Why do two isotopes of an element have the same atomic number but different mass numbers?

Who performed the oil-drop experiment?

A chemist dilutes 77.9 ml of 5.50 M sodium chloride to make a 1.93 M solution. What is the final volume of the diluted solution (in ml)

Which of there is an indication that a chemical reaction has occurred? a. freezing of substance b. a change in color of a substance c. melting of a substance d. boiling of a substance

How many neutrons does element ex have if it's atomic number is 58 and it's mass numbers 156

Consider the following reaction: Li3N (s) + 3H2O (l) → NH3 (g) + 3LiOH (l) If you need to make 24 g LiOH, how many grams of Li3N must you react with excess water?

Which would not be classified as a pure substance?

According to Boyle's law, how would you reduce the volume of a gas? a. by decreasing its pressure b. by increasing its temperature c. by decreasing its temperature d. by increasing its pressure

To what chemical reaction class does this reaction belong? 2 mg (s) + o2 (g) 2 mgo (s)

Which best illustrates how particle arrangement changes when solids change into liquids

Express in scientific notation (6.0x10^4) (3.1x10^-1)