Basic Chemistry for Biology

Subatomic Particles Proton Neutron Electron Nucleus Positive charge Identifies the atom (atomic #) Neutron No charge # can change (isotopes) Electron Electron cloud Negative charge # can change (ions)

Elements in Biology Element: pure substance that consists of only one kind of atom Six elements found in all living things: NCHOPS Nitrogen, Carbon, Hydrogen, Oxygen, Phosphorus, Sulfur The four major biomolecules in living things: Carbohydrates (CHO) – sugars/starches Lipids (CHO) – fats, waxes, steroids Proteins (NCHOS) – enzymes, structures Nucleic acids (NCHOP) – DNA/RNA

Energy Levels within an Atom

Chemical Bonds Hold two elements together (compound) Atoms want to fill their outer energy level when bonding Element Electrons 1st orbital 2nd orbital Valence e- Hydrogen 1 Carbon 6 Oxygen 8 Nitrogen 7

Chemical Bonds Chemical bond: force that holds atoms together Atoms react to form chemical bonds – WHY? Achieve stability (fill outer energy level – valence electrons) Satisfy the octet rule (full, stable outer energy level) Share electrons = covalent bond Transfer electrons = ionic bond About Hydrogen bonding…. It’s an attractive force BETWEEN molecules, NOT a real chemical bond. More on that later….

Ionic Bonds Transfer of electrons between a metal and a nonmetal Charged atoms = ions Positive (cation) or negative ions (anion) Attraction between ions = ionic bond Example: Sodium loses electron positive charge Chlorine  gains electron  negative charge Solid crystals at room temp Ex: NaCl = table salt

Covalent Bonds Electrons are SHARED between atoms to fill each atom’s outer energy level Weakest bond type (not counting H-bonds, of course) Can be any physical state at room temp

Covalent Bonds Involving Carbon Needs 4 electrons  makes 4 bonds

Methane Gas: CH4 Sharing 4 electrons =4 Covalent Bonds

Oxygen Gas: O2 Shares 2 sets (pairs) of electrons Double Bond

Water: H2O

Hydrogen Bond Weak attractive force between neighboring molecules A hydrogen of one molecule is “slightly +” and attracts the “slightly negative” side of another molecule (lone pairs of e-)

Hydrogen Bonding: Water

Van der Wals Weak attractive forces between molecules It’s a force… NOT a chemical bond Ex: Gecko’s feet and glass

Dissociation of Water Molecules Usually shortened to “H+ ion”

pH Scale Acid Neutral Base Forms H+ ions in water 1 to 6.9 Ex: Orange Juice, coffee pH of 1  strongest Neutral pH = 7 (pure water) # of H+ ions= # of OH- ions Base Forms OH- (hydroxide) in water 7.1 to 14 Ex: Ammonia, bleach FYI: pH = potential of Hydrogen ions

Buffer Solution that prevents drastic changes in pH Maintains homeostasis

Neutralization Reaction HCl + NaOH  H2O + NaCl Acid + Base  Water + Salt