Essential Chemistry for Biology: Chapter 2 Study Notes

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 2: Essential Chemistry for Biology

Matter and Elements

Chemistry is fundamental to understanding biological processes. Matter is anything that occupies space and has mass, and it exists in three physical states: solid, liquid, and gas.

Matter: Anything that has mass and takes up space.
Element: A substance that cannot be broken down into other substances by chemical means.
Elements are represented on the Periodic Table.
There are 25 elements essential to life; four of these—Hydrogen (H), Carbon (C), Nitrogen (N), and Oxygen (O)—make up about 96% of the human body’s mass.

Example: Oxygen is the most abundant element in the human body, accounting for about 65% of body mass.

Elements in Organisms

Living organisms require both major and trace elements for survival and proper function.

Major elements: Oxygen, Carbon, Hydrogen, Nitrogen
Trace elements: Elements required in minute quantities, such as Iodine (I) and Iron (Fe)
Iodine: Essential for thyroid hormone production; deficiency can cause goiter.
Iron: Required for hemoglobin in blood.

Example: Iodized salt is used to prevent iodine deficiency in populations.

Atoms and Atomic Structure

Atoms are the smallest units of matter that retain the properties of an element. They are composed of subatomic particles: protons, neutrons, and electrons.

Proton: Positively charged particle in the nucleus.
Neutron: Neutral particle in the nucleus.
Electron: Negatively charged particle orbiting the nucleus.
Atomic Number: Number of protons in an atom; determines the element.
Mass Number: Sum of protons and neutrons.

Formula:

Example: Carbon has 6 protons (atomic number 6); Carbon-12 has 6 neutrons (mass number 12).

Isotopes and Radioactivity

Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are radioactive and decay over time, emitting particles and energy.

Isotope: Atoms of the same element with different neutron numbers.
Radioactive Isotope: An isotope whose nucleus decays spontaneously.
Uses: Medical imaging (PET scans), research, nuclear power.
Risks: Uncontrolled exposure can damage DNA and harm living organisms.

Isotope	Protons	Neutrons	Mass Number
Carbon-12	6	6	12
Carbon-13	6	7	13
Carbon-14	6	8	14

Electron Arrangement and Chemical Properties

The arrangement of electrons in an atom determines its chemical behavior. Electrons occupy energy levels (shells), and the outermost shell (valence shell) is key to chemical reactivity.

Electron Shells: Energy levels where electrons are found.
Valence Electrons: Electrons in the outermost shell; involved in chemical bonding.
Atoms are most stable when their outer shell is full.

Example: Sodium (Na) has one valence electron; chlorine (Cl) has seven. Sodium donates its electron to chlorine to form NaCl.

Energy in Chemical Systems

Energy is the capacity to do work. In biological systems, energy is stored in chemical bonds and released during chemical reactions.

Potential Energy: Stored energy, such as in chemical bonds.
Kinetic Energy: Energy of motion, released when bonds are broken.

Chemical Bonding

Chemical bonds form when atoms interact to complete their outer electron shells. There are three main types of chemical bonds:

Ionic Bonds: Medium strength; formed by transfer of electrons from one atom to another, resulting in oppositely charged ions that attract.
Covalent Bonds: Strongest bond; formed by sharing pairs of electrons between atoms.
Hydrogen Bonds: Weakest bond; formed between polar molecules, such as water.

Bond Type	Strength	Example
Ionic	Medium	NaCl (table salt)
Covalent	Strong	H2O (water)
Hydrogen	Weak	Between water molecules

Example: In water, hydrogen bonds form between the slightly positive hydrogen atom of one molecule and the slightly negative oxygen atom of another.

Chemical Reactions

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

Reactants: Substances that start a reaction.
Products: Substances formed as a result of a reaction.

Example:

Hydrogen and oxygen gases react to form water.

Water and Life

Water is essential for life and has unique properties that support biological processes.

Cells are composed of 60–95% water.
Water is a solvent, facilitating chemical reactions and transport of substances.
Helps regulate body temperature and absorbs heat.
Evaporation of water cools organisms.

Example: Blood is about 90% water, enabling transport of nutrients and waste.

Properties of Water

Water’s molecular structure gives rise to several important properties:

Polarity: Water is a polar molecule with unequal charge distribution.
Hydrogen Bonding: Water molecules form hydrogen bonds with each other and other molecules.
High Heat of Vaporization: Water absorbs large amounts of heat before evaporating.
Cohesion: Attraction between like molecules (water to water).
Adhesion: Attraction between different molecules (water to other substances).
Ice Formation: Water expands and floats when frozen, important for aquatic life.
Solvent Properties: Water dissolves ionic and polar substances.

Property	Biological Importance
High Heat of Vaporization	Regulates temperature
Cohesion	Surface tension, water transport in plants
Adhesion	Helps water move through vessels
Ice Formation	Insulates aquatic environments
Solvent	Facilitates chemical reactions

Solutions, Solvents, and Solutes

Water acts as the primary solvent in cells, dissolving many chemicals and nutrients.

Solution: Homogeneous mixture of two or more substances.
Solvent: The dissolving agent (water).
Solute: The substance dissolved (e.g., salt).
Hydrophilic: Water-loving, polar substances that dissolve in water.
Hydrophobic: Water-fearing, nonpolar substances that do not dissolve easily (e.g., oils).

Water Ionization and pH

Water can ionize to form hydrogen ions (H+) and hydroxide ions (OH-), affecting the pH of solutions.

pH: Measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic).
Pure water has equal concentrations of H+ and OH- (pH 7).
Acidic solutions: [H+] > [OH-]
Basic solutions: [H+] < [OH-]

Substance	pH Value
Oven Cleaner	~13-14
Household Ammonia	~11-12
Seawater	~8
Human Blood	~7.4
Pure Water	7
Urine	~6
Grapefruit Juice	~3
Battery Acid	~1

Formula:

Acid Rain

Acid rain is caused by the dissolution of sulfur oxides (SOx) and nitrogen oxides (NOx) in water, forming sulfuric and nitric acids. This can have harmful effects on ecosystems.

Acid Rain: Precipitation with a pH lower than normal due to atmospheric pollution.
Can damage plants, aquatic life, and infrastructure.

Additional info:

Fluoride is added to water and dental products to reduce tooth decay.
Cadmium is a harmful element found in some products and is a known carcinogen.
Water intake is crucial for health; dehydration can impair metabolism and cognitive function.