1818 ACC Chemistry

1818 ACC Chemistry

Chemistry Oct 26, 2017 P3 Challenge Use dimensional analysis (factor label method) to Convert 15.2 m/min to cm/s. Objective Atomic History and Atomic Models Chemistry Oct 26, 2017 Agenda Early Theories

Daltons Atomic Theory Discovery of subatomic particles The Nucleus Quantization Assignment: Atomic History Worksheet Atomic Theory Beginnings Democritus (c. 400 BC) (unpopular, not widely known)

Matter is composed of atoms. No structure proposed. Probably considered cubic. Largely ignored in favor of Aristotles view of continuous matter for 2000 years Logical/Theoretical only. Armchair science The Scientific Revolution (Note: Galileo trial 1633) The Skeptical Chemist by Robert Boyle in 1661 (discredit Aristotle) Established There an experimental approach. Macroscopic only. was no atomic model at this time. Early Macroscopic Laws

Law of Conservation of Mass by Antoine Lavoisier in 1789 Mass is conserved in chemical reactions. Discovered oxygen in the process. Law of Definite Proportions Chemical compounds always contain exactly the same proportion of elements by mass. Can determine elemental percent composition of a compound. John Daltons Atomic Theory Based on Experimental results and early laws in 1805

Daltons Atomic Theory (First modern atomic model) 1. Matter is composed of indivisible and indestructible atoms. 2. Atoms of one element cannot be converted into atoms of another element. 3. All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements. 4. Atoms combine in simple, whole-number ratios to form compounds. Atoms are solid spheres with differing masses Subatomic particle discovered: the

electron The Cathode Ray Tube was developed by Sir William Crookes. J. J. Thomson discovered the electron with Cathode Ray tube in 1897 Measured charge to mass ratio of electron (q/m = 1.76 x 108 C/g) Data suggests the electron is 1000 times smaller than hydrogen Proposed Plum Pudding model of atom (choc chip dough ball model) Verifying subatomic particles Robert Millikans Oil-drop experiment of 1909

Accurately measured the charge of the electron q = 1.6 x 10-19 C Using Thomsons q/m ratio (q/m = 1.76 x 108 C/g) found the mass of the electron too. m = 9.1 x 10-31 kg Atomic masses are thousands of times larger Discovery of the Nucleus Ernest Rutherfords Gold Foil Experiment of 1909

Concludes a small positively charged, massive nucleus. Most of the atom is empty space Nuclear Theory of the Atom 1. Most of the atoms mass and all of its positive charge are contained in a small core called the nucleus. 2. Most of the volume of the atom is empty space through which the tiny negatively charged electrons are randomly dispersed. 3. There are equal numbers of positive and negative charged particles so atoms are electrically neutral.

Equal number of protons and electrons Neutron discovered in 1932 by James Chadwick Why so late? Bohr Atomic Model Johann Balmar observed optical line spectra from electrically excited gases (neon lights) in 1885 Niels Bohr explained optical spectra of atoms in 1913 Bohr Model of the atom was first quantized model Used fixed energy levels and restricted

orbits for the electrons Solved physics dilemma of the nuclear model Current Atomic Theory: Quantum Mechanics Developed by dozens of scientists in the early 20th century: Heisenberg, Einstein, de Broglie, Born Erwin Schrdinger often given the credit Complicated math, but exact agreement with every experimental result to date. Highly confirmed theory. Current study of QM is done by physical chemists and

physicists. Basic atomic structure is a collection of probability electron clouds called orbitals. We will learn more about QM later. Summary of Atomic Theory History 1 Scientists Contribution Atomic Model Democritus (400 BC) Idea of atoms Logical discrete bits of matter (Discredited due to Aristotle) Boyle (1661)

The Scientific Method Need to base on experiment None. Lavoisier (1789), Law of Conservation of Mass (Discovered Oxygen) None. Dalton (1805) Law of Multiple Proportions Atomic Theory Solid Spheres Atomic model Summary of Atomic Theory History 2 Scientists Contribution Atomic Model Thomson (1897)

Discovers Electron w/ Cathode Ray Tube Plum Pudding/Choc Chip Pos. dough, neg. chips Millikan (1909) Mass & Charge of Electron with Oil-drop Experiment Rutherford (1909); Discovers nucleus w/ Gold Foil experiment Positive massive nucleus, Tiny neg electrons in space Nuclear Model Summary of Atomic Theory History 3 Scientists Contribution Atomic Model

Chadwick (1932) Discovers neutrons Positive massive nucleus, Tiny neg electrons in space Nuclear model Bohr (1913) Explains atomic spectra; Solves physics charge problem Quantized planetary Bohr model Schrdinger, Heisenberg, Einstein, de Broglie, Born et al. (1915-1930) Quantum Mechanics; Waveparticle duality; Uncertainty Quantized probability electron clouds Exit Slip - Homework

Exit Slip: Who discovered the electron? Who discovered the nucleus? Whats Due? (Pending assignments to complete.) Atomic History Worksheet Whats Next? (How to prepare for the next day) Read Holt p84 - 88

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