This is an example of a chemical property.
If you count the number of electrons (small dots), you have the atomic number. In this case you have 11 so this atom is a sodium atom. Sodium has 1 valence electron (electron on the outer shell) and chlorine has 7. This means that if sodium gave one electron away and chlorine would obtain one electron, they would both have the (ideal) noble gas conformation (full outer shell).
Answer: protons
Explanation:
The atomic # identifies the amount of protons in an atom
Im unsure :( maybe try looking up a calorie calculator
