The Atom

1. The Atom Review Class #1

2. Theories of the Atom • Greeks • Matter is made up of tiny, discrete particles • Fire, Earth, Wind, Water • Boyle • Found gold and silver as being elemental • Dalton’s Theory • All elements are composed of indivisible atoms • All atoms of a given element are identical • Atoms of different elements are different, that is, they have different masses • Compounds are formed by the combination of atoms of different elements

3. Experimental Parts of Atom – pg .3 • JJ. Thomson • Cathode ray tube to show smaller units make up atom • Light ray deflected in a magnetic field • Came up with idea of electrons • PLUM PUDDING MODEL • Nucleus • Rutherford • Bombarded atom with alpha particle • Alpha particle got deflected • Concluded atoms have a dense core – NUCLEUS • Because particles repelled, nucleus must be positive too • Also concluded atom is mostly empty space • Electrons are distributed in the empty space

4. Modern Atomic Model • Bohr • Dense nucleus • Electrons found in orbits • Electrons have required energy to keep them in orbit • Not too much or too little • Called this the planetary model • Wave Mechanical Model – modern model • Energy and matter can act as waves and particles • Solar panels • Dense positive center • Electrons are in “regions of probability”

5. Questions • RB pg. 4, 1-12

6. Structure of the Atom • Nucleus contains 2 types of particles • Neutrons and protons • This is where the mass comes from • Subatomic particles • Mass of a proton is found on 1st page of reference tables • 1 amu = mass of a proton = mass of 1 proton • Mass of electron is negligible

7. Subatomic particles • Sum of number of protons and neutrons equals the mass number • Found in the periodic table as atomic mass • Measured in amu (atomic mass units) NOT grams • If measured in grams would be atomic mass * mass of an atom

8. Isotopes • All type of element on periodic table have the same number of protons • Protons define the element • Neutrons can vary from atom to atom for 1 element • Same # protons but different number neutrons = isotopes • Examples: • Carbon – 12 = 6 protons and 6 neutrons • Carbon – 13 = 6 protons and _ neutrons

9. Atomic masses • Mass number for element must be integer • We can’t have part of a proton or neutron • Why are atomic masses of elements not integers? • Weighted atomic mass • The atomic mass is an average of all the different isotopes. • If have of the carbon isotopes were carbon 12 and half were carbon 13 • Weighted atomic mass would be 12.5 • Is this the weighted atomic mass for carbon? • Which isotope is more abundant?

10. Location of electrons • Found in space around a nucleus of an atom • Energy Levels • Orbitals in an atom form series of energy levels • S holds 2 electrons • P holds 6 electrons • D holds 10 electrons • This is where S, P, and D block names come from • Electrons can move between energy levels • You can walk up a set of stairs, takes a certain amount of energy • Certain amount of energy is needed for e- to jump between energy levels (it is quantized)

12. Ground vs excited state • Ground state – e- in lowest energy • Ground state is given in periodic table on ref. tables • If e- configuration doesn’t match ground state, it has to be excited state • Excited state • Electrons possess more energy than they would if they were in ground state • Spectral lines • Visible light that is emitted when electrons fall back to their ground state • Must first add energy to be excited – we can’t see this

13. Questions • RB pg. 7, 13-36

14. Read 9 – 16 for Wed. morning