### Elements, Compounds, and Mixtures

C2: Elements, compounds and mixtures

C2.1 Purity and separating mixtures

CM2.1i arithmetic computation, ratio, percentage and multistep calculations permeates quantitative chemistry

CM2.1ii provide answers to an appropriate number of significant figures

CM2.1iii change the subject of a mathematical equation

CM2.1iv arithmetic computation and ratio when determining empirical formulae, balancing equations

C2.1a explain what is meant by the purity of a substance, distinguishing between the scientific and everyday use of the term ‘pure’

C2.1b use melting point data to distinguish pure from impure substances

C2.1c calculate relative formula masses of species separately and in a balanced chemical equation

C2.1d deduce the empirical formula of a compound from the relative numbers of atoms present or from a model or diagram and vice versa

C2.1e explain that many useful materials are formulations of mixtures (to include alloys)

C2.1f describe, explain and exemplify the processes of filtration, crystallisation, simple distillation, and fractional distillation (to include knowledge of the techniques of filtration, crystallisation, simple distillation and fractional distillation)

C2.1g describe the techniques of paper and thin layer chromatography

C2.1h recall that chromatography involves a stationary and a mobile phase and that separation depends on the distribution between the phases (to include identification of the mobile and stationary phases)

C2.1i interpret chromatograms, including measuring Rf values (to include the recall and the use of the formula)

C2.1j suggest suitable purification techniques given information about the substances involved

C2.1k suggest chromatographic methods for distinguishing pure from impure substances (to include paper, thin layer (TLC) and gas chromatography).

C2.2 Bonding

CM2.2i estimate size and scale of atoms and nanoparticles

CM2.2ii represent three dimensional shapes in two dimensions and vice versa when looking at chemical structures e.g. allotropes of carbon

CM2.2iii translate information between diagrammatic and numerical forms

C2.2a describe metals and non-metals and explain the differences between them on the basis of their characteristic physical and chemical properties (to include physical properties, formation of ions and common reactions e.g. with oxygen to form oxides )

C2.2b explain how the atomic structure of metals and non-metals relates to their position in the Periodic Table

C2.2c explain how the position of an element in the Periodic Table is related to the arrangement of electrons in its atoms and hence to its atomic number (to include group number and period number)

C2.2d describe and compare the nature and arrangement of chemical bonds in: ionic compounds, simple molecules,  giant covalent structures, polymers, metals.

C2.2e explain chemical bonding in terms of electrostatic forces and the transfer or sharing of electrons

C2.2f construct dot and cross diagrams for simple covalent and binary ionic substances

C2.2g describe the limitations of particular representations and models to include dot and cross diagrams, ball and stick models and two and three dimensional representations

C2.2h explain how the reactions of elements are related to the arrangement of electrons in their atoms and hence to their atomic number

C2.2i explain in terms of atomic number how Mendeleev’s arrangement was refined into the modern Periodic Table

C2.3 Properties of materials

CM2.3i represent three dimensional shapes in two dimensions and vice versa when looking at chemical structures e.g. allotropes of carbon

*CM2.3ii relate size and scale of atoms to objects in the physical world

*CM2.3iii estimate size and scale of atoms and nanoparticles

*CM2.3iv interpret, order and calculate with numbers written in standard form when dealing with nanoparticles

*CM2.3v use ratios when considering relative sizes and surface area to volume comparisons

*CM2.3vi calculate surface areas and volumes of cubes

C2.3a recall that carbon can form four covalent bonds

C2.3b explain that the vast array of natural and synthetic organic compounds occur due to the ability of carbon to form families of similar compounds, chains and rings

C2.3c explain the properties of diamond, graphite, fullerenes and graphene in terms of their structures and bonding

C2.3d use ideas about energy transfers and the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur

C2.3e use data to predict states of substances under given conditions (to include data such as temperature and how this may be linked to changes of state)

C2.3f explain how the bulk properties of materials (ionic compounds; simple molecules; giant covalent structures; polymers and metals) are related to the different types of bonds they contain, their bond strengths in relation to intermolecular forces and the ways in which their bonds are arranged (to include recognition that the atoms themselves do not have the bulk properties of these materials)

*C2.3g compare ‘nano’ dimensions to typical dimensions of atoms and molecules

*C2.3h describe the surface area to volume relationship for different-sized particles and describe how this affects properties

*C2.3i describe how the properties of nanoparticulate materials are related to their uses

*C2.3j explain the possible risks associated with some nanoparticulate materials

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