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Why is the atomic mass of carbon not listed as 12 on the periodic table if the universal standard is that \({ }_{6}^{12} \mathrm{C}\) has an atomic mass of exactly 12 amu?

Bromine exists as only two isotopes in nature, \({ }_{35}^{79} \mathrm{Br}\) (atomic mass \(78.918336\) amu, \% natural abundance \(=50.69 \%\) and \({ }_{35}^{81}\) Br (atomic mass \(80.916289\) amu). (a) What is the percent natural abundance for \({ }_{35}^{81} \mathrm{Br}\) ? (b) Calculate the atomic mass of the naturally occurring mixture of isotopes.

Naturally occurring hydrogen on Earth has an atomic mass of \(1.0079\) amu. Suppose you were on another planet and found the atomic mass of hydrogen to be \(1.2000\) amu. How would you explain this? (The atomic mass of \({ }_{1}^{1} \mathrm{H}\) is \(1.0078252\) amu; the atomic mass of \({ }_{1}^{2} \mathrm{H}\) is \(2.1041022\) amu.)

While an atom's mass number and its atomic mass are not the same, they are often quite close to one another. Consider the following: Uranium- 235 has an atomic mass of \(235.04393\) amu and a percent abundance of \(0.73 \%\). Uranium-238 has an atomic mass of \(238.0508\) amu and a percent abundance of \(99.27 \%\). Without doing any calculations or consulting any other sources, which of the following do you think represents the atomic mass of naturally occurring uranium? (a) \(234.04 \mathrm{amu}\) (b) \(236.03 \mathrm{amu}\) (c) \(237.03\) amu (d) \(238.03\) amu (e) \(238.07\) amu Explain how you made your choice.

(a) In what unique way did Mendeleev order the elements to make his discovery? (b) What was his discovery? (c) How does his ordering differ from the modern ordering?

How did Mendeleev's discovery aid in discovering additional elements?

If one considers just the representative elements, how many groups would the periodic table have?

Give the names associated with groups IA (1), IIA (2), VIA (16), VIIA (17), and VIIIA (18).

How does a group differ from a period in the periodic table?

Suppose you added one electron and one proton to an atom somewhere in the middle of a period. Which way would this move you on the periodic table and by how many places?