zChapter 2: The Chemical Context of Life

Chemical Context of Life zMatter (space & mass) zElement zCompound zThe atom zAtomic number (# of protons); mass number (protons + neutrons) zIsotopes (different # of neutrons); radioactive isotopes (nuclear decay) zEnergy (ability to do work); energy levels (electron states of potential energy)

Chemical Bonding zCovalent zDouble covalent zNonpolar covalent zPolar covalent zIonic zHydrogen zvan der Waals

Covalent Bonding zSharing pair of valence electrons zNumber of electrons required to complete an atom’s valence shell determines how many bonds will form zEx: Hydrogen & oxygen bonding in water; methane

Covalent bonding

Polar/nonpolar covalent bonds zElectronegativity attraction for electrons zNonpolar covalent electrons shared equally Ex: diatomic H and O zPolar covalent one atom more electronegative than the other (charged) Ex: water

Polar/nonpolar bonds

Ionic bonding zHigh electronegativity difference strips valence electrons away from another atom zElectron transfer creates ions (charged atoms) zCation (positive ion); anion (negative ion) zEx: Salts (sodium chloride)

Ionic bonds

Hydrogen bonds zHydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom (oxygen or nitrogen)

Hydrogen bonds

van der Waals interactions zWeak interactions between molecules or parts of molecules that are brought about by localized change fluctuations zDue to the fact that electrons are constantly in motion and at any given instant, ever-changing “hot spots” of negative or positive charge may develop

van der Waals interactions