Atomic Structure and Matter

What is Matter?

Matter is anything that has mass and occupies space. It is composed of atoms, which are the smallest units of matter that retain the properties of an element.

• Not Matter: Hopes, dreams, emotions, energy, heat, and sound are not considered matter because they do not have mass or occupy space.

• Atoms: The fundamental building blocks of matter. Examples include carbon (C), nitrogen (N), oxygen (O), phosphorus (P), hydrogen (H), and sulfur (S).

Levels of Biological Organization

• Atomic Level: Atoms such as C, H, O, N, P.

• Molecular Level: Atoms form bonds to create molecules and compounds (e.g., O2, CO2, H2O).

• Cellular Level: Cells are the smallest units of life.

• Tissues, Organs, Organ Systems, Organisms: Increasing complexity in biological organization.

• Populations, Communities, Ecosystems, Biosphere: Higher levels of organization involving multiple organisms and their environments.

Emergent Properties

Emergent properties arise at each level of biological organization, resulting from the arrangement and interactions of parts as complexity increases.

Atomic Structure

Subatomic Particles

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles found in energy shells around the nucleus.

Periodic Table Basics

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

• Atomic Symbol: One or two-letter abbreviation for an element (e.g., H for hydrogen).

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

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses. For example, hydrogen has three isotopes: protium (1H), deuterium (2H), and tritium (3H).

Valence Electrons and Reactivity

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

• Stable Atoms: Atoms with full outer shells (e.g., noble gases) are nonreactive.

• Ions: Atoms that have gained or lost electrons, resulting in a charge (cations are positive, anions are negative).

Chemical Bonds

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, creating oppositely charged ions that attract each other. Example: sodium chloride (NaCl).

Covalent Bonds

Covalent bonds form when atoms share valence electrons. These can be single, double, or triple bonds depending on the number of shared electron pairs.

• Single Covalent Bond: One pair of electrons shared (e.g., H2).

• Double Covalent Bond: Two pairs of electrons shared (e.g., O2).

• Triple Covalent Bond: Three pairs of electrons shared (e.g., N2).

Polarity of Covalent Bonds

• Nonpolar Covalent Bonds: Electrons are shared equally; molecules are hydrophobic.

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges (e.g., water molecules).

Hydrogen Bonds

Hydrogen bonds are weak attractions between a hydrogen atom covalently bonded to a highly electronegative atom (like oxygen or nitrogen) and another electronegative atom. They do not form compounds but are important in stabilizing structures like DNA and proteins.

Carbohydrates

Elements and Structure

• Elements: Carbon (C), hydrogen (H), and oxygen (O).

• Monomer: Monosaccharides (simple sugars).

Monosaccharides

• Definition: Simple sugars containing 5 or 6 carbons (e.g., glucose, fructose).

• Isomers: Compounds with the same chemical formula but different structures.

• Functional Groups: Polar hydroxyl and carbonyl groups.

• Examples: Glucose and fructose are isomers; ribose (in RNA) and deoxyribose (in DNA) are pentose sugars.

Disaccharides and Polysaccharides

• Disaccharides: Formed by joining two monosaccharides via dehydration synthesis (e.g., sucrose, lactose, maltose).

• Polysaccharides: Long chains of monosaccharides; serve as energy storage or structural components.

• Examples:

  • Starch: Energy storage in plants.

  • Glycogen: Short-term energy storage in animals.

  • Cellulose: Structural component of plant cell walls.

  • Chitin: Structural component in fungi cell walls and insect exoskeletons; contains nitrogen.

Dehydration Synthesis

Monosaccharides join to form disaccharides and polysaccharides through dehydration synthesis, a reaction that removes a water molecule to form a covalent bond.

Summary Table: Types of Carbohydrates