The "A" group numbers (1A, 2A, 3A, etc...) are the number of valence electrons ALL elements in that group (column) contain. Helium (He) is the exception. Helium only has 2 valence electrons. For example,
The Octet Rule
The octet rule states the following: Atoms are most stable when they have a full outermost shell of electrons. This means elements want 8 electrons in their outermost shell really badly! Elements want to be like noble gases. Although elements want 8 electrons in their outermost shell, there are two exceptions which are Hydrogen (H) and Helium (He) which are stable with 2 electrons in their outermost shell. Also, we can use this rule to predict what elements will chemically bond with one another. Watch the following video.
Lewis Dot Diagrams
Lewis Dot Structures show the bonding between atoms of a molecule, but we need to know the Lewis Dot Diagram for a specific element to be able to draw Lewis Dot Structures. There are two things you need, so you can draw a Lewis Dot Diagram: (1) the element symbol, and (2) the number of valence electrons for that element. Each valence electron is a dot, and the element symbol goes in the center. See the examples to the left. Watch the following video from 0:00 to 5:09.
Lewis Dot Structures
Lewis Dot Structures are useful when thinking about bonding, since these diagrams only show the valence electrons.
The VSEPR Theory states that there is a repulsion between electron pairs, so each atom in a molecule will achieve a geometry that minimizes this repulsion. Make different molecules with the simulation below to view the different molecular shapes that can occur.