ch2 the nature of molecules

• Atoms are composed of protons, neutrons, and electrons
• Protons are positively charged particles located in the nucleus
• Neutrons are neutral particles located in the nucleus
• Electrons are negatively charged particles found in orbitals surrounding the nucleus
• Atomic number equals the number of protons in an atom
• Atomic mass is the sum of protons and neutrons of an atom
• Isotopes are atoms of a single element that possess different numbers of neutrons
• Electrons determine the chemical behavior of atoms
• Electrons have different energy levels and occupy orbitals
• Electrons have potential energy related to their position
• During some chemical reactions, electrons can be transferred from one atom to another
• Elements in the periodic table are displayed according to valence electrons
• Inert elements have all eight electrons in the valence shell
• Ionic bonds are formed by the attraction of oppositely charged ions
• Covalent bonds form when atoms share 2 or more valence electrons
• Differences in electronegativity dictate how electrons are distributed in covalent bonds
• Polar covalent bonds involve unequal sharing of electrons, such as in H2O where oxygen has more affinity to electrons than hydrogen, making H2O a polar molecule
• Hydrogen bonds are weak electrical attractions between neighboring water molecules due to the polarity of water
• An ionic bond results from a transfer of electrons, creating positive and negative ions that attract each other, while a covalent bond is the result of two atoms sharing electrons
• Chemical reactions involve the formation or breaking of chemical bonds, with reactants being the original molecules and products being the resulting molecules from the reaction
• The extent of a chemical reaction is influenced by temperature, concentration of reactants and products, and catalysts. Many reactions are reversible
• Water's ability to form hydrogen bonds is one of its most important properties, allowing weak chemical associations between water molecules
• Water has high specific heat, high heat of vaporization, and solid water is less dense than liquid water due to hydrogen bonding
• Polar molecules and ions are soluble in water, making it a good solvent. Water also organizes nonpolar molecules and causes hydrophobic substances to aggregate
• Water can form ions through the spontaneous breaking of covalent bonds. Pure water is considered neutral with a pH of 7
• An acid increases [H+] in water, lowering the pH, while a base combines with H+ to lower [H+]. Buffers resist changes in pH by releasing or absorbing hydrogen ions