area to volume ratio of nanoparticles; and the uses and risks of nanoparticulate materials.

The 17 subtopics

Each one has its own page.

• Purity, and melting point dataWhat pure means to a chemist and in everyday speech, orange juice and spring water as mixtures, why chemists need the strict definition, and how a sharp melting point shows purity.Open →
• Relative formula mass and empirical formulaeWhat relative atomic, molecular and formula mass mean, calculating relative formula masses such as CO₂ and Ca(OH)₂, why the totals balance on both sides of an equation, what an empirical formula is, and working out empirical and molecular formulae from molecules, models, diagrams and relative formula mass.Open →
• Formulations, and separating mixturesWhat a formulation is and why it is never pure, examples such as paints, medicines and brass, the jobs of the pigment and solvent in a paint, why proportions matter and alloys are harder than pure metals, and how filtration, crystallisation, simple distillation and fractional distillation separate mixtures.Open →
• Paper and thin layer chromatographyHow a paper chromatogram is set up with a pencil baseline above the solvent, what a thin layer plate is made of and its advantage over paper, choosing a solvent, revealing colourless spots with a locating agent or ultraviolet light, the stationary and mobile phases in paper and thin layer chromatography, and why substances separate.Open →
• Interpreting chromatograms and Rf valuesWhat an Rf value means, the formula and where the distances are measured from, worked Rf calculations, why Rf never exceeds 1, why the solvent must match, and reading purity and identity from a chromatogram.Open →
• Choosing a purification methodMatching filtration, simple distillation, crystallisation and fractional distillation to mixtures, the property each relies on, purifying rock salt, choosing paper or thin layer chromatography, and how gas chromatography works.Open →
• Metals and non-metals in the Periodic TableThe typical physical properties of metals and non-metals, the ions each forms and why, metal oxides as basic and non-metal oxides as acidic, graphite as a non-metal that conducts, where metals and non-metals sit in the Periodic Table, why metallic character increases down a group, the elements beside the stepped line, and predicting ion charges from outer electrons.Open →
• Electron arrangement and position in the Periodic TableWhat the group and period numbers say about electron shells, reading a position from an arrangement such as 2,8,1, atomic number and electrons, ordering by atomic number, and why Group 0 sits at the right.Open →
• Ionic, covalent and metallic bonding comparedThe bonding and arrangement of particles in ionic compounds, simple molecules, giant covalent structures, polymers and metals, which kinds of atom each type of bonding joins, electron transfer and sharing, the electrostatic attractions that hold ionic, covalent and metallic bonds together, the ions in sodium chloride and magnesium oxide, and why atoms bond at all.Open →
• Dot and cross diagrams, and the limits of modelsWhy dots and crosses are used, the diagrams for hydrogen chloride, oxygen, methane, sodium chloride and magnesium oxide, and what dot and cross, ball and stick and flat drawings each fail to show.Open →
• Reactions, electron arrangement and Mendeleev's tableWhy a group reacts alike, the reactivity trends in Groups 1, 7 and 0, predicting how an atom with 2,8,7 reacts, how Mendeleev ordered the elements and left gaps, and ordering by atomic number.Open →
• Carbon's four bonds, and the variety of organic compoundsWhy a carbon atom forms four covalent bonds and never five, how many bonds remain after a double bond, why carbon forms so many compounds in chains, branches and rings, homologous series such as the alkanes, ring structures, compounds with the same formula but different properties, and natural and synthetic organic compounds.Open →
• Diamond, graphite, fullerenes and grapheneThe structures of diamond and graphite, why diamond is hard and does not conduct while graphite is soft, slippery and conducting, what graphene is and why it is strong, light and conducting, what a fullerene is, buckminsterfullerene C₆₀, and why fullerenes melt at far lower temperatures than diamond.Open →
• Bond strength, intermolecular forces and predicting stateWhy simple molecular substances melt and boil at low temperatures without breaking covalent bonds, why ionic compounds, giant covalent structures and metals have high melting points, why boiling points rise as molecules get larger, and predicting whether a substance is a solid, liquid or gas at a given temperature from its melting and boiling points.Open →
• Bulk properties of ionic, molecular and giant structuresWhy bulk properties belong to many atoms rather than one, why ionic compounds conduct only when molten or dissolved and are brittle, why simple molecular substances are often gases or liquids and do not conduct, why metals are malleable and conduct, why giant covalent structures are insoluble, why polymers soften on heating, and identifying a structure from its properties.Open →
• Nanoparticles: size and surface area to volumeThe size range of nanoparticles, nanometres in metres, how many atoms or molecules fit across one, why they cannot be seen with a light microscope, calculating the surface area to volume ratio of cubes and how it changes as particles get smaller, and why nanoparticles make effective catalysts, react faster and behave differently from the bulk material.Open →
• Uses and risks of nanoparticulate materialsUses of nanoparticles in sun creams, wound dressings, catalysts, sports equipment, self-cleaning glass, electronics and medicine delivery, why their colour can differ from the bulk, and the risks of them entering cells, lungs and the bloodstream, harming river bacteria and being highly reactive, with the uncertain long-term effects, the limits of ordinary safety tests and the case for labelling.Open →

What you need to know

Answer each one before you reveal it.

Take Elements, Compounds and Mixtures further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Stationary phase vs Mobile phase

  Stationary phase: the paper or plate coating that does not move. Mobile phase: the solvent that travels through the paper or plate.

• 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.

• Diamond vs Graphite

  Diamond: carbon with each atom bonded to four others in a rigid lattice. Graphite: carbon in flat layers of hexagonal rings that slide and conduct.

Questions from this topic

Each one with the model answer underneath.

1. 1

   In science, what does it mean to say that a substance is pure?

   Model answer

   A pure substance is a single element or a single compound, with nothing else mixed into it.

2. 2

   What does the word 'pure' usually mean when it is used about food or drink in everyday language?

   Model answer

   In everyday use it means nothing has been added, so the product is natural or unadulterated.

3. 3

   Why would a carton labelled 'pure orange juice' not count as pure to a chemist?

   Model answer

   Because orange juice is a mixture of water, sugars, acids and many other compounds rather than one single compound.

4. 4

   Is bottled spring water a pure substance in the scientific sense?

   Model answer

   No, because it is a mixture of water with dissolved minerals and gases.

5. 5

   Can a mixture of two elements ever be described as pure in the scientific sense?

   Model answer

   No, because a pure substance contains only one element or only one compound.

6. 6

   A sample contains nothing but copper atoms. Is it an element, a compound or a mixture, and is it pure?

   Model answer

   It is an element, and it is pure because only one kind of atom is present.

What is inside Levo

Six ways to work the same material.

Elements, Compounds and Mixtures revision questions

What does Elements, Compounds and Mixtures cover in OCR GCSE Chemistry A?

17 subtopics: purity, and melting point data, relative formula mass and empirical formulae, formulations, and separating mixtures, paper and thin layer chromatography, interpreting chromatograms and rf values, choosing a purification method, metals and non-metals in the periodic table, electron arrangement and position in the periodic table, ionic, covalent and metallic bonding compared, dot and cross diagrams, and the limits of models, reactions, electron arrangement and mendeleev's table, carbon's four bonds, and the variety of organic compounds, diamond, graphite, fullerenes and graphene, bond strength, intermolecular forces and predicting state, bulk properties of ionic, molecular and giant structures, nanoparticles: size and surface area to volume and uses and risks of nanoparticulate materials. Each one has its own page with questions and model answers.

How is Elements, Compounds and Mixtures organised?

By the OCR J248 specification, subtopic by subtopic, so it matches the order you are taught it in.