When it comes to defining, explaining, expressing, discussing and telling what ionization energy is, many give variety of defination, explaination, expression, discussion and teaching from different angles but still arriving at the same point thereby confusing some learners like me at the end of the whole show. My question to this great honourable forum is this: What is the exact and precise defination to the term ionization energy? Another question: It is known and widely accepted fact that ionization energy generally decreases steadily down a given group and increases from left to right, what does that mean? How can I visualize it (the statement) for a better understanding? So folks, what do you have to say about the above questions?