Living organisms are composed of the same set of chemical elements as the rest of the universe. An atom consists of a nucleus of protons and neutrons and a characteristic configuration of electrons in orbitals around the nucleus. An atom’s chemical properties are determined by its atomic structure.
learning outcomes
You should be able to:
Compare the elements found in living tissue with elements found in nonliving matter.
Explain the role that the outermost electron shell plays in determining how an atom may combine with other atoms.
Explain how elements can be grouped according to their chemical properties in a periodic fashion.
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Describe how the configuration of the valence shell influences the placement of an element in the periodic table.
Elements with the same number of valence electrons are placed in the same vertical groups in the periodic table. For example, the electrons in sodium occupy the following shells (in order from the nucleus outward): 1s2, 2s2, 2p6, 3s1. Having one electron in the valence shell places sodium in Group 1. Lithium and potassium, which likewise have one electron in the valence shell, are in Group 1 as well.
How does bonding help a reactive atom achieve stability?
An atom is stable when its eight electrons occupy its outermost shell (with the exception of hydrogen, which is stable with two electrons). In bonding, atoms either share electrons with, or donate to or receive electrons from, another atom to achieve stability.
Would you expect the elemental composition of Earth’s crust to be the same as that of the human body? Explain your answer.
The human body has the same elemental composition as Earth’s crust but in very different proportions.
You have been introduced to the individual players on the biochemical stage—