- Defines default valence and charge (range) and valence electrons for
- several s- and p-block periodic elements. The values allow checking for
- abnormal charge/valence on the defined element. A value of 'n/a' means it is
- not checked. If a valence value is in specified parentheses then it is
- considered fixed and valid for all charge states, if a value is in square
- brackets it is only valid for neutral atoms

- It should be noted that the model used is only for checking abnormal valence
- and not adding implied hydrogens. The model follows a simple pattern which
- leads to incorrect results (e.g. 5 valent carbon cation ion - [C+H5]) but 
- matches observed warnings from the Daylight Depict, daylight.com/daycgi/depict 

- period 1
H     (0),1       -1,1     1	

He    0           0,0      2

- period 2
Li    (0),[1]     0,1      1
Be    n/a         n/a      2

B     0,3         0,0      3
C     [0],2,4     -1,1     4
N     [0],3,(5)   -3,1     5
O     [0],2       -2,1     6
F     (0),(1)     -1,0     7
Ne    0,0         0,0      8

- period 3
Na    (0),[1]     0,1      1
Mg    0,2         0,2      2

Al    n/a         n/a      3
Si    n/a         n/a      4
P     [0],3,5     -3,1     5
S     [0],2,4,6   n/a      6 
Cl    [0],1,3,5,7 n/a      7
Ar    0           0,0      8

- period 4 (excluding d-block)
K     (0),[1]     0,1      1
Ca    0,2         0,2      2

Ga    n/a         n/a      3
Ge    n/a         n/a      4
As    [0],3,5     -3,1     5
Se    [0],2,4,6   n/a      6
Br    [0],1,3,5,7 n/a      7
Kr    0           0,0      8

- period 5 (excluding d-block)
Rb    n/a         n/a      1
Sr    0,2         0,2      2

In    n/a         n/a      3
Sn    n/a         n/a      4
Sb    n/a         n/a  	   5
Te    [0],2,4,6   n/a      6
I     [0],1,3,5,7 n/a      7
Xe    0           0,0      8

- period 6 (excluding d-block and f-block)
Cs    n/a         n/a      1
Ba    0,2         0,2      2

Tl    n/a         n/a      3
Pb    n/a         n/a      4
Bi    n/a         n/a      5
Po    n/a         n/a      6
At    [0],1,3,5,7 n/a      7
Rn    0           0,0      8

- period 7 (excluding d-block and f-block)
Fr    n/a         n/a      1
Ra    0,2         0,2      2