This document discusses atomic structure and isotopes. It defines the basic particles that make up an atom including protons, neutrons, and electrons. It explains that isotopes are atoms of the same element that have different numbers of neutrons. The document provides examples of isotopic symbols and how to determine the number of protons, neutrons, and electrons in different carbon and zinc isotopes. It also discusses how atomic mass is calculated based on the relative abundances of an element's naturally occurring isotopes.

1. Atomic Structure
Isotopes

2. Atomic Structure
particle symbol location charge mass
proton p+ nucleus 1+ 1 amu
neutron no nucleus 0
No charge
1 amu
electron e - Electron
cloud
1- 1/1840 amu

3. Matter
Atoms
nucleus electron cloud
Neutrons protons = electrons (in a neutral atom)
• The number of protons in an atom equals it’s atomic number
• Every atom has a unique atomic number
• Since electrons are easily gained or lost they determine the
overall charge of an atom

5. Isotopes
• Atoms with the same number of protons but
different numbers of neutrons
• Another way to say – atoms of the same
element with different numbers of neutrons
• An elements mass number is the number of
protons plus the number of neutrons
• REVIEW: to determine the number of
neutrons subtract the atomic number from the
mass number
• Mass # – atomic # = # of neutrons

6. Isotopes of Lithium

7. Isotopic symbols

8. Isotopic symbols
NOTE: Unlike on the periodic
table where the atomic number
is at the top of the box and the
average atomic mass is at the
bottom in isotopic symbols the
mass number is at the top and
the atomic number is at the
bottom.
If X is Hydrogen and its mass number is 2 then the isotopic symbol
would be
2H
1

9. Isotopic symbols
If X is Fluorine and its mass
number is 20 then the correct
isotopic symbol is
Fluorine – 20.

11. If the atom has a charge the charge is written
to the upper right side of the symbol. If the
charge is either negative or positive 1 the 1 is
not written but understood to be 1.

12. Determine the number of neutron in each isotope
1. 238 – 92 = 146 neutrons
2. 84 – 36 = 48 neutrons
3. 35 – 17 = 18 neutrons
4. 14 – 6 = 8 neutrons

13. Isotope Example
35Cl 37Cl
17 17
chlorine - 35 chlorine - 37

14. Isotopes of Carbon
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the
number of protons, neutrons, and electrons in each of these carbon atoms.
12C 13C 14C
6 6 6
#P _______ _______ _______
#N _______ _______ _______
#E _______ _______ _______

15. Solution
12C 13C 14C
6 6 6
#P __6___ _ 6___ ___6___
#N __6___ _ _7___ ___8___
#E __6___ _ 6___ ___6___

16. Zinc problem
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30 2) 35 3) 65
B. Number of neutrons in the zinc atom
1) 30 2) 35 3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37 2) 65 3) 67

17. Solution to Zinc Problem
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67

18. Isotope or nuclide notation
• C-14 and C -12
When you see the symbol of the element and a
dash, the number after it is the mass number.
This is another way of modeling isotopes.

19. Atomic Mass
 Listed on the periodic table
 Gives the mass of “average” atom of each element compared to
12C
 Average atom based on all the isotopes and their abundance %
 Atomic mass is not a whole number … mass number is a whole
number
Na
22.99

20. Calculating Atomic Mass
 Percent(%) abundance of isotopes
 Mass of each isotope of that element
 Weighted average =
mass isotope1*(%) + mass isotope2*(%) + …
100 100

21. Atomic Mass of Magnesium
Isotopes Mass of Isotope Abundance
24Mg = 24.0 amu 78.70%
25Mg = 25.0 amu 10.13%
26Mg = 26.0 amu 11.17%
(24)(.787) + (25)(.1013) + 26(.1117) =
18.888 + 2.5325 + 2.9042 = 24.3 amu