LU1 Sem 1 Student Version 2023 PDF

LEARNING UNIT 1 CHEMISTRY AND CHEMICAL NOMENCLATURE  Content 1.2.1 Matter, elements and compounds 1.2.2 Symbols and formulae 1.2.3 Measurement in scientific study 2  Learning Outcomes i. Define matter, element, compound, mixture, atom,...

LEARNING UNIT 1 CHEMISTRY AND CHEMICAL NOMENCLATURE  Content 1.2.1 Matter, elements and compounds 1.2.2 Symbols and formulae 1.2.3 Measurement in scientific study 2  Learning Outcomes i. Define matter, element, compound, mixture, atom, molecule and ion. ii. Define the term symbols and formulae. iii. Define types of measurements and their units. 3  Principles of Chemistry Chemistry deals with the properties and MyRA transformation of matter and the energy associated with those changes. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 4  Principles of Chemistry MyRA Figure 1: Digestion of food in our bodies as an example of chemical reactions Source: Wikimedia Commons PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 5  Matter, elements and compounds Element Only one type of atom Example: Na, O2 Matter occupies space and have mass, exists in solid, liquid or gaseous Compound state two or more elements chemically bonded together Example: H2O, NaCl PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 6  Matter, elements and compounds Figure 2: Electrolysis of water Source: McGraw Hills The electrolysis of water (compound) to form hydrogen (element) and oxygen (element). PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 7  Matter, elements and compounds Mixtures are impure matter consists of two or more elements or compounds that are mixed without combining chemically. Can be separated using physical or mechanical Source: https://kaiserscience.wordpress.com/chemistr means. y/what-is-matter/ PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 8  Matter, elements and compounds Heterogeneous mixtures versus Homogenous mixtures Not uniformly Uniformly distributed distributed Immiscible Miscible Different phase Single phase Separable by Inseparable by mechanical means mechanical means Known as suspension or Known as solution colloid PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 9  Matter, elements and compounds Atom Na, Na,C,C, HeHe the smallest neutral particle of an element that can take part in a chemical reaction. Molecule O2O , CO , CO 2 a neutral particle made up of either 2 2 atoms of the same element or atoms of different elements. Ion Na++, SO 2– Na , SO442– a charged particle of either one atom or atoms of different elements. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 10  Matter, elements and compounds Physical Chemical chemical Properties Properties reaction a substance shows by a substance shows as it itself, without changes into or changing into or interacts with another interacting with substance (or another substance. substances). PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 11  Matter, elements and compounds Physical Chemical Properties Properties colour reactivity with acids melting point flammability density corrosiveness electrical conductivity oxidation states smell electronegativity PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 12  Symbols and formulae Symbols abbreviations to denote a chemical element one or two-letters (occasionally three) with the first letter capitalised Represent not only element but also specific amount eg. O represent one atom of oxygen or 1 mole of oxygen atoms. (1 mole = 6.02  1023) Avrogado constant Na represent one atom of sodium or 1 mole of sodium atoms. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 13  Symbols and formulae Formulae representing chemical compounds/combination of the symbols of the constituent elements. eg. H2O represent water or 1 mole of water molecule. NaCl represent sodium chloride or 1 mole of sodium chloride. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 14  Symbols and formulae Measurement in scientific study - SI Base Units Physical Quantity Unit Unit (Dimension) Name Abbreviation Mass Kilogram kg Length Meter m Time Second s Temperature Kelvin K Electric Current Ampere A Amount of Substance Mole mol Luminous intensity Candela cd PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 15  Symbols and formulae Derived unit - are combination of these seven base units. For example, the derived unit for speed is meter per second (m/s), which comes from the base unit for length (m) divided by the base unit for time (s). PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 16  Measurement in scientific study Scientific Notation For quantities that are much smaller or much larger than the base unit, we use prefixes and exponential (scientific) notation. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 17  Measurement in scientific study Prefix Symbol Number Word Exp. Notation tera T 1,000,000,000,000 trillion 1012 giga G 1,000,000,000 billion 109 mega M 1,000,000 million 106 kilo k 1,000 thousand 103 hecto h 100 hundred 102 deka da 10 ten 101 - - 1 one 100 deci d 0.1 tenth 10-1 centi c 0.01 hundredth 10-2 milli m 0.001 thousandth 10-3 micro  0.000001 millionth 10-6 nano n 0.000000001 billionth 10-9 pico p 0.000000000001 trillionth 10-12 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 18  Measurement in scientific study Exponential (scientific) notation A practical way of writing very large or very small quantities They are expressed in the form: SINGLE DIGIT A  10n where 1 ≤ A < 10 and n is an integer eg. 0.0000123 written as 1.23  10−5 123000 written as 1.23  105 (3 s.f.) or 1.2300  105 (5 s.f.) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 19  Measurement in scientific study Exercise 1. Convert the following to exponential notation: (a) 75 000 000 (b) 0.0006042 2. Convert the following to conventional notation: (a) 1.38 × 105 (b) 8.41 × 10−6 3. Calculate the following using exponential notation: (a) (5.5 × 1012)(3.1 × 10−6) (b) (1.7 × 10 −5)  (8.2 × 10−8) (c) (1.45 × 104) + (3.2 × 103) − (3.22 × 105) 20  Measurement in scientific study Volume In chemistry, the most important volume units are liter (L) and milliliter (mL). 1 L = 1 dm3 = 10−3 m3 1 mL = 1 cm3 = 10−3 dm3 = 10−3 L Mass and Weight The mass of an object refers to the quantity of matter it contains and it is constant. The weight of an object depends on its mass and the strength of the local gravitational field pulling on it. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 21  Measurement in scientific study Density The density of an object is its mass divided by its volume: mass Density = volume Mass and volume are examples of extensive properties, those dependent on the amount of substance present. Density is an intensive property, one that is independent of the amount of substance present. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 22  Measurement in scientific study Temperature and Heat Temperature is a measure of how hot or cold a substance is relative to another substance. Heat is the energy that flows between objects that are at different temperatures. Temperature scales: Celsius (oC), Kelvin (K) and Fahrenheit (oF) Zero point in the Kelvin scale, 0 K, (absolute zero) equals −273 oC. T (in K) = T (in oC) + 273 T (in oC) = T (in K) − 273 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 23  Measurement in scientific study The Fahrenheit scale differs from the other scales in its zero point and in the size of its unit. 100 degrees Celsius equals to 180 degrees Fahrenheit, o 180 o 9 o 1 C= F= F 100 5 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 24  Measurement in scientific study To convert a temperature in oC to oF, first change the degree size and then adjust the zero point: 0 degree celcius = 32 o 9 o degree F T (in F) = T (in C) + 32 5 To convert a temperature in oF to oC, first adjust the zero point and then change the degree size: o o 5 T (in C) = [T (in F) - 32] × 9 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 25 Measurement in scientific study Exercise Mercury melts at 234 K. What is its melting point in oC and oF? Answer: -39oC; -38.2oF 26  Content Content 1.2.4 Uncertainty in measurement – significant figures 1.2.5 Precision and accuracy 1.2.6 Dimensional analysis  Learning LearningOutcomes Outcomes i. Determine significant figure in scientific writing. ii. Define precision and accuracy terms. iii. Convert various units using dimensional analysis.  Uncertainty in measurement – significant figures Every measurement includes some uncertainty.  0.1 kg express potatoes weighs 2.0  0.1 kg of uncertainty in the between 1.9 and potatoes measurements 2.1 kg. chemicals  0.001 kg express 2.036  0.001 kg of weighs between uncertainty in the chemical 2.035 and 2.037 measurements kg 2.036  0.001 more certainty than 2.0  0.1 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 29  Uncertainty in measurement – significant figures Both certain and uncertain digits recorded in a measurement is called significant figures. The greater the number of significant figures in a measurement, the greater the certainty. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 30  Uncertainty in measurement – significant figures (a)The smallest division: 10mL Beaker (b)Volume of water in the beaker: 48mL (c) The reading error: 10/10= +-1mL (d)Significant figures of this volume: 2.s.f (e)State the certain and uncertain number in the reading: 4(certain), 8(uncertain) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 31  Uncertainty in measurement – significant figures (a)The smallest division: 1mL Graduated Cylinder (b)Volume of water in the beaker: 36.5mL (c) The reading error: 1/10= +-0.1mL (d)Significant figures of this volume: 3.s.f (e)State the certain and uncertain number in the reading: 3,6( certain), 5(uncertain) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 32  Uncertainty in measurement – significant figures Burette (a)The smallest division: 0.1mL (b)Volume of water in the beaker: 20.38mL (c) The reading error: 0.1/10= +-0.01mL (d)Significant figures of this volume: 4.s.f (e)State the certain and uncertain number in the reading: 2,0,3(certain), 8(uncertain) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 33  Uncertainty in measurement – significant figures Examples of significant figures (a)0.123 - 3 significant figures (b)106 - 3 significant figures (c)0.001 oC has only 1 significant figure (d)0.012 g has 2 significant figures (e)0.0230 mL has 3 significant figures (f)0.20 g has 2 significant figures PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 34  Uncertainty in measurement – significant figures 50,600 calories may be 3, 4, or 5 significant figures 1. Write the above number in 3 significant figures. 2. Write the above number in 4 significant figures. 3. Write the above number in 5 significant figures. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 35  Uncertainty in measurement – significant figures Rounding should be done on the final answer to avoid accumulating rounding off errors. 12.6 is 12.51 is rounded rounded Rounding off to 13 to 13 12.4 is 11.5 is 12.5 is rounded rounded rounded to 12 to 12 to 12 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 36  Uncertainty in measurement – significant figures Examples 121.7968 (round to 2 decimal point or 5 significant figures): 121.80 121.7948 (round to 2 decimal point or 5 significant figures): 121.79 43.55 (round to 1 decimal point or 3 significant figures): 43.6 43.85 (round to 1 decimal point or 3 significant figures): 43.8 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 37  Uncertainty in measurement – significant figures Exercise 1. Determine the number of significant figures for each of the following quantities. (a) 0.0030 L (b) 0.1044 g (c) 53.069 m (d) 23 046 mL (e) 2 500 s (f) 250 oC 2. Round the following number to the number of significant figures as indicated. (a) 2.0560 [3 s.f.] (b) 0.000372 [2 s.f.] (c) 300.6 [2 s.f.] (d) 602 200 [3 s.f.] (e) 62.85 [3 s.f.] (f) 0.005 315 [3 s.f.] 38  Uncertainty in measurement – significant figures Significant Figures in Arithmetic Numbers to be added or subtracted having same number of digits 7.26 x 10-4 5.345 – 6.69 x 10-4 + 6.728 0.57 x 10-4 12.073 Answer should have the same decimal place as the individual numbers PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 39  Uncertainty in measurement – significant figures Numbers to be added or subtracted do not have same number of digits 18.9984032 + 18.9984032 + 83.80 121.7968064 not significant limit the significant figures in the answer to the least certain one, ie. rounded to 121.80 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 40  Uncertainty in measurement – significant figures Multiplication and Division 3.26 x 10-5 4.3179 x 10-5 34.60 X 1.78 X 3.6  2.46287 5.8028 x 10-5 1.554444 x 10-4 14.04865 not significant 1.6 x 10-4 14.05 The answer contains the same no. of s.f. as the number in the calculation having the fewest s.f. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 41  Uncertainty in measurement – significant figures Exercise 1. Give the correct number of significant figures for: 4500, 4500. , 0.0032, 0.04050 2. Give the answer to the correct number of significant figures: (a) 4503 + 34.90 + 550 = ? (b) 1.367 − 1.34 = ? (c) (1.3  103)(5.724  104) = ? (d) 6305/0.010 = ? Answer: 1. 2 or 3 or 4, 4, 2, 4 ; 2a. 5088 (4 s.f.) ; b. 2.7  10-2 (2 s.f.) ; c. 7.4  107 (2 s.f.) ; d. 6.3  105 (2 s.f.) 42  Precision and accuracy Accuracy Indicates the closeness of the measurement to its true value PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 43  Precision and accuracy Precision Is the closeness of data to other data that have been obtained in exactly the same way PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 44  Precision and accuracy Accurate values that agree well with each other PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 45  Precision and accuracy Example The concentration of a solution was determined 3 times: Result: 1.74 M, 1.73 M and 1.75 M  average = 1.74 M Yes, very precise! The true concentration: 2.32 M …but, not accurate! PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 46  Precision and accuracy Examples of Precision and Accuracy Low Accuracy High Accuracy High Accuracy High Precision Low Precision High Precision If you are playing soccer and you always hit the left goal post instead of scoring, then you are not accurate, but you are precise! PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 47  Precision and accuracy All measurements involve a certain degree of error (bias). Examples of Bias The scales read "1 kg" when there is nothing on them. You measure your height wearing shoes with thick soles. A stopwatch that takes half a second to stop when clicked. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 48  Precision and accuracy Degree of Accuracy Accuracy depends on the instrument you are measuring with. As a general rule: The degree of accuracy is half a unit each side of the unit of measure. If your instrument measures in "1"s, then any value between 6½ and 7½ is measured as "7" If your instrument measures in "2"s. then any value between 7 and 9 is measured as "8" PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 49  Precision and accuracy Exercise 1. If your instrument measures in "1"s then any value between which two values would be measured as "5"? 2. If your instrument measures in "5"s then any value between which two values would be measured as "45"? Answer: 1. 4½ and 5½ 2. 42½ and 47½ 50  Precision and accuracy Ways of expressing accuracy Absolute Errors – the difference between the expected value and the measured value. eg. A 2.62 g sample was analyzed to be 2.52 g, the absolute error is: 2.62 g – 2.52 g = I −0.10 g I = 0.10 g (same unit as the measurement) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 51  Precision and accuracy Ways of expressing accuracy Relative Error – the absolute error divided by the exact value. 0.10 = 0.038 2.62 Percentage Error - relative error expressed in terms of per 100 0.10 × 100% = 3.8 % 2.62 Relative Accuracy – the measured value divided by the exact value 2.52 = 0.96 2.62 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 52  Dimensional analysis A technique that is used to change any unit(s) from one to another Three basic concepts in unit conversion: 1. We can multiply or divide any quantity by one, and the result will still be equal to the original quantity. eg. 6(1)=6 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 53  Dimensional analysis 2. The numeral one (1) can be written in many different ways when written in a fraction form. As long as the numerator of the fraction equals the denominator of the fraction, the fraction is equal to one (1). 1 2 4 10 𝑓𝑒𝑒𝑡 𝑚𝑖𝑙𝑒𝑠 eg. 1= = = = = = 1 2 4 10 𝑓𝑒𝑒𝑡 𝑚𝑖𝑙𝑒𝑠 Any definition involving units can be made into a unit definition (conversion factor) equal to one. 12 𝑖𝑛𝑐ℎ𝑒𝑠 2 𝑓𝑒𝑒𝑡 eg. 1= = 1 𝑓𝑜𝑜𝑡 24 𝑖𝑛𝑐ℎ𝑒𝑠 In dimensional analysis we multiple by definitions (conversion factors) that equal one. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 54  Dimensional analysis 3. Reviewing fraction multiplication, we can first cancel before multiplying. eg. 2 6 1  = 3 8 2 3 and 6 can cancel to 1 and 2 2 and 8 can cancel to 1 and 4 2 and 4 can cancel or simplify to 1 and 2. Any top can be canceled with any bottom when multiplying. Units act like numbers but are separate from the number. Units can also cancel tops and bottoms. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 55  Dimensional analysis Example 1 Converting 3 inches to feet 3 inches can be written as a fraction by putting it over 1 3 inches 1 Take this fraction and multiply by one (1), the conversion factor, so by cancellation we get to a new unit, feet. 3 inches 1 foot  = ? ft 1 12 inches PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 56  Dimensional analysis Example 2 How many decades are in 5 centuries? Start with 5 centuries and proceed to multiply by definitions that equal one (1) until the unit has changed from centuries into decades. 5 𝑐𝑒𝑛𝑡𝑢𝑟𝑖𝑒𝑠 100 𝑦𝑒𝑎𝑟𝑠 1 𝑑𝑒𝑐𝑎𝑑𝑒 × × = ? 𝑑𝑒𝑐𝑎𝑑𝑒𝑠 1 1 𝑐𝑒𝑛𝑡𝑢𝑟𝑦 10 𝑦𝑒𝑎𝑟𝑠 Canceling the numbers and units we get the answer 50 decades. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 57  Dimensional analysis Exercise 1. How many seconds are in one year? Hint: start with 1 year and proceed to multiply by ones until the unit has changed from years into seconds. 1 year 365 days =     = ? sec 1 1 year 58  Dimensional analysis Exercise 2. What is the density of mercury (13.6 g/cm3) in units of kg/m3? 3. How many atoms of hydrogen can be found in 45 g of ammonia, NH3? Given: 1 mole of NH3 has a mass of 17 grams. 1 mole of NH3 contains 6.02 x 1023 molecules of NH3. 1 molecule of NH3 has 3 atoms of hydrogen in it. 4. What is the molarity of a solution containing 14.8 g of KOH in 750 mL aqueous solution? 59  Dimensional analysis Answer 1. 𝑘𝑔 13.6 𝑔 (100 𝑐𝑚)3 1 𝑘𝑔 ?𝐷 3 = 3 × 3 × 𝑚 1 𝑐𝑚 (1 𝑚) 1000 𝑔 13.6 𝑔 1 × 106 𝑐𝑚3 1 𝑘𝑔 = 3 × 3 × 1𝑐𝑚 1𝑚 1000 𝑔 = 1.36 × 104 𝑘𝑔 𝑚−3 2. ? 𝑎𝑡𝑜𝑚𝑠 𝐻 1 𝑚𝑜𝑙 𝑁𝐻3 6.02 × 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁𝐻3 = 45 𝑔 𝑁𝐻3 × × 17 𝑔𝑁𝐻3 1 𝑚𝑜𝑙 𝑁𝐻3 3 𝑎𝑡𝑜𝑚𝑠 𝐻 × = 4.8 × 1024 𝑎𝑡𝑜𝑚𝑠 𝐻 1 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑁𝐻3 3. 14.8 𝑔 1 𝑚𝑜𝑙 1000 𝑚𝐿 × 𝑥 = 0.352 𝑚𝑜𝑙 𝐿−1 750 𝑚𝐿 56.1 𝑔 1𝐿 60  Content Content 1.3.1 Properties of fundamental particles 1.3.2 Effect of electric and magnetic fields on subatomic particles 1.3.3 Atomic number and mass number 1.3.4 Isotopes  Content Content 1.4.1 Relative isotopic mass and relative atomic mass 1.4.2 Relative molecular mass and relative formula mass 1.4.3 Isotopic abundance  Learning Outcomes Learning Outcomes i. Describe the properties of subatomic particles. ii. Define the term isotopes. iii. Calculate relative isotopic mass, relative atomic mass, relative molecular mass and relative formula mass. iv. Calculate the average atomic mass of an element given the relative abundances of isotopes or a mass spectrum.  Properties of fundamental particles What is inside this atomic model? PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 64  Properties of fundamental particles Subatomic Relative Relative Location Particle Atomic Mass Charge Proton, p 1 +1 In the nucleus Neutron, n 1 Neutral In the nucleus Orbiting in Electron, e– –1 shells outside the nucleus From the table, 1. What is the charge of a nucleus? 2. If the atom is neutral, what can be deduced on the number of protons and electrons? PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 65  Properties of fundamental particles Exercise 1. Draw five protons in the nucleus of the atom. Label them with their charge. 2. Draw six neutrons in the nucleus of the atom. 3. Draw two electrons in the first energy level and label them with their charge. 4. Draw three electrons in the second energy level and label them with their charge. 5. What element is represented by the diagram? 66  Effect of electric fields on subatomic particles What can you deduce from the figure above? If the electron are proton attract to deflected more than the negatively charge protons electron attract to positively charge neutron straight line because its neutral. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 67  Effect of magnetic fields on subatomic particles What can you deduce from the figure above? If the electrons are deflected more than the protons, what is the conclusion from this observation? PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 68  Atomic number and mass number The standard representation for an atom of an element shows the atomic number (left subscript) and the mass number (left superscript) of the element. Other ways of representation: 12C (with Z = 6) and carbon-12. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 69  Atomic number and mass number Exercise Complete the following table: Element Atomic Atomic Protons Neutrons Electrons number mass Li 3 7 3 4 3 P 15 31 15 16 15 Cl 17 35 17 18 17 Ni 28 59 28 31 28 K 19 39 19 20 19 atomic number= proton neutron=atomic mass-proton proton= electrons proton=atomic mass-neutron 70  Isotopes Atoms of the same element 1 1 2 H H H 1 3 1 12 6 C 13 6 C 14 6 C 35 17 Cl 37 17 Cl Same atomic number but different mass number Same number of protons and electrons, but different number of neutrons Same chemical properties Different physical properties Form compounds with the same formula PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 71  Relative isotopic mass and relative atomic mass The carbon-12 isotope is used as the standard for comparing the masses of other isotopes. Mass of one atom of the isotope Relative isotopic mass = 12 x Mass of one atom of carbon-12 Most elements exist as two or more isotopes, therefore Average mass of one atom of the element Relative atomic mass = 12 x Mass of one atom of carbon-12 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 72  Relative molecular mass and relative formula mass Relative molecular mass Average mass of one molecule of substance = 12 x Mass of one atom of carbon-12 The relative molecular mass of a compound is the sum of the relative atomic masses of all the atoms in the chemical formula. Relative molecular Mass of water (H2O) RMM = relative atomic mass of two hydrogen (H) + relative atomic mass of oxygen (O) = 2(1.01) + 16.00 = 18.02 For ionic compounds, the term Relative Formula Mass is used PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 73  Relative molecular mass and relative formula mass Exercise Calculate the formula mass for each of the substances 1. Iron (III) hydroxide, Fe(OH)3 2. Copper(II) nitrate, Cu(NO3)2 3. Ammonium sulphate, (NH4)2SO4 4. Magnesium hydroxide, Mg(OH)2 74  Isotopic abundance Isotopic Abundance is the abundance of each isotope in the mixture. It can be expressed in terms of percentage abundance or isotopic ratio. Example: Chlorine has 2 isotopes: 75.5% chlorine-35 and 24.5% chlorine-37 compare siapa lagi besar The isotopic ratio of 35Cl : 37Cl is 75.5 : 24.5 or 3 : 1 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 75  Isotopic abundance For elements that do not have isotopes (eg. F), the relative atomic mass is the same as the relative isotopic mass. For element that has isotopes, the relative atomic mass is calculated by multiplying the relative isotopic mass of each isotope by its relative abundance and adding them together. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 76  Isotopic abundance Example Calculate the relative atomic mass of silicon from the following data. Isotope Relative abundance (%) Silicon-28 92.21 Silicon-29 4.70 Silicon-30 3.09 28 x 92.21 + 29 x 4.7 + (30 x 3.09) Relative atomic mass = 100 = 28.1 PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 77  Isotopic abundance Exercise 1. Strontium has four isotopes with the following masses: 83.91 amu (0.56%), 85.91 amu (9.86%), 86.91 amu (7.00%), and 87.91 amu (82.58%). Calculate the atomic mass of strontium. Answer: 87.62 amu 2. Silver (Atomic weight 107.87) has two naturally-occurring isotopes with isotopic weights of 106.91 and 108.90. What is the percentage abundance of the lighter isotope? Answer: 51.76% 78  Content Content 1.4.4 Determination of relative atomic mass from mass spectrum 1.4.5 Interpreting mass spectra in terms of molecular fragments  Learning Outcomes Learning Outcomes i. Describe the mass spectrometer and how it works. ii. Interpret mass spectra in terms of relative abundance of isotopes of elements. iii. Interpret mass spectra in terms of molecular fragments of simple molecules.  The mass spectrometer Mass Spectrometry: Instrumental technique in which sample is converted to rapidly moving positive ions by electron bombardment. Charged particles are separated according to their masses. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 81  The mass spectrometer Mass Spectrometer is used to determine: elements present in an the relative isotopic the relative abundance unknown compound mass of element of isotopes in a sample of an element the relative atomic the relative the structure of mass of element molecular mass chemical compounds PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 82  The mass spectrometer Different parts of Mass Spectrometer PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 83  The mass spectrometer How it works? PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 84  The mass spectrometer PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 85  The mass spectrometer Five basic components of mass spectrometer Ionisation Deflection chamber chamber 01 02 03 04 05 Vapourisation Acceleration Detector chamber chamber PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 86  The mass spectrometer Vapourisation chamber To vapourise non gaseous samples (solid and liquid) in the sample inlet PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 87  The mass spectrometer Ionisation chamber High energy electrons from the electrically heated metal coil (the electron gun) bombard the gaseous sample particles One or more The sample electrons are particles may be knocked out of the fragmented into sample particles smaller particles (fragments) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 88  The mass spectrometer The cations are then pulled & Ionisation chamber accelerated by the negatively- charged plates in the acceleration chamber − + − Na(g ) + e → Na (g ) + 2e Electron from the Electrons from the electron gun & electron gun the sample One or more electrons are When electron(s) are knocked out of knocked out of the sample the sample particles, positive ions particles (cations) are formed PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 89  The mass spectrometer Acceleration chamber The positive ions are attracted towards the negative plates The electric field accelerates the positive ions to a high and constant speed PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 90  The mass spectrometer Deflection Chamber Different ions are deflected by the magnetic field by The amount different amounts of deflection depends on Mass of the ion Charge on the ion Lighter ions are Ions with +2 (or more) are deflected more deflected more than ones than heavier ones with only +1 charge These two factors are combined into the mass/charge ratio (m/e or m/z) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 91  The mass spectrometer Deflection Chamber positive ions with different Varying the strength of the magnetic field m/e ratios will be deflected to the ion detector Detector recorded as peaks on a Produces a flow of current which is amplified moving chart relative height of each peak in a mass spectrum shows Resulting chart is called the mass spectrum the relative abundance of the ions present PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 92  The mass spectrometer Vacuum pump Allow ions to reach the detector without colliding with other gaseous molecules or atoms Such collision would result in reduced sensitivity of the instrument PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 93  The mass spectrometer Exercise C B D A 1. Name the processes in A to D 2. On the diagram, sketch the path of the following ions under the same conditions: 24Mg+ 25Mg2+ 26Mg+ Source: http://sustainability.sellafieldsites.com/resources/labmouse/chemistry_as/1001.php 94  The mass spectrometer Interpretation of mass spectra Monoatomic Diatomic Molecular sample sample sample PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 95  Determination of relative atomic mass from mass spectrum Monoatomic Sample The mass spectrum of sodium shows only one peak All the atoms in a sample of sodium have the same mass It has a relative atomic mass of 23 Sodium has an atomic number of 11, so sodium atoms contain 11 protons and 12 neutrons PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 96  Determination of relative atomic mass from mass spectrum Diatomic Sample A chlorine molecule is made up of two chlorine atoms, each of which could be 35Cl or 37Cl isotopes. The peak at m/e of 70Cl2+ (35Cl-35Cl) The peak at m/e of 72Cl2+ (35Cl-37Cl) The peak at m/e of 74Cl2+ (37Cl-37Cl) PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 97  Determination of relative atomic mass from mass spectrum Diatomic Sample Chlorine has atomic number 17, so The isotope 35Cl has 17 protons and 18 neutrons. The isotope 37Cl has 17 protons and 20 neutrons. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 98  Determination of relative atomic mass from mass spectrum Determination of Relative Atomic Mass from Mass Spectrum PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 99 Determination of relative atomic mass from mass spectrum Exercise Explain the two peaks observed for the mass spectrum of boron. 100 Determination of relative atomic mass from mass spectrum Exercise Identify the chemical species for each of the peak in the mass spectrum of bromine below. 160 158 162 79 81 101  Interpreting mass spectra in terms of molecular fragments Molecular Sample When the vapourised molecular sample passes into the ionisation chamber of a mass spectrometer, it is bombarded by a stream of electrons. These electrons have a high enough energy to knock an electron off an organic molecule to form a positive ion, called the molecular ion (M+). CH3CH2OH(g) + e− → CH3CH2OH+(g) + 2e− PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 102  Interpreting mass spectra in terms of molecular fragments Fragmentation of molecular ion (M+) The molecular ions are energetically unstable, and some of them will break up into smaller pieces. The simplest case is that a molecular ion breaks into two parts - one of which is another positive ion, and the other is an uncharged free radical. M + → Y + X + molecular ion uncharged free another radical positive ion Example: PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 103  Interpreting mass spectra in terms of molecular fragments Only positively charged particles will be accelerated, deflected and detected by the mass spectrometer. The uncharged particles will get removed by the vacuum pump. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 104  Interpreting mass spectra in terms of molecular fragments Base Peak An arbitrary tallest height of 100 (most intense peak). The height of other peaks is measured relative to base peak. Represents the commonest fragment ion to be formed - either because there are several ways in which it could be produced during fragmentation of the parent ion, or because it is a particularly stable ion. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 105  Interpreting mass spectra in terms of molecular fragments M+1 peak A small peak 1 m/e unit to the right of the molecular ion peak. The M+1 peak is caused by the presence of the 13C isotope in the molecule. 13C is a stable isotope of carbon which makes up 1.11% of all carbon atoms. A ratio of approximately 1 of the 13C ions to every 99 of the 12C. That's why the M+1 peak is much smaller than the M+ peak. PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 106  Interpreting mass spectra in terms of molecular fragments The mass spectrum of ethanol CH2 OH + CH3CH2 O + CH3CH2 + CH3 + PERSONAL USE ONLY ∥ NOT FOR SALE ∥ Centre for Pre-University Studies 107  46 31 17 Fragmentation of Ethanol H H o Identifying the H C C O H fragments: o m/e = 15 is CH3 + H H o m/e = 29 is CH3CH2 + 15 o m/e = 31 is CH2OH + 29 o m/e = 45 is CH3CH2O + 45 1 Interpreting mass spectra in terms of molecular fragments Exercise 1. The molecular ion of an alkane in the spectrum below is 58. Name the alkane that the spectrum represents. What alkyl group was lost to form the intense fragment at m/e 43? 109 Interpreting mass spectra in terms of molecular fragments Exercise 2. Identify the molecular ion of an alcohol in this spectrum and name the alcohol that the spectrum represents. Answer: 32; methanol 110 TERIMA KASIH 111