2. Objectives 1. Distinguish between the early schools of thought on the nature of the atom. 2. Know the effects of politics on the development of the atomic theory 3. Know and understand Dalton’s atomic theory 4. Know the subatomic particles and their characteristics 5. Know and understand the modern model of the atom

3. Objectives (cont.) 6. Describe the behavior of light and carry out calculations. 7. Define and describe isotopes and calculate the weighted atomic mass of an element. 8. Understand the atomic emission spectra. 9. Write electron configurations.

4. The Development

5. Electron  First subatomic particle discovered  1897- JJ Thomson  Method of discovery- cathode ray tube  Passed electricity through glass tubes with most of the air removed  The ray attracted to the positive charge and deflected by the negative charge  In 1897 he realized:  Electron is negative  Mass 1/1800 of proton

6. Plum Pudding model  JJ Thomson proposed this model  Uniformly distributed individual electrons on a positive charge sphere

7. Ernest Rutherford  Rutherford’s Gold Foil Experiment (1910)  Tested the plum pudding model  Discovered:  That most of the mass of atom is in the core, named the nucleus  The nucleus is positively charged ( protons )  Most of the volume of the atom is empty space

8. James Chadwick  In 1932, he discovered the neutron  They have no charge and the mass equal to that of a proton

9. The Periodic Table

10. Development of the Periodic Table  In the 1700s, Lavoisier compiled a list of all the known elements of the time  In the 1800s, John Newlands proposed an arrangement where elements were ordered by increasing atomic mass  Newlands noticed when the elements were arranged by increasing atomic mass, their properties repeated every eighth element

11. Part 2

12. Development of the Periodic Table  Mendeleev realized there was a connection between atomic mass and elemental properties  Mendeleev noticed that as atomic mass increased the properties of elements repeated periodically  Mendeleev made predictions about the gaps in the table of the undiscovered elements

13. Development of the Periodic Table  A few problems arose with Mendeleev’s organization by atomic mass  Moseley arrange the elements by atomic number  This is the periodic table we use today

14. Periodic Table  Columns of elements are called groups  Rows of elements are called periods periods

15. Elements  Most symbols are formed from the first letter of the element’s name (and sometimes the second letter or third letter)  There are exceptions  Examples:  First letter is always uppercase and the second is always lowercase

16. Metals

17. Metalloids  Properties between metals and nonmetals

18. Groups and Families  alkali metal family(but does not include H)

19.  alkaline earth metal family

20.  Transition metals  Rare earth metals

21. Nonmetals

22.  halogens

23.  noble gases (or inert gases) noble gases

24. Chemical Formulas  Formulas show the elements and number of atoms of each in a compound  Subscripts show the number of atoms  Example:

25. SymbolChargeLocationRelative mass Electrone-In the space surrounding the nucleus 0 amu ProtonP++1In the nucleus 1 amu Neutronn0In the nucleus 1 amu SUBATOMIC PARTICLES

26. Reading the Periodic Table

27.  For gold:  Z:  A:  # protons:  # electrons:  # neutrons:  Isotopic symbol:  Family:

28. Isotopes  Atoms of the same element that have different masses  Many elements have only one stable form, while other elements have different “versions” of their atoms  Isotopes of the same element have:

30. Atomic Mass  Weighted average of the atomic masses of the naturally occurring isotopes of an element  Example: Calculate the atomic mass of nitrogen. Given: 99.63% of nitrogen is nitrogen-14 and 0.37% of nitrogen is nitrogen-15.

31.  Example: Determine the weighted atomic mass. IsotopeMass of one atom % abundance Silicon- 28 27.98 amu92.21 Silicon- 29 28.98 amu4.70 Silicon- 30 29.97 amu3.08

32. IsotopeMassAbundance Gold- 9292.0921% Gold- 9191.2071% Gold- 9090.088%

33. Review Question Which isotope of Argon is most likely to be in the highest percentage?  Ar- 36  Ar- 38  Ar- 40