Covalent Bonds and Water's Biological Importance

Single Covalent Bond

Two electrons shared between two atoms.

Double Covalent Bond

More than two electrons shared between two atoms.

Triple Covalent Bond

Even more electrons shared between two atoms.

Molecule

Defined as two or more atoms held together by Covalent Bonds.

Compound

Requires two or more different elements in a defined ratio.

Electronegativity

A measure of how strongly an atomic nucleus attracts and holds onto electrons.

Nonpolar Covalent Bonds

Formed when electrons are shared equally between two atoms of the same type.

Polar Covalent Bonds

Formed when electrons are shared unequally between two different atoms.

Weak Bonds

Result from electrostatic attractions between two atoms.

Hydrogen Bonds

Form when a H covalently bonded to one electronegative atom is attracted to another nearby electronegative atom.

Ionic Bonds

Formed when the electronegativity difference is so large that it pulls electrons from the outer shell.

Salts

Compounds formed by Ionic Bonds.

NaCl

A compound that is not a molecule, formed by ionic bonds.

Ionic bond strength

Depends on conditions; strong in dry conditions and weak in wet conditions.

van der Waals Interactions

Weak interactions that occur between molecules with nonpolar bonds at extremely close range.

Setae

Microscopic 'hairs' on gecko toes that bind to surfaces via van der Waals interactions.

Water

Essential for life; organisms are composed mostly of water (65-75%).

Aqueous Chemistry

Refers to the chemistry of living organisms that is primarily based in water.

Aqueous Chemistry

Chemistry that involves water as a solvent.

Polarity

The property of a molecule having partial positive and negative charges due to unequal sharing of electrons.

Hydrogen Bonds

Weak attractions between a hydrogen atom and an electronegative atom, allowing each water molecule to bond with up to 4 other water molecules.

Adhesion

The tendency of water molecules to stick to other substances.

Cohesion

The tendency of water molecules to stick to each other.

Specific Heat

The amount of energy required to raise the temperature of a substance.

Heat of Vaporization

The energy required to convert water from liquid to vapor.

Evaporative Cooling

The process where the energy needed to convert water from liquid to vapor transfers heat from the body to the air.

Density of Water

Solid H2O (ice) is less dense than liquid H2O, allowing ice to float.

Hydrophilic

Substances that are attracted to water and can dissolve in it.

Hydration Shell

The layer of water molecules that surrounds and interacts with solute particles.

Dissociation of Water

The rare process where water molecules split into H3O+ and OH- ions.

Mole

The mass in grams of the combined atomic masses of elements in a molecule; for water, 1 mole is 18 grams.

Concentration of Water

Pure [H2O] = 55.5 M (moles/liter).

Acid

A substance that increases the relative concentration of H+ in a solution.

Base

A substance that decreases the relative concentration of H+ in a solution.

pH Scale

A scale that expresses the acidity or alkalinity of a solution, ranging from 0 to 14.

Neutral Solution

A solution with a pH of 7.0.

Acidic Solution

A solution with a pH less than 7.0.

Basic Solution

A solution with a pH greater than 7.0.

Logarithmic Scale

A scale where each point represents a tenfold difference in concentration.

Sensitivity to pH Changes

Cells are sensitive to changes in [H+] because it can alter the ionization state of macromolecules, affecting their charge, structure, and function.

Carbon

Organisms on Earth are composed of molecules based largely on carbon.

Organic Chemistry

Carbon-Based Chemistry.

The Element Carbon

Elements are defined by the number of protons in the nucleus.

Carbon Protons and Electrons

Carbon has 6 protons (and 6 electrons).

Carbon Neutrons

Most common form has 6 neutrons.

Carbon Valence Electrons

4 electrons in outer (valence) shell.

Stability of Carbon

Carbon becomes very stable in a molecule by sharing 4 electrons.

Structure of Carbon

In a molecule, carbon is the center of an intersection with 4 branches.

Carbon-Based Molecules

Carbon can share one or more electrons with other carbons as well as with other elements.

Covalent Bonds

Carbon can form single, double, or triple covalent bonds.

Molecular Shape and Function

The type of bond determines molecular shape and function.

Hydrocarbons

Molecules consisting of ONLY Hydrogens and Carbons.

Properties of Hydrocarbons

All covalent bonds in a hydrocarbon are nonpolar.

Chemical Inertness of Hydrocarbons

Relatively chemically inert (Unreactive).

Solubility of Hydrocarbons

Relatively insoluble in aqueous solutions.

Isomers

Molecules with the same molecular formulae but with distinct arrangements of the atoms.

Structural Isomers

Differ in the covalent arrangement of atoms.

Geometric Isomers

Differ in the arrangement of groups across a C=C.

Enantiomers

Mirror-image isomer molecules.

Asymmetric Carbon

An asymmetric carbon forms covalent bonds with 4 different groups.

Pharmacological Importance of Enantiomers

Enantiomers can have different effects, as seen with drugs like Thalidomide.

Functional Groups

Small organic chemical groups that can substitute for one or more hydrogens in a hydrocarbon.

Effects of Functional Groups

Their presence increases the structural and functional diversity of the organic molecules.

Reactivity of Functional Groups

Make hydrocarbons more polar, soluble, and reactive.