AQA AS Chemistry Student Unit Guide : Unit 1 Foundation by Margaret Cross

By Margaret Cross

Pupil Unit publications are ideal for revision. every one advisor is written by way of an examiner and explains the unit necessities, summarises the proper unit content material and encompasses a sequence of specimen questions and solutions.

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Permanent charge separation). ● Permanent dipole–dipole forces exist between the molecules. ● When comparing molecules of similar size, permanent dipole–dipole forces are stronger than induced dipole–dipole (van der Waals) forces. Examples of other molecules with permanent dipole–dipole forces include chloromethane and hydrogen sulfide. An example of hydrogen bonding: water ● Water (H2O) is a polar molecule. ● The hydrogen is directly attached to a small, very electronegative, oxygen atom. ● Oxygen is electron-rich and hydrogen is electron-deficient.

Bromo- before chloroand tribromo- before dichloro-. CH2 CH Cl Br CH3 2-bromo-1-chloropropane Isomerism Isomerism occurs where molecules with the same molecular formula have a different arrangement of atoms. There are two main types of isomerism: ● structural isomerism ● stereoisomerism Both types of isomerism can be further subdivided. Note: stereoisomerism is covered in Unit 2. Structural isomerism Structural isomerism occurs when there are two or more compounds with the same molecular formula but with a different structural formula.

The induced dipole–dipole forces between the molecules are therefore relatively strong compared with those in other simple, non-polar molecules that have fewer electrons. Remember, compared with other intermolecular forces, the induced dipole–dipole forces in iodine are weak. However, they are strong enough for iodine molecules to form solid crystals at room temperature. All covalent molecules have induced dipole–dipole forces between them — for example, chlorine, bromine, methane, phosphorus and sulfur.

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