unit 2 review
Atoms and elements form the foundation of chemistry and biology. They consist of protons, neutrons, and electrons, with unique properties that determine their behavior. Understanding atomic structure and the periodic table is crucial for grasping chemical bonding and reactions.
Chemical bonds, molecular geometry, and polarity shape the interactions between atoms and molecules. These concepts are essential for comprehending biological processes, such as enzyme-substrate interactions and the properties of water. Key reactions and quantitative aspects further illuminate the chemical basis of life.
Atomic Structure Basics
- Atoms consist of protons, neutrons, and electrons
- Protons have a positive charge and are located in the nucleus
- Neutrons have no charge and are also located in the nucleus
- Electrons have a negative charge and orbit the nucleus in shells
- Atomic number represents the number of protons in an atom and determines the element
- Mass number is the sum of protons and neutrons in an atom
- Isotopes are atoms of the same element with different numbers of neutrons (carbon-12 and carbon-14)
- Electron configuration describes the arrangement of electrons in an atom's orbitals
- Electrons fill orbitals in a specific order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, etc.
- Valence electrons are the electrons in the outermost shell and determine an atom's chemical properties
- Atomic radius decreases from left to right across a period and increases down a group in the periodic table
Elements and the Periodic Table
- Elements are pure substances composed of one type of atom
- The periodic table organizes elements based on their atomic number and chemical properties
- Periods are horizontal rows in the periodic table that represent the number of electron shells
- Groups are vertical columns in the periodic table that contain elements with similar chemical properties
- Metals are located on the left side of the periodic table and are good conductors of heat and electricity (sodium, iron)
- Nonmetals are located on the right side of the periodic table and are poor conductors of heat and electricity (oxygen, chlorine)
- Metalloids have properties of both metals and nonmetals and are located along the zigzag line in the periodic table (silicon, arsenic)
- Periodic trends describe how properties such as atomic radius, ionization energy, and electronegativity change across the periodic table
Chemical Bonding Fundamentals
- Chemical bonds form when atoms share or transfer electrons to achieve a stable electron configuration
- Ionic bonds involve the transfer of electrons between a metal and a nonmetal, resulting in the formation of ions (sodium chloride)
- Cations are positively charged ions formed when an atom loses electrons
- Anions are negatively charged ions formed when an atom gains electrons
- Covalent bonds involve the sharing of electrons between two nonmetals
- Single bonds share one pair of electrons (H-H)
- Double bonds share two pairs of electrons (O=O)
- Triple bonds share three pairs of electrons (N≡N)
- Metallic bonds involve the sharing of delocalized electrons among metal atoms, resulting in a sea of electrons
- Electronegativity is a measure of an atom's ability to attract electrons in a bond
- Atoms with higher electronegativity have a greater tendency to gain electrons
- Bond polarity describes the unequal sharing of electrons in a covalent bond due to differences in electronegativity (H-Cl)
Molecular Geometry and Polarity
- Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule
- VSEPR (Valence Shell Electron Pair Repulsion) theory predicts molecular geometry based on the number of electron domains around a central atom
- Electron domains include bonding pairs and lone pairs of electrons
- Common molecular geometries include linear (CO2), trigonal planar (BF3), tetrahedral (CH4), and bent (H2O)
- Molecular polarity depends on the polarity of individual bonds and the overall molecular geometry
- Nonpolar molecules have a symmetrical distribution of charge (CO2)
- Polar molecules have an uneven distribution of charge due to the presence of polar bonds and asymmetric geometry (H2O)
- Dipole moment is a measure of the separation of charge in a polar molecule
- Intermolecular forces, such as hydrogen bonding and van der Waals forces, arise from the interactions between polar molecules
Biological Relevance of Atoms and Elements
- Carbon is the basis of organic molecules and is essential for life due to its ability to form diverse compounds
- Carbon can form single, double, and triple bonds, allowing for the creation of complex molecules (proteins, carbohydrates, lipids)
- Oxygen is crucial for cellular respiration and is a component of many biological molecules (water, amino acids)
- Nitrogen is a key component of amino acids, which are the building blocks of proteins, and nucleic acids (DNA, RNA)
- Phosphorus is essential for the formation of nucleic acids, ATP (energy currency), and phospholipids in cell membranes
- Sulfur is found in certain amino acids (cysteine, methionine) and plays a role in protein structure and function
- Trace elements, such as iron, zinc, and magnesium, serve as cofactors for enzymes and are necessary for various biological processes
- The properties of water, such as its polarity and hydrogen bonding, are crucial for life and the structure of biological molecules
Key Reactions and Interactions
- Acid-base reactions involve the transfer of protons (H+) between molecules
- Acids are proton donors and have a pH below 7 (HCl)
- Bases are proton acceptors and have a pH above 7 (NaOH)
- Neutralization reactions occur when an acid and a base react to form water and a salt
- Redox reactions involve the transfer of electrons between atoms or molecules
- Oxidation is the loss of electrons, and reduction is the gain of electrons
- Oxidation numbers are used to keep track of electron transfer in redox reactions
- Precipitation reactions occur when two soluble compounds react to form an insoluble solid (AgCl)
- Complexation reactions involve the formation of a complex ion, which is a central metal atom or ion bonded to ligands (hemoglobin)
- Enzyme-substrate interactions are crucial for biological catalysis and involve the binding of a substrate to an enzyme's active site
- Enzymes lower the activation energy of reactions, increasing reaction rates
- Enzyme specificity is determined by the shape and chemical properties of the active site
Quantitative Aspects and Calculations
- Mole concept: A mole is the amount of a substance that contains 6.022 × 10^23 particles (atoms, molecules, or ions)
- Molar mass is the mass of one mole of a substance and is expressed in grams per mole (g/mol)
- Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction
- Balanced chemical equations are used to determine the mole ratios of reactants and products
- Molarity (M) is a measure of concentration, defined as the number of moles of solute per liter of solution
- Equilibrium constants (K) describe the ratio of products to reactants at equilibrium and can be used to predict the direction of a reaction
- pH is a measure of the acidity or basicity of a solution and is calculated as the negative logarithm of the hydrogen ion concentration: pH = -log[H+]
- Thermodynamic quantities, such as enthalpy (H), entropy (S), and Gibbs free energy (G), are used to predict the spontaneity of reactions
Lab Techniques and Applications
- Spectrophotometry is used to measure the absorption of light by a sample and can be used to determine the concentration of a substance (Beer-Lambert law)
- Chromatography techniques, such as thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC), are used to separate and identify components of a mixture
- Electrophoresis is used to separate charged molecules, such as proteins and nucleic acids, based on their size and charge
- Titration is a quantitative technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration
- Acid-base titrations involve the use of a pH indicator to determine the endpoint of the reaction
- Calorimetry is used to measure the heat absorbed or released during a chemical reaction or physical process
- Microscopy techniques, such as light microscopy and electron microscopy, are used to visualize biological samples at various magnifications
- Polymerase chain reaction (PCR) is a technique used to amplify specific DNA sequences for analysis and manipulation
- Recombinant DNA technology involves the insertion of foreign DNA into a host organism for the production of desired proteins or other biomolecules