Bellwork: Get out your diagram from your research paper. Get out a sheet of paper to take some notes on. Fill in the Following Table in your notes (assume an atom unless otherwise stated: Symbol Protons Electrons Neutrons Atomic # Mass # 24 Na + 11 63 Cu 29 11 10 13 11 24 29 29 34 29 63
Development of the Atomic Theory
What does the Greek word atomos mean? The Greek word atomos means not able to be divided or indivisible.
Who was Democritus? Democritus was an ancient Greek philosopher who lived from 460-370 B.C. What did Democritus conclude about cutting matter in half? There was a limit to how far you could divide matter. You would eventually end up with a piece of matter that could not be cut.
Why weren t Democritus s ideas accepted? Aristotle believed that matter could be divided into smaller and smaller pieces forever. He held a very strong influence on popular belief and his views on this were accepted for two thousand years.
John Dalton 1776-1844 Two thousand years later a British chemist and schoolteacher brings back Democritus s idea of the atom He performed many experiments to study how elements join together to form new substances.
Summary for Dalton s Atomic Theory Atoms are tiny and indivisible. Atoms can t be created or destroyed. Atoms of the same element are the identical. Atoms of different elements are different. Atoms of different elements combine in simple whole-number ratios to form compounds.
Dalton s Theory Experimental evidence Scientific Laws Law of Conservation on Matter You can t create or destroy atoms. Law of Definite Proportions Same compounds are same ratio by mass. Law of Multiple Proportions Different compounds with the same elements are whole number multiples of the atoms. Experiments Scientific Laws Atomic Theory (observations) (Patterns) (Explanations) John Dalton realized that there must be an atom as Democritus first proposed.
Expert groups: Get together with people who researched the same scientists as you. Discuss what you need to make sure everyone knows about your scientists. Explain his experiment and procedure Discuss his findings and their significance to modern atomic theory Any problems with his ideas
Now you are going to the home groups of the number you were given. It is your job as the EXPERT to make sure everyone understands what your scientists did. You will be held responsible for this material.
Turn in Diagrams, make sure your name is on them.
Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. http://viewpure.com/idtxgjja4jw Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.
Cathode Rays (electrons) Observations: Cathode Ray Tube produces rays with constant charge to mass ratio. Cathode rays (electrons) were found in all substances tested. Conclusions and Hypotheses: The electron has a specific size and charge. All atoms contain tiny particles called electrons. Cathode rays (electrons) were attracted to the positive plate every time. Electrons are negatively charged. Neutral atoms are made up of equal amounts of (+) and (-) particles.
Thomson s Atomic Model (1897) Thomson believed that the electrons were like plums embedded in a positively charged pudding, thus it was called the plum pudding model.
Thomson- Discovered electrons: cathode rays were deflected by magnets and electric plates Found charge-to-mass ratio for electrons Proved electrons are a part of all atoms
Goldstein (1886) - Started with the hypothesis that when a neutral hydrogen atom loses an electron, a positive particle should remain. - Using cathode ray tube. He found rays traveling in the opposite direction. - Concluded that these were made a positive subatomic particles, which would later be called protons.
Rutherford s Gold Foil Experiment http:// viewpu re.com /wzalb ztdnc8 (+) Radioactive source Alpha particles are helium nuclei, He 2+ Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded
Rutherford s Findings (1911) Observations: Most of the alpha particles passed right through Some alpha particles were deflected slightly VERY FEW were greatly deflected Conclusions: The atom is mostly empty space. The nucleus is dense. The nucleus is positively charged Electrons, e -, are moving large distances outside the nucleus.
Rutherford s Conclusion (1911) Small, dense, positive nucleus. Equal amounts of (-) electrons at large distances outside the nucleus.
Millikan http://viewpure.com/xmfy Hag7Liw In 1916, he discovered the charge of the electrons!
Chadwick (1932) discovered the neutron. http://viewpure.com/_7dalvri1m4 fast forward to 5:00 min..
Neils Bohr s Atomic model (1913) Small, dense, positive nucleus. Equal amounts of (-) electrons at specific orbits around the nucleus. This incorrect version of the atom is often used to represented atoms because it shows energy levels for electrons.
Bohr s Model of the Atom Bohr s Model - an early conceptual model of the atom - classic planetary model in which electrons whirl around the small but dense nucleus: like planets orbiting the Sun - developed by the Danish physicist Niels Bohr in 1911 - each electron has a certain energy that is determined by it s path around the nucleus
Erwin Schrodinger (1926 ) Quantum Mechanical Model Like the Bohr model, the quantum mechanical model of the atom restricts the energy of electrons to certain values. Unlike the Bohr model, however, the quantum mechanical model does not involve an exact path the electron takes around the nucleus. The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.
If you need more review of the history of atomic theory: https://www.youtube.com/watch?v=nsaglvkoplq Scientists matching game
Democritus Atoms are indivisible and indestructible. 460-370 B.C. Dalton Using experimental methods determined that all matter composed of atoms, atoms of different elements are different, one atoms can not be changed into another. 1776-1844 Thomson Cathode ray Discovered electron 1897 Millikan Oil Drop Experiment Calculated charge and mass of electron 1916
Goldstein Cathode Ray Suggested the idea positively charged particles later called protons 1886 Chadwick Shot Alpha Particles into beryllium Discovered neutrons 1932 Rutherford Gold- Foil Experiment Discovered the nucleus 1911