Why is the valency of the Calcium (Ca) Bohr model, set to 2 electrons, instead of 1 electron for stability?
After following Mithoron's link, I familiarized my self with the writing on the following ChemGuide site (link).

I went into Excel spreadsheet, and had each 'sub orbital' it's own column, and came up with the following.

+---------+---------+----+---------+----+----+---------+-----+
| Shell 1 | Shell 2      | Shell 3           | Shell 4       |
+---------+---------+----+---------+----+----+---------+-----+
| 1s      | 2s      | 2p | 3s      | 3p | 3d | 4s      | SUM |
| 2       | 2       | 6  | 2       | 6  | 0  | 1       | 19  |
| 2       | 2       | 6  | 2       | 6  | 0  | 2       | 20  |
+---------+---------+----+---------+----+----+---------+-----+


This is what the overall table (link) looks like in excel; I can't attach the image directly to my post.

While googling, to get a clear understanding of S,P,D,F I came across ThoughtCo's article (link). This let me know the stability precedence, i.e. electron distribution, more clearer, as follows:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f

4s is filled before, 3d. 3s and 3p, can hold a combined maximum of 8 electrons.

The following (link) has a diagram with downward/diagonal arrows, showing how one can better remember the stability precedence.