BIO 301M - Lecture 1: Chapters 2 & 4: carbon and the...

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Lecture 1: Chapters 2 & 4: carbon and the molecular diversity of life Concept 2.3: The formation and function of molecules depend on chemical bonding between atoms Covalent Bonds A covalent bond is the sharing of a pair of valence electrons by two atoms In a covalent bond, the shared electrons count as part of each atom’s valence shell A molecule consists of two or more atoms held together by covalent bonds A single covalent bond, or single bond , is the sharing of one pair of valence electrons A double covalent bond, or double bond , is the sharing of two pairs of valence electrons Figure 2.11 Formation of a covalent bond The notation used to represent atoms and bonding is called structural formula For example, H–H This can be abbreviated further with a molecular formula For example, H 2 Figure 2.12 Covalent bonding in four molecules Covalent bonds can form between atoms of the same element or atoms of different elements A compound is a combination of two or more different elements Bonding capacity is called the atom’s valence Electronegativity is an atom’s attraction for the electrons in a covalent bond The more electronegative an atom, the more strongly it pulls shared electrons toward itself In a nonpolar covalent bond , the atoms share the electron equally In a polar covalent bond , one atom is more electronegative, and the atoms do not share the electron equally Unequal sharing of electrons causes a partial positive or negative charge for each atom or molecule Figure 2.13 Polar covalent bonds in a water molecule Ionic Bonds Atoms sometimes strip electrons from their bonding partners
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An example is the transfer of an electron from sodium to chlorine After the transfer of an electron, both atoms have charges A charged atom (or molecule) is called an ion Figure 2.14 Electron transfer and ionic bonding A cation is a positively charged ion An anion is a negatively charged ion
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BIO 301M - Lecture 1: Chapters 2 & 4: carbon and the...

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