Atomic Structure

1. Atomic Structure Atoms, Elements & Isotopes

2. proton, neutron and electron isotopes exist Dalton’s Atomic Theory • Four postulates (1808)... • All elements are composed of tiny, indivisible particles called ‘atoms’. • Atoms of the same element are identical... each element is unique • Atoms of different elements can physically mix or chemically combine (compounds). • Chemical reactions occur when atoms are separated, joined, or rearranged. • Much of this theory is still accepted, ….. with 2 exceptions.

3. Atomic Scientists • J. J. Thomson discovered electrons (e-) in 1897. • He passed an electric current through a glass tube filled with gas. • He discovered that a beam of negative charges traveled from the cathode (-) to the anode (+).

4. Atomic Scientists • E. Goldstein discovered positive particles in atoms in 1886. • He observed rays traveling in the opposite direction of cathode rays. • These particles were termed ‘ protons’ (p+) by Ernest Rutherford in 1920. • James Chaddwick discovered neutrons (n0) in 1932. • His discovery was based on the fact that different atoms’ atomic mass and atomic # (# of protons) were not adding up.

5. Atomic Scientists • Robert Millikan furthered Thomson’s work by describing the electron more in depth • all e- carry exactly one unit of negative charge. • mass of an e- is 1/1840 the mass of a hydrogen atom (p+).

6. The Bohr-Rutherford Model • Ernest Rutherford conducted the famous ‘gold foil experiment’ (1911) which concluded that: • 1. atoms are mostly space. (football arena) • 2. atoms have a solid nucleus at the centerwhich contains most of the mass • This overturned the accepted ‘plum pudding model’ of the time.

7. The Bohr-Rutherford Model • The Gold Foil Experiment... • Stats... • 98% of particles went straight through (expected) • 2% of particles deflected at large angles • 0.01% of particles deflected straight back (canon balls & tissue!)

8. The Bohr-Rutherford Model • After Rutherford’s findings, Niels Bohr further explained the atom by concentrating on the e- (1913). • Why don’t the (-) e- fall into the (+) nucleus? • Bohr proposed that the e- travel on concentric orbits around the nucleus. • Each orbit has a fixed energy (energy level) and e- do not lose energy. • The progression of the atom... Plum Pudding Rutherford Quantum Rutherford-Bohr

9. Subatomic Particles

10. 19 K Potassium 39.098 Characteristics of Elements Atomic Number Element Symbol Element Name Atomic Mass

11. Characteristics of Elements • Atomic Number : Number of p+ in an atom • identifies element (change atomic # = change of element). • # p+ = # e- in neutral atom • (+) charge = less e- than p+ • (-) charge = more e- than p+ • Atomic mass: (a.k.a. Mass Number) • mass of the nucleus • p+ + n0 • units are a.m.u. (atomic mass unit)

12. X # element symbol # X # Atomic Symbols • There are two ways to represent elements: • Symbol Form: OR atomic mass atomic # (# of p+) element symbol atomic mass • Shorthand Form: name of element followed by atomicmass. • Ex... • Aluminum - 27 • Nitrogen – 14 • Carbon – 14 • You can find mass number, atomic number, number of n0, and number of e- with either notation!

13. X # element symbol # X # Atomic Symbols • There are two ways to represent elements: • Symbol Form: atomic mass atomic # (# of p+) element symbol atomic mass OR • Shorthand Form: • name of element followed by atomic mass. • Ex...Aluminum – 27 • Find the following elements on the Periodic Table:Beryllium, Copper, Sulfur, Neonand write them in both notations.

14. atomic mass X # element symbol atomic # # (# of p+) • Now find for each element the: • atomic mass • atomic number • # of p+ (same as atomic#) • # of n0 (mass# - atomic#) • # of e- (same as # of protons) Atomic Symbols • Using the symbol form for neutral elements: • Symbol Form: • Ex... 1. Beryllium- 2. Copper - 3. Sulfur- 4. Neon -

15. Atomic Calculations • All mass of the atom is in the nucleus. • only p+ and n0 are in the nucleus. • if you know the mass of any atom, you can find the # of n0. • if you know the # of n0 and the # of p+, you can find the mass. • Ex...electrical charge on atom Manganese - 55 P +1 31 15

16. Isotopes Neon - 20 X +3 X X -1 22 22 25 Fluorine - 20 12 10 10 Neon - 22 • Isotopes: atoms of the same element with different atomic masses. • - different # of n0 !!! • Three isotopes of Carbon: • Carbon - 12 (6p+, 6n0) element of life • Carbon - 13 (6p+, 7n0) extremely rare • Carbon - 14 (6p+, 8n0) radioactive…carbon dating • Note: atomic # will NEVERchange in isotopes… only mass and # of n0 do! • Which of the following are isotopes of the same element?

17. Average Mass of Isotopes • Isotopes are naturally occurring. • The mass # of an element (periodic table) is the weighted avg. of allisotopes that exist in nature. • - abundance of isotope is just as important as mass! • Ex... • Natural copper (Cu) consists of 2 isotopes … • Copper - 63 (mass = 62 .930 g/mole) @ 69% • Copper - 65 (mass = 64 .930 g/mole) @ 31% • To calculate avg. mass... • Step 1 : mass x abundance for each isotope • Step 2 :add the two values from step 1 together • 62 .93 x .69 = 43.42 43.42 • 64 .93 x .31 = 20.13 + 20.13 63.55 g/mole

18. Average Mass of Isotopes • The average mass of an element is closest to the isotope that is mostplentiful in nature. • Ex... • Three isotopes of Oxygen: • Oxygen - 16 99 . 759% • Oxygen - 17 0.037% • Oxygen - 18 0.204% • The avg. mass (from P.T.) is closest to 16, therefore, Oxygen-16 is the isotope that is most abundant in nature.