BackWater and Carbon: The Chemical Basis of Life – Study Notes
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Atoms, Ions, and Molecules: The Building Blocks of Life
Major Elements in Living Organisms
Living organisms are primarily composed of a small set of elements, which form the basis for biological molecules and processes.
Key Elements: Hydrogen (H), Carbon (C), Nitrogen (N), and Oxygen (O) make up approximately 96% of the matter in organisms.
Complexity: These elements combine to form complex structures essential for life.
Chemical Evolution: The physical and chemical properties of these atoms allow for the formation of molecules such as water and carbon compounds, which are fundamental to chemical evolution.
Structure of Atoms
Parts of an Atom
Atoms are the smallest units of elements and consist of subatomic particles that determine their chemical properties.
Protons: Positively charged particles (+1) located in the nucleus.
Neutrons: Neutral particles (no charge) also found in the nucleus.
Electrons: Negatively charged particles (-1) that orbit the nucleus.
Element: A pure substance made of only one type of atom.
Atomic Number and Mass Number
Atoms are identified by their atomic number and mass number, which reflect their composition.
Atomic Number: The number of protons in the nucleus of an atom.
Mass Number: The sum of protons and neutrons in the nucleus.
Example: Carbon has an atomic number of 6 (6 protons) and common isotopes with mass numbers 12 and 14.
Isotopes
Isotopes are forms of an element that differ in the number of neutrons, resulting in different mass numbers.
Stable Isotopes: Do not change over time.
Radioactive Isotopes: Unstable and decay over time, releasing energy.
Example: Carbon-12 (6 neutrons), Carbon-14 (8 neutrons).
The Atomic Structure of the First Row Elements
Valence Electrons and Bonding
The number of unpaired electrons in the outermost shell (valence shell) determines how many bonds an atom can form.
Valence Electrons: Electrons in the outermost shell available for bonding.
Bond Formation: Atoms with more unpaired electrons can form more bonds, contributing to molecular diversity.
Biological Relevance: Elements such as C, H, O, N, P, and S are most abundant in biological molecules due to their bonding capabilities.
Element | Atomic Number | Valence Electrons | Common Bonds Formed |
|---|---|---|---|
Hydrogen | 1 | 1 | 1 |
Carbon | 6 | 4 | 4 |
Nitrogen | 7 | 3 | 3 |
Oxygen | 8 | 2 | 2 |
Phosphorus | 15 | 5 | 3-5 |
Sulfur | 16 | 6 | 2-6 |
Additional info: Table entries for phosphorus and sulfur bond numbers are inferred based on typical biological bonding patterns.
