Distinguishing Among Atoms Chemistry 4.3 Notes Distinguishing Among Atoms

What we know… Pg. 110 – Atoms are composed of electrons, protons, and neutrons. Protons and neutrons make up the small, dense nucleus. Electrons surround the nucleus and occupy most of the volume of the atom. **How do atoms differ from each other then?

I. Atomic Number A. Def – the # of protons found in an atom. 1. Found in the nucleus 2. Above symbol on P.T. 3. Atoms differ from each other due to the number of protons. 4. Ex: Hydrogen  1 proton 5. Ex: Oxygen  8 protons

Atomic Number 2 4 10 42 82 50 56 6. He  Be  Ne  Mo  Pb  Sn  Ba 

II. Mass Number A. Def – the total # of neutrons and protons in the nucleus of an atom. 1. Found above chemical symbol on P.T. 2. Formula: Mass # = protons + neutrons 3. Ex: Na  23 4. Ex: Al  27

Mass Number 11 7 222 52 48 65 5. B  Li  Rn  Cr  Ti  Zn 

III. What about Electrons? A. **Assume electrons = the # of protons in an atom** 1. All atoms have a charge of zero 2. Complete the following table in your notes.

Name Symbol Atomic Number Protons Neutrons Mass Number Electrons Scandium Copper Krypton Neon Phosphorus Gallium Manganese

Name Symbol Atomic Number Protons Neutrons Mass Number Electrons Sc 21 Scandium Sc 21 24 45 Copper Cu 29 35 64 Krypton Kr 36 48 84 Neon Ne 10 20 Phosphorus P 15 16 31 Gallium Ga 39 70 Manganese Mn 25 30 55

W 76 128 45 41 57 150 Symbol Protons Electrons Neutrons Atomic # Mass # W 76 128 45 41 57 150

III. Isotopes A. Def – same atom but different # of neutrons. 1. This alters the mass # 2. Chemically the same 3. Ex: Hydrogen  3 isotopes = H-1, H-2, H-3

4. Drawing an isotope 1st put in # of protons 2nd use mass # to determine the # of neutrons 5. Draw the 3 isotopes of hydrogen

6. Draw the 3 isotopes of Neon

7. Draw the 2 isotopes of Chlorine (35 and 37)

IV. Atomic Mass A. Def – a weighted average of all the isotopes in a sample of a given element. 1. reflects mass 2. reflects relative abundance B. Atomic Mass Unit 1. Def – 1/12th of a carbon-12 atom 2. Prevents using scientific notation ex: 3.155 x 10-22 g = fluorine 3. Why is the atomic mass not a whole number? isotopes 4. There are isotopes for almost every element

5. Ex: Chlorine 35.453 2 isotopes (Cl-35 and Cl-37) What would the atomic mass be? 36.000 right? Wrong we need the relative abundance

6. Cl-35 has an abundance of 75.77%. Cl-37 has an abundance of 24.23%. 35 x .7577 = 26.52 37 x .2423 = 8.965  35.485

7. Hydrogen has 3 isotopes, H-1, H-2, H-3. H-1 occurs 99 7. Hydrogen has 3 isotopes, H-1, H-2, H-3. H-1 occurs 99.99% of the time, H-2 occurs 0.015% of the time, and H-3 is negligible (can only be made in the lab). What is the atomic mass?  1.030