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A. Periodic Boxes
Three pieces of information are identified in each box:
Atomic number
Atomic symbol
Average atomic mass
B. Atomic Number- the number of protons in the nucleus of an atom
1. An element consists of atoms that have the same number of protons, therefore the same
atomic number.
Ex. C = 6, Sn = 50, Au = 79
2. isotopes- atoms of the same element that have different atomic masses
a. their nuclei have a different number of neutrons
b. there is no difference in chemical properties
c. nuclide- each variety of an atom based on mass when compared to another atom
Ex. hydrogen-1, hydrogen-2, hydrogen-3
carbon-12, carbon-14
C. Mass
1. average atomic mass- the result of average the presence of all isotopic forms of an element
2. amu (atomic mass units)- based on the carbon-12 = 12 scale, arbitrary assignment of value
3. mass number- the whole number obtained from rounding the average atomic mass; used for
counting particles; a proton = 1, a neutron = 1, an electron = 0.
D. Calculating Average Atomic Mass
If lithium-6 = 6.015 amu at 7.42% abundance and lithium-7 = 7.016 amu at 92.58%, what is the
average atomic mass?
6.015(.0742) + 7.016(.9258) = 6.941 amu for lithium atoms
The average atomic mass of boron is 10.81 amu. If the smaller abundance is boron-10 at 10.013
amu and the other isotope is boron-11 at 11.009, what are the percentages of each?
E. Subatomic Particles
1. For atoms, # protons = # electrons
2. Atomic number = # protons = # electrons
3. Mass number = # protons + # neutrons, so # neutrons = mass number - # protons
Identify the # protons, # electrons, mass number, and # neutrons for the following elements:
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