BackChemical Foundations of Biological Systems: Elements, Atoms, and the Periodic Table
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Chapter 2: Chemical Foundations of Biological Systems
Concept 2.1: Matter, Elements, and Compounds
Matter is anything that occupies space and has mass. All living organisms are composed of matter, which exists in the form of elements and compounds. Elements are pure substances that cannot be broken down by ordinary chemical reactions, while compounds are substances formed from two or more elements in fixed ratios.
Element: A substance consisting of only one type of atom, with unique chemical properties.
Compound: A substance formed when two or more elements combine chemically in a fixed ratio.
Mixture: A physical combination of two or more substances where each retains its own properties.
Essential elements are required for life, with oxygen (O), carbon (C), hydrogen (H), and nitrogen (N) making up the majority of living matter. Mineral elements and trace elements are required in smaller quantities but are crucial for regulatory, structural, and metabolic functions.
Mineral Elements (less than 1% of total mass) | Symbol |
|---|---|
Calcium | Ca |
Chlorine | Cl |
Magnesium | Mg |
Phosphorus | P |
Potassium | K |
Sodium | Na |
Sulfur | S |
Trace Elements (less than 0.01% of total mass) | Symbol |
|---|---|
Chromium | Cr |
Cobalt | Co |
Copper | Cu |
Fluorine | F |
Iodine | I |
Iron | Fe |
Manganese | Mn |
Molybdenum | Mo |
Selenium | Se |
Silicon | Si |
Tin | Sn |
Vanadium | V |
Zinc | Zn |
The Periodic Table of Elements
The periodic table organizes all known elements based on their atomic number, electron configuration, and recurring chemical properties. It is a fundamental tool for understanding chemical behavior in biological systems.
Groups (columns): Elements with similar chemical properties and the same number of valence electrons.
Periods (rows): Elements with the same number of electron shells.
Concept 2.2: Atomic Structure and Properties
Atomic Structure
An atom is the smallest unit of an element that retains its chemical properties. Atoms are composed of three types of subatomic particles: protons, neutrons, and electrons. The nucleus contains protons and neutrons, while electrons occupy orbitals around the nucleus.
Proton: Positive charge, mass of 1 amu, located in the nucleus.
Neutron: No charge, mass of 1 amu, located in the nucleus.
Electron: Negative charge, negligible mass, located in orbitals.
Particle | Charge | Mass (amu) | Location |
|---|---|---|---|
Proton | +1 | 1 | Nucleus |
Neutron | 0 | 1 | Nucleus |
Electron | -1 | 0 | Orbitals |
Atomic Number, Mass Number, and Isotopes
The atomic number is the number of protons in an atom and defines the element. The mass number is the sum of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons. Some isotopes are radioactive and have important applications in biology and medicine.
Atomic number (Z): Number of protons in the nucleus.
Mass number (A): Number of protons plus neutrons.
Isotope: Atoms of the same element with different neutron numbers.
Radioactive isotope: Unstable isotope that decays, emitting radiation.
Example: Carbon-12, Carbon-13, and Carbon-14 are isotopes of carbon. Carbon-14 is radioactive and used in radiometric dating.
Atomic Structure of Beryllium
Beryllium (Be) has an atomic number of 4 and a mass number of approximately 9. Its nuclear notation is , indicating 4 protons and 5 neutrons.
Electron Arrangement and Reactivity
The arrangement of electrons in shells (energy levels) determines an element's chemical reactivity. Electrons fill shells from the lowest to highest energy, and the outermost shell is called the valence shell. Atoms are most stable when their valence shell is full, typically with 8 electrons (the Octet Rule).
Bohr Model: Electrons orbit the nucleus in discrete energy levels (shells).
Valence electrons: Electrons in the outermost shell, important for chemical bonding.
Octet Rule: Atoms tend to gain, lose, or share electrons to achieve 8 electrons in their valence shell (except for hydrogen and helium).
The Periodic Table and Electron Configuration
The periodic table provides information about the number of electron shells, valence electrons, and types of orbitals (s, p, d, f) for each element. Electron configuration determines chemical properties and bonding behavior.
Groups: Indicate the number of valence electrons.
Periods: Indicate the number of electron shells.
Blocks (s, p, d, f): Indicate the type of orbital being filled.
Chemical Bonding and Reactivity
Atoms with incomplete valence shells are chemically reactive and can form bonds to achieve stability. Atoms with full valence shells are chemically inert (noble gases).
Covalent bond: Sharing of electron pairs between atoms.
Ionic bond: Transfer of electrons from one atom to another, resulting in oppositely charged ions.
Example: Hydrogen and chlorine can bond because they have incomplete valence shells, while neon cannot bond because its valence shell is full.
Summary Table: Electron Shells and Reactivity
Element | Valence Electrons | Reactivity |
|---|---|---|
Hydrogen (H) | 1 | Reactive |
Chlorine (Cl) | 7 | Reactive |
Neon (Ne) | 8 | Inert |
Additional info: Understanding atomic structure and the periodic table is foundational for studying biological molecules, cellular processes, and metabolism in living systems.
