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Mr Nelson. The Greek philosopher Democritus began the search for a description of matter more than 2400 years ago. He asked: Could matter be divided.

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Presentation on theme: "Mr Nelson. The Greek philosopher Democritus began the search for a description of matter more than 2400 years ago. He asked: Could matter be divided."— Presentation transcript:

1 Mr Nelson

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3 The Greek philosopher Democritus began the search for a description of matter more than 2400 years ago. He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided? 400 BC

4 This piece would be indivisible. He named the smallest piece of matter atomos, meaning not to be cut.

5 The eminent philosophers of the time, Aristotle and Plato, had a more respected, theory. Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter.

6 In the early 1800s, English Chemist John Dalton performed experiments that verified the existence of atoms.

7 1803 Daltons Model was that atoms are indivisible particles.

8 All matter is composed of atoms. Atoms of the same element are exactly alike. Atoms of different elements are different. Atoms are indestructible and cannot be divided.

9 In 1897, the English scientist J.J. Thomson proved the atom is made of even smaller particles.

10 Thomson studied the Cathode Ray Tube. As the current passed through the gas, it gave off rays of negatively charged particles.

11 the atoms of the gas were uncharged. Where had the negative charges come from? Where did they come from?

12 Thomson concluded that the negative charges came from within the atom. Thomson called the negatively charged electrons. Since the gas was known to be neutral, he reasoned that there must be positively charged particles in the atom. But he could never find them.

13 Plum Pudding model. Atoms were made from a positively charged substance with negatively charged electrons scattered around

14 In 1908 English physicist Ernest Rutherford, began work on his gold foil experiment.

15 Rutherford was trying to verify Thomsons model. He expected positively charged particles to go straight through a piece of very thin gold.

16 Most particles passed straight through the gold foil A small percentage of particles were deflected at large angles or returned to the source

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18 There are 2 reasons alpha particles deflected Density of the nucleus Repelling charges

19 An atom has a small, dense, positively charged center that repelled the positively charged particles. Named the center of the atom the nucleus The nucleus is tiny compared to the atom as a whole. The atom is mostly empty space

20 An atoms positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atoms edge.

21 Was a Jewish Scientist in Copenhagen during the onset of WWII Hitler was interested in his research of the atom. He was moved to the US to protect his knowledge.

22 Electrons travelled in a specific orbit at a certain distance from the nucleus called an energy level Worked well for Hydrogen and Helium

23 In this unit we need to be familiar with this type of symbol

24 Includes an element name a - and a number Example: Sulfur – 32 This sulfur atom has an atomic mass of 32 Since Sulfur has ______ protons & electrons It also has ______ neutrons

25 ParticleSymbolChargeMass (amu)Location Proton Neutron Electron

26 Calculate the average atomic mass of magnesium given the following information: Mg, mass = amu; percent abundance = 78.99% Mg, mass = amu; percent abundance = 10.00% Mg, mass = amu; percent abundance = 11.01%

27 Electrons are a HUGE deal in chemistry Responsible for light, color & chem reactions

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29 Electrons in atoms: when an atom absorbs energy - electrons jump to higher energy levels. An EXCITED electron jumps from its ground state to a higher energy level. When the electron returns it releases the same amount of energy that it absorbed.

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31 Light is released as photons as electrons return from different energy levels. Some of the photons are visible light Balmer Series

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33 Wave Particle

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35 Hydrogen Mercury Argon Helium

36 How many wavelengths are represented in each figure below?

37 Red Light Violet Light Low frequency Long wavelength High frequency Short wavelength Wave Comparison nm = 1 x m


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