Elements, Atoms and IonsElements, Atoms and Ions

Chapter 3Chapter 3

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 elements88 natural elements 9 elements make up 98% of the Earth’s mass9 elements make up 98% of the Earth’s mass

(see page 48)(see page 48) Elements are represented by “symbols”Elements are represented by “symbols”

One or two letter shorthand One or two letter shorthand (first letter is capital)(first letter is capital) Universally recognized Universally recognized AlAl

Oxygen Oxygen OONitrogen Nitrogen NNCobaltCobalt CoCoPotassiumPotassium KKAntimonyAntimony SbSbTungstenTungsten WW

AntimonyLead

Potassium

Early History of the AtomEarly History of the Atom

Democritus Democritus (400 BC)(400 BC) Greek philosopher Greek philosopher not a scientist 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, Proposed an atom for every type of material (gold, wood, fire…)fire…)

Atomos

Aristotle Aristotle (350 BC)(350 BC) Said that matter was “continuous”Said that matter was “continuous”

it can be divided into infinitely small piecesit can be divided into infinitely small pieces Accepted until the 17Accepted until the 17thth century century

Modern History of the AtomModern History of the Atom

John Dalton (early 1800’s)John Dalton (early 1800’s) First Modern Atomic ModelFirst Modern Atomic Model

1.1. Elements are made up of atoms.Elements are made up of atoms.

2.2. Atoms of the same element are the same.Atoms of the same element are the same.

3.3. Atoms of different elements are different.Atoms of different elements are different.

4.4. Different types of atoms combine to make compounds.Different types of atoms combine to make compounds.

Compounds always have the same relative numbers Compounds always have the same relative numbers and types of atoms.and types of atoms.

5.5. In chemical changes, atoms cannot be created or In chemical changes, atoms cannot be created or destroyed.destroyed.

KOH + HCl KOH + HCl H H22O + KClO + KCl

Antoine Lavoisier Antoine Lavoisier Work was studied Work was studied (ripped off)(ripped off) by Dalton by Dalton Law of Conservation of MassLaw of Conservation of Mass

In a normal chemical reaction, matter In a normal chemical reaction, matter cannot be created or destroyed.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.

JJ Thomson (1890’s)JJ Thomson (1890’s)Observed “Cathode Rays”Observed “Cathode Rays”

Streaks of light went from the negative cathode to Streaks of light went from the negative cathode to the positive anode the positive anode

∴ ∴ Cathode Rays are negativeCathode Rays are negative

Electrical Current

Glass Cathode Ray Tube

Anode (+)

Cathode (-)

Streaks of light were deflected by a magnetStreaks of light were deflected by a magnet

∴∴Cathode Rays are MatterCathode Rays are Matter

Cathode Rays = ElectronsCathode Rays = Electrons

Electrical CurrentN

S

““Plum Pudding” ModelPlum Pudding” ModelElectrons are stuck into a Electrons are stuck into a

positive masspositive massWhen energy is added, theWhen energy is added, the

electrons are ripped freeelectrons are ripped free + +

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