The Development of a Modern Theory of the Atom

Aristotle Democritus

Ancient Philosophy Aristotle 4 When: More than 2000 years ago 4 Where: Greece 4 What: Aristotle believed in 4 elements: Earth, Air, Fire, and Water.

The Development of a Modern Theory of the Atom Democritus ( B.C) Matter is composed of small, indivisible particles called atomos.

Ancient Philosophy AND Politics 4 Aristotle rejected Democritus’ ideas – did not believe that empty space could exist 4 Aristotle more influential 4 Ideas not science 4 Aristotle’s ideas unchallenged for two thousand years!!!

John Dalton

The Development of a Modern Theory of the Atom Dalton (published ) 1. All matter is composed of atoms, tiny, indivisible particles of an element that can not be created or destroyed. Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom 2. Atoms of one element can NOT be converted into atoms of another element. In reactions, atoms of the original substances recombine to form different substances. Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom 3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element. Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom 4. Compounds result from chemical combination of a specific ratio of atoms of different elements. Dalton’s Atomic Theory

The Development of a Modern Theory of the Atom The Cathode Ray Tube Negatively charged particles are present in all matter (later named electrons) Cathode Ray Tube Animation

The Cathode Ray Tube

J. J. Thompson

The Development of a Modern Theory of the Atom Thomson (published 1897) charge to mass ratio 1.76 x C/g

 The electrons in an atom balance out the positive, making it neutral  This can be compared to plums surrounding the pudding in plum pudding

J.J. Thompson – 1897; England 4 Thompson credited with discovering electrons 4 Thompson knew atoms were neutral, but couldn’t find the positive particle.

Robert Millikan

The Development of a Modern Theory of the Atom Millikan (published 1909) – “Oil Drop Experiment” charge of electron = 1.60 x C mass of electron = 9.10 x g Millikan's Oil Drop Experiment

The Development of a Modern Theory of the Atom Millikan Oil Drop Experiment Determined charge and mass of electron

The Development of a Modern Theory of the Atom Rutherford ( )

The Development of a Modern Theory of the Atom Rutherford (published 1910) Rutherford’s Gold Foil Experiment

The Development of a Modern Theory of the Atom Rutherford (published 1910)

1911- Rutherford’s Atomic Theory 1. Discovery of proton 2. Most of atom is empty space 3. There is a dense nucleus in the middle of every atom with protons surrounded by negative electrons which orbit around the nucleus.

James Chadwick 4 Discovered neutron!!!

ATOM BASICS

Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds 26

Subatomic Particles ParticleSymbol Charge Relative Mass Electron e Proton p Neutron n0 1 27

Atomic Structure 4 Atoms are composed of 2 regions: Nucleus Electron Cloud

Atomic Structure –Nucleus: the center of the atom that contains the mass of the atom –Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

30 Atomic Number 4 Number of protons in an atom 4 All atoms of an element have the same number of protons

31 Atomic Number -Periodic Table 11 Na Atomic Number Symbol

32 Atomic Number -Periodic Table 11 Na 11 Protons Sodium

33 Learning Check State the number of protons for atoms of each of the following: Nitrogen

34 Atomic Number -Periodic Table 7 N 7 Protons Nitrogen

35 Learning Check State the number of protons for atoms of each of the following: Sulfur

36 Atomic Number -Periodic Table 16 S 16 Protons Sulfur

37 Learning Check State the number of protons for atoms of each of the following: Barium

38 Atomic Number -Periodic Table 56 Ba 56 Protons Barium

39 Mass Number 4 Counts the number of protons and neutrons in an atom 4 Mass number= p + + n 0

40 Atomic Symbols Show the mass number and atomic number Give the symbol of the element

41 Atomic Symbols Na Mass number Atomic number 11 23

42 Learning Check Cl Mass number Atomic number How many protons? What is the element? How many neutrons?

43 Learning Check Cl Mass number Atomic number What is the element? Chlorine

44 Learning Check Cl Mass number Atomic number How many protons? p = atomic # = 17

45 Learning Check Cl Mass number Atomic number How many neutrons? n 0 = 35 (mass number– 17 (p + ) n 0 = 18

46 Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

47 Learning Check O 8 16 n 0 = p + = e - = 8 8 8

48 Learning Check P n 0 = p + = e - =

49 Learning Check Zn n 0 = p + = e - =

50 Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers

51 Isotopes Isotopes of chlorine 35 Cl 37 Cl 17 chlorine - 35 chlorine - 37

LecturePLUS Timberlake52 Learning Check 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 _______ _______ _______ #e _______ _______ _______

LecturePLUS Timberlake53 Solution 12 C 13 C 14 C #p #n #e 6 6 6

54 Learning Check An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom B.Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? Draw its atomic symbol.

55 Learning Check An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 30

56 Learning Check An atom of zinc has a mass number of 65. B.Number of neutrons in the zinc atom 35

57 Learning Check C. What is the mass number of a zinc isotope with 37 neutrons? Draw its atomic symbol. 67 Zn 30 67

58 Learning Check Write the atomic symbols for atoms with the following: A. 8 p +, 8 n, 8 e - ___________ B.17p +, 20n, 17e - ___________ C. 47p +, 60 n, 47 e - ___________

59 Solution 16 O A. 8 p +, 8 n, 8 e - 8 B.17p +, 20n, 17e - 37 Cl 17 C. 47p +, 60 n, 47 e Ag 47

60 Atomic Mass on the Periodic Table 11 Na Atomic Number Symbol Atomic Mass

61 Atomic Mass 4 Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

BEAN BAGIUM

ION 4 Ion – charged particle that forms when an atom gains or loses one or more electrons

ION 4 Cation – positively charged particle when an atom loses electrons protons(+) > electrons(-1)

CATION Ca +2 protons(+) = 20 electrons(-) = 18

ION 4 Anion – negatively charged particle when an atom gains electrons electrons(-) > protons(+)

CATION N -3 protons(+) = 7 electrons(-) = 10