1. Neutrons
Protons
Electrons

2. Structure of the Atom: 1) The nucleus: 2) Electron cloud:
There are two regions:
1) The nucleus:
With protons and neutrons
Positive charge
Almost all the atom’s mass
2) Electron cloud:
The region where the electron can be found (negative charge)
Most of the volume of an atom with almost no mass (empty space).

3. Atomic Number (Z):
Example:
Mg (Z=12) → ___ protons (+) and
___ electrons (-)
Represents the
number of protons in an atom.
In any atom the number of protons in its nucleus is equal to the number of electrons around the nucleus. 12 12

4. Mass Number (A):
Chlorine- 34 → 17 p + ___ n
Chlorine -35 → ___ p n
Is the sum of the number
of protons and neutrons in the nucleus.
Example : Magnesium-24 17 17

5. Atomic # Mass # Protons Electrons Neutrons 4 5

6. Atomic # Mass # Protons Electrons Neutrons 4 4 5

7. Atomic # Mass # Protons Electrons Neutrons 4 4 4 5

8. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5

9. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5 6 6

10. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5 6 6 6

11. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5 6 6 6 6

12. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5 6 12 6 6 6

13. Atomic # Mass # Protons Electrons Neutrons 4 9 4 4 5 6 12 6 6 6 17 35

14. Atomic # Mass # Protons Electrons Neutrons

15. Atomic # Mass # Protons Electrons Neutrons

16. Atomic # Mass # Protons Electrons Neutrons

17. Atomic # Mass # Protons Electrons Neutrons

18. Atomic # Mass # Protons Electrons Neutrons

19. Atomic # Mass # Protons Electrons Neutrons

20. Atomic # Mass # Protons Electrons Neutrons

21. Atomic # Mass # Protons Electrons Neutrons

22. Atomic # Mass # Protons Electrons Neutrons

23. Name Protons Neutrons Electrons
Neon - 20
Neon - 21
Neon - 22 10 11 12
: Atoms with the same # of
protons (or Atomic Number, Z),
but different # of neutrons (or
Mass Number, A).
Isotopes

24. X Symbol (Isotope): Mass number Atomic number
Contains the symbol of the element, the mass number and the atomic number:
THIS IS NOT THE SAME AS WHAT IS IN THE PERIODIC TABLE!
Mass
number X
Atomic
number

25. F Br Practice: 19 9 80 35 9 35 10 45 9 35 9 35 19 80 1) Find the
number of protons
number of neutrons
number of electrons
Atomic number
Mass Number 9 35 10 45 9 35 9 35 19 80

26. 2) If an element has an atomic number of 34 and a mass number of 78 what is the
number of protons
number of neutrons
number of electrons
Complete symbol 34 44 34 Se 78 34

27. Naming Isotopes: Just write the name of the element followed by
its mass number.
Example:
Carbon - 12
Carbon - 14
Uranium - 235

28. Subatomic particles in ions:
When atoms gain electrons they
become to negative ions (anions):
Neutral atom: Cl 0 (17 p e- )
Ion: Cl 1- (17 p e - )

29. Subatomic particles in ions:
When atoms lose electrons they
become to positive ions (cations):
Neutral atom: Na 0 (11 p e - )
Ion: Na 1+ (11 p e - )

30. Li Li 6 3 6 3 A neutral atom of lithium has 3 protons and 3 electrons
When lithium reacts, it typically looses one electron; giving it 3 protons and 2 electrons
Lithium ION: 3 protons (3 +) and 2 electrons (2-)
Now it has a NET charge of (1+)
1 + Li 3 6

31. No charge here: NEUTRAL ATOM (same number of protons as electrons)Li 3 6
No charge here: NEUTRAL ATOM (same number of protons as electrons)
1 + Li 3 6
Charge here: ION
Positive charge = more protons than electrons.
Negative charge = more electrons than protons.

32. Na S Al 11 23 + 11 protons; 10 electrons; 12 neutrons. 16 32 2-13 27 3+
13 protons; 10 electrons; 14 neutrons.

33. How Many Protons, Neutrons, and Electrons?
Prot. Neut. Elect. N 7 14 3- Ca 20 41 2+ Cl 17 33 1-