1. Elements, Atoms and Ions Chapter 3

2. All Matter can be broken into “elements” All Matter can be broken into “elements” 114 elements (as of this morning) 114 elements (as of this morning) 88 natural elements 88 natural elements 9 elements make up 98% of the Earth’s mass 9 elements make up 98% of the Earth’s mass (see page 48) Elements are represented by “symbols” Elements are represented by “symbols” One or two letter shorthand (first letter is capital) One or two letter shorthand (first letter is capital) Universally recognized Al Universally recognized AlAl Oxygen O Oxygen O Nitrogen N Nitrogen N CobaltCo CobaltCo PotassiumK PotassiumK AntimonySb AntimonySb TungstenW TungstenW Antimony Lead Potassium

3. Early History of the Atom Democritus (400 BC) Democritus (400 BC) Greek philosopher  not a scientist Greek philosopher  not a scientist Suggested that the world was empty space and “atoms” Suggested that the world was empty space and “atoms” Proposed an atom for every type of material (gold, wood, fire…) Proposed an atom for every type of material (gold, wood, fire…) Atomo s

4. Aristotle (350 BC) Aristotle (350 BC) Said that matter was “continuous” Said that matter was “continuous”  it can be divided into infinitely small pieces Accepted until the 17 th century Accepted until the 17 th century

5. Modern History of the Atom John John Dalton (early 1800’s) First First Modern Atomic Model 1. Elements 1. Elements are made up of atoms. 2. Atoms 2. Atoms of the same element are the same. 3. Atoms 3. Atoms of different elements are different. 4. Different 4. Different types of atoms combine to make compounds. Compounds always have the same relative numbers and types of atoms. 5. In 5. In chemical changes, atoms cannot be created or destroyed. KOH + HCl  H 2 O H 2 O + KCl

6. Antoine Antoine Lavoisier Work Work was studied (ripped off) off) by Dalton Law Law of Conservation of Mass In a normal chemical reaction, matter cannot be created or destroyed. A burning candle will get smaller and lose mass. When the candle is burned in an enclosed container, the total mass of the system does not change.

7. JJ JJ Thomson (1890’s) Observed Observed “Cathode Rays” Streaks Streaks of light went from the negative cathode to the positive anode ∴Cathode Rays are negative Electrical Current Glass Cathode Ray Tube Anode (+) Cathode (-)

8. Streaks of light were deflected by a magnet Streaks of light were deflected by a magnet ∴ Cathode Rays are Matter Cathode Rays = Electrons Cathode Rays = Electrons Electrical Current N S

9. “Plum Pudding” Model “Plum Pudding” Model Electrons are stuck into a Electrons are stuck into a positive mass When energy is added, the When energy is added, the electrons are ripped free + + + + + + + -