Chemistry Comes Alive

Matter and Its States

Matter is anything that occupies space and has mass. In the human body, matter exists in three states: solid, liquid, and gas. Mass is the actual amount of matter in an object, while weight varies with gravity. For example, your mass remains constant whether you are at sea level or on a mountaintop, but your weight is slightly less at higher altitudes due to reduced gravity.

• Solid: Bones and teeth

• Liquid: Blood, plasma

• Gas: Oxygen, carbon dioxide in lungs

Energy: Forms and Properties

Energy is less tangible than matter; it has no mass and does not occupy space. It is defined as the capacity to do work or put matter into motion. Energy is measured by its effect on matter. The greater the work, the more energy is used.

• Kinetic Energy: Energy in action (e.g., movement of atoms, muscle contraction)

• Potential Energy: Stored energy (e.g., energy in a battery, water behind a dam)

Example: A baseball player hitting a ball uses more energy than one bunting.

Forms of Energy

• Chemical: Stored in food, fuel, batteries; released during chemical changes (most important in the body)

• Electrical: Movement of charged particles (e.g., nerve impulses)

• Mechanical: Directly involved in moving matter (e.g., muscle movement)

• Electromagnetic Radiation: Energy traveling in waves (e.g., visible light, X-rays)

Chemical Elements and Atomic Structure

All matter is composed of elements, which cannot be broken down into simpler substances easily. The human body is primarily composed of four elements: carbon, hydrogen, oxygen, and nitrogen. Each element is represented by an atomic symbol, often derived from its English or Latin name.

• Atomic Number: Number of protons in the nucleus

• Mass Number: Total number of protons and neutrons

Atomic Structure of Smallest Atoms

• Hydrogen: 1 proton, 0 neutrons

• Helium: 2 protons, 2 neutrons

• Lithium: 3 protons, 4 neutrons

Isotopes and Radioisotopes

Isotopes are variants of the same element with different atomic masses due to varying numbers of neutrons. Radioisotopes are unstable isotopes that decay and release radiation, which is useful in diagnostic imaging, research, and radiation therapy.

Molecules, Compounds, and Mixtures

Atoms combine to form molecules and compounds. A molecule is two or more atoms bonded together, while a compound is a molecule with two or more different kinds of atoms. Most matter exists as mixtures, which are physically intermixed components.

• Solutions: Homogeneous mixtures (e.g., blood plasma)

• Colloids: Heterogeneous mixtures with larger particles (e.g., cytosol, Jell-O)

• Suspensions: Heterogeneous mixtures with large particles that settle out (e.g., blood)

Mixtures vs. Compounds

Bonding of Atoms and the Octet Rule

Electrons occupy electron shells around the nucleus. The outermost shell, called the valence shell, is involved in chemical reactions. Atoms strive for eight electrons in their valence shell (octet rule) by gaining, losing, or sharing electrons.

Types of Chemical Bonds

• Ionic Bonds: Transfer of electrons, forming charged ions (cations and anions)

• Covalent Bonds: Sharing of electrons; can be single, double, or triple bonds

• Hydrogen Bonds: Weak attractions between a hydrogen atom and a negative atom in another molecule

Nonpolar Covalent Bonds

Electrons are shared equally, resulting in balanced molecules with no partial charges. Examples include O2, CH4, and CO2.

Polar Covalent Bonds

Electrons are shared unequally, creating partial positive and negative charges (dipoles). Water (H2O) is a classic example.

Hydrogen Bonds

Hydrogen bonds are weak individually but strong collectively. They provide stability and are crucial for water properties, DNA structure, and protein folding.

Chemical Reactions

Chemical reactions involve the formation, rearrangement, or breaking of chemical bonds. They are represented by chemical equations, showing reactants and products.

• Synthesis (Combination): Building larger molecules from smaller ones (anabolic)

• Decomposition: Breaking down molecules into smaller units (catabolic)

• Exchange: Both synthesis and decomposition occur; atoms are exchanged

Redox Reactions

Reduction-oxidation (redox) reactions involve electron transfer. Atoms are reduced when they gain electrons and oxidized when they lose electrons. These reactions are central to metabolism, such as cellular respiration:

Energy Flow in Chemical Reactions

• Exergonic: Release energy (catabolic, oxidative)

• Endergonic: Absorb energy (anabolic)

Rate of Chemical Reactions

• Temperature: Higher temperature increases rate

• Concentration: Higher concentration increases rate

• Particle Size: Smaller particles increase rate

• Catalysts: Speed up reactions without being consumed; enzymes are biological catalysts

Biochemistry: Organic and Inorganic Compounds

Inorganic Compounds

• Water: Most abundant; high heat capacity, solvent properties, reactivity, cushioning

• Salts: Ionic compounds; dissociate into electrolytes (e.g., NaCl, CaCO3, KCl)

• Acids: Proton donors; release H+ ions (e.g., HCl, H2CO3)

• Bases: Proton acceptors; release OH– ions (e.g., HCO3–, NH3)

pH Scale

• Acidic: pH 0–6.99

• Neutral: pH 7

• Alkaline (Basic): pH 7.01–14

Buffers

Buffers resist changes in pH by releasing or binding H+ ions.

Organic Compounds

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, ribose)

• Disaccharides: Double sugars (e.g., sucrose, lactose)

• Polysaccharides: Many sugars (e.g., starch, glycogen)

Lipids

• Triglycerides: Energy storage, insulation, protection

• Phospholipids: Cell membrane structure

• Steroids: Cholesterol, hormones, vitamin D

• Eicosanoids: Prostaglandins, inflammation, blood clotting

Proteins

• Amino Acids: Building blocks; joined by peptide bonds

• Structural Levels: Primary, secondary (α helix, β sheet), tertiary, quaternary

• Fibrous Proteins: Structural (e.g., collagen, keratin)

• Globular Proteins: Functional (e.g., enzymes, antibodies)

Enzymes

Enzymes are biological catalysts that lower activation energy and speed up reactions. They are specific to substrates and often require cofactors or coenzymes.

Nucleic Acids

• DNA: Genetic blueprint; double helix; base pairing (A-T, G-C)

• RNA: Protein synthesis; single-stranded; base pairing (A-U, G-C)

ATP

ATP (adenosine triphosphate) is the cell's energy currency. Energy released from glucose breakdown is stored in ATP, which powers cellular processes.

(loss of phosphate group releases energy)

Example: Terminal phosphate group transfer enables work in cells.

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