1. Chapter 3.2 Structure of Atoms

2. Objective 1: Describe the evidence for the existence of electrons, protons, and neutrons, and describe the properties of these subatomic particles. Define atom: smallest particle of an element that retains the chemical properties of that element. Subatomic particles: Protons Neutrons Electrons

3. Discovery of the Electron Late 1800’s – J.J. Thomson discovered the electron through experiments with cathode-ray tubes. Electron Properties Relative Charge Mass Number actual mass - 1 0 9.109 x 10-31 kg Plum Pudding Model of atom

4. Discovery of Atomic Nucleus In 1911 – Ernest Rutherford – Gold Foil Experiment Showed that there was a small – dense positively charged nucleus of an atom. Proton Properties Relative Charge Mass Number actual mass + 1 1 1.673 x 10-27 kg

5. Neutrons Discovered in 1932 by James Chadwick British Scientist Neutron Properties Relative Charge Mass Number actual mass 0 1 1.675 x 10-27 kg

7. Nucleus compared to rest of atom - approximately size of marble compared to a large football stadium.

10. Many naturally occurring elements can contain different numbers of neutrons.

11. Isotope – at0ms of the same element that have different masses.n n n Protium 99.985 % Deuterium 0.015 % Tritium Trace Three isotopes of Hydrogen

13. Symbol – A

14. Protium has 1 proton and 0 neutrons

15. Mass number = #p + #n

16. = 1 + 0

17. = 1

18. What is the mass number deuterium and tritium?

21. Name of atom – mass number

22. Uranium - 235

23. Nuclear symbol

24. A X A : mass number, Z : atomic number, X : symbol of element