The Chemical Level of Organization Flashcards
Chemistry
is the foundation of all living organisms. All basic physiological processes of life take place at the chemical level.
Chemical Bonds
Reactive atoms, such as hydrogen and oxygen, become more stable by gaining, losing or sharing electrons to fill their outer energy levels. Interaction between the outer electrons of two atoms forms a chemical bond which holds the atoms together.
Chemical bonds can be strong or weak. Two or more atoms joined together with strong bonds are molecules. A compound is two or more elements joined together by any chemical bond, strong or weak.
The chemical activity of a molecule or compound is different from that of the individual atoms.
There are 3 basic types of chemical bonds: ionic, covalent and hydrogen.
Ionic bonds
form between atoms with opposite electrical charges (ions).
An atom that loses electrons (electron donor) has a net positive charge, and is called a cation.
An atom that gains electrons (electron acceptor) has a net negative charge, and is an anion.
Table salt (sodium chloride) is an example of an ionic compound.
The sodium atom (Na) has only 1 electron in its outer energy level, which is easily lost, resulting in a positive sodium ion (Na+).
Chlorine (Cl) has 7 electrons in its outer level. Adding 1 electron forms a negative chloride ion (Cl-).
A sodium ion and a chloride ion join together in an ionic bond to form a neutral ionic compound, sodium chloride (NaCl).
Covalent bonds
occur when atoms share, rather than gain or lose electrons, forming molecules.
In covalent bonding, each atom contributes the same number of electrons to the bond, called electron pairs.
A single covalent bond shares 1 electron pair, signified in chemical notation by a single line (–).
A double covalent bond shares 2 electron pairs, indicated by a double line (==).
Carbon dioxide has 2 double covalent bonds.
Within one molecule, atoms can share electrons equally or unequally, creating molecules of different shapes.
Molecules that share electrons equally (such as oxygen, O2) have symmetrical shapes, and a uniform electrical charge over the surface of the molecule. This is called a nonpolar covalent bond.
Molecules that share electrons unequally (such as water, H2O) have an asymmetrical shape, polarizing the positive and negative charge around the molecule like a magnet. Although the water molecule is neutral overall, the hydrogen side of the molecule is more positive and the oxygen side is more negative.
Because water is a polar molecule, it interacts chemically with both positive and negative ions, dissolving ionic compounds such as NaCl.
Hydrogen bonds
are weak attractions between the positive, hydrogen side of one polar molecule and the negative side of another polar molecule. Hydrogen bonds influence the shape of larger molecules, which is important to molecules such as proteins and DNA.
Hydrogen bonds between water molecules cause surface tension, which repels small particles.
States of Matter
Molecules can exist in any of 3 states of matter, from less random to more random:
solids have constant shape and volume
liquids have constant volume but change shape easily
gases change shape and volume freely
Matter changes states with changes in temperature and pressure. For example, water changes from solid ice, to liquid, to gaseous water vapor.
Decomposition reactions
break larger molecules into smaller parts.
When chemical bonds are broken, energy is released. Catabolism is work done by cells using kinetic energy from decomposition reactions.
Hydrolysis
is a decomposition reaction in which bonds of large molecules are broken, and the components of water molecules (H+ and OH-) added to the ends of the fragments.
Hydrolysis is one of the reactions used in digestion.
Synthesis reactions
are the opposite of decomposition. Small molecules join together to form larger molecules.
Synthesis reactions require energy. Anabolism (opposite of catabolism) is the use of energy to synthesize molecules within the cell.
Dehydration Synthesis
(condensation) removes the water components (H+, OH-) from the ends of molecular fragments so they can join together, releasing water.
Exchange Reactions
are paired decomposition and synthesis reactions. The reactants exchange components to produce new products.
Reversible Reactions
Synthesis reactions can reverse to become decomposition reactions, and decomposition reactions can reverse to become synthesis reactions.
(*) Reversible reactions tend to reach an equilibrium in which the opposing reaction rates are balanced. If reactants are added or removed, reaction rates adjust until a new equilibrium is reached.
Water
Water is the most important molecule in the body. Water makes up 2/3 of our body weight; and is required for most chemical reactions and physiological functions.
(*) Most of our body weight is water. Water is the key structural and functional component of cells and their control mechanisms, the nucleic acids.
Water’s Properties
Water has some special properties resulting from its polar nature and hydrogen-bonding capabilities:
(1) solubility: A solution is a uniform distribution of one substance (the solute) in a medium (the solvent). Many organic and inorganic compounds dissolve in water (an aqueous solution).
(2) reactivity: In our bodies, most reactions either involve water (e.g. hydrolysis, condensation), or occur in water.
(3) high heat capacity: The ability to absorb and retain heat. Because water has a high heat capacity, it remains a liquid over a broad range of temperatures.
(4) lubrication: Friction between water molecules is low.
Universal Solvent
Water is called the universal solvent because of its ability to form aqueous solutions.
