1. Unit II: Atoms and The Periodic Table
ATOMIC NUMBER, ATOMIC MASS, AND ISOTOPES

2. Subatomic Particles
Particles which make up the atom are called subatomic particles.

3. Atom: Nucleus
Protons
Neutrons

4. Atom: Nitrogen
Electrons
Energy Levels

10. Ordinary Hydrogen
Tritium
Deuterium

11. Isotopes Isotopes are:
Different forms of the same element with the SAME # of Protons but with DIFFERENT #’s of Neutrons

13. Also called “Hydrogen – 3”
Mass Number
Mass Number = Total Protons + Neutrons in an isotope of an element
Mass Number
P + N 3H
1 P + 2 N’s
Also called “Hydrogen – 3”

14. Called Nuclear Notation
Mass Number 3H
Called Nuclear Notation

15. 41Ca Practice Problem 20 To find P’s and N’s from Nuclear Notation
Mass # = P + N
To find # of
Neutrons, put
Atomic Number
Here:
41Ca 20 21
Calcium’s atomic
Number = 20
Subtract to get #
of Neutrons
20 Protons
So it has 21 Neutrons

16. Find the # of Protons and # of Neutrons in Each of the Following Isotopes:

17. Find the # of Protons and # of Neutrons in Each of the Following Isotopes:

18. Now Try the Other Way

19. Now Try the Other Way

20. Now Try the Other Way

21. Now Try the Other Way

22. Neutral Atom In a Neutral Atom of an Element:
The # of Electrons(-) = The # of Protons(+)

23. Ion An ion is an atom where: In a + ion (cation) In a - ion (anion)
# of e-’s ¹ ≠ # of p’s
In a + ion (cation)
# of e-’s < # of p’s
In a - ion (anion)
# of e-’s > # of p’s

24. Example #1
The ion Ca 2+
has 20 protons (atomic #) and it has 18 e-’s (2 less –’s than +’s, hence a 2+ charge)

25. Example 2
The ion Se 2-has 34 protons (atomic #) and it has 36 e-’s (2 more –’s than +’s, hence a 2- charge)

26. Example 3
An atom of Bi has 83 protons (atomic #) and it has 83 e-’s (e-’s are equal to protons, hence, no charge (neutral))

27. Isotopes Continued The isotope: 56Fe 3+ has 26 protons
30 neutrons (56-26)
23 electrons (26-3)

28. Isotopes Continued The isotope: 76As 3- has 33 protons
43 neutrons (76-33)
36 electrons (33 +3)

29. Isotopes Continued The isotope: 201Au+ has 79 protons
122 neutrons (201-79)
78 electrons (79 - 1)

30. An isotope has 46 protons, 58 neutrons and 42 electrons
An isotope has 46 protons, 58 neutrons and 42 electrons. Write the nuclear notation:
Answer: 104Pd 4+

31. An isotope has 52 protons, 79 neutrons and 54 electrons
An isotope has 52 protons, 79 neutrons and 54 electrons. Write the nuclear notation:
Answer: 131Te2-

32. Finding (average) atomic mass using isotope abundances
Assumption: Assume
mass of a neutron = mass of proton = 1 u (atomic mass unit)
this is not “exactly” correct
The mass of a proton = u
The mass of a neutron = u

33. Example #1 Chlorine in nature is 75.77% 35Cl and 24.23% 37Cl
Using these: Find the average atomic mass of Cl
Change % to decimals