1. Unit 3

2.  smallest particle of an element that can exist alone or in combinations with other atoms

3.  The idea that all matter composed of atoms  The structure of the atom has changed overtime as scientific advances have been made.

4.  First proposed by early Greek philosophers like Democritus in approximately 400 B.C.  All matter is made of “atomos” which means in destructible.

5.  First to develop atomic theory based on experimental evidence  Early 1800s  Based his theory on several laws known at the time

6.  Remember this one?  Mass cannot be created or destroyed in a chemical reaction

7. Any sample of a compound always has the same composition. NaCl 39.34% Sodium by mass 60.66% Chlorine by mass

8. The mass ratio for one of the elements in a compound that combines with a fixed mass of another element can be expressed in small whole numbers. Elements always combine in “whole” number increments. Water: H 2 OHydrogen peroxide: H 2 O 2

9. Applies to different compounds formed from the same elements. Name of Compound Description% Oxygen by mass % Nitrogen by mass Formula Nitrogen dioxide Poisonous brown gas in smog 69.5630.44NO 2 Nitrogen monoxide Colorless gas that reacts readily with oxygen 53.3246.68NO Dinitrogen monoxide “laughing gas” anesthetic 36.3563.65N2ON2O

10. 1. Atoms are the smallest particle of matter and can’t be divided.

11. 2. Atoms of a given element are identical in size, mass, and other properties

12. 3. Atoms can’t be created or destroyed in chemical reactions (Law of Conservation of Mass)

13. 4. Atoms can combine in small whole number ratios (law of definite/multiple proportions)

14.  Discovered the electron with the cathode ray tube experiment  http://www.physics.uq.edu.au/people/ mcintyre/applets/cathoderaytube/crt.ht ml http://www.physics.uq.edu.au/people/ mcintyre/applets/cathoderaytube/crt.ht ml

16.  Was a student of Thomson  Investigated the plum pudding model with the famous gold foil experiment  Bombarded gold foil with alpha particles (large and positive)

17.  Rutherford concluded that an atom contains a nucleus  Nucleus: small, dense, positive region in atom. › Contains most of the mass, but takes up little space

18.  The gold foil experiment eventually led Rutherford to the discovery of the proton

20. 1. Chadwick (1932) proposed the idea of a neutral particle with the same mass a proton, the neutron

21.  When nuclear chemistry became the “cool” thing to study, Chadwick knew there had to be something present to stabilize the nucleus!

22.  Suggested that electrons have to be in fixed energy levels

23.  Electrons are attracted to protons, so why do electrons not collapse into the nucleus and implode?  Reason! Electrons are in fixed energy levels. THESE ARE NOT HOW THE ORBIT!!!!!!!!!!!!!  Still the nuclear model

24.  Introduced quantum theory (mathematically based) to explain the probability of finding electrons, orbitals (not to get confused with orbits!)

25.  Modern day view of atom  What a beauty!!!!