2-1 CHEM 100, Fall 2014 LA TECH Instructor: Dr. Upali Siriwardane Office: CTH 311 Phone Office Hours: M,W, 8:00-9:30 & 11:30-12:30 a.m Tu,Th,F 8: :00 a.m. Or by appointment Test Dates : Chemistry 100(02) Fall 2014 September 29, 2014 (Test 1): Chapter 1 & 2 October 20, 2014 (Test 2): Chapter 3 & 4 November 12, 2014 (Test 3) Chapter 5 & 6 November 13, 2014 (Make-up test) comprehensive: Chapters 1-6 9:30-10:45:15 AM, CTH 328

2-2 CHEM 100, Fall 2014 LA TECH REQUIRED : Textbook: Principles of Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro - Pearson Prentice Hall and also purchase the Mastering Chemistry Group Homework, Slides and Exam review guides and sample exam questions are available online: and follow the course information links. OPTIONAL : Study Guide: Chemistry: A Molecular Approach, 2nd Edition- Nivaldo J. Tro 2nd Edition Student Solutions Manual: Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro 2nd Text Book & Resources

2-3 CHEM 100, Fall 2014 LA TECH 2.1 Imaging and Moving Individual Atoms…………… Early Ideas about the Building Blocks of Matter…… Modern Atomic Theory and the Laws That Led to It… The Discovery of the Electron……………………… The Structure of the Atom…………………………… Subatomic Particles: Protons, Neutrons, and Electrons in Atoms……………………………………………… Finding Patterns: The Periodic Law and the Periodic Table………………………………………… Atomic Mass: The Average Mass Of an Element’s Atoms Molar Mass: Counting Atoms by Weighing Them………66 Chapter 2. Atoms and Elements

2-4 CHEM 100, Fall 2014 LA TECH Chapter 2. KEY CONCEPTS Atom Imaging Radioactivity Subatomic Particles Electrons Electronic Charge Nuclear atom Protons Neutrons Atomic number (Z) Size of Atoms Three chemical Laws Dalton's atomic theory Interpreting chemical formulas and chemical reaction. Isotopes Isotopic symbols Atomic Mass Units Mass Spectrometer isotope masses and % composition? Average atomic weights Periodic Table Abundance of Elements Earth's Atmosphere Concept of mole Gram to mole conversion

2-5 CHEM 100, Fall 2014 LA TECH 1) What are following experimental techniques that are being used to image individual atoms? a) STM (SPM)b) AFM (SPM)c) SEM (e-beam)d) TEM (e-beam)

2-6 CHEM 100, Fall 2014 LA TECH Scanning Tunneling Microscope

2-7 CHEM 100, Fall 2014 LA TECH Microscopes 1) Optical Microscopes 2) SPB-Scanning Probe Microscopy a)STM-Scanning Tunneling Microscope b) Atomic Force Microscope 3) Electron beam Techniques a)SEM-Scanning Electron Microscope b)TEM-Transmission Electrum Microscope Microscopy

2-8 CHEM 100, Fall 2014 LA TECH Alchemist: Discovery of Elements Early scientist observed chemical changes of matter. They called these changes chemical reactions when there are changes in substances or the physical & chemical properties of the matter. They also observed a pattern or a repeatable observation during chemical reactions.

2-9 CHEM 100, Fall 2014 LA TECH Law of the Conservation of Matter Lavoisier proposed from his experimental evidence the following law: Matter is neither created nor destroyed in a chemical reaction. Total mass of used reactants = Total mass of products producedTotal mass of used reactants = Total mass of products produced Total number of reactant atoms = Total number of product atomsTotal number of reactant atoms = Total number of product atoms

2-10 CHEM 100, Fall 2014 LA TECH Law of Conservation of Mass: Law of Constant Proportions: Law of Multiple Proportions: Three Observed Chemical Laws:

2-11 CHEM 100, Fall 2014 LA TECH Early scientist observed changes of matter They called these changes chemical reactions when there are changes in substances or the chemical properties of matter. They also observed a pattern or a repeatable observation in chemical reactions. They observed that Mass was neither destroyed nor created (E.g. Hydrogen (4g) + oxygen (32g) gives water 36g after the reaction), and elements combine in Constant Proportions (E.g. 36g of water contains 4g of hydrogen and 32g of oxygen) and in compounds in 1:8 Multiple Proportion (E.g. In CO, 1g C contains 1.33 g of O and In CO 2 1g C contains 2.66 g of O).

2-12 CHEM 100, Fall 2014 LA TECH Law of multiple proportions: Two elements A and X can form different compounds by combining in different proportions.Two elements A and X can form different compounds by combining in different proportions. –These combinations can be represented as a ratio. For example: For example: –A molecule of carbon dioxide (CO 2 ) has a ratio of 1 C atom to every 2 atoms of oxygen, or 1:2. –A molecule of hydrogen peroxide (CO) has a ratio of 1 C atom to 1 atom of oxygen, or 1:1. Law of Multiple Proportions

2-13 CHEM 100, Fall 2014 LA TECH 2) What are the patterns of observations in conducting chemical reactions by early chemists? a) b) c)

2-14 CHEM 100, Fall 2014 LA TECH 3) What theory John Dalton came up with to explain the body of chemical observations and laws?

2-15 CHEM 100, Fall 2014 LA TECH Dalton’s atomic theory All matter is composed of atoms -- the smallest particle of an element that takes part in a chemical reaction. All atoms of an element are alike. Compounds are combinations of atoms of one or more elements. The relative number of atoms each element is always the same. Atoms cannot be created or destroyed by a chemical reaction. They only change how they combine with each other.

2-16 CHEM 100, Fall 2014 LA TECH 4) What are the postulates of Dalton’s atomic theory? a) b) c) d)

2-17 CHEM 100, Fall 2014 LA TECH 5) How was Dalton’s atomic theory modified based on new experimental observations leading to the discovery of the electron, nucleus, protons and neutrons? Reword Dalton’s postulates to accommodate new observations and particles. a) b) c) d)

2-18 CHEM 100, Fall 2014 LA TECH Radioactivity Becquerel (1896) – Uranium ore emits rays that “fog” a photographic plate. Marie and Pierre Curie (1898) – Isolated 2 new elements (Po and Ra) that did the same. radioactivity – Marie Curie called the phenomenon radioactivity.

2-19 CHEM 100, Fall 2014 LA TECH 6) What is radioactive decay?

2-20 CHEM 100, Fall 2014 LA TECH Radioactivity Types of Radiation Alpha rayα (positive charge) Beta rayβ (negative charge) Gamma rayγ (no charge) Electrical behavior:+ attracted to - (opposites attract) (like charges repel) (like charges repel) Radioactive material Electrically Charged plates screen + − Beam of α, β, and γ α γ β

2-21 CHEM 100, Fall 2014 LA TECH 7) What are following radiation? a)  b)  c) 

2-22 CHEM 100, Fall 2014 LA TECH 8) Which of the following radiation,  and  is most harmful?

2-23 CHEM 100, Fall 2014 LA TECH Electrons Thomson (1897) studied cathode rays and discovered the electron: Beam travels from the cathode (-) to the anode (+). – the beam flies through a ring anode and hits a fluorescent screen. The cathode rays come from the cathode metal. They are negative particles – electrons (e − ). fluorescent screen – high voltage + cathode ray

2-24 CHEM 100, Fall 2014 LA TECH Electrons Thomson showed that electric and magnetic fields deflect the beam. – – high voltage + + From the deflections, Thomson calculated the mass/charge ratio for an e - : = −5.60 x g/C (Coulomb (C) = the SI unit of charge)

2-25 CHEM 100, Fall 2014 LA TECH The Discovery of the Electron, Nucleus Subatomic Particles: Protons, Neutrons, and Electrons in Atoms 9) How did Thompson know that every element has electrons? 10) How did Thompson know that an electron has a negative charge?

2-26 CHEM 100, Fall 2014 LA TECH 11) In the Millikan’s oil drop experiment, how did he remove electrons from atoms? 12) In the Millikan’s oil drop experiment, where did some of the electrons removed from atoms ended up? 13) In the Millikan’s oil drop experiment, why was some oil drops had multiples (1,2,3 of −1.60 x ) of charges?

2-27 CHEM 100, Fall 2014 LA TECH 14) Thomson calculated the mass/charge (m/e) ratio for an e- to be = −5.60 x g/C. and then Millikan found the charge on an e- to be −1.60 x C. What is the mass on an electron?

2-28 CHEM 100, Fall 2014 LA TECH 15) In the Rutherford’s experiment, what caused a few α’s were deflected through large angles and some came almost straight back!

2-29 CHEM 100, Fall 2014 LA TECH Electronic Charge Robert Millikan (1911) studied electrically- charged oil drops. For a single charged drop, he measured: – the time to fall a fixed distance, and – to rise the same distance in an electric field. He showed that each drop had a charge that was an integer multiple of −1.60 x C. (The charge of an electron. ) The modern value is − x C. (Often written in “atomic units” as charge = −1).

2-30 CHEM 100, Fall 2014 LA TECH Millikan’s Experiment

2-31 CHEM 100, Fall 2014 LA TECH Mass of an Electron The experiments by Thomson and Millikan gave the mass/charge ratio and charge of an e −. The modern value is: m e = x g = (−1.60 x C)/(−5.60 x g/C) = 8.96 x g m e = charge x mass charge

2-32 CHEM 100, Fall 2014 LA TECH J. J. Thomson (plum-pudding model) electrons -The atom is composed of a positive cloud of matter in which electrons are embedded. Explains the positive (+), negative (-) charged behavior of matter Atomic Structure: Plum-Pudding Model

2-33 CHEM 100, Fall 2014 LA TECH Nuclear Atom Thompson thought it was a ball of uniform positive charge, with small negative dots (e - ) stuck in it. However “plum pudding” model was short lived and was changed to Nuclear model.

2-34 CHEM 100, Fall 2014 LA TECH Gold foil experiment: Could not explain Thomson’s plum-pudding atom model. Led to the discovery of the atom’s nucleus. Rutherford’s Gold Foil Experiment Setup

2-35 CHEM 100, Fall 2014 LA TECH From the gold foil experiment, the following conclusions were proposed: The atom contains a tiny, dense center called the nucleus. The atom contains a tiny, dense center called the nucleus. The nucleus has essentially the entire mass of the atom. The nucleus has essentially the entire mass of the atom. – The electrons weigh so little they give practically no mass to the atom. The nucleus is positively charged. The nucleus is positively charged. – The amount of positive charge balances the negative charge of the electrons. – The electrons are dispersed in the empty space of the atom surrounding the nucleus. Rutherford & the Nucleus: Gold Foil Experiment

2-36 CHEM 100, Fall 2014 LA TECH Rutherford estimated that the charge of the nucleus of an atom was about one half of the atomic mass. Moseley, while working for Rutherford, developed a more accurate measurement. While working with cathode rays on metal targets, he measured the wavelength of the X-rays produced. He found that a direct relationship exists between the metal’s atomic number and the square root of the frequency. Determination of nuclear charge

2-37 CHEM 100, Fall 2014 LA TECH Moseley, Henry & Gwyn Jeffreys 1887–1915, English physicist. studied the relations among x-ray spectra of different elements. concluded that the atomic number is equal to the charge on the nucleus based on the x-ray spectra emitted by the element. explained discrepancies in Mendeleev’s Periodic Law. Discovery of Protons and Atomic Number

2-38 CHEM 100, Fall 2014 LA TECH Moseley concluded that the charge of the nucleus was an integer. Further, it was the same as the number of electrical units (electrons) but of opposite charge. Moseley concluded that the charge of the nucleus was an integer. Further, it was the same as the number of electrical units (electrons) but of opposite charge. Atomic number X-Ray Frequency 1/2 Determination of nuclear charge

2-39 CHEM 100, Fall 2014 LA TECH Summary of Subatomic Particles ParticleChargeMass (g)Mass (amu) Proton Neutron Electron +1.6 x C zero x C 1.7 x g 9.1 x g x Remember: Atoms are usually electrically neutral, Indicating equal numbers of protons and electrons!

2-40 CHEM 100, Fall 2014 LA TECH Atomic number, Z Atomic number, Z The number of protons in the nucleus The number of electrons in a neutral atom The integer on the periodic table for each element

2-41 CHEM 100, Fall 2014 LA TECH Relative size of atom and atomic nucleus

2-42 CHEM 100, Fall 2014 LA TECH Ions Charged single atom Charged cluster of atoms Cations : positive ions Anions : negative ions Ionic compounds: combination of cations and anions with zero net charge

2-43 CHEM 100, Fall 2014 LA TECH Nuclear Notation X = atomic symbol A = mass number Z = atomic number C-12, carbon-12 X A C 12 Z X A 6 C 12

2-44 CHEM 100, Fall 2014 LA TECH Mass Number, A integer representing the approximate mass of an atom equal to the sum of the number of protons and neutrons in the nucleus