chemical bonds

• octet rule: atoms tend to form bonds so that each atom has 8 electrons in its valence shell (full- for He it's only 2)
• metals loose electrons (groups 1a-3a) to become cations
• nonmetals gain electrons (groups 5a-7a) to become anions
• chemical bond: a force that holds atoms together and makes them function as 1 unit
• bonding energy: amount of energy required to break a bond
• atoms bond if they can achieve the lowest possible energy state by bonding
• covalent bond: when the electrons are shared by the nuclei of 2 atoms (between nonmetals)
• ionic bond: a force of attraction between an atom that looses electrons easily and an atom that has a high electron affinity (between nonmetal and metal ions)
• electronegativity: a measure of the tendency of an atom to attract a bonding pair of electrons
• non-polar covalent bond: the electronegativity difference is less than 0.5
• polar covalent bond: electronegativity difference is between 0.5 and 2
• in an ionic bond, the electronegativity difference is more than 2
• ionic compounds have strong attractive forces and are very stable

  • 35, orderdered, repetitive crystal lattice
  • structures depend on size and charge of the ions
  • ions break free from the crystal lattice, which allows for electric conduction
• solubility: the ability of a solute to dissolve in a solvent
• melting point: the temperature at which a solid changes to a liquid
• boiling point: the temperature at which a liquid turns into gas
• polyatomics: a molecule containing two or more atoms of the same element
• to name an ionic compound, the cation goes before the anion

  • formula: cation -> ion (charge superscripts are switched with the subscript of the other atom)
• the strengths of ionic bonds depend on the charges of the ions and the distance between them
• increasing charge increases bond strength
• metallic bonding is when metal atoms lose electrons to form positive ions that are held together by electrostatic attraction
• covalent bonding occurs when non-metal atoms share one or more pairs of valence electrons
• bond dipole: a measurement of the strength of the attraction (electronegativity) between two bonding atoms (points towards the most EN atom)
• dipole moment: "net", represents all of the bond dipoles, measurement of the separation of opposite electrical charges (partial + and partial -)

  • polar molecules have a dipole moment, but no symmetry
  • non-polar molecules have symmetry, but no dipole moment
• when bonds break, energy is released into the system through an endothermic process. when bonds form, energy is released by the system through an exothermic process
• electronegativity: a measure of the tendency of an atom to attract a bonding pair of electrons
• metallic compounds: 3d repeating array of cations in crystal structure (metal ions and delocalized valence electrons)

  • very high melting & boiling points
  • luster: shiny (free electrons move and excited electrons re-emit light)
  • ductile: can be drawn into thin wires
  • malleable: can be drawn into thin sheets
  • conductive: can conduct heat & electricity
  • sea of electrons: delocalized valence electrons that are free to move around and shared among all the metal ions
• dipole-dipole polar molecules are somewhat strong

  • a hydrogen bond is a type of dipole-dipole bond: strongest intermolecular force, H is attracted to N, O, and F
• london dispersion forces can be polar or non-polar and are the weakest intermolecular forces

  • an increase in mass/attraction increases boiling & melting point
  • an increase in mass/attraction decreases volatility
• hydrophobic effect: non-polar substances repel water due to their lack of attraction to it