Chemistry Review Section Pages 3 to 33 “Quantum Chemistry” Target Completion Date: October 1
Pages with a PINK background are supplementary . Not material for a test! About Slide Icons Very Important Points • You should either note or highlight items from this slide. Some items from this slide WILL be on tests! Important Sample Problems • Always hand-copy important sample problems in your note book, and refer back to them when doing assignments. Similar problems will be on tests! Look at this! (usually charts, diagrams or tables) • You don’t need to copy this, but you must read and understand the diagrams or explanations here. Concepts will be tested, but not the details. Information only. Don’t copy! • This is usually background information to make a topic more interesting or to fill in details, or to give examples of how to use a table. Not directly tested. Review Stuff • Not part of the material you will be tested on, but you are expected to remember this from grade 10. It may be indirectly tested. R
R Conversions • You must be able to do ALL standard metric conversions, especially: • Litres to millilitres, millilitres to litres • Grams to kilograms, kilograms to grams • Other conversions you will learn during the course of the year: • Temperature: degrees celcius (℃) to kelvins (K) • Pressure: kilopascals (kPa) to millimetres (mmHg)
Quick Conversions The table on the left gives the eight most commonly used prefixes in the metric system. It also includes five rows that do not have prefixes. The middle row is for the unit: metre, litre, gram, newton, or any other legal metric unit. This table can be used to quickly convert from one metric amount to an equivalent. Make a copy of this table on the margin of the front cover of your notebook, and learn how to use it. Lets do an example. Let’s find how many centimetres there are in 2.524 km Conversion: 2.524 km ? cm 00 cm Add extra zeros if necessary 2 524 km There are five steps in the table between “kilo” and “centi”, so we have to move the decimal five places to the right. If we were going up the table we would move left. Answer: 2524 km = 252 400 cm
R Density • Density is the relationship between the volume of an object and its mass. Density is an important characteristic property of matter. • This is a review formula from last year: ρ V m or Where: ρ= the density of the object, in g/cm3 or g/mL m = the mass of the object, in g V = the volume of the object, in cm3 or mL The density of water is 1 g/mL. This is not true of other substances. Objects with less density than water will float. Objects with greater density will sink. ρw= 1 g/mL = 1 g/cm3
Solving Problems • When solving Chemistry problems on a test or exam, it is important not only to find the correct answer, but to justify it. While solving the problem you should: • Show your data, the information you used to solve the problem. • Show your work, including the formulas you used and the substitutions you made. • Write an answer statement, a sentence that clearly states your final answer. • Include the correct units for your answer. Never just give a number—you must specify what the number means!
Suggested Solution Method Problem: A block of material has a length of 12.0 cm, a width of 5.0 cm, and a height of 2.0 cm. Its mass is 50.0 g. Find its density. Arrange your solution like this: List all the information you find in the problem, complete with units, and the symbols. Data: l = 12 cm. w = 5.0 cm h =2.0 cm m =50g V = ? To Find: ρ(density) Write down all the formulas you intend to use: Formulas: V = lwh ρ= Show the substitutions you make, and enough of your calculations to justify your solution: V =12cm x 5cm x 2 cm = 120 cm3 𝜌= 50 g / 120 cm3 = 0.46 g/cm3 Always state your answer in a complete sentence, with appropriate units. Answer: The density of the block is 0.46 g/cm3 (or 0.46 g/mL)
Problems on Conversions and Density • Convert the following: • 125 mL to L d) 30 mL to L g) 75 mL to L • 450 g to kg e) 4500 mL to L h) 0.035L to mL • 2.5 L to mL f) 1.35 kg to g i) 0.56L to mL • Find the density of a 4cm x 3cm x 2cm block that has a mass or 480 g. Justify your solution. • Find the width of a cube whose density is 5 g/cm3 and whose mass is 135 g. Justify your solution. Also: Do the worksheets entitled “Density” and “Metric Conversions”
Overview: Significant FiguresKnowing how much to round an answer. In the sciences, we have an particular way of determining how much precision we need in the observations and answers we record. The method of rounding is called significant digits or significant figures. There is a detailed section in the appendix to your textbook on pages 394 to 397. Unfortunately, a few of the details given there are, well… I won’t say wrong, let’s just call them “uncertain”.
Uncertainty In math, numbers are considered pure, abstract things. In math, 2.00, 2.0 and 2 are considered the same, they all represent perfect number 2. In science, numbers are considered to be measurements, and all measurements have some degree of uncertainty. They are almost never considered perfect! The absolute uncertainty of a measurement is usually ½ of a measuring instruments smallest gradation. If a graduated cylinder is marked in millilitres, then each measurement taken with that cylinder has a ±0.5 mL uncertainty. In science, 2 mL, 2.0 mL and 2.00 mL are different!
Correct precision • It is considered improper in science to imply that a measurement is more precise than it really is. • If you have a graduated cylinder that is marked in 1 mL increments, you can record it to between the two smallest marks: eg. 20.0 ±0.5 mL or 25.5±0.5 mL are acceptable readings. • With the same graduated cylinder, it would be wrong to write 20 ±0.5 mL or 25 ±0.5 mL or even 20.00 ±0.5 mL • In science 20 mL, 20.0 mL and 20.00 mL have different meanings with respect to precision.
Rules for Significant Figures Interpreting Significant Digits • All non-zero digits are ALWAYS significant • Zeros between significant digits are ALWAYS significant. • Zeros at the beginning of a number are NEVER significant. • Zeros at the end of a number MAY be significant. • Exponents, multiples, signs, absolute errors etc. are NEVER significant.
Examples of Rule 1, 2 and 3 Rule 1. Non-zero digits are ALWAYS significant. 1.234 has 4 significant digits 145 has 3 significant digits 19567.2 has 6 significant digits Rule 2. Zeros between significant digits ARE significant. • has 4 significant digits 5007.4 has 5 significant digits 20000.6 has 6 significant digits Rule 3. Zeros at the beginning are NEVER significant. 007 has 1 significant digit 0.0000005 has 1 significant digit 0.025 has 2 significant digits
Explaining Rule 4 Rule 4. Zeros at the end of a number MAY be significant. Your textbook says that they are ALWAYS significant, but this is contrary to what most textbooks say. If there is a decimal point, there is no problem. All textbooks agree, the zeros are ALL significant. 3.00000 has 6 significant digits 5.10 has 3 significant digits 10.00 has 4 significant digits If there is NO decimal, the situation is ambiguous, and a bit of a JUDGEMENT CALL. If you trust the source to be precise, then you count all the zeros at the end. If you have reason to believe the person was estimating, then you don’t count any of the zeros at the end. 5000 has 1 or 4 significant digits 250 has 2 or 3 significant figures 123 000 000 has 3 or 9 significant figures In a test situation, assume the numbers are precise, unless something in the question states otherwise. Trusted precise source Estimated source
Rule 5 Rule 5: Exponents and their bases, perfect multiples, uncertainties (error values), signs etc. are NEVER significant. 6.02x 1023 has 3 significant digits 504.1 mL x 3has 4 significant digits 5.3±0.5 mL has 2 significant digits –5.432x 10-5has 4 significant digits In each case, the blue part is significant, the greenpart is NOT significant. Note: The term Significance in this usage is not the same as importance. A digit may be “insignificant” but still very important. The significant digits guide you to the correct way of rounding numbers to show precision. The insignificant digits may serve as “placeholders”, making sure the decimal point is in the right place. An important job, but not one that adds to the precision of the answer.
Same Number, Different Precision Try to avoid the “ambiguous” situation in your answers. If an answer ends in zero, or worse, in several zeros, indicate whether it should be interpreted as “exactly” or “approximately”. Better still, convert it to scientific notation, and leave only the zeros you know are accurate. Eg. If your answer is 2500 mL, but you only measured to the nearest 10mL, then write 2.50 x 103 mL. That way every one will know its accurate to 3 significant figures *Your textbook says to call this 3 significant figures. Traditional measurement would call it 1 significant figure. Written this way it is ambiguous. Avoid writing answers that end with zeros and no decimal!
Math with Significant Figures • The basic rule for math is that you do not improve significance by multiplying or dividing numbers: 53.81 m x 2.43 m = 131 m2NOT130.7583 m2 !!! Why? Because the least precise measurement had 3 significant digits, so our answer should not have more than 3 significant digits! The technique for addition and subtraction is slightly different (see p.396 ) but the concept is the same. You cannot make your result better than your measurements!
Page 4 R Topic 1: Organization of Matter 0.1.1 O O C H • 0.1.1 Atoms and Molecules • All matter is composed of atoms. • The atoms that make up most matter are assembled into molecules. • A molecule may contain one atom, or it may contain several thousand atoms, or any number between. • A molecule is represented by its formula • Water molecules, for example, are represented by the formula H2O, shown below: CO2 H N NH3 H One atom Ne Ne Cl Cl S several thousand atoms O DNA 2 atoms of hydrogen 1 atom of oxygen SCl2 18 H2O H H
Page 4 Cl– Cl Na Na+ cation anion 0.1.2 • Chemical Formulas and Ions • Some matter is formed from ions instead of normal atoms or molecules. • For the most part, we treat ions the same way as regular atoms, but there are a few very technical differences. • Ions are atoms (or clusters of atoms) that have become positively or negatively charged by losing or gaining one or more electrons. • Positive ions are called cations (ca+ions), • Negative ions are called anions (aNions) • Metals almost always form cations (+), non-metals may form anions (-) Notice the slightly stronger wording with respect to metals than nonmetals! 19
Sample Ions Metal Ions (+) + Cations – Anions Non-Metal Ions (-) Notice that some elements can form more than one type of ion. Compounds of the same element can differ quite a bit, for example, red iron oxide (rust) has Fe3+ ions, black iron oxide (wustite) contains Fe2+ ions. Note also, that most negative ions have the name ending changed to –ide. 21
2– O Big Fat Ions(Polyatomic Ions) + H O S O N H O H O O 3– P H – O O Cl O • Polyatomicions are ions that are composed of a cluster of atoms, instead of a single atom. • For example, the nitrate ion (NO3–) looks like this: • But it acts like a single, negatively charged particle in reactions. • Polyatomic ions are sometimes called radicals. • They are not the same as molecules. O N- O O O Na+ Na+ + NO3- NaNO3 N- O O
Common Polyatomic Ions (p.422) 3- 2- 1- 1- 23 This information is important when naming ternary ionic compounds. Click to skip ahead to Ionic Naming Rules
R Representation of Atoms 0.2.0 H • Early Representations • Democritus (c.450 BC) suggested that matter was made of particles. • John Dalton (1800) represented the atoms as spheres (like microscopic bowling balls) • J.J. Thomson represented the atom as a “plum pudding” of positive charge with negative charged electrons scattered inside “like rasins” • You studied the historic importance of these models last year, so you will not be tested on them this year. We will concentrate on the three most widely used representations on the slides that follow. C N O P S Cl Dalton models Original and Modern + - - - - - 24
R Page 5 0.2.1 1. Rutherford-Bohr Model • Rutherford discovered that the atom has a dense nucleus containing positively charged protons. • Negatively charged electrons move around this nucleus in paths that resemble an orbit. • Later, Bohr calculated that there were different orbital energy levels or “shells” that could hold different numbers of electrons. Early Rutherford model Revised Bohr model 25
Page 5 0.2.2 2. The Simplified Atomic Model • The simplified atomic model that we often use today adds neutrons (discovered by James Chadwick after the Bohr-Rutherford model had been proposed)to the protons in the nucleus. • We often draw this in a simplified way, showing the nucleus as a full circle, and the electron “shells” as half-circles. Symbol: The symbol of the element Electrons: 2 in first shell, 8 in 2nd 1 in 3rd 11p+ 12n0 Na The Atomic Number, Z, is the number of protons in the element. The configuration is the arrangement of the electrons in the shells 2e- 8e- 1e- Nucleus: If asked for a complete simplified model, give the #protons and #neutrons (if known) in the nucleus. Otherwise, just draw a full circle. Z=11, configuration: 2,8,1 26
WARNING • Be careful how you draw them! • The diagram must show the nucleus! Unacceptable! Unacceptable! Nucleus is not shown. Nucleus is confused with 1st shell Nucleus shown as solid circle. Labelled with element symbol beside. Nucleus shown as full circle. Labelled with #protons and neutrons. ACCEPTABLE ACCEPTABLE
Page 6 The Sub-atomic Particles nucleons 28
R 0.2.3 3. Lewis Model: (AKA Lewis electron dot notation) • Lewis notation is a way of drawing a representation of the valence electrons of an atom • When sketching an atom, write the symbol, and then arrange dots around it to represent its valence electrons. • Example: N has 5 valence electrons N • The “odd” or unpaired electrons are available for the purpose of bonding. • When bonding, atoms gain, lose or share electrons in order to get a total of 8 electrons around each atom. 2 paired electrons 1 5 3 “odd” unpaired electrons 4 2 3 29
The preferred way of drawing Lewis diagrams of the first ten elements is shown below: However, the dots may be moved around to show different arrangements. All of the drawings of Beryllium shown below might be correct in some circumstances. Sometimes electrons are removed from one atom to others in order to get 8 Sometimes showing the bonding between atoms requires clever movement of dots, as in the drawing of a nitrogen molecule (N2) shown here: 30
The Modern Model(Optional Enrichment) • The Modern Model of the Atom • Of course, the Rutherford-Bohr model and the Simplified Model do not perfectly represent what happens inside the atom. No model can! • A more complete model, The Modern or Electron-Cloud model exists, but is more complicated and extremely difficult to draw. • The Modern Model more accurately explains the relationship between the atom and the periodic table, and allows you to produce simplified models of elements in the transition area of the periodic table. 31
The Modern Model(Optional Enrichment) • The 2-8-8 vs. 2-8-18 problem. • You have probably been taught how to draw Simplified Models for the first 20 elements • If so, you have noticed that for the elements potassium and calcium, the third shell only holds 8 electrons—but Bohr said it should hold up to 18! • The models you have been taught can’t explain why, but the modern model includes a concept called “orbitals” or subshells, and a filling pattern called the “aufbaudiagram” that explain this . 32
The Modern Model(Optional Enrichment) • You are not required to learn the Aufbau diagram or the modern electron cloud model, but if time permits, I will show you how it works near the end of the review section. In the meantime: • You must know that the third shell CAN hold up to 18 electrons, but often doesn’t. • And you must learn how the periodic table can be used to figure out the electron arrangement of many elements past the first 20. • But that is part of the next lesson… 33
Atomic Model Exercises • Draw Simplified Models of the first 20 elements. • Draw Lewis Models of the first 20 elements. • Convert the following: • 125 cm to m d) 320 mL to L g) 750 mL to L • 280 g to kg e) 45000 mm to km h) 0.0035km to cm • 4.63 L to mL f) 5.52 kg to g i) 0.45L to mL
Periodic Classification Overview The periodic table is a useful arrangement of the elements, into regions, families and periods that have important meanings. It is also a source of much additional information about the elements. With careful interpretation of the table, we can find the number of protons an atom has, the approximate number of neutrons, and the arrangement of electrons in the atom and in its ions.
In-line Notation of Element Information • An alternative to the periodic table is in-line notation of elements and isotopes. Note that the arrangement of information in this notation system is not the same as the arrangement in most periodic tables. • Examples of inline notation: • In-line notation is designed to be more compact, but less complete presentation of the information in a full periodic table.
In-Line Notation for a Carbon-14 atom(carbon-14 is an isotope, or alternate form of normal carbon) An average carbon atom weighs 12.01 amu according to the periodic table. But no atom of carbon has that exact weight. For every thousand atoms that weigh exactly 12 amu, a few weigh more. This one weighs 14 amu Valence (4) or Ionic Charge (4–) or Oxidation # (–4) Isotope or Mass number. Represents the number of nucleons in a particular atom C 14 4– Valence is the number of bonds the atom is likely to form. Ionic charge is the most likely charge an ion will have. Atomic number “Z” represents the number of protons in this atom 2 6 Subtracting the Mass # and the Atomic # “Z” gives the number of neutrons in the atom Number of atoms in a molecule, such as C2H4 (6p+, 8n0, 10e-) Configuration of this atom 8
Information in your Periodic Table • 8 Atomic number (Z) The number of protons 2- Ionic charge 3.44 0.65 Atomic Radius Electronegativity O 1314 1.43 Density (g/L gas) (g/mL solid/liquid) Ionization Energy -218.3 -182.9 Melting Point (°C) Symbol Boiling Point (°C) Electronegativity is a rating of how well the atom attracts electrons, on a scale from 0 to 4 Name Oxygen The English name of the element 15.999 Atomic weight (amu) Ionization Energy is how much energy it takes to remove an electron (kj/mol) (or g/mol) Also the molar mass in g/mol The symbol is a 1 or 2 letter abbreviation of the element’s name, or sometimes its Latin name. The first letter is always uppercase. If there is a second letter it MUST be written in lowercase. (eg. For sodium, Na is correct, na or NA are absolutely unacceptable!) 38
The Periodic Tablewith Regions shaded ↑ The properties and region associations of these 10 elements are hypothetical ↑ The heavy “staircase” line was the traditional separation between metals & non-metals but we now know it is not a sharp division. 39
The Periodic Tablewith Families Shaded VIIIA: Noble Gases IIA: Alkaline Earths IA: Alkali Metals VIIA: Halogens VI: Oxygen Family IVA: Carbon Family IIIA: Boron Family V: Nitrogen Family IB: Coin Metals Iron Triad ↑ The properties and family associations of most elements in period 7 are hypothetical↑ Lanthanides Actinides 40
The Periodic Tableand Valence Electrons (electrons in outermost shell) THREE (III) EIGHT (VIII) SIX (VI) ONE (I) TWO (II) FOUR (IV) FIVE (V) SEVEN (VII) FIVE (V) SEVEN (VII) THREE (III) FOUR (IV) SIX (VI) TWO ONE ↑ The properties and family associations of these synthetic elements are hypothetical ↑ If the square is the same colour as the arrow above, it obeys its family with respect to valence. If the square is rainbow shaded, it is polyvalent, and not obeying its family rules. If the square is partly shaded, then it obeys its family rules most of the time. 41
The Periodic Table with Periods shaded 1st Period = 1 shells 2nd Period = 2 shells 3rd Period = 3 shells 4th Period = 4 shells 5th Period = 5 shells 6th Period = 6 shells 7th Period = 7 shells ↑ The properties and family associations of these 10 elements are hypothetical ↑ 6th Period = 6 shells 7th Period = 7 shells The periods of the table show how many shells of electrons an element normally has. 42
Use the Periodic Table to Find the Electron Arrangement of an Atom Eg. Find the electron arrangement of Iodine (I) SEVEN (VII) 5th Period = 5 shells 53 Iodine is at the intersection of Period 5 and Family VII. Its number is 53. It has a total of five shells, 7 electrons in the outermost shell, and will have 53p+, and normally 53 e-. From this we can USUALLY figure out the electron arrangement. Five shells 53p+ 2 8 18 18 7e- Total 53, So far: 35, left: 18
Periodic Table Exercises • Write the name and symbol of each of the first 20 elements. (bragging rights if you can do it without looking!)
Naming Compounds • There are four sets of rules for naming compounds: • The binary ionicrules: • For compounds containing only two elements, joined by an ionic bond. • The ternary ionicrules: • For compounds containing 3 or more elements, including a polyatomic ion. • The covalent rules: • For two elements joined by covalent bonds (usually two non-metals) • The organic rules: • Used for compounds that contain carbon atoms bonded to each other covalently. 45
The Binary Ionic Rules • First name the element on the left side of the compound’s formula. • Then name the element on the right hand side of the compound’s formula, but change the suffix to “ide” • For example: NaCl sodium chloride BaCl2 barium chloride CaO calcium oxide K2S potassium sulphide Al2O3 aluminum oxide Ca2C calcium carbide 1+ 1– Cl- Ba2+ Cl- Na+ Cl- K+ K+ S2- Ca2+ O2- Ca2+ C4- Ca2+ O2- Al O2- Al 3+ 3+ O2- 46
Ionic Rules No No! • When naming an ionic compound (and that includes most compounds that contain a metal) YOU SHOULD NOT USE A PREFIX! • Do NOT say: calcium difluoride for CaF2 • It’s Wrong. The correct name is just calcium fluoride. • Do NOT say: dialuminum trioxide for Al2O3 • It’s Wrong. The correct name is aluminum oxide. There are, or rather there USED to be, a few exceptions to this. Chromium dioxide was an acceptable name for CrO2, and is still used occasionally. Now the name chromium(IV)oxide is preferred for the compound, since it obeys the ionic rules. Monosodium glutamate is an organic compound that does not follow the rules.
Dealing with Polyvalent Metals • Some metal elements have more than one possible valence. Copper, for example, can have a valence of 1+ or 2+, depending on what compound it is in (eg. CuCl or CuCl2). Since we don’t use prefixes in naming ionic compounds, we shouldn’t use copper dichloride. We need a new rule! • If a metal is polyvalent, we include its current valence in roman numerals inside parenthesis within an ionic compound name, for example: • CuCl = Copper (I) chloride (not copper monochloride) • CuCl2 = Copper (II) chloride(not copper dichloride!) This copper ion has a charge of 1+ This copper ion must have a charge of 2+ 49
Polyvalent ElementsThe elements with flashing circles have more than one positive valence. C Cr Mn Fe Co Ni Ti Cu Pd Sn Sb Ru Pt Po Tl Bi Au Hg Pb Sm Eu U 50