General Chemistry Concepts (Atoms, Ions, and Molecules). PDF

General Chemistry Concepts (A Quick Review of Atoms, Ions, and Molecules) Atom: the smallest particle or unit of an element Zoom in atoms  remove e– Hydrogen atom H+  add e–...

General Chemistry Concepts (A Quick Review of Atoms, Ions, and Molecules) Atom: the smallest particle or unit of an element Zoom in atoms  remove e– Hydrogen atom H+  add e– e– Hydrogen atom H– Ions: charged atoms or molecules, formed by adding or removing electrons e– H+ ion H– ion  Molecule: a single structure made of two or more atoms (The atoms can be the same element or different elements.) add another H neutral H2 hydrogen atom Compound: a structure made of two or more atoms of different elements 2 + H 2O  remove or add e– Molecules Ions rem her (can be called “compounds” if made ov ot eo to s of two or more ra d n tom dd bo a different elements) e– Atoms (smallest unit of an element)  Question Please identify each of the following as an atom, an element, an ion, a molecule, or a compound: (Note: for some of the listed substances, more than one of these categories may apply.) A. H 2O B. NH4+ C. NH3 D. H2 E. C6H12O6 F. H 3O + G. F– H. Na I. Ar J. O22–  Question Please identify each of the following as an atom, an element, an ion, a molecule, or a compound: (Note: for some of the listed substances, more than one of these categories may apply.) A. H2O molecule B. NH4+ C. NH3 D. H2 E. C6H12O6 F. H 3O + G. F– H. Na I. Ar J. O22–  molecules (2 or more bonded atoms) Compounds (2 or more bonded atoms of different elements)  Question Please identify each of the following as an atom, an element, an ion, a molecule, or a compound: (Note: for some of the listed substances, more than one of these categories may apply.) A. H2O molecule compound B. NH4+ ion C. NH3 molecule compound D. H2 molecule E. C6H12O6 molecule compound F. H3O+ ion G. F– ion H. Na element I. Ar element J. O22– ion General Chemistry Concepts (Elements vs Compounds and Naming Ionic Compounds)  Monatomic and Diatomic Elements In our last video, we learned that atoms are the smallest particle or “unit” of an element. You can think of an atom as being like a single “piece” of a given element. In their simplest form, most elements can and do have a single-atom formula. For example, elemental sodium’s formula is Na (just one atom); elemental cesium’s formula is Cs (also one atom); and so forth. Such elements are called monatomic elements. There are, however, some elements that do NOT stably exist in nature as uncharged single atoms. Instead, these elements –called diatomic elements– pair up.  The Seven Diatomic Elements You should memorize the seven diatomic elements. They are: Blue = metal Red = nonmetal Green = Metalloid  The Seven Diatomic Elements This means that these seven elements, in their simplest form (or formula), You shoulddo NOT exist memorize the as single seven atomselements. diatomic by themselves. Instead, they They are: exist as two atoms bonded together. Blue = metal For example, in its Redsimplest = nonmetalstructural formula, hydrogen does not exist as H (though H+ andGreen H– ions are possible). Instead, it exists as two H atoms = Metalloid bonded together: H2. The same is true for the rest. Nitrogen’s simplest formula is N2 (not N). Oxygen’s is O2 (not O). Fluorine’s is F2 (not F), and so on, down the line: H2, N2, O2, F2, Cl2, Br2, and I2. As far as you need to know, we will assume that other than these seven diatomic elements, the rest of the elements’ formulas will just be monatomic. Note: Some people think helium is diatomic. It’s not. Its formula is just He, not He2.  What are Allotropes? In addition to the seven polyatomic elements, there are some other elements that CAN (but do not have to) exist in nature with various elemental formulas. For example, oxygen can exist as either O2 (oxygen gas) or O3 (ozone). Sulfur has many different elemental formulas, including S6, S8, and S12. Molecules with different formulas, whose atoms are all of the same element, are called allotropes. In other words, O2 and O3 are allotropes of oxygen, and S6, S8, and S12 are three different allotropes of sulfur.  Back to Compounds In our last video, we also learned that compounds are molecules comprised of two or more different elements bonded together. Examples include H2O and CO2. I’ll now teach you about two different classes of compounds: Compounds Ionic compounds: metal + nonmetal (contain ionic bonds) Molecular compounds: two or more nonmetals (contain covalent bonds)  Metals and Nonmetals And what do I mean when I say metals and nonmetals? Blue = metal Red = nonmetal Green = Metalloid  Back to Compounds In our last video, we also learned that compounds are molecules comprised of two or more different elements bonded together. Examples include H2O and CO2. I’ll now teach you about two different classes of compounds: Compounds Ionic compounds: metal + nonmetal (contain ionic bonds) Examples: NaCl, CuCl2 Exception: Although it does not contain any metals, NH4Cl is ionic. Molecular compounds: two or more nonmetals (contain covalent bonds) Examples: H2O, CO2  Naming Ionic Compounds 1. Name the metal. 2. Write the metal’s oxidation state as a Roman numeral in parenthesis. (Skip this step for metals in Columns I and II of the periodic table, as well as Al (it’s always +3), Zn (always +2), Cd (always +2), and Ag (always +1).  Naming Ionic Compounds No Roman numbers for these metals. For all other metals, you have to put Roman numerals. + 3 + + 1 2 + 2 + + 1 2  Naming Ionic Compounds 1. Name the metal. 2. Write the metal’s oxidation state as a Roman numeral in parenthesis. (Skip this step for metals in Columns I and II of the periodic table, as well as Al (it’s always +3), Zn (always +2), Cd (always +2), and Ag (always +1). 3. Name the nonmetal using an “ide” ending. NaCl – sodium chloride CsF – cesium fluoride MgO – magnesium oxide  Polyatomic Ions One more issue we have to worry about is the existence of polyatomic ions: ions that are made up of two or more atoms. For instance, I require my students to memorize the following polyatomic ions: Cations Anions Ammonium NH4+ acetate CH3COO− sulfate SO42− Cyanide CN− carbonate CO32− Nitrate NO3− hydroxide HO− Phosphate PO43- permanganate MnO4−  Polyatomic Ions One more issue we have to worry about is the existence of polyatomic ions: ions that are made up of two or more atoms. For instance, I require my students to memorize the following polyatomic ions: However, the EXAM requires you to memorize a lot more! (You can access the full list at https://datbootcamp.com/blog/common-ions-you-need-to-know/.)  Question Please provide a correct name for each of the following compounds: MgF2 FeCl3 SnF2 SnF4 Fe(NO3)2 NH4Cl Al2O3 FeCl2  Question Please give the empirical formula for the following molecules: Ammonium chloride Iron (III) cyanide Magnesium sulfate Ammonium sulfate  Question Please name the following ionic compounds: FeCO3 Fe(CN)3 MgSO4 Al(OH)3 CsNO3 Zn3(PO4)2 (NH4)2SO4 +2 General Chemistry Concepts (Naming Molecular Compounds and Molecular Acids)  Ionic vs. Molecular Compounds In our last video, we learned about two classes compounds: Compounds Ionic compounds: metal + nonmetal (contain ionic bonds) Exception: Although it does not contain any metals, NH4Cl is ionic. Molecular compounds: two or more nonmetals (contain covalent bonds)  Metals and Nonmetals And what do I mean when I say metals and nonmetals? Blue = metal Red = nonmetal Green = Metalloid  Ionic vs. Molecular Compounds In our last video, we also learned about two classes compounds: Compounds Ionic compounds: metal + nonmetal (contain ionic bonds) Exception: Although it does not contain any metals, NH4Cl is ionic. Molecular compounds: two or more nonmetals (contain covalent bonds) In our last video, we also learned how to name ionic compounds. In this video, we’ll learn how to name molecular compounds and molecular acids.  Naming Molecular Compounds AX BY 1. Give the appropriate numerical prefix to the first element: Mono = one Di = two Tri = three Tetra = four Penta = five Hexa = six Hepta = seven Octa = eight Nona = nine (Skip this step if X = 1.) 2. Name the first element by using its regular name on the periodic table. 3. Give the appropriate numerical prefix to the second element.  Naming Molecular Compounds AX BY 4. Name the nonmetal using an “ide” ending: N2O – dinitrogen monoxide (laughing gas) SF6 – sulfur hexafluoride (a contrast agent for ultrasound imaging) H2O – dihydrogen monoxide  Naming Binary Acids H–one other element 1. Hydro + insert the name of element 2, replacing “ine” with “ic acid”. 2. Examples: HF – hydrofluoric acid HCl – hydrochloric acid HBr – hydrobromic acid HI – hydroiodic acid  Naming Oxyacids HX –MIDDLE ATOMY – OZ 1. If Z = 0-2, then the name is: hypo + insert the name of element 2, replacing “ine” with “ous acid”. 2. If Z = one more, then the name is: insert the name of element 2, replacing “ine” with “ous acid”. 3. If Z = one more, then the name is: insert the name of element 2, replacing “ine” with “ic acid”. 4. If Z = one more, then the name is: per + insert the name of element 2, replacing “ine” with “ic acid”.  Naming Oxyacids HX –MIDDLE ATOMY – OZ In other words, you use “hypo” for the formula with the fewest oxygen atoms and “per” for the formula with the most oxygen atoms: Formula: HClO HClO2 HClO3 HClO4 Name: Hypochlorous acid Chlorous acid Chloric acid Perchloric acid  Naming Oxyacids HX –MIDDLE ATOMY – OZ In other words, you use “hypo” for the formula with the fewest oxygen atoms and “per” for the formula with the most oxygen atoms: Formula: HClO HClO2 HClO3 HClO4 Name: hypochlorous acid chlorous acid chloric acid perchloric acid  Naming Oxyacids HX –MIDDLE ATOMY – OZ EXAMPLES: Formula: H3PO2 H3PO3 H3PO4 H3PO5 hypophosphorous phosphorous perphosphoric Name: phosphoric acid acid acid acid Formula: H3PO2 H3PO3 H3PO4 H3PO5 hypophosphorous phosphorous perphosphoric Name: phosphoric acid acid acid acid  Naming Oxyacids HX –MIDDLE ATOMY – OZ EXAMPLES: Formula: H3PO2 H3PO3 H3PO4 H3PO5 hypophosphorous phosphorous perphosphoric Name: phosphoric acid acid acid acid Formula: H2SO2 H2SO3 H2SO4 H2SO5 hyposulfurous Name: sulfurous acid sulfuric acid persulfuric acid acid Seven Strong Acids You Should Know There are seven strong acids whose names and formulas I require my students to memorize. They are: Binary Acids: Oxyacids: Chloric acid, HClO3 Hydrochloric acid, HCl Perchloric acid, HClO4 Hydrobromic acid, HBr Nitric acid, HNO3 Hydroiodic acid, HI Sulfuric acid, H2SO4  Question Please give the name or chemical formula (whichever one isn’t provided) for each of the following molecular compounds: Tetraphosphorus hexasulfide PCl3 Dinitrogen tetroxide Cl2O3 SF6  Question Please give the name or chemical formula (whichever one isn’t provided) for each of the following molecular acids: HCN H2SO4 H2SO3 Hydroiodic acid HClO4 HClO3  Question Please give the name or chemical formula (whichever one isn’t provided) for each of the following molecular acids: H3PO4 H3PO3 HNO3 HNO2 H2CO3 Hydrobromic acid HI General Chemistry Concepts (Metric Units and Dimensional Analysis)  SI (Système International) Units We scientists typically use and publish our findings in international units of measurement, called SI (for “Système International”) units. Each physical quantity uses a different base as its SI unit: Physical Quantity Name of Base Unit Abbrevation Length Meter m Time Second s or sec Temperature Kelvin K Substance amount Mole Mol Electric current Ampere A or amp Luminous intensity Candela Cd Mass kilogram kg I also strongly advise you to memorize that 1 cm3 = 1 mL.  SI (Système International) Units Unfortunately, for the EXAM, you need to memorize the following SI unit prefixes and their amounts: Terra – 1012 Giga – 109 Mega – 106 Kilo – 103 Centi – 10–2 Milli – 10–3 Micro – 10–6 Nano – 10–9 Unit Conversion/Dimensional Analysis With these prefix values in mind, we can now interconvert from one set of units to another. This process is called unit conversion or dimensional analysis. Here are the steps: Step 1: Write down the value, from your problem, that you want to convert (this is usually the value that has no units in its denominator). Step 2: Draw a set of parentheses to the right of it, with a horizontal line in the middle. Unit Conversion/Dimensional Analysis With these prefix values in mind, we can now interconvert from one set of units to another. This process is called unit conversion or dimensional analysis. Here are the steps: Step 1: Write down the value, from your problem, that you want to convert (this is usually the value that has no units in its denominator). Step 2: Draw a set of parentheses to the right of it, with a horizontal line in the middle. Step 3: Write units (no numbers yet!) that relate to each other on the top and bottom of the horizontal line. These should cancel out the units you started with and take you to the units where you want to go. Be sure to focus on units. (Units!!!!) Multiple sets of parentheses may be necessary. Unit Conversion/Dimensional Analysis With these prefix values in mind, we can now interconvert from one set of units to another. This process is called unit conversion or dimensional analysis. Here are the steps: Step 4: Put numbers on the top and the bottom of the horizontal line in your parentheses. As you do this, make sure that each set of parentheses (with numbers and units) conveys a true statement. Step 5: Multiply out all the numbers. This should cancel out the units you started with and take you to the units where you want to go. If applicable, express your answer with the correct number of significant figures. (We’ll talk about this later on.)  Example Problem A modern advertising blimp balloon has a volume of about 8.41 × 106 L. Convert this to gallons. (Note: 1 gal = 3.785 L) Step 1: Write down the value, from your problem, that you want to convert: 8.41 × 106 L Step 2: Draw a set of parentheses to the right of it, with a horizontal line in the middle. 8.41 × 106 L  Example Problem Step 3: Write units (no numbers yet!) that relate to each other on the top and bottom of the horizontal line. These should cancel out the units you started with and take you to the units where you want to go. Be sure to focus on units. (Units!!!!) Multiple sets of parentheses may be necessary. In this case, put L on the bottom of the fraction to cancel out the L you start with. Then put gal (the value we want to get to) on top: 6 gal 8.41 × 10 L L  Example Problem Step 4: Put numbers on the top and bottom of each set of parentheses that go with the units in that set of parentheses. As you do so, make sure that each set of parentheses (with numbers and units) conveys a true statement. In this case, we know that 1 gal = 3.785 L, so put 3.785 on the bottom (with the L) and 1 on top (with the gal). 6 1 gal 8.41 × 10 L 3.785 L  Example Problem Now that I’ve written in the numbers, I ask myself: did I put my numbers in the correct place? In this case, are there really 3.785 L in 1 gal? If so, then my parentheses are written correctly. If not, then I need to rewrite them until I have a true statement inside the parentheses. 6 1 gal 8.41 × 10 L 3.785 L  Example Problem Step 5: Multiply out all the numbers. This should cancel out the units you started with and take you to the units where you want to go. If applicable, express your answer with the correct number of significant figures. (We’ll talk about this later on.) You cannot use a calculator on the EXAM, so all the questions they give you will either involve simple arithmetic you can do without a calculator, OR they will be left as an un-simplified expression. In this case, for example, the correct multiple-choice answer might look like: 6 1 gal 8.41 × 10 L = gal 3.785 L  Example Problem Step 5: Multiply out all the numbers. This should cancel out the units you started with and take you to the units where you want to go. If applicable, express your answer with the correct number of significant figures. (We’ll talk about this later on.) You cannot use a calculator on the EXAM, so all the questions they give you will either involve simple arithmetic you can do without a calculator, OR they will be left as an un-simplified expression. In this case, for example, the correct multiple-choice answer might look like: 8.41 × 106 / 3.785 Converting Between Mass and Volume Just so you know, to convert between mass and volume, we use density: mass Density = volume  Questions How many seconds are in a day? How many hours are in a year? How many kg are there in 7×1025 μg? How many sec are there in 5.2 ×1018 ns? Please convert 20 km to cm. If you’re going 50 miles/hour, how many feet/second are you traveling?  Questions On average, hummingbirds fly at 30 miles/hour. Convert this speed to m/s. (Note: 1 m = 3.28 feet and 1 mile = 1.61 km.) The Brooklyn Bridge is 277 feet tall. Convert this to meters. (Note: 1 m = 3.28 feet.) In a vacuum, light travels at a speed of 2.998 x 108 m/s. Convert this to miles per hour. (Note: 1 mile = 1.61 km.)  Questions What is the mass in kilograms of 18.5 gallons of gasoline? (Note: the density of gasoline is 0.70 g/mL.) What is the density, in g/cm3, of a 1.5 kg cube whose edges are each 5 cm? The density of aluminum is 2.7 g/mL. What volume (in L) would a 50.2 g sample of aluminum occupy?  Lab Concepts (Significant Figures and % Error)  Significant Figures There’s always some uncertainty in the last integer of any measured value. When we take values that we’ve measured and then multiply, divide, add, or subtract them with each other, the uncertainties of each value compound together to make the final answer even more uncertain. To avoid this increased uncertainty, we follow special rules called significant figure rules.  Significant Figures To determine the number of significant figures in a value, read the number from left-to-right, starting with the first digit that’s not zero. Then remember: 1. Zeroes between nonzero digits are always significant: 1005 kg (four sig-figs); 7.03 cm (three sig-figs). 2. Zeroes at the start of a number are never significant: 0.02 g (one sig-fig); 0.0026 cm (two sig-figs). 3. Zeroes at the end of a number are significant only if the zeroes are AFTER a decimal point: 0.0200 g (three sig-figs); 3.0 cm (two sig-figs).  Significant Figures When adding or subtracting values, your answer should have the same number of decimal places as the value that has the fewest decimal places. When the answer contains more than the correct number of significant figures, it must be rounded off. When multiplying or dividing values, your answer should have the same number of significant figures as the value with the fewest significant figures. When the answer contains more than the correct number of significant figures, it has to be rounded off.  Precision Versus Accuracy Precision is how close a series of measurements are to each other. The closer they are, the “more precise” they are. The precision of a measurement is not the same as its accuracy. Accuracy is how close a measurement is to reality. This archer is precise This archer is precise This archer is imprecise but not accurate. and accurate. and inaccurate.  Percent Error Calculations When conducting experiments, the values that we calculate usually differ slightly from the values we actually obtain or measure in the lab. The difference between calculation (theory) and reality is called percent error. Similar to percent yield, this is calculated as follows: (actual – theoretical) % error = × 100 theoretical  Questions After carrying out the following operation, the reported value should have how many significant figures? (6.943 cm – 5.81 cm) × 3.23 cm A. 2 B. 3 C. 4 D. 5 E. 6  Questions Which measurement below contain 3 significant figures? I. 0.02 cm II. 1.32 mL III. 0.000500 kg A. I and II B. I and III C. II and III D. II only E. I, II, and III  Questions Which of the following has the same number of significant figures as the number 1.00310? A. 5 × 106 B. 299.782 C. 7.92 D. 9.234 E. 300  Lab Concepts (Basic Lab Safety)  The Basics If you encounter any safety questions on the EXAM, the best strategy is to just use common sense. In the lab: Always wear proper personal protective equipment (ppe): a lab coat, safety glasses or goggles, and lab gloves. Don’t run around naked. Don’t hide things. Don’t endanger other people  How to Properly Heat a Test Tube To safely heat a test tube: Use a test tube holder, not your hand. Heat the test tube using a water bath, not an open flame  How to Properly Heat a Test Tube Insert footage of: Heating a test tube using holder Heating a test tube using my hand Heating a test tube using a water bath Heating a test tube using an open flame  How to Properly Dilute a Strong Acid To safely dilute a strong acid: Always ADD THE ACID TO WATER, not the other way around. The reason is because when a strong acid dissolves in water, the process is very exothermic, so it produces a lot of heat. If you add acid to the water, the water can help disperse this heat. If you add water to the acid, the acid spatters everywhere.  How to Properly Heat a Test Tube Insert footage of: Adding acid to water Adding water to acid (with spattering)  Lab Concepts (Weights, Measures, and pH)  Weighing or Measuring Dry Reagents When weighing things using a lab balance or scale, be sure to weigh your sample on a weigh paper. (Tip: you need to first tare, or pre-weigh separately, the weigh paper in order to get an accurate measurement.) How do you properly transfer a powdered reagent from its bottle to your weigh paper? Answer: To avoid contamination, never stick your measuring spoon into the bottle! Instead, pour some of the reagent onto a separate weigh paper and then transfer it in portions, as needed. Also, to avoid contamination, do NOT pour the excess reagent back into the bottle.  Weighing or Measuring Dry Reagents Get footage of: Taring a weigh paper Sticking a measuring spoon into a bottle Pouring some of the reagent onto a separate weigh paper Transferring it in portions onto the weigh paper on the balance Pouring the excess reagent back into the bottle  Measuring Liquid Reagents Certain liquids –especially water– form a curved bottom along their upper surface when poured into a graduated cylinder. This curved bottom is called a meniscus. Thus, when measuring liquid reagents like water by pouring them into a graduated cylinder, we must read the graduated cylinder correctly by reading the center-bottom of the curved meniscus as the true reading, not the raised sides. Errors in misreading your liquid’s volume, when caused by looking at the liquid from an indirect angle, are called parallax errors.  Using a pH Meter When using a pH meter, or pH probe (same thing): Calibrate the probe by using calibrated buffers. We usually use a calibrated buffer of pH 4 and pH 10. Rinse the pH probe with deionized water in-between samples. Also, be sure to dab the probe dry so you don’t throw off the measurement.