ATOMIC THEORY

OBJECTIVES By the end of the lesson you should be able to: Describe how the atomic theory was developed and who was involved in the process

HISTORICAL UNDERSTANDING Chinese: world was based on 5 elements (earth, water, fire, metal and wood) Balance

HISTORICAL UNDERSTANDING Greeks: Democritus argued that matter could be endlessly divided until reaching the atomos (smallest piece) We use the word atom today from this origin Atoms cannot be divided any further or destroyed Matter is made of tiny particles that exist in empty space

HISTORICAL UNDERSTANDING Aristotle did not agree; he believed Earth, air, fire, and water! Nobody challenged the idea again for 2000 years!

Alchemists in the Middle Ages tried to turn common metals into gold - nobody succeeded! They tried for 1000 years!

ATOMIC THEORY DEVELOPMENT The Revolution! John Dalton, J.J. Thomson, Ernest Rutherford and Niels Bohr all played a very important part in the development of the atomic theory

JOHN DALTON (1766 – 1844) Dalton’s Atomic Theory: All matter is made up of small particles called atoms Atoms cannot be created, destroyed or divided into smaller particles All atoms of the same element are identical in mass and size but they are different in mass and size from atoms of other elements Compounds are created when atoms of different elements link together in definite proportions

JOHN DALTON (1766 – 1844)

J.J. THOMSON (1856 – 1940) Used electric currents in gas discharge tubes to determine that currents were negative charges Found all substances could produce these currents so all substances had negative charges Atoms therefore had smaller negative charges which he called electrons

J.J. THOMSON (1856 – 1940) Proposed the “Raisin Bun Model” which was a positively charged bun with negatively charged raisins in it

ERNEST RUTHERFORD (1871 – 1937) Student of J.J. Thomson Shot positive (alpha) particles at a piece of gold foil and saw that some bounced off while most went straight through Discovered nucleus of an atom (dense positively charged centre of an atom) Nucleus is made of positive charges and neutral charges

Rutherford Video Explained

NIELS BOHR (1885 – 1962) Worked under Rutherford and knew that around the nucleus were negative charges Found that gases would glow if an electric current passes through them (i.e. Neon signs) Negative charges have certain amount of energy and are in “orbit” around the nucleus like planets around the sun.

A REVOLUTION

HISTORY of the ATOM TIMELINE Antoine Lavoisier makes a substantial number of contributions to the field of Chemistry J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897 Niels Bohr proposes the Bohr Model in 1913 James Chadwick discovered the neutron in in 1932 1766 – 1844 1871 – 1937 1887 – 1961 460 – 370 BC 1700s 1800s 1900s Erwin Schrodinger describes the electron cloud in 1926 Democritus proposes the 1st atomic theory John Dalton proposes his atomic theory in 1803 Ernest Rutherford performs the Gold Foil Experiment in 1909 1891 – 1974 1743 – 1794 1885 – 1962 1856 – 1940 Click on picture for more information

PROGRESSION of the ATOMIC MODEL Democritus & John Dalton + - The structure of an atom, according to: Democritus & John Dalton James Chadwick J.J. Thomson Neils Bohr Ernest Rutherford Erwin Schrodinger

ATOMIC STRUCTURE

A REVOLUTION

ATOMIC STRUCTURE Atoms are made up of 3 smaller sub-atomic particles Protons Neutrons Electrons

ATOMIC STRUCTURE Energy Shells Nucleus Protons and neutrons are found in the nucleus of the atom Electrons are found around the nucleus in “energy shells” or “orbitals” Energy Shells Nucleus

SUB-ATOMIC PARTICLES Name Symbol Relative Mass Electric Charge Location in Atom Proton p+ 1 + Nucleus Neutron no Electron e- 1/1837 - Shells

Draw an atom! Include the 3 sub-atomic particles in the correct locations (part of nucleus, around nucleus) and their charge (positive, neutral, negative) Be sure to clearly label your drawing!