Atomic History and Structure:

1. 0 Atomic History and Structure:

2. What comes to mind when you think of the term “atom”? How do we know what we know about atoms? List any people you can think of.

3. Thales of Miletus (600BC) • Noticed what we call static electricity with amber • Things would be attracted to it when rubbed • It was a “magical property” • The term electron comes from the Greek word for amber: “elektron”

4. Kanada (~600-501BC) • Indian attributed with first proposing the idea of atoms (called “parmanu” or “anu”) • 5 elements • Earth • Fire • Water • Air • Ether • Atoms were indestructable and eternal

5. Empedocles (450BC) • 4 elements: • Earth • Wind • Fire • Water • Everything was different combinations of these • This idea didn’t really change until1661!

6. Proposed the idea of atoms • That two things exist • Atoms • Empty space. Leucippus (~490 BC)

7. Student of Leucippus • Matter is made up of “eternal, indivisible, indestructible and infinitely small substances which cling together in different combinations to form the objects perceptible to us” • “Atomos” Democritus (420BC) From :http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=ac20#ixzz1UvX6le4i 100 Greek Drachma, 1967

8. Originally opposed the idea of atoms, then • Added hot/cold or moist/dry to the four elements: • earth (cold and dry) • air (hot and moist) • fire (hot and dry) • water (cold and moist) • The differences in matter where a result of different balances of these atoms • Changing the balance could change matter • ex: what we know as copper changed to gold • Aristotle 384 BC – 322 BC

9. 0 Benjamin Franklin (1752) • Franklin believed object had 1 of 2 charges (+/-) • Opposites attract, like charges repel (Coulomb’s Law, which the Greeks knew a little about) • Kite experiment (among others): • Electric charges run from + to – • Lightening is electricity • Words he gave us: • battery, conductor, condenser, charge, discharge, uncharged, negative, minus, plus, electric shock, and electrician.

10. 0 J.L. Proust (1794*) • Law of constant composition: • A given compound always contains the same elements in the same proportion • In other words…a given compound always has the same composition, regardless of where it comes from. • Ex: H2O is always 89% oxygen and 11% H by mass *not published or recognized until 1811

11. Dalton’s Atomic Theory ~1800 • John Dalton (1766-1844) proposed an atomic theory • While this theory was not completely correct, it revolutionized how chemists looked at matter and brought about chemistry as we know it today instead of alchemy

12. Dalton’s Atomic Symbols

13. 0 Dalton’s Atomic Theory • Elements are made of very small indivisible particles called atoms. • All atoms of a given element are identical (all hydrogen atoms are identical). • The atoms of an element are different than the atoms of another element (hydrogen is different than helium). • Atoms of one element can combine with the atoms of another element to make compounds. A given compound should have the same relative numbers and types of atoms. • Atoms are indivisible in chemical processes…they are not created or destroyed just reorganized.

14. Problems with Dalton’s Atomic Theory? 1. matter is composed of indivisible particles Atoms Can Be Divided, but only in a nuclear reaction 2. all atoms of a particular element are identical Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)! 3. different elements have different atoms YES! 4. atoms combine in certain whole-number ratios YES! Called the Law of Definite Proportions 5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except for nuclear reactions that can change atoms of one element to a different element

15. 0 Michael Faraday (1832) • atoms contain particles with an electric charge • structure of atoms related to electricity • The electron was the fundamental particle of electricity

16. JJ Berzelius (1779-1848) • Came up with how we write chemical formulas • Symbols for elements • Subscripts to indicate numbers of each element (he used superscripts, though!) • Considered one of the fathers of modern chemistry • Along with • John Dalton • Antoine Lavoisier • Robert Boyle

17. Up until the 1900’s…. • Atomic structure was thought about, but not well known. It took a few more people to really put things together, and build off of each other’s knowledge to come up with what we know today.

18. 0 • Lord William Thomson Kelvin (1903) • Proposed the Plum Pudding Model, but didn’t name it • Electrons embedded in a positive, spherical cloud

19. JJ Thomson (1904) • Discovered electrons (1897) • cathode ray tube • Called electrons corpuscles • Name electron came from George JohnstoneStoney, who proposed the concept in 1874 and 1881, and the word came in 1891 • Named the “Plum Pudding” model of the atom (1904)

20. 0 Cathode Ray Tube

21. 0 Cathode ray tube

22. HantaroNagaoka (1904) • Proposed the planetary (Saturnian) model of the atom • Positive, massive nucleus • Electrons bound to the nucleus via gravity in charged rings • Both were confirmed by Rutherford • He abandoned the model in 1908 due to errors that were not confirmed by new studies (charged rings)

23. 0 Rutherford’s Gold Foil Experiment • alpha (α) particles: positively charged particles directed at thin metal foil • most particles made it through → empty space • others were deflected back → since alpha particles are positive, they had to bounce off of something positive So…there is a dense positive charge (nucleus) that the electrons move around. Gold Foil Animation

24. Rutherford’s experiment led to the nuclear view of the atom (1909/ published 1911) (side note- it was actually Geiger- Marsden Experiment. Scientists Hans G. and undergraduate Ernest M. worked for Rutherford.) “It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center, carrying a charge.[2]” —Ernest Rutherford

25. Gold Foil and the Models of the Atom

26. JJ Thomson (1912) • Determined isotopes of atoms exist (1912) • Used anode rays • Found Ne deflected in two different paths using what we now call mass spectroscopy

27. Niels Bohr (1885-1962) • Bohr Model or the Solar System Model • Niels Bohr in 1913 introduced his model of the hydrogen atom. • Electrons circle the nucleus in orbits, which are also called energy levels. • An electron can “jump” from a lower energy level to a higher one upon absorbing energy, creating an excited state. • The concept of energy levels accounts for the emission of distinct wavelengths of electromagnetic radiation during flame tests.

28. Bohr’s Orbit Model (1913) Electrons occupy orbitals around the nucleus according to their energy..

29. Glenn Seaborg(1912-1999 ) • Discovered 8 new elements. • Only living person for whom an element was named.

30. Which brings us to the modern day view of the atom….

31. ATOMIC STRUCTURE The atom is mostly empty space • protons and neutrons in the nucleus. • the number of electrons is equal to the number of protons. • electrons in space around the nucleus. • extremely small. • One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

32. ATOMIC COMPOSITION • Protons (p+) • positive (+) electrical charge • mass = 1.672623 x 10-24 g • relative mass = 1.007 atomic mass units (amu) • but we can round to 1 • Electrons (e-) • negative (-) electrical charge • relative mass = 0.0005 amu • but we can round to 0 • Neutrons (no) • no electrical charge • mass = 1.009 amu • but we can round to 1

33. The following four slides are for additional information only; you will not be tested on the fundamental particles. However, they could appear as extra credit on a test or quiz.

34. He Subatomic Particles can also be further broken down into Fundamental Particles • Quarks • component of protons & neutrons • 6 types • Up, down • Spin, charm • Top, bottom • 3 quarks = 1 proton or 1 neutron

35. Subatomic Particles and Quarks

36. What about electrons? • Electrons are electrons • They are not made from quarks • Which is why they weigh so much less than p+ or no • Classified as a lepton

37. Subatomic Particles More information at http://www.lns.cornell.edu/~nbm/NBM_INTRO_TO_HEP1.htm

38. Atomic number Atom symbol AVERAGE Atomic Mass Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981

39. Atoms are neutral because the numbers of protons and electrons are equal - the opposite charges cancel. • 11 electrons • 11negative charges • 11 protons • 11 positive charges

40. 0 Ions • A charged atom because of a gain or loss of electrons. • If an atom is neutral, the # of p+= # of e- • If it has lost1 e-, the atom has a 1+ charge • If it has gained 1 e-, the atom has a 1- charge

41. IONS • Taking awayelectrons from an atom gives a CATION with a positive charge • Addingelectrons to an atom gives an ANION with a negative charge. • Atoms may gain or lose more than 1 e- • To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! • Examples: Na+ Ca+2 I- O-2 Na Ca I O compared to

42. PREDICTING ION CHARGES In general • metals lose electrons ---> cations • nonmetals gain electrons ---> anions

43. -3 -2 -1 +1 +2 Charges on Common Ions -/+4 +3 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.

44. Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units • Mass Number (A) • =(# protons) + (# neutrons) • NOTon the periodic table…(that is the AVERAGE atomic mass on the table) • Ex: A boron atom can have A = 5 p + 5 n = 10 amu

45. 0 Atomic Math On periodic table- but not all PTs look exactly like this set up, but they have the same information

46. Think Back… • John Dalton stipulatedthat all atoms of a particular element were identical • Their atomic numbers were the same, and also their #’s of neutrons were identical • In 1912, J.J. Thomson discovered that this was not accurate • In an experiment measuring the mass-to-charge ratios of positive ions in neon gas, he made a remarkable discovery: • 91% of the atoms had one mass • The remaining atoms were 10% heavier • All of the atoms had 10 protons, however some had more neutrons

47. Isotopes 0 • atoms with the same number of protons (Z) but a different number of neutrons • same element, different atomic mass number (A)

48. 0 1H (hydrogen): A=1 Z=1 2H (Deuterium): A=2Z=1 3H (Tritium): A=3Z=1

49. Isotopes & Their Uses Bone scans with radioactive technetium-99.

50. Isotopes & Their Uses The tritium content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.