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1、Quantitative chemistry 1 Quantitative chemistry some fundamental concepts C hemistry is a science that deals with the composition structure and reactions of matter It is involved with looking at the properties of materials and interpreting these in terms of models on a sub microscopic scale Investig
2、ations form an important part of any study of chemistry This involves making observations and using these in the solution of problems A typical investigation requires choosing a problem working out a way of attempting to solve it and then describing both the method the results and the manner in whic
3、h these are interpreted Namely a scientist chooses imagines does and describes Along with many other syllabuses practical investigations are a requirement of IB Chemistry Matter occupies space and has mass It can be subdivided into mixtures and pure substances Mixtures consist of a number of differe
4、nt substances not chemically combined together Thus the ratio of these components is not constant from one sample of mixture to another The different components of a mixture often have different physical properties such as melting point and density and chemical properties such as flammability and ac
5、idity The properties of the mixture are similar to those of the components e g a match burns in both air and pure oxygen though they will vary with its exact composition The fact that the different components of the mixture have different physical properties means that the mixture can be separated b
6、y physical means for example by dissolving one component whilst the other remains as a solid A pure substance cannot be separated in this way because its physical properties are constant throughout all samples of that substance Similarly all samples of a pure substance have identical chemical proper
7、ties for example pure water from any source freezes at 0 oC Pure substances may be further subdivided into elements and compounds The difference between these is that an element cannot be split up into simpler substances by chemical means whilst a compound can be changed into these more basic compon
8、ents The interpretation on a sub microscopic scale is that all substances are made up of very tiny particles called atoms Atoms are the smallest particles present in an element which can take part in a chemical change and they cannot be split by ordinary chemical means An element is a substance that
9、 only contains one type of atom so it cannot be converted into anything simpler by chemical means note type does not imply that all atoms of an element are identical Some elements are composed of a mixture of closely related atoms called isotopes refer to Section 2 1 All elements have distinct names
10、 and symbols Atoms can join together by chemical bonds to form compounds Compounds are therefore made up of particles of the same type but these particles are made up of different types of atoms chemically bonded together This means that in a compound the constituent elements will be present in fixe
11、d proportions such as H2O water H2SO4 sulfuric acid CO2 carbon dioxide and NH3 ammonia The only way to separate a compound into its component elements is by a chemical change that breaks some bonds and forms new ones resulting in new substances The physical and chemical properties of a compound are
12、usually totally unrelated to those of its component elements For example a match will not burn in water even though it is a compound of oxygen The mole concept and Avogadro s constant 2 Formulas 3 Chemical equations 4 Mass and gaseous volume relationships in chemical reactions 5 Solutions 070823 Che
13、m Chap 1 8 indd 16 12 2007 10 35 06 AM Chapter 1 2 SubstanceProportionsPropertiesseparation Element Copper a pure element Contains only one type of atom These will depend on the forces between the atoms of the element Cannot be converted to a simpler substance by chemical means Compound Water a comp
14、ound of oxygen and hydrogen Always contains two hydrogen atoms for every oxygen atom Totally different from its elements e g water is a liquid but hydrogen and oxygen are gases Requires a chemical change e g reacting with sodium will produce hydrogen gas Mixture Air a mixture of nitrogen oxygen argo
15、n carbon dioxide etc The proportions of the gases in air especially carbon dioxide and water vapour can vary Similar to its constituents e g supports combustion like oxygen Can be carried out by physical means e g by the fractional distillation of liquid air Figure 102 The properties of a typical el
16、ement compound and mixture Figure 101 The particles in an element a compound and a mixture ElementCompoundMixture core the types of atoms There are 92 kinds of atoms and hence 92 chemical elements that occur naturally and about another seventeen that have been produced artificially Only about thirty of these elements are usually encountered in school chemistry and most of this would deal with about half of these shown in bold type in Figure 103 Each element is given a symbol that is used to writ
