1. Chemistry Atomic structure Chapter 4, and Chapter 5, p. 146-148

2. Today’s summary 4.1, 4.2, 4.3, P. 146-148 Webquest on atomic emission spectra

3. 4.1 history of the atom in thought Early ideas about matter Democritus John Dalton – Daltons atomic theory vs Democritus – Dalton = scientific method for experimental evidence

4. 4.1 conservation of mass Mass, matter is not created or destroyed in ordinary chemical reactions Nuclear reactions are a separate topic; NOT ordinary

5. 4.2 Defining the Atom How we discovered the structure of the atom Who, which experiments

6. First Electrons In CRTs, cathode ray tubes Stream of electrons was observed Sir William Crookes Mass and charge: J.J. Thompson Electromagnetic fields There is a particle smaller than an atom

7. Mass of electron Thompson was able to determine the charge to mass ratio of the charged particle Milikan calculated the mass of an electron Robert Milikan-oil drop experiment- determined charge of an electron

8. The plum pudding (blueberry muffin model) Created by JJ Thomson The model was a circle with electrons in a disorganized pattern The model was changed to Rutherford’s model

9. The nucleus Rutherford – The Gold Foil Experiment Protons and neutrons make up the dense center Protons have positive charge Neutrons have negative charge Incredibly dense

10. Nucleus, slide 2 Positively charged nucleus react with positive alpha particles casing deflections Electrons around the nucleus are negatively charged

11. Completing the model of the atom Made of 3 subatomic – electron, proton, and neutron. Atoms are shaped with small dense nucleus of positive charge surrounded by negative charge Mostly consisted of fast moving electrons

12. 4.3 how atoms differ Atomic number Henry Moseiev discovered that atoms of each element contain a unique positive charge in their nuclei # of protons in an atom identifies it as an atom of a particular element. # of protons= atomic # and # of electrons

13. Isotopes and mass number Isotopes: atoms with the same # of protons but different #’s of neutrons Mass of Isotopes: isotopes containing more neutrons have a greater mass Isotope Notation: each isotope of an element is identified with a # called the mass # Mass # = Atomic # + # of Neutrons

14. Mass of atoms The atomic mass unit is what you measure the mass of an atom with The atomic mass is the weighted average mass of the isotopes. The atomic mass unit is one twelfth the mass of a carbon-12 atom. The standard of atomic mass unit is Carbon-12, AMU is one-twelfth the mass of carbon atom Atomic mass depends on the number of protons and neutrons

15. Atomic Emission Spectra Electromagnetic Radiation- A form of energy exhibiting wavelike behavior as it travels through space (described by wave length, frequency, amplitude, and speed) Electromagnetic Spectrum- Includes all forms of electromagnetic radiation Atomic Emission Spectrum- A set of frequencies of electromagnetic waves given off by atoms of an element, consists of a series of fine lines of individual colors.

16. p. 146-148 When atoms have no added energy they are in their ground state. When atoms acquire energy their electrons become exited and orbit at a further distance from the nucleus. Bohr assigned each orbit a different value called a quantum number. When the atom returns to its ground state the electrons revert to their closer orbits which release light energy that can be observed as the atomic emission spectrum.