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# 127868127 chemistry-reviewers

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### 127868127 chemistry-reviewers

1. 1. 1The English System of UnitsThere are several systems of units, each containing units for properties such as length, volume, weight, andtime. In the English system the units are defined in an arbitrary way.Length: inch (in), foot (ft), yard (yd), mile (mi)12 in = 1 ft 5280 ft = 1 mi3 ft = 1 yd 1760 yd = 1 miVolume: fluid ounce (oz), cup (c), pint (pt), quart (qt), gallon (gal)2 c = 1 pt 32 oz = 1 qt2 pt = 1 qt 4 qt = 1 galWeight: ounce (oz), pound (lb), ton16 oz = 1 lb 2000 lb = 1 tonTime: second (s), minute (min), hour (h), day (d), year (y)60 s = 1 min 24 h = 1 d60 min = 1 h3651/4 d = 1 yPractice Problem 1Convert 6.5 feet into inches.The Metric SystemThe Metric System is based on the fundamental units of measure for length, volume, and mass.Length: meter (m)Volume:liter (L)Mass : gram (g)Base units in the Metric System can be converted into units that are more appropriate for the quantity beingmeasured by adding a prefix to the name of the base unit. The common metric prefixes are given below.Metric System PrefixesPrefix Symbol Meaningfemto- F x 1/1,000,000,000,000,000 (10-15)pico- P x 1/1,000,000,000,000 (10-12)nano- N x 1/1,000,000,000 (10-9)micro- x 1/1,000,000 (10-6)milli- M x 1/1,000 (10-3)centi- C x 1/100 (10-2)deci- D x l/10(10-1)kilo- K x 1,000 (103)mega- M x 1,000,000 (106)giga- G x 1,000,000,000 (109)tera- T x 1,000,000,000,000 (1012)The base units of length and volume are linked in the metric system. By definition, a liter is equal to thevolume of a cube exactly 10 cm tall, 10 cm long, and 10 cm wide. Because the volume of this cube is 1000cubic centimeters and a liter contains 1000 milliliters, 1 milliliter is equivalent to 1 cubic centimeter.1 mL = 1cm3The base units of volume and weight are also linked. The gram was originally defined as the mass of 1 mL ofwater at 4 degrees Celsius.1g = 1mL H2O at 4 CPractice Problem 2:Convert 0.135 kilometers into meters.
2. 2. 2Mass Versus WeightMass is a measure of the amount of matter in an object, so the mass of an object is constant.Weight is a measure of the force of attraction of the earth acting on an object. The weight of an object is notconstant.Mass is a more fundamental quantity than weight. There is no English equivalent to the verb weigh that canbe used to describe what happens when the mass of an object is measured. You are therefore likely toencounter the terms weigh and weight for operations and quantities that are more accurately associatedwith the term mass.SI Units of MeasureIn 1960 the International System of Units was proposed as a replacement for the Metric System. The sevenbase units for the SI system are given below.SI Base UnitsPhysical Quantity Name of Unit Symbollength meter mmass kilogram kgtime second stemperature kelvin Kelectric current ampere Damount of substance mole molluminous intensity candela cdDerived Si UnitsThe units of every measurement in the SI system must be derived from one or more of the seven base units.Some of the common derived SI units used in chemistry are given below.Common Derived SI Units in ChemistryPhysical Quantity Name of Unit SymbolDensity kg/m3electric charge coulomb C (A s)electric potential volt V (J/C)Energy joule J (kg-m2/s2)Force newton N (kg-m/s2)Frequency hertz Hz (s-1)Pressure pascal Pa (N/m2)velocity (speed) meters per second m/sVolume cubic meter m3Non-SI UnitsStrict adherence to SI units would require changing directions such as "add 250 mL of water to a 1-L beaker"to "add 0.00025 cubic meters of water to an 0.001-m3container." Because of this, a number of units that arenot strictly acceptable under the SI convention are still in use. Some of these non-SI units are given below.Non-SI Units in Common UsePhysical Quantity Name of Unit SymbolVolume liter L (10-3m3)length angstrom D (0.1 nm)Pressure atmosphere atm (101.325 kPa)torr mmHg (133.32 Pa)
3. 3. 3energy electron volt eV (1.601 x 10-19J)temperature degree Celsius EC (K - 273.15)concentration molarity M (mol/L)Unit ConversionsLength1 m = 1.094 yd 1 yd = 0.9144Volume1 L = 1.057 qt 1 qt = 0.9464Mass1 g = 0.002205 lb 1 lb = 453.6 gPractice Problem 3The record for the Kentucky Derby is held by Secretariat, who ran the 10 furlongs in 1 minute, 59.4 seconds.Calculate his average speed in miles per hour.Practice Problem 4Calculate the volume in liters of a cubic container 0.500 meter tall.Practice Problem 5What is the value of a gold ingot 20.0 cm long by 8.5 cm wide by 6.0 cm tall, if the mass of a cubic centimeterof gold is 19.3 grams and the price of gold is \$356 per ounce?ElementsAny substance that contains only one kind of an atom is known as an element. Because atoms cannot becreated or destroyed in a chemical reaction, elements such as phosphorus (P4) or sulfur (S8) cannot be brokendown into simpler substances by these reactions.Example: Water decomposes into a mixture of hydrogen and oxygen when an electric current is passedthrough the liquid. Hydrogen and oxygen, on the other hand, cannot be decomposed into simplersubstances. They are therefore the elementary, or simplest, chemical substances - elements.Each element is represented by a unique symbol. The notation for each element can be found on the periodictable of elements.The elements can be divided into three categories that have characteristic properties: metals, nonmetals, andsemimetals. Most elements are metals, which are found on the left and toward the bottom of the periodictable. A handful of nonmetals are clustered in the upper right corner of the periodic table. The semimetalscan be found along the dividing line between the metals and the nonmetals.AtomsElements are made up of atoms, the smallest particle that has any of the properties of the element.JohnDalton, in 1803, proposed a modern theory of the atom based on the following assumptions.1. Matter is made up of atoms that are indivisible and indestructible.2. All atoms of an element are identical.3. Atoms of different elements have different weights and different chemicalproperties.4. Atoms of different elements combine in simple whole numbers to form compounds.5. Atoms cannot be created or destroyed. When a compound decomposes, the atomsare recovered unchanged.CompoundsElements combine to form chemical compounds that are often divided into two categories.Metals often react with nonmetals to form ionic compounds. These compounds are composed of positiveand negative ions formed by adding or subtracting electrons from neutral atoms and molecules.
4. 4. 4Nonmetals combine with each other to form covalent compounds, which exist as neutral molecules.The shorthand notation for a compound describes the number of atoms of each element, which is indicatedby a subscript written after the symbol for the element. By convention, no subscript is writteCharacteristics of Ionic and Covalent CompoundsIonic Compounds Covalent CompoundsContain positive and negative ions(Na+Cl-)Exist as neutral molecules (C6H12O2)Solids suchs as table salt (NaCl(s))Solids, liquids,or gases (C6H12O6(s),H2O(l), CO2(g))High melting and boiling pointsLower melting and boiling points(i.e., often exist as a liquid or gas atroom temperature)Strong force of attraction betweenparticlesRelatively weak force of attractionbetween moleculesSeparate into charged particles inwater to give a solution that conductselectricityRemain as same molecule in waterand will not conduct electricityDetermining if a Compound is Ionic or CovalentCalculate the difference between the electronegativities of two elements in a compound and the average oftheir electronegativites, and find the intersection of these values on the figure shown below to helpdetermine if the compound is ionic or covalent, or metallic.Practice Problem 1:For each of the following compounds, predict whether you would expect it to be ionic or covalent.(a) chromium(III) oxide, Cr2O3(b) carbon tetrachloride, CCl4(c) methanol, CH3OH(d) strontium fluoride, SrF2Practice Problem 2:Use the following data to propose a way of distinguishing between ionic and covalent compounds.Compound Melting Point ( oC) Boiling Point ( oC)Cr2O3 2266 4000SrF2 1470 2489CCl4 -22.9 76.6
5. 5. 5CH3OH -97.8 64.7Practice Problem 3:Which of the following compounds should conduct an electric current when dissolved in water?(a) methanol, CH3OH(b) strontium fluoride, SrF2Fundamental Subatomic ParticlesParticle Symbol Charge MassElectron e--1 0.0005486 amuProton p++1 1.007276 amuNeutron no0 1.008665 amuThe number of protons, neutrons, and electrons in an atom can be determined from a set of simple rules.The number of protons in the nucleus of the atom is equal to the atomic number (Z).The number of electrons in a neutral atom is equal to the number of protons.The mass number of the atom (M) is equal to the sum of the number of protons and neutrons in thenucleus.The number of neutrons is equal to the difference between the mass number of the atom (M) andthe atomic number (Z).Examples: Lets determine the number of protons, neutrons, and electrons in the following isotopes.12C 13C 14C 14NThe different isotopes of an element are identified by writing the mass number of the atom in the upper leftcorner of the symbol for the element. 12C, 13C, and 14C are isotopes of carbon (Z = 6) and therefore contain sixprotons. If the atoms are neutral, they also must contain six electrons. The only difference between theseisotopes is the number of neutrons in the nucleus.12C: 6 electrons, 6 protons, and 6 neutrons13C: 6 electrons, 6 protons, and 7 neutrons14C: 6 electrons, 6 protons, and 8 neutronsPractice Problem 1:Calculate the number of electrons in the Cl-and Fe3+ions.Electromagnetic RadiationMuch of what is known about the structure of the electrons in an atom has been obtained by studying theinteraction between matter and different forms of electromagnetic radiation. Electromagnetic radiation hassome of the properties of both a particle and a wave.Particles have a definite mass and they occupy space. Waves have no mass and yet they carry energy as theytravel through space. In addition to their ability to carry energy, waves have four other characteristicproperties: speed, frequency, wavelength, and amplitude. The frequency (v) is the number of waves (orcycles) per unit of time. The frequency of a wave is reported in units of cycles per second (s-1) or hertz (Hz).The idealized drawing of a wave in the figure below illustrates the definitions of amplitude and wavelength.The wavelength (l) is the smallest distance between repeating points on the wave. The amplitude of thewave is the distance between the highest (or lowest) point on the wave and the center of gravity of the wave.If we measure the frequency (v) of a wave in cycles per second and the wavelength (l) in meters, the productof these two numbers has the units of meters per second. The product of the frequency (v) times thewavelength (l) of a wave is therefore the speed (s) at which the wave travels through space.vl = s