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the mass of cobalt-60 in a sample decreased from 0.800g to 0.200g over a period of 10.5 years. from this information, calculate the half-life of cobalt-60.

The half-life of cobalt-60 in this sample is 5.25 years.

Explanation:

Step One: How many half-live(s) in 10.5 years?

The mass of a radioactive element drop by one-half every half-life. This mass will drop by another one-half after another half-life, and so on so forth. In other words,

.

For this sample:

.

Referring to the table, two half-lives have elapsed before the mass drop to 0.200 grams. There are two half-lives in 10.5 years.

Step Two: What's the length of each half-life?

There are two half-lives in 10.5 years. The length of each half-life will be

.

Alternative approach to step one: find the number of half-live(s) in 10.5 years with a scientific calculator.

In case the ratio between current mass and initial mass is between two entries, the tabular approach will no longer work. The number of half-lives in the 10.5 years can still be found using logarithm.

.

For this question,

.

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

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~ trueboss72