How many electrons (dots or pairs in bonds) should surround each element in a lewis diagram (excluding hydrogen)?

The number of dots, electrons, surrounding the element in a Lewis diagram varies depending on what element it is, and what element it is bonding with to create a bond or several bonds. Its all dependent on what element you're being asked to make a Lewis diagram for and which elements your are boning.

the volume of fluid displaced would equal the volume of the gas. use a gas syringe - this is a laboratory instrument that can be used to withdraw a certain volume of gas from a closed system or to measure the volume of gas from a chemical reaction.

why do the isotopes of a particular element behave differently in nuclear reactions but the same in chemical reactions? chemical reactions involve changes to electrons in an atom; isotopes do not differ in electrons, and so they react the same way during chemical changes.