These are electrons in an atom's outer shell that can participate in forming chemical bonds with other atoms - just like walls and beams in our house blueprint analogy.
Covalent Bonding: This type of bond happens when two or more elements share electron pairs - similar to sharing living space within our house blueprint analogy.
These are several Lewis structures that represent a single ion or molecule but differ only by position of electrons – think different design layouts for same square footage in our house blueprint analogy.