Structure of Atom

1. Structure of Atom

2. Atom • Smallest particle of an element • Atomic Structure – arrangement of smaller particles within an atom

3. Two Main Regions In Atom • Nucleus – very small dense central region protons – positively charged particles neutrons – neutral particles ● Electron Cloud – large region around nucleus electrons – negatively charged particles

4. Discovery of Electrons • JJ Thomson – used Crooke’s Tube (cathode ray tube) • Gas under low pressure in a sealed glass tube • Has a positive end (Anode) and negative end (Cathode) • When anode and cathode are connected to the + and – terminals of a battery, the tube produces a beam of particles called electrons

7. Thomson’s Atom • Plum-pudding model • Since total atom is neutral, there must be an equal number of + and - charges • Atom is a positively charged area with negative electrons randomly spread throughout

8. Nucleus • Ernest Rutherford – Gold foil experiment • Shot positive charged particles at a very thin piece of gold foil

9. Florescent Screen Lead block Uranium Gold Foil

10. What he expected

11. What he got

12. +

13. + How he explained it • Atom is mostly empty space • Small dense, positive piece at center • Alpha particles are deflected by it if they get close enough

14. Rutherford’s Model Of Atom • Positively charged nucleus containing protons and neutrons with negatively charged particles in orbit around it • Electrons stay in orbit due to attraction between + and – charges

15. Problems With Rutherford Model • Charged particle when moving in a curved path give off light so they lose energy • If they lose energy, they would gradually get closer and closer to the nucleus and crash into it

16. Bohr Model of Atom • Similar to Rutherford model, but in this model electrons orbit in specific, well defined energy level • A gain or loss of energy moves the electron from one energy level to another • Positively charged protons and neutral neutrons held together tightly by the Strong Nuclear Force