chm 12901 general chemistry with a biological focus unit 3 study guides

Key Concepts and Definitions

• Chemical bonding involves the interaction between atoms to form molecules or compounds
• Electrons play a crucial role in chemical bonding as they are shared, transferred, or attracted between atoms
• Valence electrons are the electrons in the outermost shell of an atom and participate in bonding
• Electronegativity measures an atom's ability to attract electrons in a chemical bond
  • Atoms with higher electronegativity have a stronger pull on shared electrons
• Ionic bonds form when electrons are completely transferred from one atom to another, creating ions
• Covalent bonds occur when electrons are shared between atoms to form a stable molecule
• Metallic bonds are the attraction between positively charged metal ions and delocalized electrons

Types of Chemical Bonds

• Ionic bonds form between metals and nonmetals due to the complete transfer of electrons
  • Metals lose electrons to form positively charged cations, while nonmetals gain electrons to form negatively charged anions
  • The resulting electrostatic attraction between the ions holds the compound together (sodium chloride)
• Covalent bonds involve the sharing of electrons between two nonmetals
  • Single covalent bonds share one pair of electrons (hydrogen molecule)
  • Double and triple covalent bonds share two or three pairs of electrons, respectively (oxygen and nitrogen molecules)
• Coordinate covalent bonds occur when one atom donates both electrons to form the shared pair (ammonium ion)
• Metallic bonds are formed by the attraction between positively charged metal ions and delocalized electrons
  • The delocalized electrons are free to move throughout the metal structure, contributing to properties like electrical conductivity and malleability (copper wire)
• Polar covalent bonds have an unequal sharing of electrons due to differences in electronegativity between the bonded atoms (water molecule)

Atomic Structure and Electron Configuration

• Atoms consist of a positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons
• Electrons occupy specific energy levels or shells around the nucleus, with each shell having a maximum number of electrons
• The electron configuration of an atom represents the distribution of electrons in its atomic orbitals
  • Orbitals are designated as s, p, d, and f, with each type having a specific shape and energy level
• The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with 8 electrons in their outermost shell (valence shell)
  • Exceptions to the octet rule include atoms with fewer than 8 electrons in their valence shell (hydrogen and helium) and atoms that can expand their valence shell (transition metals)
• Hund's rule states that electrons fill orbitals of the same energy level singly before pairing up, and they do so with parallel spins
• The Aufbau principle describes the order in which electrons fill atomic orbitals, starting from the lowest energy level and working up

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 pairs (bonding and lone) around the central atom
  • Electron pairs repel each other and arrange themselves to minimize repulsion, leading to specific geometries (tetrahedral, trigonal planar, linear)
• Molecular polarity depends on the geometry and the polarity of individual bonds within the molecule
  • Nonpolar molecules have a symmetrical distribution of charge (carbon dioxide)
  • Polar molecules have an uneven distribution of charge due to the presence of polar bonds and asymmetric geometry (water)
• Dipole moment is a measure of the separation of charge in a molecule, with the arrow pointing from the positive to the negative end
• Resonance structures occur when a molecule can be represented by multiple Lewis structures, with the actual structure being a hybrid of these (benzene)

Intermolecular Forces

• Intermolecular forces are attractive forces between molecules, which influence properties like boiling point, melting point, and solubility
• Dipole-dipole forces occur between polar molecules, where the partially positive end of one molecule attracts the partially negative end of another
  • Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to a highly electronegative atom like oxygen or nitrogen (water molecules)
• London dispersion forces (induced dipole-induced dipole) are weak attractive forces that result from temporary fluctuations in electron distribution, creating momentary dipoles
  • These forces are present in all molecules, but their strength increases with the size and surface area of the molecule (gecko feet adhesion)
• Ion-dipole forces occur between an ion and a polar molecule, such as the attraction between sodium ions and water molecules in an aqueous solution
• Van der Waals forces is a collective term for all intermolecular forces, including dipole-dipole, London dispersion, and ion-dipole interactions

Biological Relevance of Chemical Bonding

• Chemical bonding plays a crucial role in the structure and function of biological molecules
• Covalent bonds are essential in the formation of organic molecules like proteins, carbohydrates, and nucleic acids
  • Disulfide bonds between cysteine residues help stabilize protein tertiary structure
  • Phosphodiester bonds link nucleotides in DNA and RNA
• Hydrogen bonding is critical for the unique properties of water, such as its high specific heat capacity and surface tension, which are essential for life
  • Hydrogen bonds also contribute to the secondary structure of proteins (alpha helices and beta sheets) and the base pairing in DNA
• Ionic bonds are important in maintaining the structure and function of bones and teeth, as well as in nerve and muscle function
  • Calcium phosphate, a key component of bones and teeth, is held together by ionic bonds
• Metallic bonds are found in some essential trace elements, such as iron in hemoglobin, which is crucial for oxygen transport in the blood
• Intermolecular forces influence the folding and stability of biological macromolecules, as well as their interactions with other molecules (enzyme-substrate binding)

Problem-Solving and Calculations

• Determine the type of bonding in a compound based on the electronegativity difference between the atoms
  • If the difference is greater than 1.7, the bond is considered ionic; if less than 0.4, the bond is nonpolar covalent; values in between indicate a polar covalent bond
• Calculate the formal charge on an atom in a molecule by subtracting the number of non-bonding electrons and half the number of bonding electrons from the number of valence electrons in the neutral atom
• Predict the molecular geometry using VSEPR theory by counting the number of electron pairs (bonding and lone) around the central atom and applying the corresponding geometric arrangement
  • For example, a molecule with 4 electron pairs (tetrahedral), 3 electron pairs (trigonal planar), or 2 electron pairs (linear)
• Determine the polarity of a molecule by evaluating the polarity of individual bonds and the overall molecular geometry
  • If the molecule is symmetrical and contains nonpolar bonds, it is nonpolar; if it has polar bonds and an asymmetric geometry, it is polar
• Calculate the lattice energy of an ionic compound using the Born-Haber cycle, which takes into account the energy required to form the gaseous ions and the energy released when the ions combine to form the solid

Lab Techniques and Experiments

• Conductivity tests can be used to distinguish between ionic and covalent compounds
  • Ionic compounds conduct electricity when dissolved in water or molten, while covalent compounds do not
• Melting point and boiling point measurements can provide insight into the strength of intermolecular forces in a substance
  • Higher melting and boiling points indicate stronger intermolecular forces
• Solubility tests can help determine the polarity of a substance and the type of intermolecular forces present
  • "Like dissolves like" principle: polar substances dissolve in polar solvents, while nonpolar substances dissolve in nonpolar solvents
• Spectroscopic techniques, such as infrared (IR) and Raman spectroscopy, can be used to identify the presence of specific functional groups and bond types in a molecule
  • IR spectroscopy detects the vibrations of bonds, while Raman spectroscopy measures the scattering of light by molecules
• X-ray crystallography can determine the three-dimensional structure of a molecule or crystal, providing information about bond lengths, angles, and the arrangement of atoms
• Molecular modeling software can be used to visualize and predict the geometry, polarity, and intermolecular forces of molecules based on their structure and composition