Fundamental Concepts in General Biology: Atoms, Molecules, and Chemical Bonds

Atoms, Molecules, and Chemical Bonds

Atoms and Elements

Atoms are the basic units of matter and the defining structure of elements. Elements are pure substances consisting of only one type of atom, each distinguished by its atomic number (number of protons).

• Atom: The smallest unit of an element that retains its chemical properties.

• Element: A substance made of only one kind of atom. Examples include Carbon (C), Oxygen (O), and Hydrogen (H).

• Cation: An atom or molecule that has lost one or more electrons, resulting in a positive charge.

• Anion: An atom or molecule that has gained one or more electrons, resulting in a negative charge.

Example: Sodium (Na) loses an electron to become Na+ (a cation), while Chlorine (Cl) gains an electron to become Cl- (an anion).

Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds. The main types of chemical bonds are ionic, covalent, and hydrogen bonds.

• Ionic Bond: Formed when one atom transfers electrons to another, resulting in oppositely charged ions that attract each other.

• Covalent Bond: Formed when two atoms share one or more pairs of electrons.

• Hydrogen Bond: A weak bond between a hydrogen atom in one molecule and an electronegative atom (such as oxygen or nitrogen) in another molecule.

Example: Table salt (Sodium chloride, NaCl) is formed by an ionic bond between Na+ and Cl-. Water (H2O) molecules are held together by covalent bonds, and hydrogen bonds occur between water molecules.

Properties of Water

Water is essential for life due to its unique chemical and physical properties, which arise from its molecular structure and hydrogen bonding.

• Cohesion: The attraction between molecules of the same substance (e.g., water molecules sticking together).

• Adhesion: The attraction between molecules of different substances (e.g., water molecules sticking to glass).

• Polarity: Water is a polar molecule, meaning it has a partial positive charge on one side and a partial negative charge on the other.

• Solvent Properties: Water can dissolve many substances due to its polarity, making it an excellent solvent.

Example: Water's cohesion allows for surface tension, while adhesion helps water move up plant stems (capillary action).

Organic Molecules

Organic molecules are compounds primarily made of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. They form the basis of life.

• Carbohydrates: Molecules composed of carbon, hydrogen, and oxygen; serve as energy sources and structural components.

• Lipids: Hydrophobic molecules including fats, oils, and steroids; important for energy storage and cell membranes.

• Proteins: Polymers of amino acids; perform a wide range of functions including catalysis, structure, and transport.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

Example: Glucose (C6H12O6) is a simple carbohydrate; triglycerides are a type of lipid.

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

• Hydroxyl Group (-OH): Found in alcohols; makes molecules polar.

• Carbonyl Group (C=O): Found in aldehydes and ketones.

• Carboxyl Group (-COOH): Found in organic acids.

• Amino Group (-NH2): Found in amino acids.

Example: The carboxyl group in amino acids gives them acidic properties.

Table: Comparison of Bond Types

Bond Type	Definition	Strength	Example
Ionic	Transfer of electrons between atoms	Strong (in solid state)	NaCl (table salt)
Covalent	Sharing of electron pairs between atoms	Strong	H2O (water)
Hydrogen	Attraction between a hydrogen atom and an electronegative atom	Weak	Between water molecules

Key Equations

• General formula for carbohydrates:

$C_n(H_2O)_n$

• Example of ionic bond formation:

$\text{Na} \rightarrow \text{Na}^+ + e^-$ $\text{Cl} + e^- \rightarrow \text{Cl}^-$

Additional info: Some content and terminology were inferred from context and standard biology curriculum, as the original notes were fragmented and partially unclear.