PowerPoint to accompany. Chapter 1. Introduction: Matter, Measurement and Molecules

Transcription

1 PowerPoint to accompany Chapter 1 Introduction: Matter, Measurement and Molecules

2 CHEMISTRY study of matter & changes it undergoes matter is anything that has mass and takes up space - study of physical & chemical properties of matter - what changes occur in these properties, in the course of/as the result of a chemical reaction, & how these changes may be observed - why the reaction involved does (or doesn t ) occur understand, & be able to explain macroscopic changes from an atomic/molecular (submicroscopic) perspective slide 2 of 45 States (Phases) of Matter - solid, H 2 O(s); liquid, H 2 O(l); gas, H 2 O(g) - phase transitions specific P/T values, governed by properties of atoms/molecules

3 Matter - atoms are building blocks of matter - each element is made of same kind of atom/molecules* - compounds made of two or more different kinds of elements bonded together slide 3 of 45

4 slide 4 of 45

5 Pure Substances, Elements & Compounds pure substance - has distinct properties & unvarying/constant composition eg. NaCl(s), H 2 O(l), HCN(g) - element - substance that cannot be decomposed into simpler substances eg. Cl 2 (g), Br 2 (l), I 2 (s); Ne(g), Hg(l), Au(s) - compound - substance composed of 2 or more different elements 2 or more different kinds of atoms eg. UF 6 (g), H 2 O(l), CaCO 3 (s) slide 5 of 45 Law of Constant Composition/Definite Proportions (Joseph Proust ca 1800)...elemental composition of pure substance is always the same - different samples of pure compound have the same elemental composition - elements present in such samples have same proportion by mass

6 Mixtures - combination of 2 or more substances, in which each substance retains own chemical identity & can thus be separated from each other - 2 types: heterogeneous: - mixture of visibly different composition, properties or appearance eg. sand in H 2 O(l) (s, l), sand & NaCl (s, s), petrol & H 2 O(l) (l, l) homogeneous: - mixture of visibly uniform composition, properties & appearance throughout eg. NaCl(aq) (s,l), air (g,g), stainless steel (s,s), soda water (g,l) slide 6 of 45 Properties: - physical: measurement without changing identity/composition eg. mass, chemical:must involve change in chemical identity eg. flammability, reactivity - extensive: dependent on quantity of sample involved eg. mass, volume intensive: independent of quantity eg., m.p., b.p.; useful for identification

7 Classification of Mixtures slide 7 of 45

8 Physical Separation of Mixtures Separates a homogeneous mixture on the basis of differences in boiling point. slide 8 of 45

9 The Scientific Method - systematic approach to solving problems - checking answers to calculation problems to see that they are both physically and commonsensically meaningful slide 9 of 45 Units of Measurement SI Units: Temperature - SI unit of temperature called the Kelvin - based on the properties of gases - K = O C (but T(K) = T( O C); why?) - no negative Kelvin temperatures, as 0 K (= O C; absolute zero ) is physically unattainable (~1 nanok) point at which all atomic/molecular movement ceases

10 Units of Measurement SI Units: Système International d Unités Metric System: - prefixes convert base units into units appropriate for item being measured. Tera T slide 10 of 45

11 Units of Measurement Derived SI Units: Volume, V; E - 1 m 10 d(eci)m 100 c(enti)m 1000 m(illi)m - 1 L 1 dm 3 (a cube 1 dm x 1 dm 1 x dm) - 1 ml 1 cm 3 (a cube 1 cm x 1 cm 1 x cm) - 1 kl 1 m 3 (a cube 1 m x 1 m x 1 m) ie. 1 m dm cm mm 3 1 kl 10 3 L 10 6 ml 10 9 (micro)l Derived SI Units: Density, or d; I - physical property; units are usually - g cm -3 (g/cm 3, g ml -1, g/ml) for liquids & solids - g dm -3 (g/dm 3, g L -1, g/l) for gases slide 11 of 45 density = mass/volume = m/v

12 Uncertainty in Scientific Measurements - different laboratory measuring devices have different uses & are calibrated to varying degrees of accuracy & precision cm 3 gradmecyl & syringe 0.5/0.2/0.1 cm 3 - burette 0.02/0.01 cm 3 (ie 20/10 L) - measurements should always be given to the highest possible precision* attainable with instrument, & quoted in specific format - accuracy: proximity of reading(s) to true value precision: proximity of readings to each other slide 12 of 45 Significant Figures - all digits of a measured quantity, including those that have been estimated, & are thus uncertain, are called significant figures - greater number of significant figures greater certainty in measurement

13 CHEM 110 sem sem slide 13 slide 13 of 45 Significant Figures 1. any figure that is not zero is significant: snot/units 845 ml s.f mg s.f. 2. zeroes between non-zero figures are significant: 1906 ml s.f J s.f. 3. exact ( counting ) numbers by definition have an number of s.f., so physical constants defined to be exact numbers do so also...: 1 atm kpa 760 mmhg; 0 O C 32 O F K all s.f. 4. leading zeroes (to the left of the first non-zero figure) are not significant: snot/units kg s.f L s.f. 5. trailing zeroes (to the right of the last non-zero figure) are significant only if the number has a d.p.: mm s.f mm s.f. 6. in measurements without a d.p., the number of s.f. is ambiguous: 1200 mm?? either: i) use snot OR ii) 1200.

14 slide 14 of 45 Using Significant Figures in Calculations - all calculations governed by two fundamental rules multiplication/division - number of s.f. in final answer is the LEAST of numbers of s.f. in each of original measurements addition/subtraction - number of d.p. in final answer is the LEAST of numbers of d.p. in each of original measurements Eg. 1 Calculate i) volume, in mm 3, of a box of length cm, breadth x 10-1 m, & height 4.2 mm ii) density ( ) of a pure liquid, in g cm -3, if g of it is needed to fill the box completely i) 6.9 x 10 4 mm 3; ii) 1.5 g cm -3 Eg. 2 An empty container of mass g has a mass of 86.1 g when filled with dm 3 of a pure liquid. Determine the of this liquid in g cm g cm -3

15 1.6 slide 15 of 45 Early Atomic Theory John Dalton each element is composed of very small, indestructable, particles called atoms* - all atoms* of given element are physically & chemically identical to each other, but atoms of a particular element are different from atoms of all other elements - Law of Conservation of Mass - atoms are neither created or destroyed in chemical reactions - mass reactants start = mass products completion* - Law of Constant Composition - different samples of a pure compound have the same elemental composition - elements present in such samples have same proportion by mass - Law of Multiple Proportions - if 2 elements (C & O) can combine to form 2 or more different compounds (CO & CO 2 ), the different masses of one element (O) combining with a fixed mass of the other (C) can be expressed as a simple integral ratio

16 1.7 The Discovery of Atomic Structure Cathode Rays & Particles (JJ Thomson, 1897) - electrical discharges from cathode originally thought to be new form of radiation - showed that radiation emitted was - independent of cathode material used - deflected by magnetic/electric fields - findings consistent with model in which beam / rays composed of negatively charged (-) particles with charge/mass ratio of x 10 8 C g -1, or Electron Charge & Mass (Robert Millikan, 1909) - oil drop experiment x 10-9 g C -1 slide 16 of 45 - (-) charge on oil drops found always to be a multiple of minimum value of 1.6(02) x C ie x C must be charge of single electron (e - ) - mass of single e - determined to be x g - only 1/1836 of mass of an H atom - first subatomic particle

17 1.7 Radioactivity - spontaneous emission of high-energy radiation, as result of radioactive decay - first (serendipitous) report, in a uranium ( ) salt (Henri Becquerel, 1896) - decay occurs via 1 of 3 pathways (Rutherford, ) - particle (He 2+ ion) emission - particle (e - ) emission - ray emission slide 17 of 45 Nuclear Atom (Rutherford, 1910) - gold ( ) foil experiment - observed scatter/deflection pattern obtained by shooting particles (He 2+ ) at very thin sheet of ( ) foil - most particles undeflected, as expected, but some were not, which wasn t.. - experimental results best explained using the nuclear atom model - most of an atom s total volume is effectively empty space, surrounding a very small (nucleic volume of atomic volume), very dense ( g cm -3 ) atomic nucleus

18 slide 18 of 45

19 1.8 Modern Atomic Structure - more than % of atom mass & entire Q + centred in atomic nucleus, where nucleons (protons, p + (Rutherford, 1919) & neutrons, n O (Chadwick, 1932) are collectively bound together by strong nuclear force - atomic nucleus surrounded by much larger atomic volume, containing as many e - as p +, so atom is electrically neutral & held together by force of Coulombic/ electrostatic attraction slide 19 of 45

20 1.8 Modern Atomic Structure - more than % of atom mass & entire Q + centred in atomic nucleus, where nucleons (protons, p + (Rutherford, 1919) & neutrons, n O (Chadwick, 1932) are collectively bound together by strong nuclear force - atomic nucleus surrounded by much larger atomic volume, containing as many e - as p +, so atom is electrically neutral & held together by force of Coulombic/ electrostatic attraction slide 20 of 45

21 Atomic (Z) & Mass (A) Numbers - atoms of different elements have different numbers of p + in their nuclei mass number (A) number of p + & n O atomic number (Z) number of p + (number of e - in neutral atom) Z A E element symbol slide 21 of 45

22 Isotopes - atoms of same element having different numbers of n O in their nuclei - ie. same Z, different A, or same Z, different N - chemical properties largely similar, but physical properties, & particularly the nucular ones involving radioactive nuculei, can be very different - each Mg ( ) atom is one of three naturally occurring isotopes 24 Mg; 25 Mg; 26 Mg Mg-24; Mg-25; Mg-26 - three isotopes of H individually named: - protium ( 1 H, 1 p + /0 n O ); deuterium ( 2 H, 1 p + /1 n O ); tritium ( 3 H, 1 p + /2 n O ) slide 22 of 45 - four isotopes of C: - 11 C; 12 C; 13 C (NMR probes & MRI scanners); 14 C( radiocarbon dating)

23 Isotopes Eg. 3 Complete the table below: Element name Symbol p + N o e - A Au Ba Pb Strontium 90 CHEM 110 sem sem slide 23 slide 23 of 45 Experimentally... - High Resolution Mass Spectrometry (p. 28) used for very precise (4-6 d.p.; 7-10 s.f. in total) measurements of the masses of an element s isotopes & their naturally occurring abundances do: Q 1.44,

24 1.9 Atomic Mass The Atomic Mass Scale - more than % of atom mass & entire Q + centred in atomic nucleus, where nucleons (protons, p + (Rutherford, 1919) & neutrons, n O (Chadwick, 1932) are collectively glued together by strong nuclear force - atomic nucleus surrounded by immensely larger, virtually empty atomic volume, containing as many e - as p +, so atom is electrically neutral & held together by electromagnetic (Coulombic) attraction slide 24 of 45 - extremely small SI masses of individual atoms (~4 x g) too awkward for everyday usage, so masses expressed in unified atomic mass units (amu, u): 1 amu (u) = x g 1 g = x amu (u)

25 Average Atomic Masses of Naturally Occurring Elements - use average masses in real world calculations, as even smallest weighable sample (~1 g 10-6 g) involves gobsmackingly large (~10 15, or 10 quadrillion) numbers of atoms - noeaams calculated as weighted average of an element s isotopic masses (IMs) & naturally occurring abundances AAM = (IM x % ab/100) or (IM x fr ab) Eg. 4 a) Naturally occurring Mg has three isotopes: 24 Mg %, u 25 Mg %, u link Calculate its AAM. 26 Mg %, u slide 25 of 45 b) Naturally occurring Pb has four isotopes: 204 Pb 1.40 %, Pb %, Pb %, link Calculate its AAM. 208 Pb %,

26 Eg. 5 link Chlorine has two naturally occurring stable isotopes: 35 Cl u 37 Cl u If the (average) atomic mass of naturally occurring elemental Cl is u, what are the % abundances of the two isotopes? do: antimony, chromium, & nickel AM from IM s & abundances copper, rubidium abundances from IM s & AM* 1.10 p. 29 slide 26 of 45 The Periodic Table - rapid post-dalton growth in experiment-based chemical knowledge showed very quickly that many elements could be grouped together on basis of similarities in their physical & chemical properties - arrangement of elements in order of Z showed that these similarities occurred in repetitive/periodic patterns, & agreed so closely with experimentally acquired data, that phys/chem properties of 2 missing elements were accurately predicted before their being reported as formally discovered, &/or phys/chem properties characterized

27 The Periodic Table CHEM 110 sem sem slide 27 slide 27 of 45

28 The Periodic Table Metals, Non-Metals, & Metalloids Metals Metalloids Non-Metals slide 28 of 45

29 The Periodic Table Groups & Periods Groups (columns) Periods (rows) slide 29 of 45

30 The Periodic Table Groups Alkali Metals Group 1 s-block elements Groups 1 & 2 Alkali Earth Metals Group 2 Transition Metals d-block elements Groups 3-12 Main group elements p-block elements Groups slide 30 of 45 Lanthanides Actinides f-block elements

31 The Periodic Table p-block groups Cyanogens Group 15 Chalcogens Group 16 Halogens Group 17 Noble Gases Group 18 slide 31 of 45

32 1.11 p. 31 Molecules & Molecular Compounds - other than 6 noble gas elements (group 18/8A; He, Ne, Ar, Kr, Xe, Rn), which occur naturally only as single isolated atoms, all other elements found naturally only as molecules, molecular compounds or ions - 7 elements (H 2, N 2, O 2, *F 2, *Cl 2, *Br 2, *I 2 ) occur naturally as diatomic molecules - different allotropes &/or polymorphs of P, Si, S - molecules almost always contain only nonmetals slide 32 of 45 - name of element furthest left on PT written first - both elements in same group on PT, element with higher Z written first - name of 2 nd element given the ending -ide - Greek prefixes used to indicate number of atoms of each element N 2 O 4 is dinitrogen tetroxide P 4 S 10 is tetraphosphorus decasulfide

33 1.11 p. 31 Molecules & Molecular Compounds - other than 6 noble gas elements (group 18/8A; He, Ne, Ar, Kr, Xe, Rn), which occur naturally only as single isolated atoms, all other elements found naturally only as molecules, molecular compounds or ions - 7 elements (H 2, N 2, O 2, *F 2, *Cl 2, *Br 2, *I 2 ) occur naturally as diatomic molecules - different allotropes &/or polymorphs of P, Si, S - molecules almost always contain only nonmetals slide 33 of 45 - name of element furthest left on PT written first - both elements in same group on PT, element with higher Z written first - name of 2 nd element given the ending -ide - Greek prefixes used to indicate number of atoms of each element N 2 O 4 is dinitrogen tetroxide P 4 S 10 is tetraphosphorus decasulfide

34 1.11 p. 31 Molecules & Molecular Compounds - other than 6 noble gas elements (group 18/8A; He, Ne, Ar, Kr, Xe, Rn), which occur naturally only as single isolated atoms, all other elements found naturally only as molecules, molecular compounds or ions Elements, Molecules & Chemical Formulae - 7 elements (H 2, N 2, O 2, *F 2, *Cl 2, *Br 2, *I 2 ) occur naturally as diatomic molecules - sundry others: P 4, S 8, O 3, C (graphite & diamond// buckyballs & nanoassemblies) slide 34 of 45 Inorganic Nomenclature - systematic rules leading to unique name for each substance (> 40 x 10 6 ) - sufficiently informative that substance s chemical formula can be deduced from it - based on division of substances into categories: - organic: C, H, N, O, S, Hal, Cu, Fe, Ca, Zn...etc - inorganic: organic i) molecular (preceding 2 slides) ii) ionic iii) acids

35 1.13 p. 33 Ions & Ionic Compounds - atomic nucleus completely unaffected by chemical processes, BUT - atoms can become ions by losing or gaining e - in chemical reaction [O] - cations have + ive charges & are usually formed by elements on LHS of PT [R] - anions have - ive charges & are usually formed by elements on RHS of PT - atoms* with electric charge (p + e - ) due to gain/loss of e - (not p + ) - ionic compounds generally formed between metals & non-metals slide 35 of 45

36 Cation Charges slide 36 of 45

37 Cation Charges slide 37 of 45 - C + formed from metal atoms have same name as metal: - Na + is sodium ion; Ca 2+ is calcium ion; Al 3+ is aluminium ion - in metals that can form 1+ different(ly charged) C +, + ive charge shown by (I), (II), (IV) - Cu + is copper(i) ion; Cu 2+ is copper(ii) ion; Au 3+ is gold(iii) ion; Pb 4+ is lead(iv) ion - cations formed from non-metal atoms have names that end in -ium - NH 4+ is ammonium ion

38 Anion Charges slide 38 of 45

39 - each element is composed of very small, indestructable, particles called atoms* - all atoms* of given element are physically & chemically identical to each other, but atoms of a particular element are different from atoms of all other elements - Law of Conservation of Mass - atoms are neither created or destroyed in chemical reactions slide 39 of 45 - mass reactants start = mass products completion* - Law of Constant Composition - different samples of a pure compound have the same elemental composition - elements present in such samples have same proportion by mass - Law of Multiple Proportions - if 2 elements (C & O) can combine to form 2 or more different compounds (CO & CO 2 ), the different masses of one element (O) combining with a fixed mass of the other (C) can be expressed as a simple integral ratio

40 Molecules and Chemical Formulae The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. Notice how the composition of each compound is given by its chemical formula. CHEM 110 sem sem slide 40 slide 40 of 45 Figure 1.29

41 Writing Formulae - as compounds are electrically neutral, the formula of a compound can easily be constructed simply by: - writing value of + ive charge on cation as subscript on anion, & - writing value of - ive charge on anion as subscript on cation - formula can then be simplified, if subscripts are not in the lowest whole number ratio, by dividing throughout by smallest coefficient - Ca 2 O 2 becomes CaO, Al 2 Cl 6 becomes AlCl 3 slide 41 of 45

42 Inorganic Nomenclature - systematic rules leading to unique name for each substance (> 40 x 10 6 ) - sufficiently informative that substance s chemical formula can be deduced from it - based on division of substances into categories: - organic: C, H, N, O, S, Hal, Cu, Fe, Ca, Zn...etc - inorganic: organic i) ionic ii) molecular iii) oxyanions & acids slide 42 of 45

43 Oxyanion & Acid Nomenclature & Formulae - ClO ClO 3 - ClO 2 ClO - perchlorate ion (one more O atom than chlorate) chlorate ion (one more O atom than chlorite) chlorite ion (one more O atom than hypochlorite) hypochlorite ion slide 43 of 45 - acids containing anions whose names end in -ide are named by changing the -ide ending to -ic, adding the prefix hydro- to this anion name, and then following with the word acid - acids containing anions whose names end in -ate/-ite are named by changing the -ate ending to -ic or the -ite ending to -ous and then adding the word acid

44 Eg. 4 a) Naturally occurring Mg has three isotopes: 24 Mg %, u 25 Mg %, u Calculate its AM. 26 Mg %, u AM = (IM x % ab/100) = {[ x (78.90/100)] + [ x (10.00/100)] + [ x (11.10/100)] } = back = u (amu) [24.306] b) Naturally occurring Pb has four: 204 Pb 1.40 %, Pb %, Pb %, Calculate its AM. 208 Pb %, slide 44 of 45 back AM = (IM x % ab/100) = = u (amu) [207.22]

45 Eg. 5 Chlorine has two naturally occurring stable isotopes: 35 Cl u 37 Cl u If the (average) atomic mass of naturally occurring elemental Cl is u, what are the % abundances of the two isotopes? Assume that the fractional abundance of 35 Cl is z......then the fr ab of 37 C is 1-z ( fr ab = 1) AM = (IM x fr ab) = [( ) x z] + [( ) x (1-z)] = z z = z ( = ) z = dp 6 dp slide 45 of 45 back % ab 35 Cl = 75.76% % ab 37 Cl = %