1. Structure of an atom

2. What are atoms made of…? UE

3. Negligible (very small)
Structure of an Atom
Atoms consist of three smaller subatomic particles call the proton, neutron and electron
Subatomic particle
Location
Mass
Charge
Proton
 Nucleus
1 amu  +
Neutron
Nucleus
1 amu
No charge
Electron
 In orbit
Negligible (very small) -

4. Structure of an Atom
Each element has a different number of protons, neutrons and electrons which gives it unique physical and chemical properties
Atomic Number
= # of protons
Mass Number
= # of protons + # of neutrons
= all the heavy particles (the nucleus)

5. # neutrons = mass # - atomic #
Therefore to determine the number of neutrons we can use the following equation:
# neutrons = mass # atomic #
(protons + (protons)
neutrons)

6. Standard Atomic Notation
> mass # (larger number)
K > chemical symbol
> atomic # (smaller number)
Therefore a potassium atom contains:
_____ protons (atomic number)
_____ electrons (same as # of protons)
_____ neutrons (mass number – atomic number) 19 19 20

7. Question Write the atomic notation for the following:
An atom of nitrogen with 7 protons and 8 neutrons 15 N 7
An atom of bromine with 35 protons and 36 neutrons 71 Br 35

8. Fill in the following table:
Symbol
Atomic Number
Mass Number
Number of Protons
Number of Neutrons
Number of electrons Br O Li 21 59 27 65
201
121 17

9. Answers:
Symbol
Atomic Number
Mass Number
Number of Protons
Number of Neutrons
Number of electrons Br
35  80 35 45 O 8  16 8 Li 3 7 4
 Sc 21
45  24
 Co
27  59 27
 32
 27
 Zn
 30 65 30
 Hg
 80
201
80 
121
 Cl
 17 17 18

10. Isotopes
Isotopes are two or more forms of an element with the same # of protons and different # of neutrons.
Isotopes of an element have the same chemical and physical properties.
All atomic masses listed on the periodic table are averages taken from the percent abundance of each isotope of an element

11. Chlorine has two common Isotopes Cl-35 and Cl-37
Mass #
Atomic #
Protons
Neutrons
Electrons
Cl-35
Cl-37

12. Chlorine has two common Isotopes Cl-35 and Cl-37
Mass #
Atomic #
Protons
Neutrons
Electrons
Cl-35
 35 17
 17
 18
Cl-37
 37
 20

13. Example
For each of the following isotopes, calculate the number of protons, neutrons and electrons
C- 12 and C – 13
b) Ne – 20, Ne-21, Ne-22

14. Example
For each of the following isotopes, calculate the number of protons, neutrons and electrons
C- 12 and C – 13
C-12: 6p+, 6n, 6e-
C-13: 6p+, 7n, 6e-
Ne – 20, Ne-21, Ne-22
Ne-20: 10p+, 10n, 10e-
Ne-21: 10p+, 11n, 10e-
Ne-22: 10p+, 12n, 10e-

15. Bohr – Rutherford Diagrams
Bohr and Rutherford discovered that the electrons of an atom are arranged in energy shells or orbits around the nucleus.
Each orbit has a maximum number of electrons that it can hold.
Bohr-Rutherford diagrams may be used to create visual representations of atoms
Shell
Maximum # of e- 1 2 8 3 4 18

16. Bohr Rutherford Diagrams
Draw a circle to represent a nucleus.
2. In this circle write the number of protons and number of neutrons. Include the letter “P” next to the number of protons and “N” next to the number of neutrons. Also write the element symbol.
3. In circles around the nucleus, which represent the electron shells or orbitals, draw one dot for each electron in the atom. Electrons should be drawn in pairs except for electrons in the first shell.
4. Once one orbital has reached its ‘full’ capacity, move onto the next orbital until all electrons are accounted for.

17. Example
23 Na 11

18. Practice
Draw B-R diagrams for:
Mg B F H

19. To Do / For Homework Read the textbook pages 245-249
Complete the Worksheets
Atomic Structure Worksheet
Bohr-Rutherford Diagrams Worksheet