Atomic History and Structure:

Transcription

1 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 ( ) No2ced what we call with amber Things would be a;racted to it when rubbed It was a magical property The term electron

4 Kanada (~ BC) Indian a;ributed with first proposing the idea of atoms (called or ) 5 elements Atoms were indestructable and eternal

5 4 elements: Empedocles (450BC) Everything was different combina2ons of these This idea didn t really change un2l!

6 Leucippus (~ BC) Proposed the idea of atoms That two things exist

7 Democritus ( ) Student of Leucippus Ma;er is made up of eternal, indivisible, indestruc2ble and infinitely small substances which cling together in different combina2ons to form the objects percep2ble to us From : h;p:// PlainTextHistories.asp?historyid=ac20#ixzz1UvX6le4i 100 Greek Drachma, 1967

8 Aristotle 384 BC 322 BC Originally opposed the idea of atoms, then Added or 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 Changing the balance could change matter ex: what we know as copper changed to gold

9 Benjamin Franklin ( ) Franklin believed object had 1 of 2 charges (+/- ) Opposites a;ract, like charges repel (Coulomb s Law, which the Greeks knew a li;le about) Kite experiment (among others): Electric charges run from + to Words he gave us:

10 J.L. Proust ( *) Law of constant composi2on: In other words a given compound always has the same composi2on, regardless of where it comes from. Ex: H 2 O is *not published or recognized un2l 1811

11 Dalton s Atomic Theory ~ John Dalton ( ) proposed an atomic theory While this theory was not and brought about chemistry as we know it today instead of alchemy

12 Dalton s Atomic Symbols

13 Dalton s Atomic Theory

14 Problems with Dalton s Atomic Theory? 1. ma;er is composed of indivisible par2cles 2. all atoms of a par2cular element are iden2cal 3. different elements have different atoms YES! 4. atoms combine in certain whole- number ra2os YES! Called 5. In a chemical reac2on, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements. Yes, except

15 Michael Faraday ( ) atoms contain par2cles with structure of atoms related to electricity The electron was the fundamental

16 JJ Berzelius ( ) Came up with how we write chemical formulas for elements 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 unjl 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 Lord William Thomson Kelvin ( ) Proposed the Plum Pudding Model, but

19 JJ Thomson Discovered ( ) cathode ray tube Called electrons corpuscles Name electron came from George Johnstone Stoney, who proposed the concept in 1874 and 1881, and the word came in 1891 Named the Plum Pudding model of the atom ( )

20 Cathode Ray Tube

21 Hantaro Nagaoka ( ) Proposed the planetary(saturnian) model of the atom Electrons bound to the nucleus via Both were by Rutherford He abandoned the model in due to errors that were not confirmed by new studies (charged rings)

22 Rutherford s Gold Foil Experiment alpha (α) par2cles: directed at thin metal foil most par2cles made it through others were deflected back since alpha par2cles are posi2ve, they had to bounce off of something So there is a dense Gold Foil Anima2on

23 Rutherford s experiment led to the nuclear view of the atom ( / published ) (side note- it was actually Geiger- Marsden Experiment. Scien2sts 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 2ssue paper and it came back and hit you. On considera2on, I realized that this sca;ering backward must be the result of a single collision, and when I made calcula2ons 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

24 Gold Foil and the Models of the Atom

25 James Chadwick ( ) Worked with. Proved the existence of the. same mass as a proton, but with its mass was about than the proton's.

26 JJ Thomson Determined ( ) Used anode rays Found Ne deflected in two different paths using what we now call mass spectroscopy

27 R. A. Millikan - Measured the charge of the electron (1909). In his famous oil-drop experiment, Millikan was able to determine the charge on the electron independently of its mass. Then using Thompson s charge-to-mass ratio, he was able to calculate the mass of the electron. e = x coulomb e/m = x 10 8 coulomb/gram m = x gram Goldstein - Conducted positive ray experiments that lead to the identification of the proton. The charge was found to be identical to that of the electron and the mass was found to be x g.

28 Millikan s Experiment X- rays.

29 Millikan s Experiment - - X- rays give some electrons a charge Some drops would hover (not fall) - From the mass of the drop and the charge on the plates, he calculated the mass of an electron

30 Millikan oil drop experiment Millikan did another experiment to determine the mass of the ve par2cles (electrons). The experiment used mainly to determine the magnitude of the electron charge and using e/ m to get m- value. 30

31 Niels Bohr ( ) Bohr Model or the Solar System Model Niels Bohr in introduced his Electrons, which are also called. An electron can jump from a lower energy level to a higher one upon absorbing energy, crea2ng an excited state. The concept of energy levels accounts for the emission of dis2nct wavelengths of electromagne2c radia2on during flame tests.

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

33 Glenn Seaborg ( ) Discovered new elements. Only living person for whom.

34 Which brings us to the modern day view of the atom.

35 ATOMIC STRUCTURE The atom is mostly protons and neutrons in the. the number of electrons is the number of protons. electrons in space. extremely small. One teaspoon of water has.

36 ATOMIC COMPOSITION Protons ( ) posi2ve (+) electrical charge mass = x g rela2ve mass = atomic mass units ( ) but we can round to 1 Electrons ( ) nega2ve (- ) electrical charge rela2ve mass = amu but we can round to 0 Neutrons ( ) no electrical charge mass = amu but we can round to 1

37 The following four slides are for addi2onal informa2on only; you will not be tested on the fundamental par2cles. However, they could appear as extra credit on a test or quiz.

38 Subatomic ParJcles can also be further broken down into Fundamental ParJcles Quarks component of protons & neutrons 6 types Up, down Strange, charm Top, bo;om He 3 quarks = 1 proton or 1 neutron

39 Subatomic Par2cles and Quarks

40 What about electrons? Electrons are electrons They are not made from quarks Which is why they weigh so much less than p + or n o Classified as a lepton

41 Subatomic Par2cles More information at

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

43 Atoms are neutral because the numbers of - the opposite charges cancel. 11 electrons + 11 negative charges 11 protons 11 positive charges

44 Ions A charged atom because of a gain or loss of electrons. If an atom is neutral, the If it has, the atom has a 1+ charge If it has, the atom has a 1- charge

45 IONS! Taking away electrons from an atom gives a Adding electrons to an atom gives an Atoms may 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 compared to Na Ca I O

46 PREDICTING ION CHARGES In general metals lose electrons > nonmetals gain electrons >

47 Charges on Common Ions By losing or gaining e-, atom has same number of.

48 Mass Number, A C atom with 6 protons and 6 neutrons is the mass standard = Mass Number (A) = A Z 10 5 B NOT on the periodic table (that is the AVERAGE atomic mass on the table) Ex: A boron atom can have A =

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

50 Think Back John Dalton s2pulated that all atoms of a par2cular element were iden2cal In 1912, J.J. Thomson discovered that this was not accurate In an experiment measuring the mass- to- charge ra2os of posi2ve ions in neon gas, he made a remarkable discovery: All of the atoms had 10 protons, however some had

51 Isotopes atoms with the same number of protons ( ) but a different same element, different

52 1H ( ): A=1 Z=1 2H ( ): A=2 Z=1 3H ( ): A=3 Z=1

53 Isotopes & Their Uses

54 Isotopes & Their Uses The 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.

55 Learning Check Which of the following represent isotopes of the same element? Which element? 234 X 234 X 235 X 238 X

56 Atomic Math: Summary Atomic number (Z) (Atomic) Mass Number (A) Atomic Mass (also called Atomic Weight) (accounts for all the isotopes) is

57 CounJng Protons, Neutrons, and Electrons Protons: Atomic Number (from periodic table) Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) Electrons: If it s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and - ) If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each nega2ve charge, add an extra electron. For each posi2ve charge, subtract an electron (Don t add a proton!!! That changes the element!)

58 Learning Check Coun2ng State the number of protons, neutrons, and electrons in each of these ions. 39 K + 16 O Ca #p + #n o #e -

59 Learning Check Coun2ng Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C #p + #n o #e -

60 Learning Check An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is 1) 14 2) 16 3) 34 C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34 X 2) 34 X 3) 36 X

61 Atomic Symbols: Nuclide Nota2on l Nuclide l Show the name of the element, a hyphen, and the mass number in hyphen nota2on l Show the mass number and atomic number in nuclear symbol from mass number atomic number

62 Nuclide notajon: p +, charge, and average atomic mass Mass number ( ) Atomic number (number of ) Cl number of A-Z =20 As atoms have no charge, the number of electrons is the same as the number of protons. This atom has.

63 Nuclide notajon ions Mass number Atomic number 23 Na + 11 number of neutrons= 1+ charge than the number of protons. This atom has.

64 Nuclide notation ions Mass number Atomic number 16 O 2 8 number of neutrons= charge means than the number of protons. This atom has.

65 Learning Check Write the nuclear symbol form for the following atoms or ions: A. 8 p +, 8 n, 8 e - B. 17p +, 20n, 17e - C. 47p +, 60 n, 46 e -

66 Learning Check 1. Which of the following pairs are isotopes of the same element? 2. In which of the following pairs do both atoms have 8 neutrons? A. 15 X 15 X 8 7 B. 12 X 14 X 6 6 C. 15 X 16 X 7 8

67 Isotopes and Average Atomic Mass We are used to calcula2ng # s of p +, n o and e - using whole numbers; however on the Periodic Table we o en see a decimal number à Why? Atomic Mass (on the Periodic Table) The average of the isotopic masses In a weighted average we must assign greater importance give greater weight to the quan2ty that occurs

68 Isotopes and Atomic Mass The atomic mass for each element on the periodic table reflects the in nature. The mass on the periodic table is

69 AMUs and Atomic Weight ( ) is the unit for relative atomic masses of the elements 1 amu = 1 amu = x10-24 grams Protons (p + ) mass = x g rela2ve mass = atomic mass units (amu) but we can round to 1* Electrons (e - ) rela2ve mass = amu but we can round to 0* Neutrons (n o ) mass = amu but we can round to 1* *most 2mes, like now; when we get to nuclear chemistry, we will not be able to!

70 Compara2ve Example Your Grades To calculate your overall average, we use a weighted average instead of a simple average since different tasks are worth more For example: /100 Your mark Exams 30 80% Course work 30 75% Applied Science 10 70% Final 30 70%

71 To Calculate Average Atomic Mass You add up for each isotope to get the weighted average Frac2onal abundance Ex: If something has 3 isotopes:

72 Example Naturally occurring copper exists with the following abundances: 69.17% is Cu- 63 w/ atomic mass amu 30.83% is Cu- 65 w/ atomic mass amu

73 Learning Check: 3 Isotopes of Ar occur in nature 0.337% as Ar- 36, amu 0.063% Ar- 38, amu 99.6% Ar- 40, amu Calculate the Average Atomic Mass

74 In J.J. Thomson s experiment, he found that the percent abundances of neon are as follows: Neon 20 = 90.51% Neon 21 = 0.27% Neon 22 = 9.22% Calculate the average atomic mass of neon showing all of your work

75 If a mass is not specifically given for an isotope Then make the assump2on that the mass is the same as the atomic mass number It isn t exactly correct, but it will be close

76 AVERAGE 11 B ATOMIC MASS 10 B Boron is 20% 10 B and 80% 11 B. That is, 11 B is 80 percent abundant on earth. For boron, atomic weight=

77 CalculaJng & Abundance Chlorine has two isotopes: chlorine- 35 (mass amu) and chlorine- 37 (mass amu). What is the percent abundance of these two isotopes if chlorine's atomic mass is ?

78 Problem 1 The two naturally occurring isotopes of nitrogen are nitrogen- 14, with an atomic mass of amu, and nitrogen- 15, with an atomic mass of amu. What are the percent natural abundances of these isotopes? The atomic mass of nitrogen is amu

79 End of Chapter