An ionic compound is a compound that is formed by ions, so one of the elements must donate electrons (which is the cation, the positive ion), and the other will receive these electrons (which is the anion, the negative ion).
The power of an element has to attract the electrons is called electronegativity, and so, as higher is the difference of electronegative of the elements, it is more probable that one of them will "still" the electrons and will form an ionic compound. The percent of this ionic character can be found by the Pauling's equation:
*100%
Where is the electronegativity difference of the elements. Thus, consulting an electronegativity table:
When you eat food, your body can use the chemical energy in the food to make your muscles move so you can breathe, walk, run, jump, lift things, and do all the other things you need to do to live. The chemical energy in the food gets changed into the mechanical energy of moving muscles.