Biology Chapter 2: The Chemical Basis of Life

Chemical Fundamentals

• Elements are fundamental substances, over 100 known, with 92 naturally occurring; indivisible by chemical reactions.
• Matter possesses mass and occupies physical space.
• Mass is a property indicating weight in a gravitational field.

Atoms and Subatomic Particles

• Atoms are the smallest units of matter retaining element properties.
• Protons have a positive charge, neutrons are neutral, and electrons have a negative charge.
• The atomic nucleus consists of protons and neutrons tightly bound together.
• Atomic number indicates the number of protons, unique to each element; affects chemical behavior.
• Mass number is the total of protons and neutrons in an atom’s nucleus.

Isotopes and Radioisotopes

• Isotopes are variants of elements differing in neutron count but having the same proton count.
• Radioisotopes possess unstable nuclei that decay radioactively.

Energy Concepts

• Energy is the capacity to instigate change. Kinetic energy relates to an object's motion.

Electron Configuration

• Electrons occupy various shells with energy levels increasing further from the nucleus.
• Valence electrons, found on the outermost shell, dictate an atom's chemical behavior.

Chemical Bonds

• Various types of chemical bonds include:
  • Covalent bonds, involving shared valence electrons, are strong.
  • Ionic bonds occur when one atom strips an electron from another, forming charged ions.
  • Hydrogen bonds are weak, noncovalent attractions among hydrogen and electronegative atoms.
  • Van der Waals interactions occur due to transient charge distributions among atoms.

Bonding Structures

• Molecules consist of atoms bound by covalent bonds, represented in Lewis dot structures and molecular formulas.
• Structural formulas illustrate the arrangement of atoms, showing single, double, and triple bonds.

Electronegativity and Polarity

• Electronegativity measures an atom’s affinity for electrons in a bond; affects bond type.
• Polar covalent bonds arise from unequal sharing of electrons, while nonpolar covalent bonds involve equal sharing.

Ions and Compounds

• Ions are charged atoms; cations carry a positive charge, while anions carry a negative charge.
• Salts, formed through ionic bonds, are also known as ionic compounds.

Chemical Reactions

• Reactants undergo change in reactions to form products, maintaining chemical equilibrium when concentrations stabilize.

Biochemical Elements

• Four elements (Oxygen, Carbon, Hydrogen, Nitrogen) constitute 96% of living matter.
• Essential elements, about 20-25 of the 92 known elements, support life and reproduction.
• The most abundant atom in the universe is Hydrogen, characterized by one proton and one electron.

Human Body Composition

• Elements comprising the human body: Oxygen (65%), Carbon (~20%), Hydrogen (~10%), Nitrogen (~3%), Calcium (~2%), Phosphorus (~1%).