The valence electrons (VE) are the electrons in the outer shell of an atom. The valence electrons are the ones involved in forming bonds to adjacent atoms. Therefore, the number of VE is important for determining the number of bonds an atom will form, the number of unpaired electrons, and an atomâs formal charge.
An exclamation point denotes something called a factorial. The formal definition of #n!# (n factorial) is the product of all the natural numbers less than or equal to #n#. In math symbols: #n! = n*(n-1)*(n-2)...#. Trust me, it's less confusing than it sounds. Say you wanted to find #5!#. You just multiply all the numbers less than or equal to #5# until you get to #1#: #5!
A line segment can be viewed as a degenerate case of an ellipse in which the semiminor axis goes to zero, the foci go to the endpoints, and the eccentricity goes to one. A standard definition of an ellipse is the set of points for which the sum of a point's distances to two foci is a constant; if this constant equals the distance between the foci, the line segment is the result.