Chemistry Comes Alive

States of Matter

Matter exists in three basic states, each with distinct physical properties.

• Solid: Definite shape and volume; particles are tightly packed and vibrate in place.

• Liquid: Definite volume but no definite shape; particles are less tightly packed and can move past each other.

• Gas: No definite shape or volume; particles are far apart and move freely.

States of Energy

Energy is the capacity to do work and exists in two basic states:

• Kinetic Energy: Energy of motion (e.g., movement of muscles, flow of blood).

• Potential Energy: Stored energy (e.g., energy stored in chemical bonds, a stretched spring).

Forms of energy include chemical, electrical, mechanical, and radiant (electromagnetic) energy.

Elements in the Human Body

Four elements make up about 96% of the human body:

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

Structure of the Atom

An atom consists of a nucleus (containing protons and neutrons) and electrons orbiting the nucleus.

• Protons: Positive charge (+1), mass ≈ 1 atomic mass unit (amu), located in the nucleus.

• Neutrons: No charge (0), mass ≈ 1 amu, located in the nucleus.

• Electrons: Negative charge (–1), mass ≈ 1/2000 amu, located in electron shells around the nucleus.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses but identical chemical properties.

Electrons and Reactivity

The number and arrangement of electrons, especially in the outermost shell (valence shell), determine an atom's chemical reactivity.

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Anion: Negatively charged ion (gained electrons).

• Cation: Positively charged ion (lost electrons).

Molecular Formulas

Molecular formulas indicate the types and numbers of atoms in a molecule. For example, represents a molecule with 6 carbon, 12 hydrogen, and 6 oxygen atoms.

Atomic Number vs. Atomic Mass

• Atomic Number: Number of protons in the nucleus; defines the element.

• Atomic Mass: Sum of protons and neutrons in the nucleus.

Chemical Bonds

Atoms combine by forming chemical bonds:

• Ionic Bonds: Transfer of electrons from one atom to another, forming ions (e.g., NaCl).

• Covalent Bonds: Sharing of electron pairs between atoms.

  • Non-polar Covalent: Equal sharing of electrons (e.g., O2).

  • Polar Covalent: Unequal sharing, resulting in partial charges (e.g., H2O).

• Hydrogen Bonds: Weak attractions between a hydrogen atom (already covalently bonded) and an electronegative atom (e.g., between water molecules).

Water: Polarity and Solvent Properties

Water is a polar molecule, making it an excellent solvent for ionic and polar substances. Its polarity allows it to form hydrogen bonds, contributing to its high heat capacity and surface tension.

Molecules, Compounds, and Mixtures

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Molecule containing two or more different elements (e.g., H2O).

• Mixtures: Physical combinations of substances. Types:

  • Solutions: Homogeneous mixtures (e.g., salt water).

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

  • Suspensions: Heterogeneous mixtures with large, often visible particles (e.g., blood).

pH Scale and Buffers

The pH scale measures hydrogen ion concentration:

• pH < 7: Acidic

• pH = 7: Neutral

• pH > 7: Basic (alkaline)

Normal body fluid pH is about 7.4. Buffers help maintain pH stability by absorbing or releasing H+ ions.

Chemical Reactions

• Hydrolysis: Addition of water to break bonds (e.g., digestion of proteins).

• Dehydration Synthesis: Removal of water to form bonds (e.g., formation of peptide bonds).

• Exergonic Reactions: Release energy.

• Endergonic Reactions: Absorb energy.

• Reversibility: Many reactions are reversible, indicated by a double arrow ().

• Factors Affecting Rate: Temperature, concentration, particle size, and catalysts (enzymes).

Organic vs. Inorganic Compounds

• Organic Compounds: Contain carbon; include carbohydrates, lipids, proteins, and nucleic acids.

• Inorganic Compounds: Generally do not contain carbon; include water, salts, acids, and bases.

Carbohydrates

• General Formula:

• Monomers: Monosaccharides (e.g., glucose).

• Polymers: Disaccharides (e.g., sucrose), polysaccharides (e.g., glycogen, starch).

• Functions: Main energy source for cells, structural roles (e.g., cellulose in plants).

Proteins

• General Formula: Composed of amino acids (monomers) linked by peptide bonds.

• Structures:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets (hydrogen bonding).

  • Tertiary: 3D folding due to side chain interactions.

  • Quaternary: Association of multiple polypeptide chains.

• Fibrous vs. Globular: Fibrous proteins (e.g., collagen) provide structure; globular proteins (e.g., enzymes) are functional.

• Denaturation: Loss of structure and function due to heat, pH, or chemicals.

• Functions: Enzymes, structural support, transport, movement, defense.

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy. Factors affecting enzyme activity include temperature, pH, and substrate concentration.

Nucleic Acids

• Monomers: Nucleotides (composed of a sugar, phosphate group, and nitrogenous base).

• Polymers: DNA and RNA.

• Complementary Base Pairing: In DNA, A pairs with T, C pairs with G.

• Functions: Store and transmit genetic information.

• DNA vs. RNA: DNA is double-stranded, contains deoxyribose, and uses thymine; RNA is single-stranded, contains ribose, and uses uracil.

• ATP: Adenosine triphosphate is the primary energy carrier in cells. Structure: adenine, ribose, and three phosphate groups.

Lipids

• General Formula: Mostly hydrocarbons; not a fixed formula but high C and H, low O.

• Saturated Fats: No double bonds between carbon atoms; solid at room temperature (e.g., butter).

• Unsaturated Fats: One or more double bonds; liquid at room temperature (e.g., olive oil).

• Phospholipids: Glycerol backbone, two fatty acids, and a phosphate group; form cell membranes.

• Functions: Energy storage, insulation, protection, cell membrane structure, signaling molecules (e.g., steroids).