1 3 ATOMIC THEORY OBJECTIVES By the end

1. 3 – 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 • Draw and describe an atom using 4 major properties

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

HISTORICAL UNDERSTANDING • Greeks: argued that matter could be endlessly divided until reaching the atomos (smallest piece) • We use the word atom today from this origin

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: 1. All matter is made up of small particles called atoms 2. Atoms cannot be created, destroyed or divided into smaller particles 3. 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 4. 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

A REVOLUTION

ATOMIC STRUCTURE • Atom: smallest part of an element that keeps the properties of the element • Is made up of 3 smaller sub-atomic particles • Protons • Neutrons • Electrons

SUB-ATOMIC PARTICLES Name Symbol Relative Mass Electric Charge Location in Atom Proton p+ 1 + Nucleus Neutron no 1 0 Nucleus 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!