Bohr's Atomic Model For Calcium

	1	2	13	14	25	16	17	18
1	1 H							2 He
2	3 Li	4 Be	5 B	6 C	7 N	8 O	9 F	10 Ne
3	11 Na	12 Mg	13 Al	14 Si	15 P	16 S	17 Cl	18 Ar
4	19 K	20 Ca

Here are the Bohr Model "Rules" again:

The number of protons equals the atomic number. And the number of electrons equals the number of protons.

The number of energy levels occupied by electrons equals the period number of the element.

The maximum number of electrons allowed in each energy level equals the number of elements in each period.

The number of electrons in the highest used energy level(valence level) equals the group number.

The total number of protons and neutrons equals the atomic mass number.

Consider calcium (Ca), element 20. Use mass number 38.

Period number is 4, so 4 energy levels needed.
Group number is 2, so there are 2 electrons in the valence energy level (4th. level here)
Lower energy levels are filled, so 2, 8, 8 electrons in those lower energy levels.
Atomic number 20 tells us there are 20 protons (and 20 electrons).
Mass number of 38 means there must be 18 neutrons along with 20 protons. (38=18+20)

So the calcium model has 20p+, 18n^o, 20e-, energy levels = 4, valence e- = 2, so the energy levels are filled in a pattern of 2e-, 8e-, 8e-, 2e-. Here is the model.

Bohr Model of a calcium atom. Pencil sketch of Bohr model.

Now you try sodium (Na), element 11, and use mass number 12. Look at the periodic table, and make a sketch of the Bohr Model of a sodium atom. Click here to find out.

Sketch the Bohr Models of helium (He), neon (Ne), and argon (Ar). What do you notice that is "special" about the number of electrons in the energy levels of these atoms?

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