The Chemical Context of Life Chapter 2: The Chemical Context of Life

Chemical Context of Life Matter (has volume & mass) Element; compound The atom Atomic number (proton #); mass number (protons + neutron) Isotopes (different # of neutrons); radioactive isotopes (nuclear decay) Energy (ability to do work); energy levels (electron states of potential energy)

Chemical Bonding Covalent Double covalent Nonpolar covalent Ionic Hydrogen van der Waals

Covalent Bonding Sharing pair of valence electrons Number of electrons needed to complete an atom’s valence shell determines how many bonds will form Ex: Hydrogen & oxygen bonding in water; methane

Polar/nonpolar covalent bonds Electronegativity: attraction for electrons Nonpolar covalent electrons shared equally Ex: diatomic H (H2) and O (O2) Polar covalent 1 atom more electronegative than other(s) Creates partial charges Ex: water

Polar/nonpolar bonds

Ionic bonding High electronegativity difference strips valence electrons away from another atom Electron transfer creates ions (charged atoms) Cation (positive ion); anion (negative ion) Ex: Salts (sodium chloride)

Hydrogen bonds H atom is covalently bonded to 1 electronegative atom (N,O,F) It is also attracted to an electronegative atom (N, O, F) on a separate molecule Is not a real bond, is an intermolecular attraction (weaker than bond)

van der Waals interactions Weak interactions between molecules or parts of molecules Due to localized charge fluctuations Caused by electrons constant motion At any given instant, ever-changing “hot spots” of negative or positive charge may develop from electron’s locations