The Chemistry of Life

Atoms: The Smallest Unit of Matter

Atoms are the fundamental building blocks of all matter, forming the basis for chemical elements and compounds essential to life. Understanding atomic structure is crucial for grasping the principles of Anatomy & Physiology.

• Matter: Anything that occupies space and has mass (e.g., organisms, rocks, oceans).

• Chemical Elements: Pure substances composed of only one type of atom.

• Atom: The smallest unit of an element, and thus the smallest unit of matter.

• Atoms make up both living and non-living matter.

• Example: Atoms are the smallest units of matter, forming the basis for all substances.

Atomic Structure

Atoms are composed of three main subatomic particles, each with distinct properties and locations within the atom.

• Proton: Positively charged, mass of 1 atomic mass unit (AMU), located in the nucleus.

• Neutron: No charge, mass of 1 AMU, located in the nucleus.

• Electron: Negatively charged, almost no mass, found orbiting the nucleus.

Elements of Life

Only a subset of all known elements are found in living organisms. The periodic table organizes these elements based on their chemical properties.

• Approximately 97% of the mass of most life is composed of Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur (CHNOPS).

• Trace Elements: Required for life in small amounts.

• Periodic Table: Arranges all known elements and highlights those essential for life.

Atomic Properties

Each atom of an element has unique properties that distinguish it from others.

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

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

• Atomic Mass: The average total mass of all atoms of an element, considering isotopes.

• Example: Atomic properties of a carbon atom.

Electron Orbitals & Energy Shells

Electrons occupy specific regions around the nucleus called orbitals, which are organized into energy shells.

• Electron Orbitals: 3D regions where electrons are likely to be found.

• Energy Shells: Shells closer to the nucleus are lower in energy; distant shells are higher in energy.

• Valence Electrons: Electrons in the outermost energy shell (valence shell).

• 1st shell holds up to 2 electrons; 2nd shell holds up to 8 electrons.

The Octet Rule

The octet rule states that atoms are more stable when their valence shells are fully occupied, typically with eight electrons.

• Atoms are less reactive when their outer valence shells are full.

• 1st energy shell holds up to 2 electrons; 2nd energy shell holds up to 8 electrons.

Isotopes

Isotopes are atoms of the same element that differ in the number of neutrons, resulting in different mass numbers.

• All isotopes have the same atomic number (protons) but different mass numbers (protons + neutrons).

• Atomic Mass: Average mass of all isotopes of an element.

• Example: Atomic mass of carbon's three isotopes.

Radioactive Isotopes

Radioactive isotopes are unstable and break down, emitting energy as rays or particles. They are used in medicine and radiometric dating.

• Half-life: Time required for half of the radioactive atoms in a sample to decay.

• Example: Radioactivity of Carbon-14.

Introduction to Chemical Bonding

Chemical bonds are attractive forces between atoms, holding them together to form molecules and compounds.

• Molecule: Substance containing two or more chemically bound atoms (e.g., O2).

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

• Chemical Formula: Reveals the types and numbers of atoms in a molecule (e.g., C6H12O6).

Intramolecular vs. Intermolecular Bonds

Bonds can occur within a molecule (intramolecular) or between molecules (intermolecular).

• Intramolecular Bonds: Interactions between atoms within the same molecule.

• Intermolecular Bonds: Interactions between atoms of different molecules.

Ions: Anions vs. Cations

Ions are atoms or molecules with a net electrical charge, resulting from the gain or loss of electrons.

• Anion: Negatively charged ion resulting from the gain of an electron.

• Cation: Positively charged ion resulting from the loss of an electron.

Ionic Bonds

Ionic bonds are electrical attractions between oppositely charged ions (cations and anions), formed by the transfer of electrons.

• Transfer of electrons fills the valence shells of both atoms and creates charges.

• Example: Formation of ionic bond in sodium chloride (NaCl).

Covalent Bonds

Covalent bonds involve the sharing of electrons between two atoms. There are two main types: nonpolar and polar covalent bonds.

• Nonpolar Covalent Bond: Equal sharing of electrons between atoms with similar electronegativities.

• Polar Covalent Bond: Unequal sharing of electrons between atoms with different electronegativities, resulting in partial charges (δ).

• Electronegativity: A measure of an atom’s attraction to electrons (scaled from 0-4).

Summary Table: Subatomic Particles

This table summarizes the properties of protons, neutrons, and electrons.

Additional info: Table values inferred from standard atomic theory.