1. Atomic Structure

2. Subatomic Particles In the nucleus: Protons Mass  1 amu Charge = +1 Neutrons Mass  1 amu Charge = 0 In the electron cloud: Electrons Mass  1 / 1836 amu Charge = -1

3. Subatomic Particles Nucleus Tiny, dense, positively charged Nucleus Tiny, dense, positively charged Electron Cloud Diffuse, negatively charged Electron Cloud Diffuse, negatively charged

4. Atomic Number (Z) Atomic Number (Z) – number of protons in the nucleus of an atom of that element Atomic number of oxygen = 8 All oxygen atoms have 8 protons. No other type of atom has 8 protons. Atomic number of titanium = 22 All titanium atoms have 22 protons. No other type of atom has 22 protons.

5. Mass Number (A) Mass Number (A) – combined number of protons and neutrons. A = protons + neutrons Number of neutrons = Mass Number (A) – Atomic Number (Z) What is the mass number of an atom that has 8 protons and 9 neutrons? ANSWER: 8 p + + 9 n 0 = 17 How many neutrons are in a titanium atom with a mass number of 48? ANSWER: A – Z = (48 – 22) = 26 neutrons

6. Atomic and Mass Numbers What are the atomic and mass numbers of the following atoms? = protons= neutrons Z = A = Z = A = Z = A = Z = A = 1 1 1 2 2 4 3 7

7. Isotopes Isotopes – have the same number of protons but diff. numbers of neutrons. Example: All carbon atoms have 6 protons. Some carbon atoms have 6 neutrons, and some have 7 neutrons. Some carbon atoms have A = 12, and some have A = 13.

8. Isotopes Three isotopes of oxygen: 8 p + 8 n 0 8 p + 9 n 0 8 p + 10 n 0 Oxygen - 17 O - 17 Oxygen - 18 O - 18 Oxygen - 16 O - 16 Z A

9. Average Atomic Mass Average Atomic Mass – weighted average mass of the atoms in a naturally occurring sample of the element The atomic mass given on the P.T. is a weighted average.

10. Average Atomic Mass of Neon Atomic Number Avg. Atomic Mass

11. Calculating Average Atomic Mass An artificial sample of carbon contains 80% C-12 and 20% C-13. What is the average atomic mass of the sample? First, convert the percentages to decimals. 80% = 0.80 20% = 0.20 Multiply the decimals by the masses: 0.80 x 12 = 9.6 0.20 x 13 = 2.6 Add the results: 9.6 + 2.6 = 12.2 amu

12. Calculating Average Atomic Masses A sample of iron contains 5.000% Fe-54 90.00% Fe-56 3.000% Fe-57 2.000% Fe-58 What is the average atomic mass of the sample? ANSWER: 55.97 amu