Atoms, Elements, and Compounds

Introduction to Atoms and Elements

Atoms are the fundamental units of matter, forming the basis of all substances. Elements are pure substances consisting of only one type of atom, each identified by a unique symbol on the periodic table.

• Element: A substance that cannot be broken down into other substances by chemical reactions.

• Compound: A substance composed of two or more different elements combined in a fixed ratio.

• Essential elements: Elements required for life (e.g., C, H, O, N) make up about 96% of living matter.

• Trace elements: Required in small amounts, such as iron and iodine.

• Atoms: The smallest unit of an element, consisting of protons, neutrons, and electrons.

Subatomic Particles and Isotopes

Structure of the Atom

Atoms are composed of three main subatomic particles: protons, neutrons, and electrons. Isotopes are variants of elements with different numbers of neutrons.

• Protons: Positively charged particles found in the nucleus.

• Neutrons: Neutral particles found in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Radioactive isotopes: Unstable isotopes that decay, emitting particles and energy; used in dating fossils, medical imaging, and research.

Chemical Bonds and Interactions

Types of Chemical Bonds

Chemical bonds form when atoms interact to achieve stable electron configurations. The main types of bonds are covalent, ionic, and hydrogen bonds.

• Covalent bonds: Atoms share electrons to complete their valence shells.

• Ionic bonds: Electrons are transferred from one atom to another, creating oppositely charged ions that attract each other.

• Hydrogen bonds: Weak bonds between polar molecules, important in water and biological molecules.

• Electronegativity: The attraction of an atom for shared electrons; differences in electronegativity determine bond polarity.

• Nonpolar covalent bonds: Electrons are shared equally.

• Polar covalent bonds: Electrons are shared unequally, resulting in partial charges.

Example: In water (H2O), oxygen is more electronegative than hydrogen, resulting in polar covalent bonds and hydrogen bonding between molecules.

Water: Properties and Importance

Unique Properties of Water

Water's molecular structure and hydrogen bonding give rise to its unique properties, which are essential for life.

• Cohesion: Attraction between water molecules due to hydrogen bonding.

• Adhesion: Attraction between water molecules and other substances.

• Surface tension: Water's resistance to external force at the surface.

• Specific heat: Water can absorb or release large amounts of heat with little temperature change.

• Evaporative cooling: As water evaporates, the surface cools because the hottest molecules leave as vapor.

• Solvent properties: Water dissolves polar and ionic substances (hydrophilic), but not nonpolar substances (hydrophobic).

Example: Water's high specific heat helps stabilize temperatures in organisms and environments.

Key Terms & Definitions

Essential Chemistry Vocabulary

• Element: Substance that cannot be broken down by chemical reactions.

• Compound: Substance of two or more elements in a fixed ratio.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Covalent bond: Bond formed by sharing electrons between atoms.

• Ionic bond: Bond formed by transfer of electrons, creating ions.

• Hydrogen bond: Weak bond between polar molecules.

• Cohesion: Attraction between water molecules.

• Adhesion: Attraction between water and other substances.

• Specific heat: Heat required to change temperature of 1g by 1°C.

• Hydrophilic: Substance attracted to water.

• Hydrophobic: Substance repelled by water.

Elements in Biological Molecules

Major Elements in Living Organisms

Biological molecules are primarily composed of carbon, hydrogen, oxygen, and nitrogen, with some sulfur and phosphorus. These elements form the basis of macromolecules essential for life.

• Organic compounds: Contain carbon and make up most biological macromolecules.

Properties of Carbon

Carbon's Versatility in Biology

Carbon's ability to form four covalent bonds allows for a diversity of stable and complex molecules, making it the backbone of biological macromolecules.

• Valence: Carbon has four valence electrons, enabling it to form long chains and rings.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen; serve as energy sources.

Functional Groups

Role of Functional Groups in Molecules

Functional groups are specific groups of atoms within molecules that determine their chemical properties and reactivity.

• Common functional groups: Hydroxyl (-OH), carbonyl (C=O), carboxyl (-COOH), amino (-NH2), sulfhydryl (-SH), phosphate (-PO4), methyl (-CH3).

• Functional groups influence molecular behavior and interactions.

Types of Biological Molecules

Major Classes of Biomolecules

There are four main classes of biological macromolecules: carbohydrates, lipids, proteins, and nucleic acids. Each class has distinct structures and functions.

• Carbohydrates: Sugars and their polymers; monomers are monosaccharides (e.g., glucose, C6H12O6).

• Lipids: Hydrophobic molecules, not true polymers; include fats, phospholipids, and steroids.

• Proteins: Polymers of amino acids; perform a wide range of functions.

• Nucleic acids: DNA and RNA; polymers of nucleotides.

Formation and Breakdown of Polymers

Polymerization and Hydrolysis

Macromolecules are formed by joining monomers through dehydration reactions and broken down by hydrolysis.

• Dehydration reaction: Removes water to form a new bond between monomers.

• Hydrolysis: Adds water to break bonds between monomers.

Example: Formation of a peptide bond between amino acids during protein synthesis.

Carbohydrates

Structure and Function

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined by glycosidic linkage (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides; serve as storage (starch, glycogen) or structural materials (cellulose, chitin).

Lipids

Types and Functions

• Fats: Glycerol and fatty acids; triglycerides have three fatty acids.

• Saturated fats: No double bonds; solid at room temperature.

• Unsaturated fats: One or more double bonds; liquid at room temperature.

• Phospholipids: Form cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with four fused rings (e.g., cholesterol, hormones).

Proteins

Structure and Function

• Polymers of amino acids: 20 types, linked by peptide bonds.

• Levels of structure: Primary (sequence), secondary (coils/folds), tertiary (3D shape), quaternary (multiple polypeptides).

• Denaturation: Loss of protein's shape and function due to environmental changes.

Nucleic Acids

DNA and RNA

• Nucleotides: Monomers of nucleic acids; consist of a sugar, phosphate, and nitrogenous base.

• DNA: Double-stranded helix; bases are A, T, C, G.

• RNA: Single-stranded; bases are A, U, C, G.

• Genetic information: Sequence of bases encodes instructions for protein synthesis.

Key Terms & Definitions (Polymers and Proteins)

• Monomer: A single building block unit for polymers.

• Polymer: A chainlike molecule formed from monomers.

• Dehydration reaction: Joins monomers by removing water.

• Hydrolysis: Splits polymers into monomers by adding water.

• Functional group: Group of atoms affecting molecular function and reactivity.

• Peptide bond: Covalent bond connecting amino acids in proteins.

• Denaturation: Loss of protein's 3D shape and function due to environmental changes.

Summary Table: Types of Biological Molecules

Key Equations

• General formula for monosaccharides:

• Dehydration reaction (example for two monosaccharides):