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Unit 2 – Atomic Theory Chapter 4 & 11.2 Unit Test:

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1 Unit 2 – Atomic Theory Chapter 4 & 11.2 Unit Test:

2 Democritus Lived around 400 B.C. Came up with the concept of the atom

3 John Dalton - 1807 Known for Billiard Ball Model Called the father of Atomic Theory

4 Dalton’s Atomic Theory - 1807 All matter is composed of atoms which are indivisible All atoms of the same element are identical Atoms of different elements are different Atoms bond in different proportions to form compounds (Law of Definite Proportions)

5 J. J. Thomson - 1903 Discovered the electron (1 st subatomic particle) through experiments with cathode ray tube Plum Pudding model (or Chocolate Chip Cookie model)

6 Thomson’s Model “Pudding” or “Cookie” is the positive charge and most of the mass of the atom “Plums” or “Chocolate Chips” are the scattered electrons POSITIVE CHARGE ELECTRONS

7 Ernest Rutherford - 1911 Nuclear Model (atom contains a nucleus) Gold foil Experiment

8 Rutherford’s Experiment

9 Rutherford’s Model Atoms have:  A nucleus  Protons (positive charge) in nucleus  Mostly open space  Electrons found somewhere around the nucleus

10 Niels Bohr - 1913 Planetary Model Electrons (e - ) have definite path around the nucleus (orbit) e - arranged around the nucleus according to energy level e - with lowest energy level are closest to nucleus

11 Bohr’s Model

12 Quantum Mechanical Model - 1923 Electron Cloud (modern theory) Calculates the probability of finding the electron within a given space Electrons, instead of traveling in defined orbits, travel in diffuse clouds around the nucleus

13 Quantum Mechanical Model Present Model of the Hydrogen Atom

14 Stepwise Timeline of Atomic Theory Dalton 1803 Thomson 1897 Rutherford 1909 Bohr 1913 Modern Theory

15 Subatomic Particles amu – atomic mass unit; based on carbon-12 1 amu = 1/12 mass of C-12 = mass H Impractical to use actual mass of subatomic particles NameSymbolRelative Mass ChargePosition Proton 1 H or p + 1 amu1Nucleus Electrone-e- 0 amuOutside Neutron 1n1n1 amu0Nucleus

16 Elements of the Periodic Table Atomic Number  Identifies element  # protons  # electrons in neutral atom Atomic Mass  a.k.a. mass number  # protons + # neutrons Atomic Number Atomic Symbol Atomic Mass

17 Isotope Notation Element Symbol with mass number and atomic number Can also be the element name dash mass number X Mass Number Atomic Number or Element- Mass

18 Practice Symbol# Protons # neutrons # electrons Atomic Number Mass Number 9109919 2859 15094 3065

19 Isotopes Atoms of the same element with different numbers of neutrons Think of it as different sized shirts! 6 neutronsCarbon-12 7 neutronsCarbon-13 8 neutronsCarbon-14

20 Isotopes

21 Average Atomic Mass Mass listed on the periodic table Determined by averaging the masses of all naturally occurring isotopes of that element Explains why the atomic mass is usually not a whole number

22 Finding Average Atomic Mass You are told there are 3 isotopes of Cycreekium and their percent abundance:  Cycreekium-20; 10%  Cycreekium-22; 20%  Cycreekium-23; 70% Find their average atomic mass!

23 Finding Average Atomic Mass Formula: % abundance as decimal × atomic mass for each isotope; sum results for avg. atomic mass. 10% × 20amu = 0.10 × 20amu = 2.0amu 20% × 22amu = 0.20 × 22amu = 4.4amu 70% × 23amu = 0.70 × 23amu = 16.1amu Total: 22.5amu

24 Percent Abundance If you are given information about an elements isotope you can estimate the most abundant isotope! Example: Carbon-12, Carbon-13, Carbon-14. Look at the atomic mass on the periodic table. Which isotope is the mass closest to?

25 End of Unit 2 Notes! Study for Unit 2 Test on:

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