1. The Structure of Atoms
Thanks to those 7 scientists (and many more) what do we know about atoms today?!

2. Structure of atoms
Atoms can’t be broken into smaller pieces, BUT they are made of smaller pieces!
Those smaller pieces all on their own don’t act like the element the atom is from.
Atom: the smallest particle of an element with the chemical properties of that element.

3. Two areas of an Atom Nucleus: made up of:
Protons (+ positive), mass number = 1
Neutrons (0 neutral), mass number = 1
Make up the mass of the atom +

4. Electrons (- negative) Around the nucleus Tiny, mass number = 0
Lots of space between the nucleus and the electrons. -

5. Subatomic Particles
Protons, neutrons and electrons

6. Subatomic Particles Subatomic Particle Charge Location Mass proton
positive (+)
nucleus
1 amu
neutron
neutral (0)
electron
negative (-)
around nucleus
~1/2000 amu

7. Defining an Atom
Nuclei (plural of nucleus) made of protons and neutrons
Number of Protons (+) = number of electrons (-)
Atoms are neutral!
# protons tells us what kind of element an atom is!

8. Holding it all together
Nuclear forces hold protons and neutrons together
The positive force of the nucleus holds the electrons near the nucleus.
Positive and negative attract.

9. Mass number = protons + neutrons
Everything heavy in an atom
Electrons aren’t heavy at all!

10. C 6 Carbon 12.011 Atomic Number (= number of protons) Element Symbol
Element Name
Average atomic mass

11. Protons
Neutrons
Mass number
Electrons
Element

12. + -

13. Protons
Neutrons
Mass number
Electrons
Element 2 4
Helium

14. - + + + - -

15. + - +

16. - - - + + - + + - + + + - -

17. - - - + + + + - + + - + + + + - - - - -

18. - - - + - + + + - + + - + + + + + - - - - -

19. - - - + + + - + + - + + + - - -

20. 2 4 Helium 3 6 Lithium 5 10 Boron 7 14 Nitrogen 20 Neon 11 22 Sodium 8
Protons
Neutrons
Mass number
Electrons
Element 2 4
Helium 3 6
Lithium 5 10
Boron 7 14
Nitrogen 20
Neon 11 22
Sodium 8 16
Oxygen

21. Which element…?
Has 20 protons?

22. Which element…?
Has 15 protons?

23. Which element…?
Has 17 protons?

24. Which element…?
Has 53 protons?

25. Which element…?
Has 79 protons?

26. Which element…?
Has 40 electrons?

27. Which element…?
Has 77 electrons?

28. Which element…?
Has 50 electrons?

29. Which element…?
Has 118 electrons?

30. C 6 Carbon 12.011 Atomic Number (= number of protons) Element Symbol
Element Name
Average atomic mass

31. Protons: defining an atom
Atomic number: Atoms of different elements have different numbers of protons.

32. Trends in Atomic Numbers
Atomic numbers increase to the right and down the Periodic Table of the Elements.
Check it out.

34. Isotopes

35. Average atomic mass + - 6 C
12.01 + + -

36. But why is the atomic mass (on the periodic table) different from the mass number (protons + neutrons)?
Carbon atomic mass = amu
Mass number = 12 amu

37. Isotopes
Atoms of the same element can have different numbers of neutrons.
Because these atoms have the same number of protons, they are the same element, and acts the same
More or fewer neutrons only changes the mass of the atom!
Isotopes are atoms of the same element with different masses because of different numbers of neutrons
Identified by mass number

38. Naming Isotopes
Mass number (A): the total number of protons and neutrons in the nucleus of an isotope
Hyphen Notation:
Element-Mass number
Hydrogen-3

39. Nuclear Symbol

40. Nuclear symbols Helium-4: 4 is the mass number
The total number of protons plus neutrons
This helium isotope can also be written:
4He 2
4 is the mass number, 2 is the number of protons
Write the nuclear symbol for Carbon-13
13C 6

41. Nuclear symbols Helium-4: 4 is the mass number
The total number of protons plus neutrons
This helium isotope can also be written:
4 is the mass number, 2 is the number of protons (from the periodic table)

42. Isotope Notation
Mass number
Atomic number
Al-27
Aluminum-27

43. + -

44. - +

45. - + + -

46. + - +

47. - - + - + + + + - -

48. - - - + + - + + - + + + - -

49. - - - + + - + + - + + + - -

50. - - + + - - + + + + - -

51. + - +

52. - - + - + + + + - -

53. - - - + + - + + - + + + - -

54. - - - + + - + + - + + + - -

55. Practice naming Isotopes
The notation Sn-117 represents an isotope of the element ____________.
Its mass number is ________.
Since its atomic number is __________, the atom contains
_________ protons,
_________ electrons and
_________ neutrons.

56. Cesium-133 is an isotope whose mass number is _________.
Its atomic number is ________.
The atom contains _______ protons,
________ electrons and
________ neutrons.

57. An isotope contains 27 protons and 39 neutrons
An isotope contains 27 protons and 39 neutrons. The isotope is an atom of the element ____________.
Its atomic number is _________.
This atom has _______ electrons.
Its mass number is __________.

58. Applications of Isotopes
Over time (a long time!) one isotope can lose neutrons and turn into another.

59. Measure the % of C-14 to calculate age

60. What objects have been dated using carbon-14 isotopes?

61. Shroud of Turin

62. The Giant Periodic Table Project6 C
Carbon
12.011

63. The Giant Periodic Table Project
Be neat
Be bold! We need to be able to read this from anywhere in the room!
Be creative, but not cluttered.
Be accurate.
Atomic mass to TWO digits (Ex: 12.01) is ideal.

64. Calculating your grade
Your averages for each of the categories are:
Tests: 79%
Labs: 88%
Homework: 65%
Class work: 90%
Let’s imagine that your grade in biology was based on the following:
40% Tests
30% Labs
20% Homework
10% Class work

65. Now you try: Your averages for each of the categories are: Tests: 90%
Labs: 70%
Homework: 85%
Class work: 95%
Let’s imagine that your grade in biology was based on the following:
40% Tests
30% Labs
20% Homework
10% Class work

66. Mixtures of Isotopes
In nature, elements occur as a mixture of isotopes.
We use the weighted average of the isotope masses – average atomic mass
On the periodic table, the average atomic mass is below the element name.
Check it out.

67. Example: Chlorine In nature, chlorine exists as: 75.77% chlorine-35

68. In nature, the element lithium has isotopes in the following natural abundance:
Calculate the average atomic mass.

70. Copper has two naturally occurring isotopes
Copper has two naturally occurring isotopes. They are present in the following percents:
69.09%
30.91
Calculate the average atomic mass.

71. Calculate the average atomic mass of Ne

72. So what if someone gives us the mass of a sample of an element?
How do we figure out how many atoms we have?
We use…
THE MOLE

73. The mole Mole: The SI unit for amount of substance
Contains as many particles as there are atoms in 12 grams of carbon-12
There are 6.022x1023 atoms in 12 grams of carbon-12
Avogadro’s Number = 6.023x1023

74. Molar Mass
The mole: the amount of a substance that contains one Avogadro’s number (that is, 6.022x1023) of particles.
Molar mass is the mass of one mole of a pure substance (units: g/mol)

75. Find the molar mass of…
Oxygen

76. Find the molar mass of…
Phosphorus

77. Find the molar mass of…
Sodium

78. Find the molar mass of…
Gold