Key Concept: Isotope Notation, Ions and Shell Diagrams

Notes

Sample Questions:

1.(JUNE 2000 416): The atomic number of fluorine(F) is 9 and its mass number is 19. Which correctly represents the simplified model of a fluorine atom?

 

# of protons

# of neutrons

# of electrons in 1st shell

# of electrons in 2nd shell

A

10

9

2

8

B

9

10

2

7

C

9

19

2

7

D

19

9

2

9




2.(JUNE1999 416): Two isotopes of chlorine are found in nature. What is the difference between these two isotopes?

  1. Number of electrons
  2. Number of protons
  3. Number of neutrons
  4. Number of energy levels or electron orbits




3.(JUNE 1999 416): Sulfur (S) has several isotopes. One of these has a mass number of 34. Draw a simplified atomic model to represent this isotope.

 

4.(JUNE 2000 416) The atomic number of chlorine (Cl) is 17 and its mass number is 35. Which of the following correctly represents the simplified model of a chlorine atom?

 

# of protons

# of neutrons

# of electrons in 1st shell

# of electrons in 2nd shell

# of electrons in 3rd shell

A

17

17

2

8

8

B

17

35

2

8

7

C

17

18

2

8

7

D

18

35

2

8

8

 

Notes:

1

 Example

# of protons = atomic number from periodic table

# of neutrons = mass number - protons

# of electrons in 1st shell: maximum 2/

Total # of electrons = protons - charge

# of electrons in 2nd shell: maximum:8

# of electrons in 3rd shell: maximum 8 for first 20 elements

# of electrons in 4th shell:

2H

1

1

1

0

0

0

9Be

4

9 - 4 = 5

2

2

    

31P

15

16

2

8

5

  

40Ca

20

20

2

8

8

2