LIFE 102 Lecture Notes - Lecture 2: Covalent Bond, Electronegativity
1/23/17
➔ 4 kinds of bonds:
◆ Covalent bonds: sharing of a pair of valence electrons by 2 atoms
● In a covalent bond, the shared electrons count as part of each atom’s
valence shell (like counting your own money and your spouse’s money
together)
● Carbon: 4, Nitrogen: 3, Oxygen: 2
● A molecule consists of 2 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
● 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
○ Deltas mean not an entire charge (positive or negative)
◆ Ionic bonds: where atoms sometimes strip electrons from their bonding partners
● Ex: the transfer of an electron from sodium to chlorine
● After the transfer, both have charges
● A charged atom (or molecule) is called an ion
◆ A hydrogen bond forms when a hydrogen atom covalently bonded to one
electronegative atom is also attracted to another electronegative atom
● In living cells, the electronegative partners are usually oxygen or nitrogen
● If electrons are distributed asymmetrically in molecules or atoms, they
result in “hot spots” of positive or negative charge
○ Van Der Waals interactions are attractions between molecules
that are close together as a result of these charges
◆ It’s actually the attraction of electrons in one atom toward
the nucleus of an adjacent molecule
(Biological molecules recognize and interact with each other with a specificity based on:
- Molecular shape
- Arrangement of positive and negative charges
Molecules with similar shapes and charge distributions can have similar biological effects)
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Document Summary
Covalent bonds: sharing of a pair of valence electrons by 2 atoms. In a covalent bond, the shared electrons count as part of each atom"s valence shell (like counting your own money and your spouse"s money together) A molecule consists of 2 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. 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. Deltas mean not an entire charge (positive or negative) Ionic bonds: where atoms sometimes strip electrons from their bonding partners. Ex: the transfer of an electron from sodium to chlorine. A charged atom (or molecule) is called an ion.
