Essay on atoms and elements

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COMPOUNDS AND MIXTURES
In this unit you will learn to .. distinguish between elements and compounds and how they are represented by symbols and formulae - these show the relative numbers and types of atom present recognise chemical change as a process in which atoms join together in new ways distinguish between compounds and mixtures distinguish between chemical reactions in which new compounds are formed and the formation of mixtures investigate temperature changes as liquids cool use line graphs and choose appropriate scales for eg time, temperature or mass data. distinguish between elements, compounds and mixtures in terms of the particles they contain name and describe some common mixtures and use knowledge about separation techniques to suggest how they might be separated identify melting and boiling points as the fixed temperatures at which elements and compounds change state and use the particle model to explain changes of state know mixtures do not change state at fixed temperatures
Its handy if you ... can name some elements know that there are approximately 100 elements which are the building blocks for all materials know that elements are composed of tiny particles called atoms know that compounds are formed when atoms of different elements join have explored a number of chemical reactions have made and separated mixtures
Some important words for you to understand, use and spell correctly words with precise scientific meaning, eg element, compound, mixture, atom, composition, pure names of compounds, eg sodium carbonate, calcium chloride, hydrochloric acid
How are elements and compounds different? that elements contain only one kind of atom that compounds contain more than one kind of atom chemically bonded (joined) together that formulae indicate the (relative) numbers of atoms in a compound distinguish between elements and compounds in terms of names and symbolic formulae
How do compounds differ from the elements from which they are made? that compounds contain elements that are chemically combined that the properties of a compound are different from those of the elements from which it is made that a compound always contains the same elements in fixed proportions and relate this to interpreting formulae for compounds in terms of the relative numbers of atoms of different elements effect of heating a mixture of iron and sulphur powders in ignition tubes - a red glow and no yellow powder left after their tube has cooled - what evidence for suggesting chemical change - to extract the contents - does it still contains a mixture or if a new chemical (compound) has been made? write a word, picture or symbol equations for the reaction show that the compound iron sulphide behaves differently from its constituent elements sulphur and iron, eg by adding a small amount of dilute acid to both and observing the differences in the way the mixture behaves compared to the compound. names of compounds eg water, carbon dioxide, copper carbonate - compare the compounds with the elements from which they are made - describe differences between compounds and the elements from which they are made consider the formulae of some of the oxides made in unit 8E ‘Atoms and elements’, eg magnesium, sodium and aluminium oxides, and the fact that compounds are made from elements in fixed proportions - pictures showing particles in examples of elements, compounds and various mixtures of elements and/or compounds
Do compounds react chemically? that compounds can react chemically observe a number of test tube chemical reactions in which visible changes occur, eg mixing sodium carbonate solution and iron(II) chloride solution; adding dilute hydrochloric acid to solid magnesium carbonate; adding dilute ammonia solution to copper sulphate solution; heating sucrose identify appropriate indications of chemical reactions state that chemical reactions took place between the compounds note that some physical
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