Atoms, Chemical Bonds, Water Properties, and Buffers: General Biology Study Guide

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Atoms and Atomic Structure

Key Terms and Definitions

Understanding the structure of atoms is fundamental to biology, as atoms form the basis of all matter.

Atom: The smallest unit of an element that retains the properties of that element.
Element: A substance consisting of only one type of atom.
Atomic Number: The number of protons in the nucleus of an atom; determines the element.
Isotopes: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.
Nucleus: The center of the atom, containing protons and neutrons.
Proton: Positively charged subatomic particle found in the nucleus.
Neutron: Electrically neutral subatomic particle found in the nucleus.
Electron: Negatively charged subatomic particle located outside the nucleus.
Chemical Symbol: Shorthand way of representing an element (e.g., C for carbon).

Example: Carbon-12 (12C) has 6 protons, 6 neutrons, and 6 electrons.

Comparing Atoms and Isotopes

Atoms with the same atomic number but different atomic masses are called isotopes.
Isotopes of an element have the same number of protons but different numbers of neutrons.

Example: Cobalt-60 (60Co) is a radioactive isotope of cobalt. When it decays, a neutron becomes a proton and an electron, changing the element.

Subatomic Particles Table

The following table summarizes the number of protons, neutrons, and electrons in neutral atoms of common elements:

Element	Protons	Neutrons	Electrons
Carbon-12 or 12C	6	6	6
Hydrogen-1 or 1H	1	0	1
Oxygen-16 or 16O	8	8	8
Nitrogen-14 or 14N	7	7	7
Phosphorus-31 or 31P	15	16	15
Sulfur-32 or 32S	16	16	16

Chemical Bonds

Types of Chemical Bonds

Atoms combine to form molecules through chemical bonds, which are essential for the structure and function of biological molecules.

Covalent Bond: A bond formed when two atoms share one or more pairs of electrons.
Polar Covalent Bond: A type of covalent bond where electrons are shared unequally, resulting in partial charges on atoms.
Ionic Bond: A bond formed when one atom donates an electron to another, resulting in oppositely charged ions that attract each other.
Hydrogen Bond: A weak bond between a hydrogen atom (already covalently bonded to an electronegative atom) and another electronegative atom; not a true bond but important in biology.

Properties and Examples

Electronegativity: The tendency of an atom to attract electrons toward itself in a chemical bond.
Polarity: Molecules with uneven distribution of charges (e.g., water).
Example: In water (H2O), oxygen is more electronegative than hydrogen, creating a polar molecule.

Properties of Water

Structure and Polarity

Water is a polar molecule, with oxygen having a partial negative charge and hydrogens having partial positive charges. This leads to hydrogen bonding between water molecules.

Cohesion: Attraction between molecules of the same substance (e.g., water molecules stick together).
Adhesion: Attraction between molecules of different substances (e.g., water and glass).
Surface Tension: The result of cohesion at the surface of water, allowing small objects to float.
Capillarity (Capillary Action): The ability of water to move up narrow tubes against gravity, due to cohesion and adhesion.
High Specific Heat: Water can absorb or release large amounts of heat with little temperature change, stabilizing environments.
High Heat of Vaporization: Water requires a lot of energy to change from liquid to gas, helping organisms cool off via evaporation.
Density of Ice: Ice is less dense than liquid water, so it floats, insulating aquatic life in winter.

Example: Water droplets on a penny demonstrate cohesion and surface tension.

Water as a Solvent

Universal Solvent: Water dissolves many substances due to its polarity, facilitating chemical reactions in cells.
Hydrophilic: Substances that dissolve in water (e.g., salts, sugars).
Hydrophobic: Substances that do not dissolve in water (e.g., oils, nonpolar molecules).

Water and Temperature Regulation

Water stabilizes temperature due to its high specific heat and high heat of vaporization.
This property is crucial for maintaining stable environments for living organisms.

Capillary Action in Plants

Capillary action allows water to move from roots to leaves in plants, driven by cohesion and adhesion.

Acids, Bases, and Buffers

pH Scale

The pH scale measures the concentration of hydrogen ions (H+) in a solution.

Acidic: pH less than 7; higher concentration of H+.
Neutral: pH equal to 7.
Basic (Alkaline): pH greater than 7; lower concentration of H+.

Equation:

Buffers and Homeostasis

Buffers are substances that minimize changes in pH by accepting or donating H+ ions. They are essential for maintaining homeostasis in biological systems.

Example: The bicarbonate buffer system in blood helps maintain a stable pH.
When acids or bases are added to a solution, buffers help resist drastic changes in pH.

How Buffers Demonstrate Homeostasis: By stabilizing pH, buffers help maintain the internal environment necessary for life processes.

Summary Table: Properties of Water

Property	Description	Biological Importance
Cohesion	Water molecules stick to each other	Surface tension, transport in plants
Adhesion	Water molecules stick to other substances	Capillary action in plants
High Specific Heat	Resists temperature change	Stabilizes climate and body temperature
High Heat of Vaporization	Requires much energy to evaporate	Cooling effect (sweating, transpiration)
Density of Ice	Ice is less dense than liquid water	Insulates aquatic life in winter
Universal Solvent	Dissolves many substances	Facilitates chemical reactions

Practice and Application

Identify the number of protons, neutrons, and electrons in given isotopes.
Classify types of chemical bonds in biological molecules.
Explain how water's properties support life (e.g., capillary action, temperature regulation).
Describe how buffers maintain pH in biological systems.

Additional info: The original material included matching, fill-in-the-blank, and multiple-choice questions, as well as lab station prompts. The above notes synthesize and expand on these concepts for comprehensive study.