Presentation on theme: "Section 4.3 How Atoms Differ. Objectives Explain the role of atomic number in determining the identity of an atom Define an isotope and explain why atomic."— Presentation transcript:
Objectives Explain the role of atomic number in determining the identity of an atom Define an isotope and explain why atomic masses are not whole numbers Calculate the number of electrons, protons, and neutrons in an atom given its mass number and atomic number
Atomic Number References the number of protons in the nucleus of an atom of a particular element Every element has a unique atomic number Atomic Number = # of protons = # of electrons IN A NEUTRAL ATOM!!!
Mass of the Atom Expressed in the atomic mass unit (amu) 1 amu = 1.66054 x 10 -24 g 1 g = 6.02214 x 10 23 amu
Atomic Weight Determined by average atomic masses of the isotopes of an element Atomic Weight = Sum of multiplying the abundance of each isotope by its atomic mass
Isotopes: There are 23 known isotopes of krypton, 6 stable and 17 unstable. Natural krypton contains the 6 stable isotopes.
Atomic Weight Problem Naturally occurring chlorine is 75.78% 35 Cl, which has an atomic mass of 34.969 amu, and 24.22% 37 Cl, which has an atomic mass of 36.966 amu. Calculate the average atomic weight of chlorine.