Not the best drawing but hope thats correct
The particles are atoms, his theory is the atomic theory
Acid - base indicators (also known as pH indicators) are substances which change color with pH. They are usually weak acids or bases. you use them if you want to know if a solution is an acid or it it's a base
Valence electrons are the electrons in the outermost shell of an element on the periodic table. Atoms want to be able to have a full outer shell and they can share or trade electrons in order to achieve this. Valence electrons are also super super important in chemical reactions. The number of valence electrons determines what group that specific atom or element is in on the periodic table. This affects the reactivity of the element.
Balanced equation:
Ca(OH)2+H2SO4=CaSO4+2 H20<span />