1. Atomic
Structure

2. Atoms are made
up of 3 subatomic
particles

3. Protons
Neutrons
and…

4. Electrons !

5. are located in the nucleus of an atom.
Protons
and
Neutrons
are located in the nucleus of an atom.

6. Electrons
Whiz around the outside of the nucleus in energy levels, also known as orbitals, electron clouds, or shells

7. Each particle
has a mass...

8. measured in
a.m.u.'s
(atomic mass units)

9. Protons have a
mass of 1 amu

10. Neutrons also
have a mass
of 1 amu

11. Electrons barely weigh
anything at all!
(1/1836 amu)

12. Each particle
is assigned a charge...

13. Protons have
a positive (+)
electrical charge

14. Neutrons have
no charge (0)

15. Electrons have
a negative ( - )
electrical charge

16. Let's build an atom!

17. We’ll use the element sodium
as an example…
Sodium Na

18. Sodium has the atomic number 11, and an atomic mass number of 23.

19. Step 1:
Find the # of protons!

20. 11 23 Step 1: Sodium Na There are 11 protons + in one atom of sodium
The smaller number is
the atomic number.
It tells the number of
protons in the atom
( the atom's identity)
Sodium 11 Na 23
There are 11 protons + in one atom of sodium

21. Na atomic # 11 23 p+ p+ p+ p+ p+ p+ p+ p+ p+ p+ p+
There are 11 protons + in the nucleus of a sodium atom

22. Step 2:
Find the # of neutrons!

23. Sodium
Step 2: 11 Na
Subtract the number of protons + (11) from the number of particles in the nucleus (23)
23 minus 11 =
12 neutrons 23
The larger number is the
atomic mass number. It tells the number of
protons and neutrons together.
There are 23 particles, or atomic mass units.
11 protons + 12 neutrons = 23 amu’s total

24. 23
Protons and neutrons 11
Protons - -
= 12 neutrons

25. Na atomic # 11 23 mass # p+ no p+ no no no p+ p+ no no p+ no p+ p+ p+
11 protons +
12 neutrons o
11 protons + 12 neutrons = 23 amu

26. Step 3:
Find the # of electrons!

27. Therefore, the number of
Step 3:
Most atoms are
electrically neutral.
Therefore, the number of
electrons can also be
determined by the
atomic number. There
are usually the same
number of electrons as
there are protons.
Sodium 11 Na 23
11 electrons -
11 protons usually means 11 electrons, too

28. Na e- atomic # 11 e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no noL K e- e-
11 electrons - total

29. atomic # 11 Na
11 electrons - orbit in energy levels, or shells, around the densely packed nucleus of the sodium atom.

30. atomic # 11 Na
But there are specific numbers of electrons that can fit in each energy level of the atom.

31. Na Only 2 electrons - can fit in the first, or “K” shell atomic # 11no no p+ p+ no no p+ no p+ p+ p+ no no p+ no e- e- p+ p+ no no p+ p+ no no K
2 electrons - so far…. (9 more to go)

32. Na 8 electrons - can fit in the second, or “L” shell atomic # 11 e- e-no no p+ p+ no no p+ no p+ p+ e- p+ e- no no p+ no e- e- p+ p+ e- no no p+ p+ e- no no M L K e- e-
10 electrons - so far……. ( added)… one more to go!

33. Electrons also fit in the valence, or outside shell, which in this case is the “M” shell.
atomic # 11 Na e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no no p+ no e- e- p+ p+ e- no no p+ p+ e- no no M L K
We only need to add one more electron for sodium, which fits easily in the “M” shell. e- e-
11 electrons – total ( )

34. All together now....

35. Sodium atom Na e- atomic # atomic # 11 e- e- 23 mass # 23 -11 = 12 nop+ p+ no p+ p+ no e- no no e- p+ p+ no no e- e- p+ p+ no no p+ p+ e- e- no p+ no no M L K
11 protons +
12 neutrons e- e-
11 electrons -

36. Review

37. Protons have a
mass of 1 amu

38. Protons have
a positive (+)
electrical charge

39. Neutrons
have a mass
of 1 amu

40. Neutrons have
no charge (0)

41. Electrons weigh
only 1/1836 amu

42. An electron's charge
is negative ( - )

43. Sodium 11 Na 23

44. Sodium atom Na e- atomic # 11 e- e- 23 mass # no no p+ p+ no no p+ noL K
11 protons +
12 neutrons o 11 electrons - e- e-

45. Congratulations!
You are an
atom builder!