Chapter 3: Chapter 3: Atoms, the Building Atoms, the Building

Blocks of MatterBlocks of Matter

Atomic Theory has Evolved!Atomic Theory has Evolved!

Leave a couple of lines!

Law of Conservation of MassLaw of Conservation of Mass

Mass is neither created nor destroyed during an ordinary chemical reaction or physical change.

Remember the Candle Lab:

C25H52 + O2 + E CO2 + H2O + C + E

Draw a picture and explain Draw a picture and explain why it happens?why it happens?

Leave about a half a page for an activity…

Pioneers of the Pioneers of the Atomic TheoryAtomic Theory

Chapter 3Chapter 3

Observant people have been looking at matter and pondering why different phenomenon occur for hundreds of years.

Early Philosophers- Early Philosophers- Aristotle and DemocritusAristotle and Democritus

Didn’t agree!!

Dead Dude #1- DemocritusDead Dude #1- Democritus

Ancient philosopher- 460BC

Matter is made of indivisible particles.

Atomos means “that which cannot be further broken down”

ShortcomingsShortcomings

It is a conceptual definition, not based on science.

Doesn’t talk about subatomic particles.

Dead Dude#2- DaltonDead Dude#2- DaltonExplained the LawsExplained the Laws John Dalton (early

1800s)

Atom is a solid, indestructible mass (like a billiard ball)

All Atomic Theory builds on Dalton’s LawAll Atomic Theory builds on Dalton’s Law

1. All matter is made of tiny particles called atoms.

2. All atoms of a given element are identical in size, mass and properties Atoms of each element are different.

3. Atoms cannot be subdivided, created or destroyed.

4. Compounds consist of atoms of different elements combined together. Compounds have constant composition (fixed ratio of atoms).

5 Chemical reactions involve the rearrangement of those atoms.

Dead Dude #3Dead Dude #3

J.J Thomson- 1850

A ball of positive mass containing a number of electrons that are embedded.

Getting the idea that there are protons and electrons (nucleus).

ShortcomingsShortcomings

Doesn’t explain the existence of electrons outside the nucleus or their importance in bonding.

No neutrons- can’t explain radioactivity or the existence of isotopes.

What did experiments with the What did experiments with the cathode ray tubes teach us?cathode ray tubes teach us?

Late 1800’sLate 1800’s

Discovery of and experiments using the cathode ray tube led to our understanding of the electron.

Millikan Oil Drop ExperimentMillikan Oil Drop Experiment

Henri Becquerel- 1897Henri Becquerel- 1897

Researched newly discovered X-rays (Phosphorescence).

Accidently discovered that uranium emits radiation that could be measured using photographic plates.

Discovered Radioactivity- electrically charged particles.

The Dr’s Curie- 1898The Dr’s Curie- 1898Discovered new elements- Polonium and Radium.

Very unstable elements that give off energy.

This led to an under- standing of Alpha, Beta and Gamma particles.

Dead Dude #4Dead Dude #4

Rutherford Model- 1905

– Mass of the atom is concentrated in the center of a positively charged region called the nucleus.

– The Planetary Model

Gold Foil Experiment- Draw this and leave some room to Gold Foil Experiment- Draw this and leave some room to write about the experiment.write about the experiment.

ShortcomingsShortcomings

Doesn’t place the electrons.

Doesn’t include neutrons.

Bohr Model-1920Bohr Model-1920

Believed that electrons traveled in precise orbits around the nucleus of an atom

Schrodinger Quantum Schrodinger Quantum Mechanical Model.Mechanical Model.

Describes mathematically the wave properties of electrons and other very small particles

The nucleus is at the center of the atom and the electrons are in the electron cloud.