General Biology Study Notes: Chemical Elements, Water, and Life

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Chapter 2: Chemical Elements and Compounds

Elements and Compounds

All matter consists of chemical elements in pure form and in combinations called compounds. Elements are substances that cannot be broken down into simpler substances by chemical means, while compounds are substances formed from two or more elements in fixed ratios.

Element: A pure substance consisting of only one type of atom (e.g., Oxygen, Carbon).
Compound: A substance formed when two or more elements combine chemically (e.g., Water (H2O)).
Emergent Properties: New characteristics that arise when elements combine to form compounds.
Example: Table salt (Sodium chloride, NaCl) has properties different from its constituent elements sodium and chlorine.

Structure of Atoms

An atom is the smallest unit of an element, composed of subatomic particles: protons, neutrons, and electrons. The arrangement and number of these particles determine the atom's properties.

Subatomic Particles: Protons (+), Neutrons (0), Electrons (-).
Atomic Number: Number of protons in the nucleus; defines the element.
Atomic Mass: Sum of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons.
Energy Levels: Electrons occupy specific energy levels or shells around the nucleus.
Electron Distribution: Determines chemical reactivity and bonding.
Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Formation and Function of Molecules

Molecules are formed when atoms bond together through chemical bonds. The type of bond affects the molecule's properties and function.

Covalent Bonds: Atoms share electrons (e.g., H2O).
Ionic Bonds: Atoms transfer electrons, resulting in charged ions (e.g., NaCl).
Weak Chemical Bonds: Hydrogen bonds and van der Waals interactions; important for biological molecules.
Molecular Shape: Determines function; three-dimensional structure is crucial in biology.
Example: The double helix structure of DNA is stabilized by hydrogen bonds.

Chemical Reactions

Chemical reactions involve the making and breaking of chemical bonds, resulting in the transformation of substances.

Reactants: Starting materials in a reaction.
Products: Substances formed from the reaction.
Example: Photosynthesis:

Chapter 3: Water and Life

Polar Covalent Bonds in Water

Water molecules have polar covalent bonds, resulting in a partial positive charge on hydrogen and a partial negative charge on oxygen. This polarity leads to hydrogen bonding between water molecules.

Polarity: Unequal sharing of electrons creates partial charges.
Hydrogen Bond: Weak attraction between the hydrogen atom of one water molecule and the oxygen atom of another.
Example: Water's high surface tension is due to hydrogen bonding.

Emergent Properties of Water

Water exhibits several properties that make it essential for life, including cohesion, moderation of temperature, and its role as a solvent.

Cohesion: Water molecules stick together due to hydrogen bonding.
Adhesion: Water molecules stick to other surfaces.
Surface Tension: Cohesion at the surface of water creates a "skin".
Moderation of Temperature: Water has a high specific heat, allowing it to absorb and release heat slowly.
Evaporative Cooling: As water evaporates, it removes heat, cooling surfaces.
Floating of Ice: Ice is less dense than liquid water, so it floats.
Solvent of Life: Water dissolves many substances, facilitating chemical reactions.
Example: Water dissolves salts and sugars, enabling transport in living organisms.

Acidic and Basic Conditions

Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH-), affecting pH. Acids increase H+ concentration, while bases decrease it.

Acid: Substance that increases H+ concentration.
Base: Substance that decreases H+ concentration.
pH Scale: Measures acidity or basicity; ranges from 0 (acidic) to 14 (basic).
Buffer: Substance that minimizes changes in pH.
Example: Blood contains buffers to maintain pH near 7.4.

Table: Comparison of Acidic and Basic Solutions

Property	Acidic Solution	Basic Solution
pH	< 7	> 7
H+ Concentration	High	Low
OH- Concentration	Low	High
Example	Lemon juice	Ammonia solution

Key Equations

Photosynthesis:
pH Calculation:

Additional info:

Emergent properties of water include its role in temperature regulation, solvent capabilities, and support of life processes.
Isotopes are used in medicine and research, such as radioactive tracers.
Buffers are crucial in maintaining homeostasis in biological systems.