Bellwork: Get out your diagram from your research paper. Get out a sheet of paper to take some notes on. Fill in the Following Table in your notes (assume an atom unless otherwise stated:

Symbol Protons Electrons Neutrons Atomic # Mass #

24 Na+ 11

11 10 13 11 24

63 Cu 29

29 29 34 29 63

Development of the Atomic Theory

What does the Greek word atomos mean?

• The Greek word “atomos” means not able to be divided

or “indivisible.”

Democritus was an ancient Greek philosopher who lived from 460 - 370 B.C.

What did Democritus conclude about cutting matter in half? There was a limit to how far you could divide matter. You would eventually end up with a piece of matter that could not be cut.

Who was Democritus?

• Aristotle believed that matter could be divided into smaller and smaller pieces forever.

• He held a very strong influence on popular belief and his views on this were accepted for two thousand years.

Why weren’t Democritus’s ideas accepted?

John Dalton 1776-1844 • Two thousand years later

a British chemist and schoolteacher brings back Democritus’s idea of the atom

• He performed many experiments to study how elements join together to form new substances.

Summary for Dalton’s Atomic Theory

Atoms are tiny and indivisible. Atoms can’t be created or destroyed. Atoms of the same element are the identical.

Atoms of different elements are different. Atoms of different elements combine in simple whole-number ratios to form compounds.

Dalton’s Theory

Experimental evidence Scientific Laws

Law of Conservation on Matter You can’t create or destroy atoms. Law of Definite Proportions Same compounds are same ratio by mass. Law of Multiple Proportions

Different compounds with the same elements are whole number multiples of the atoms.

Experiments Scientific Laws Atomic Theory (observations) (Patterns) (Explanations)

John Dalton realized that there must be an atom as

Democritus first proposed.

Expert groups: Get together with people who researched the same scientists as you. Discuss what you need to make sure everyone knows about your scientists. Explain his experiment and procedure Discuss his findings and their significance to modern atomic theory Any problems with his ideas

Now you are going to the home groups of the number you were given. It is your job as the EXPERT to make sure everyone understands what your scientists did. You will be held responsible for this material.

Turn in Diagrams, make sure your name is on them.

Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle. http://viewpure.com/IdTxGJjA4Jw

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

Cathode Rays (electrons)

Observations: Cathode Ray Tube produces rays with constant charge to mass ratio.

Conclusions and Hypotheses:

Cathode rays (electrons) were found in all substances tested.

Cathode rays (electrons) were attracted to the positive plate every time.

Electrons are negatively charged.

Neutral atoms are made up of equal amounts of (+) and (-) particles.

All atoms contain tiny particles called electrons.

The electron has a specific size and charge.

Thomson’s Atomic Model (1897)

Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Thomson-

Discovered electrons: cathode rays were

deflected by magnets and electric plates

Found charge-to-mass ratio for electrons

Proved electrons are a part of all atoms

Goldstein (1886) - Started with the hypothesis that when a neutral

hydrogen atom loses an electron, a positive particle should remain.

- Using cathode ray tube. He found rays traveling in the opposite direction.

- Concluded that these were made a positive subatomic particles, which would later be called protons.

Rutherford’s “Gold Foil Experiment”

Alpha particles are helium nuclei, He2+ Particles were fired at a thin sheet of gold foil Particle hits on the detecting screen (film) are recorded

Radioactive source

(+) http://viewpure.com/wzALbzTdnc8

Rutherford’s Findings (1911)

The atom is mostly empty space. The nucleus is dense. The nucleus is positively charged Electrons, e-, are moving large distances outside the nucleus.

Observations: Most of the alpha particles passed right through Some alpha particles were deflected slightly VERY FEW were greatly deflected

Conclusions:

Rutherford’s Conclusion (1911)…

Small, dense, positive nucleus. Equal amounts of (-) electrons at large distances outside the nucleus.

Millikan http://viewpure.com/XMfYHag7Liw

In 1916, he discovered the charge of the electrons!

Chadwick (1932) discovered the neutron.

http://viewpure.com/_7DAlvRI1M4 fast forward to 5:00 min..

Neils Bohr’s Atomic model (1913)

Small, dense, positive nucleus. Equal amounts of (-) electrons at specific orbits around the nucleus.

This incorrect version of the atom is often used to represented atoms because it shows energy levels for electrons.

Bohr’s Model of the Atom • Bohr’s Model

- an early conceptual model of the atom

- classic planetary model in which electrons whirl around the small but dense nucleus: like planets orbiting the Sun

- developed by the Danish physicist Niels Bohr in 1911

- each electron has a certain energy that is determined by it’s path around the nucleus

Erwin Schrodinger (1926 ) Quantum Mechanical Model Like the Bohr model, the quantum mechanical model of the atom restricts the energy of electrons to certain values. Unlike the Bohr model, however, the quantum mechanical model does not involve an exact path the electron takes around the nucleus.

The quantum mechanical model determines the allowed energies an electron can have and how likely it is to find the electron in various locations around the nucleus.

If you need more review of the history of atomic theory: https://www.youtube.com/watch?v=NSAgLvKOPLQ Scientists matching game

Democritus Atoms are indivisible and

indestructible.

Dalton Using experimental methods

determined that all matter composed

of atoms, atoms of different elements

are different, one atoms can not be

changed into another.

Thomson Cathode ray Discovered

electron

Millikan Calculated

charge and

mass of electron

1897

1916

460 - 370

B.C.

1776-1844

Oil Drop

Experiment

Goldstein Cathode Ray

Chadwick Discovered

neutrons

Rutherford Gold- Foil

Experiment

Discovered

the nucleus 1911

1932

1886 Suggested the idea

positively charged

particles later called

protons

Shot Alpha Particles into

beryllium