1. 1.1 The Nature of Atoms Learning Goals...... determine the number of protons, electrons and neutrons in an atom or ion... distinguish between a cation and an anion... calculate the isotopic abundance of an isotope

2. The Modern Atomic Theory

3. If an atom loses or gains electrons it is no longer called an atom. It is called an ion. An ion has a full outer shell of electrons. An ion has an electric charge. All chemical reactions involve atoms trying to get a full outer shell of electrons. (the OCTET rule) When an atom reacts with another atom, it will either 1. Lose electrons to form a stable positive ion (called a CATION). 2. Gain electrons to form a stable negative ion (called an ANION). or 3. Share electrons to form a stable molecule.

4. _________ protons ________ neutrons ________ electrons _________ protons ________ neutrons ________ electrons _________ protons ________ neutrons ________ electrons 14 7 80 35 40 20 Indicate the number of protons, neutrons, and electrons for each atom or ion Br Ca N 2+ Recall: Atomic number = # of protons Atomic Mass = protons + neutrons electrons = protons (in a neutral atom) positive ion has lost electrons negative ion has gained electrons

5. · Isotopes are atoms with the same number of protons and electrons, but have a different number of neutrons. · They are still the same element. Ex) The normal Lithium atom is lithium-7. It has 4 neutrons. There are a few Lithium atoms that don't have 4. Those atoms may have 3 or 5 neutrons. Li-6 and Li-8 are considered an isotope of the element lithium. Isotopes

6. Cl 35 17 Cl 37 17 _________ protons _________ neutrons _________ electrons _________ protons _________ neutrons _________ electrons Indicate the number of protons, neutrons, and electrons for each isotope.

7. ISOTOPIC ABUNDANCE - the relative amount in which each isotope is present in an element AVERAGE ATOMIC MASS -the average of the masses of all the element’s isotopes -this is the mass found on the periodic table Calculating Average Atomic Mass Ex) Naturally occurring silver has two isotopes. Calculate the average atomic mass of silver if 47 Ag 107 has a mass of 106.9u and a relative abundance of 51.8% and 47 Ag 109 has a mass of 108.9u and a relative abundance of 48.2%. Average atomic mass =(106.9u)(0.518) + (108.9u)(0.482) = 107.9u

8. Calculating Isotopic Abundance Ex)Boron exists as two naturally occurring isotopes: 5 B 10 (10.01u) and 5 B 11 (11.01u). Calculate the relative abundance of each isotope. Note: you know your %’s need to add up to 100%. As a decimal they need to add up to 1) Let x represent the abundance of boron-10 and let y represent the abundance of boron-11. (10.01)(x) + (11.01) = We can get the average atomic mass from the periodic table M = 10.81u 10.01x + 11.01- 11.01x = 10.81 10.01x -11.01x = 10.81 - 11.01 -x = - 0.20 x = 0.20 20% boron-10 80% boron-11 x+y = 1 y = 1- x 1- x 10.81 (y) (1-x)

9. HOMEWORK WS "Atomic Structure" WS "Calculating Relative Abundance of Isotopes" Can I...... determine the number of protons, electrons and neutrons in an atom or ion... distinguish between a cation and an anion... calculate the isotopic abundance of an isotope