Week 2 Chemistry 101
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This 9 page Class Notes was uploaded by Jonathan Warburton on Friday September 4, 2015. The Class Notes belongs to Chemistry 101 at University of Alabama - Tuscaloosa taught by Paul Rupar in Summer 2015. Since its upload, it has received 17 views. For similar materials see General Chemistry in Science at University of Alabama - Tuscaloosa.
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Date Created: 09/04/15
00 00000 The Elements Each element has a specific number of protons within its nucleus The number of protons in the nucleus of an atom is called the atomic number The atomic number uses the symbol 2 Eg an atom with a 22 is a helium atom it has 2 protons in its nucleus There are about 116 different elements Each element has a different number of protons or Z number Each Element is given a symbol The periodic table lists the elements in order of their Z Chemists care very much about protons and electrons because the chemistry of an element is determined by its atomic number The chemistry of fluorine z 9 is very different from the chemistry of neon z10 Isotopes All atoms of a given element have the same number of protons However the number of neutron can vary These are called isotopes 99 of all carbon atoms have 6 nquot0 1 of all carbon atoms have 7 nquot0 ltltlt1 of carbon atoms have 8 n quotO 28 Mass Number SI Element 14 Atomic Number Random Note about AMUs Since the masses of neutrons and protons are not exactly 1 amu the masses of isotopes are not whole numbers OHS Neutral atoms have an equal number or protons and electrons During Chemical reactions atoms gain or lose equot to become charged to form ions Z never changes in chemistry 101 Examples of common ions Fquot the fluoride ion forms by giving a fluorine atom one extra electron Caquot2 calcium ion formed by removing two electrons from a calcium ion The properties of ions are very different from the parent element For example Sodium Na metal reacts violently with water Chlorine gas CL2 is highly corrosive and toxic However sodium chloride which is composed of Naquot cations and CIA is not toxic and not very reactive The law of Conservation of Mass 0 In a chemical reaction matter is neither created or destroyed The mass of what you end up with must equal the mass that you started with 0 Always The law of Definite Prooortions All samples of a pure substance always have the same proportions of their constituent elements 0 Ex 18g of water is composed of 16g of oxygen and 2 g hydrogen M 0 Parts of Dalton s Atomic Theory are still viewed to be mostly correct after 200 years 0 Elements are made up of atoms 0 All atoms of a given element are identical 0 Atoms cannot be created or destroyed 0 Compounds are made of atoms combined in whole number ratios 0 During a chemical reaction atoms are separated and combined 0 What part of Dalton s theory are known to be somewhat incorrect o All atoms of a given element are identical 0 Atoms cannot be created or destroyed JJ Thomson and the Cathode Rav Tube 0 Glass tube containing metal electrodes from which almost all the air has been evacuated When connected to a high voltage power supply a glowing area is seen emanating from the cathode The beam is deflected by external charges and magnets Similar to an oldschool TV The cathode rays are made of tiny particles These particles have a negative charge 0 because the beam always deflected toward the plate 0 The amount of deflection was related to two factors the charge and mass of the particles Every material tested contained these same particles The charge mass ratio of these particles was 176 x 10A8 Cg o C coulomb SI unit of charge 0 the chargemass of the hydrogen ion is 58 x 10quot4 Cg Thomson s Conclusions Millikan s Oil Drob Experiment Small drops of oil were suspended within the chamber As the drops of oil fell through the air they were negatively charged by ionizing radiation Millikan applied an electric field to stop the oil drops from falling By knowing the mass of the oil drops how and the strength of electric field Millikan could measure the amount of charge on the drops 0 What Millikan found was remarkable The charge on each drop was a multiple of 160 x 10quot19 C o This is the charge of an electron Millikan was also able to determine the mass of an electron by combining his data with Thomson s 9x10A28g Electrons Electrons are tiny negatively charged particles All atoms are made from electrons The electron has a charge of 160 x 10quot19 C The electron has a mass of 91x10A28g The cathode rays are made of streams of electron The Plumpuddind model of the Atom 0 For the first time the atom was shown to be divisible Atoms have inner structure Moving Beyond Pudding Background Alpha particles are positively charged particles are positively emitted by some radioactive materials Alpha Particles Composed of 2 protons and 2 neutrons Are heavier than electrons Rutherford s Gold Foil Experiment lf atom was like a plum pudding all the a Over 98 of the alpha particles went straight through About 2 of the alpha particles went through but were deflected by large angles About 0005 of the alpha particles bounced off the gold foil Rutherford s Conclusion 0 Most alpha particles travel straight through the foil Therefore matter and atoms is mostly empty space O A few alpha particles bounce back from the foil Therefore there must be something very small very dense and positively charged within matter Rutherford s Interpretation 0 O 0000 O The atom contains a dense center called the nucleus The nucleus is 10quot11 times smaller than the atom Most of the mass of the atom is in the nucleus The nucleus is positively charged balancing the electrons The electrons are in the empty space surrounding the nucleus Rutherford proposed that the nucleus is composed of particles that are positively charged He called them protons The charge of protons is the same magnitude as the electron but opposite sign Charge 160 x 10A19 C and a mass 167262 x 10A24g Atomic Mass and Mass Spectrometrv Learnind Obiectives Calculated the average atomic mass of an element Interpret simple mass spectra Relates mass spectra to the average atomic mass of an element The Atomic Mass 0 Many elements have multiple stable isotopes The ratio of different isotopes within a sample of constant Eg Chlorine O Chlorine has 2 common isotopes 35Cl and 37Cl 0 35Cl is 7577 abundant 37Cl is 2433 abundant Atomic mass 3542 amu Mass Spectrometry There are many different ways for a scientist to measure the mass of an isotope A Mass Spectrometer can measure the mass of atoms and molecules How it works It works by moving ions past magnets and measuring how much the ions are deflected by the magnets O Lighter ions are deflected more by the magnets Heavier ions are deflected less A mass spectrum is a graph that vies the relative mass and relative abundance of each particle Relative mass of the particle is plotted on the xaxis Relative abundance of he the particle is plotted on the yaxis What is Mass Spectrometry good for O 0 Determining isotopic ratios Measuring the mass of molecules Can be applied to proteins Commonly used in forensic analysis Common used in medical diagnostics Chapter 2 Measurements and Units Qualitive o Subjective to the observer Quantitative o Measurable Units 0 A standard upon by which to specify a measurement 0 SI Unitslnternational System of Units Mass Kilogramskg Time Secondss Temp Kelvink Length Metersm Quantity of Substance Molesmol Measurements 0 Always will have a value with a unit 0 Eg 300g 0 Reliability of a measurement Depends on the instrument used Uncertainty Assume 1 Last digit of a measurement Significant Figures 0 The more significant figures in a measurement the more precise the measurement 0 Rules All nonzero digits19 are significant lnterior zeroszeros in between nonzero digits are significant Leading zeroszeros to the left of a nonzero digit are not significant and our only placeholders Trailing zeroszeros to the right of a nonzero digit Trailing zeros after a decimal point are significant 0 Ex 0001 Trailing zeros before a decimal point are significant 0 Ex 1400 Trailing zeros before an implied decimal point are ambiguous and not considered significant 0 Ex 1200 m 0 To avoid the ambiguity use scientific notation Ex1200 12 x10quot3 lnexact Numbers 0 0 Results from a measurement or observation and contains some uncertainty Has a specific number of significant figures Exact Numbers 0 O O O 0 Results from counting objects or part of a definition Ex 10 fingers lnfinite significant figures Conversion Factors 60s 1 min Numbers part of an equation K C 27315 0 Operations 0 O O Multiplication Division Addition Subtraction Rounding Always round after all operations are done However keep track of the number of significant figures after each question 0 Learning Objectives 0 Use Dimensional analysis to convert between different units Including units raised to the power 0 Implement problemsolving strategies to solve problems 0 Solving Chemical Problems Units 0 Always write every number with its units 0 Always include units in calculation 0 Units get multiplied and divided 0 Only add and subtract numbers of the same units 0 Unit Conversion 0 You need two things A measurement to convert A conversion factor There are exactly 254 cm in an inch 0 Ex 54234 gt cm gt 54234 in x 254cm 1 in 13775436 13775 cm 0 Dimensional Analysis 0 Arrange conversion factors so that the starting units cancel 0 String Conversion factors 0 Units raised to a power 0 Watch out when converting between units raised to powers Ex 1inquot2 gt cmquot2 gt 254cm1inquot2 gt 64515cmA21A2 inquot2 gt 64516 cmquot2 1 inquot2 Problem Solving Strategies 0 What do I know 0 What do I need to know How many liters in 1 mquot3 1m 100cm 1000mm 1cmquot3 1ml 1L 1000ml mquot3 gt cmquot3 gt mL gt L 0 Learning objective 0 Work with units of energy and density 0 Calculate the density of an object 0 Calculate the kinetic energy of an object 0 Define endothermic and exothermic Units of Measurement 0 Science uses a system called the International System of UnitsSl which is based on the metric system Meters Kilograms Seconds Kelvins Moles Mass 0 The Si units of mass are kilogramskg o Grams are also commonly used 1kg 10009 c 1 kg 220le this is not exact and has 3 sig gs 0 Temperature Temperature is the measure of the average kinetic energy of matter The US uses the Fahrenheit scale The rest of the world used the Celsius scale Science use the Kelvin scale Celsius is a nice scale Much easier to remember than Fahrenheit Water freezes at 0 C Water boils at 100 C A pleasant day outside is 25 C OOOOO The coldest possible temperature is 273 C C F3219 0 C K273 K C 273 0 Kelvin The SI world uses the Kelvin scale Similar to Celsius but de nes the coldest possible temperaturequotabsolute zeroquot to 0K 0 Nitrogen will liquefy at 321 F What is this temperature in degrees Celsius What is this temperature on the Kelvin scale Derived Units 0 A combination of other units Eg miles per hour mileshour Velocity is a combination of distance and time 0 Can you think of another common derived unit Volume 0 Volume is a measure of space Units for volume derived from quotcubed lengthsquot Eg cubic feet used to measure the trunk space in your car or the volume of natural gas The SI unit of volume is mquot3 Other common units of volume used be scientists Liters Learning Objectives 0 Work with units of energy and density 0 Calculate the density of an object Dens y 0 Ratio of mass to volume 0 Density MassVolume Energy 0 Capacity to do work Work is the action of a force applied across a distance 0 All matter possesses energy 0 Energy is classi ed as either kinetic or potential energy Kinetic energy is energy of motion 0 Cars Driving 0 Motion of atoms molecules protons electrons Thermal energy is a form of kinetic energy Potential energy is energy that is stored in the matter 0 Position of matter relative to other things 0 Chemical potential energy 0 Electrostatic forces between atoms molecules electrons 0 Energy can be converted from one form to another 0 When matter undergoes a chemical or physical change the amount of energy in the matter changes as well 0 Conservation of energy Total energy is the same Spontaneous Processes 0 Materials that have high potential energy are less quotstablequot 0 Spontaneous process tend occur when something can low its potential energy Changes in Energy 0 If a process results in an object have less potential energy it has quotlostquot energy Converted to kinetic energy During conversion from potential to kinetic work can be performed Learning objective 0 Know the Mole What is the mole Why we use the mole How to use the mole Atoms and molecules are really really small 0 When the lecture started your professor39s water bottle had about 167 000 000 000 000 000 000 000 molecules of water The mole o Atoms are very very very small 0 1 mol 6022 x 10quot23 things 6022 x 10quot23 is a very big number Why 602 x 10quot23 o The mass of 1 mol of a pure compound is numerically equal to its amu mass in grams 0 If something has a mass of 45 amu 602 x 10quot23 of this thing has a mass of 45g
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