The measure of distance from one point to another is?

The distance from one point to another is the distance traveled by a light beam between them.

If you have the coordinates of the 2 points, then the distance between them is

√ of [ (the difference in their x-values)² + (the difference in their y-values)² ]

Both models are effective because they show the valence electrons, and these valence electrons indicate the reactivity of an element.

Heat is involved in chemical change in two ways; chemical changes either result in heat being added to or removed from an object, and chemical changes require a certain amount of heat before they can take place.