Electrons and Energy
As mentioned previously, the precise location of an electron at any given moment cannot be determined. However, the Bohr model allows us to see electrons in their expected energy level (or shell). The first, inner most shell, can hold up to 2 electrons. The second shell can hold up to 8. the third shell can hold 8 or 18. If it has enough electrons to fill it up to 18, then it can hold 18. However, if there are not, then the 3rd shell holds only 8 and the additional electrons are shown in the 4th layers. There are more than 3 shells, but for our purposes, we will not go further than this.
The electrons in the outter most shell are called valence electrons. The number of valence electrons influences the types of bonds an atom will make. You can determine the number of valence electrons easily by looking at the periodic table. If you skip the middle elements, the groups can be numbered 1 to 8. Every atom in group 1 has 1 valence electron. Every atom in group 18 has 8 valence electrons.
The electrons in the outter most shell are called valence electrons. The number of valence electrons influences the types of bonds an atom will make. You can determine the number of valence electrons easily by looking at the periodic table. If you skip the middle elements, the groups can be numbered 1 to 8. Every atom in group 1 has 1 valence electron. Every atom in group 18 has 8 valence electrons.
Compounds and Molecules
A compound is when two or more elements have bonded together (cannot be separated by physical means). A molecule is the smallest part of a compound that still has the properties of the particular compound. The chemical formula tells you the number of each kind of atom in a molecule. The formula for water is H2O and indicates that there are two hydrogens and one oxygen.