Key term
Edexcel GCSE Combined Science Chemistry 1SC0
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
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
Key Concepts in Chemistry
Dot and cross diagrams for simple molecules
- 2 things to know
- Papers 3 and 4
Overview
The 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.
What you need to know
Answer each one before you reveal it.
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Key term
Describe the bonding in a molecule of hydrogen chloride.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe the bonding in a molecule of hydrogen.
Model answer
The two hydrogen atoms share one pair of electrons, so each ends up with a full first shell of two.
- 2
Describe the bonding in a molecule of hydrogen chloride.
Model answer
The hydrogen atom and the chlorine atom share one pair of electrons, forming a single covalent bond.
- 3
Describe the bonding in a molecule of water.
Model answer
The oxygen atom shares one pair of electrons with each of the two hydrogen atoms.
- 4
How many covalent bonds does the carbon atom form in methane, and why?
Model answer
It forms four bonds, because carbon has four outer electrons and needs four more to fill its outer shell.
- 5
Describe the bonding in a molecule of oxygen.
Model answer
The two oxygen atoms share two pairs of electrons, giving a double bond.
- 6
Describe the bonding in a molecule of carbon dioxide.
Model answer
The carbon atom forms a double bond with each of the two oxygen atoms.
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