Structure of the Nucleus

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Average Atomic Mass & % Abundance

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Presentation transcript:

Structure of the Nucleus The same element could have atoms with different masses, which he called isotopes. There are two isotopes of chlorine found in nature, one that has a mass of about 35 amu and another that weighs about 37 amu. The observed mass is a weighted average of the weights of all the naturally occurring atoms. The atomic mass of chlorine is 35.45 amu. Tro's "Introductory Chemistry", Chapter 4

Tro's "Introductory Chemistry", Chapter 4 Isotopes All isotopes of an element are chemically identical. Undergo the exact same chemical reactions. All isotopes of an element have the same number of protons. Isotopes of an element have different masses. Isotopes of an element have different numbers of neutrons. Isotopes are identified by their mass numbers. Protons + neutrons. Tro's "Introductory Chemistry", Chapter 4

Isotopes, Continued Atomic Number. Mass Number Number of protons. Z Mass Number = Protons + Neutrons. Whole number. A Percent natural abundance = Relative amount found in a sample.

Tro's "Introductory Chemistry", Chapter 4 Neon 9.25% 22 12 10 Ne-22 or 0.27% 21 11 Ne-21 or 90.48% 20 Ne-20 or Percent natural abundance A, mass number Number of neutrons Number of protons Symbol Tro's "Introductory Chemistry", Chapter 4

Tro's "Introductory Chemistry", Chapter 4 Isotopes Cl-35 makes up about 75% of chlorine atoms in nature, and Cl-37 makes up the remaining 25%. The average atomic mass of Cl is 35.45 amu. Cl-35 has a mass number = 35, 17 protons and 18 neutrons (35 - 17). Cl 35 17 Atomic symbol A = Mass number Z = Atomic number AX Z = X-A Tro's "Introductory Chemistry", Chapter 4

Practice—Complete the Following Table. Tro's "Introductory Chemistry", Chapter 4

Mass Number Is Not the Same as Atomic Mass The atomic mass is an experimental number determined from all naturally occurring isotopes. The mass number refers to the number of protons + neutrons in one isotope. Natural or man-made. Tro's "Introductory Chemistry", Chapter 4

Example 4. 9─Ga-69 with Mass 68. 9256 Amu and Abundance of 60 Example 4.9─Ga-69 with Mass 68.9256 Amu and Abundance of 60.11% and Ga-71 with Mass 70.9247 Amu and Abundance of 39.89%. Calculate the Atomic Mass of Gallium.

Tro's "Introductory Chemistry", Chapter 4 Practice—If Copper Is 69.17% Cu-63 with a Mass of 62.9396 Amu and the Rest Cu-65 with a Mass of 64.9278 Amu, Find Copper’s Atomic Mass. Tro's "Introductory Chemistry", Chapter 4