The simple view of the bonding in methane You will be familiar with drawing methane using dots and crosses diagrams, but it is worth looking at its structure a bit more closely. There is a serious mis-match between this structure and the modern electronic structure of carbon, 1s 2 2s 2 2p x 1 2p y 1.
Lack of sun exposure: Lack of sun exposure is a major cause of low vitamin d level especially if you live in the northern us. Less likely would be lack of vitamin d in food, but also a possibility if you are on a very restrictive diet.
A lower-than-normal level can be due to a vitamin D deficiency, which can result from: 1  Lack of exposure to sunlight. 2  Lack of enough vitamin D in the diet. 3  Liver and kidney diseases.  Poor food 1  absorption. Use of certain medicines, including phenytoin, phenobarbital, and rifampin.