Substances have different tendencies to donate or accept electrons. When a really good donor meets a great acceptor, the chemical reaction releases a lot of energy. Oxygen (O2) is the best electron acceptor and is used in many aerobic reactions (reactions with oxygen). Hydrogen gas (H2) is a good electron donor.
When O2 and H2 are combined, along with a catalyst, water (H2O) is formed. This example of a redox reaction can be written like this:

A calorie is equal to 4.18 joules and 1000 calories is equal to 1 Calorie. A Calorie with a capital "c" is what food is measured in.
The electron configuration of lithium atom is:
![Li:[He]2s^1](https://tex.z-dn.net/?f=Li%3A%5BHe%5D2s%5E1)
The number "2" is the value of the principal quantum number "n". Letter "s" is associated with the value of secondary quantum number "l" and it is equal to zero. The value of "m" (or magnetic quantum number) is zero too. The quantum number set for the highest energy electron will be (2, 0, 0, 1/2).
- Frequency=v=2×10^15Hz
- Energy=E
Using planks quantum theory



