Anatomy & Physiology I and II

Anatomy & Physiology Study Guide • Other atom—the electron acceptor—gains those same electrons and becomes an anion, with a negative (−) charge • Attraction between the opposite charges draws the two ions together Covalent Bonds Some atoms fill their outer electron shells by sharing electrons, instead of losing or gaining electrons. This sharing creates covalent bonds between the atoms involved. The sharing of one pair of electrons creates a single covalent bond. The sharing of two pairs of electrons creates a double covalent bond. The sharing of three pairs of electrons creates a triple covalent bond. Single Covalent Bond Double Covalent Bond Hydrogen gas ( H − H ): Two atoms of hydrogen each share their solitary electron in a single covalent bond. Oxygen gas ( O = O ): An atom of oxygen has 6 electrons in its valence shell; thus, two more would make it stable. Two atoms of oxygen achieve stability by sharing two pairs of electrons in a double covalent bond. Triple Covalent Bond Nitrogen (N ≡ N) : An atom of nitrogen has 5 electrons in its valence shell; thus, three more would make it stable. Two atoms of nitrogen achieve stability by sharing three pairs of electrons in a triple covalent bond. Covalent bonds usually form molecules in which the outer energy levels of the atoms involved are complete. A free radical is an ion or molecule with unpaired electrons in its outermost shell or energy level. Free radicals are highly reactive. Almost as fast as it forms, a free radical enters additional reactions that are typically destructive. For example, free radicals can damage or destroy vital compounds, such as proteins. Evidence suggests that the cumulative damage produced by free radicals inside and outside our cells is a major factor in the aging process.

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