Chemistry 4.3 Notes Distinguishing Among Atoms. What we know… Pg. 110 – Atoms are composed of...
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Transcript of Chemistry 4.3 Notes Distinguishing Among Atoms. What we know… Pg. 110 – Atoms are composed of...
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 nucleus2. Above symbol on P.T.3. Atoms differ from each other due to the number of protons.4. Ex: Hydrogen 1 proton5. Ex: Oxygen 8 protons
6. He Be
Ne Mo
Pb Sn Ba
Atomic Number
2
4
10
42
82
50
56
II. Mass NumberA. 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 + neutrons3. Ex: Na 234. Ex: Al 27
5. B Li Rn Cr Ti Zn
Mass Number
11
7
222
52
48
65
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 SymbolAtomic Number
Protons NeutronsMass
NumberElectrons
Scandium
Copper
Krypton
Neon
Phosphorus
Gallium
Manganese
Name SymbolAtomic Number
Protons NeutronsMass
NumberElectrons
Scandium Sc 21 21 24 45 21
Copper Cu 29 29 35 64 29
Krypton Kr 36 36 48 84 36
Neon Ne 10 10 10 20 10
Phosphorus P 15 15 16 31 15
Gallium Ga 31 31 39 70 31
Manganese Mn 25 25 30 55 25
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 NeonNe-20
Ne-21
Ne-22
7. Draw the 2 isotopes of Chlorine (35 and 37)
IV. Atomic MassA. Def – a weighted average of all the isotopes in a sample
of a given element.1. reflects mass2. reflects relative abundance
B. Atomic Mass Unit1. Def – 1/12th of a carbon-12 atom2. Prevents using scientific notation
ex: 3.155 x 10-22 g = fluorine3. Why is the atomic mass not a whole number?
isotopes4. 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 99.99% 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