Chem 121 1st Edition Lecture 3 Outline of Last Lecture II. What is Chemistry? III. What is Matter?a. Categories of matterIV. Pure SubstancesV. Mixtures vs. CompoundsVI. Scientific Approach to KnowledgeVII. 3 Natural Laws of MatterOutline of Current Lecture VIII. AtomsIX. ElectronsX. ElementsXI. IsotopesXII. Atomic MassesCurrent LectureAtoms: Smallest identifiable particles- Building blocks of matter- 91 natural atoms, 20 synthetic (manmade) atoms- Types of machines to view atoms: Scanning tunneling microscopy, and atomic force microscopyHow did atoms and molecules evolve? Prehistoric theory: Democritus believed that atoms “do not cut” and that atoms compose matter. His hypothesis was not believed for almost 2,000 years.Modern theory: Dalton adopted the atomic theory, and started thinking about the composition of matter. He put all three theories together and tried to explain things better. Dalton believed that all matter is made of atoms, atoms are invisible, all atoms of a given element are identical in mass and properties, and that compounds are formed by a combination of two or more different kinds of atoms. Electrons-CRT- Joseph John Thomson (1897)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Negatively charged particle- Identical electrons from different cathode (atom)- Metal used didn’t make a difference- Beam deviated from the plane towards positive plate- Beam itself has negative charge-Oil-Drop experiment- Robert Millikan (1909) What does an atom look like?Atom must be something (+) positive to balance out the charge of the electron. -Experimental results found by Ernest Rutherford (1911)- Most particles pass through, some particles bounced back (1 in 20,000)- Ernest Rutherford wanted to prove JJ Thomson’s theory; he later joined JJ Thomson’s experiment.Elements- No elements have the same name or same symbol- Defined by number of protons- Atomic number (Z) = # of protons- Periodic table is arranged in increasing order of ZIsotopes: Number of Neutrons Vary- Isotope: have same chemical behaviors- **Same # of p+ but different # n0 (neutrons)- **Subtraction between A & Z gives the number of neutrons- A= # p+ + # n0 = Z+ #n  #n0 = A-Z- **Natural abundance of carbon:12C : 98.89% (9889 12C atoms per 10000 C atoms)13C: 1.11% (111 13C atoms per 1000 C atoms)14C: traceAtomic Masses**Atomic Mass Unit (amu)- 1 amu = 1/12 mass of a 12C atom = 1.66054 x 10-24g- Mass of a 12C atom= 12 amu exactly- 1 amu= 1 Dalton (D)Atomic Mass (weight): average mass of the masses of its naturally occurring isotopes weighted according to their abundance** Atomic mass= (mass of isotope #1 x % abundance #1) + (mass of isotope #2 x % abundance #2) + …** Atomic mass of C= (massc-12 x abundance) + (massc-13 x abundance)** Abundance of isotope 1 + abundance of isotope 2 = 100% = 1 Molecules and IonsIon: charged atom or a cluster of atoms** Cations: Positively charged ions by losing electron(s)# of p+ > # e- Charge= # of p+ - # of e-** Anions: Negatively charged ions by gaining electron(s)# of p+ < # e-** Ion has the same atomic mass as the parental