Chemical Details

The difference between a physical change and a chemical change is that a physical change is reversible, but a chemical change is not and when the change is made in the chemical change it is something different from before.  For example: when you freeze water you can reverse by unfreezing it, that is a physical change.  But when you burn wood, you cannot unburn it, this is like a chemical change.   Elements Elements are the basic chemical unit and are represented by a 1 or 2 letter abbreviation, phosphorus (P), sodium (Na), oxygen (O), magnesium (Mg). Compounds Compounds are made from combinations of elements. Sodium chloride's abbreviation is NaCl and it is made up of one atom of Na (sodium) and one atom of Cl (chlorine). Ions Any element or compound that has an electrical charge is an ion. Ions are normally written with their charge (+ or -) after the symbol. Na+ is the sodium ion because it has a single positive charge. Cl- is the chloride ion since it has a single negative charge Chemical formulas (or more correctly: formulae) are designations of molecules and compounds in shorthand notation, similar to that used in Algebra.