chemistry

• Solids have a very thick structure that atoms can wiggle a little bit but are in fixed positions, there is some movement and vibration but they do not flow and cannot be compressed
• Liquids have more movement of atoms but they are not in fixed positions, they can flow but cannot be compressed
• Gases have a lot of movement, the atoms are not in fixed positions, they can flow and can be compressed
• Energy is required to change from a solid to a liquid or liquid to gas, energy is released when changing from gas to liquid or liquid to solid
• Melting point


  The temperature at which a solid turns into a liquid
• Boiling point


  The temperature at which a liquid turns into a gas
• Melting point and boiling point are the same number for the opposite processes (melting/freezing, boiling/condensing)
• At room temperature, a substance with a melting point of 19°C and a boiling point of 74°C will be a liquid
• The state symbol for solid is S, liquid is L, gas is G, and aqueous is Aq
• When a liquid and solid or liquid and gas mix, you will see bubbles or a loss of mass
• Plum pudding model


  Old model of the atom with a large cloud of positive charge and negative electrons dotted throughout
• Rutherford's gold foil experiment

  Fired alpha particles at a thin gold foil, most went straight through, some were reflected a little, some were reflected a lot, suggesting a small positive nucleus and large negative outer region
• Rutherford discovered the nucleus, Chadwick discovered neutrons, Bohr developed the current atomic model
• Atomic structure


  Electrons in shells around a nucleus containing protons and neutrons
• Atomic number


  Number of protons in an atom
• Mass number


  Number of protons plus neutrons in an atom
• Isotopes have the same atomic number but different mass numbers
• The periodic table lists all known elements, with their atomic number, mass number, and other properties
• Compound


  Two or more elements chemically bonded together
• Calculating relative formula mass (Mr)


  Add up the relative atomic masses of all the elements in the compound
• Empirical formula


  The simplest whole number ratio of the elements in a compound
• The mass on the periodic table represents the average mass of all the isotopes of an element
• Separation techniques


  • Distillation
  • Evaporation
  • Filtration
  • Fractional distillation
  • Chromatography
• For chromatography, the start line should be drawn in pencil, not pen
• Rf value


  Distance moved by the spot / distance moved by the solvent
• A pure substance melts at a single temperature, a mixture melts over a range of temperatures
• Groups


  Vertical columns in the periodic table, indicate number of outer shell electrons
• Periods


  Horizontal rows in the periodic table, indicate number of electron shells
• Determining electronic configuration


  Draw shells, fill with electrons up to maximum per shell
• Ionic bonding


  Transfer of electrons from metals to nonmetals
• Metals form positive ions, nonmetals form negative ions in ionic bonding
• In an atom, the positive and negative charges cancel out to give a neutral charge
• Oxygen


  In group six, has six electrons in its outer shell
• Ionic bonding


  1. Oxygen keeps the electrons it already had, electrons from magnesium are transferred to oxygen

  2. Draw square brackets around the ions and indicate the charge
• Sodium


  Atomic number 11, has 11 protons in the nucleus and 11 electrons
• In an atom, the positive charges and negative charges cancel each other out, so the overall charge is 0
• When sodium forms an ion, it loses an electron, so it has one more proton than electron, giving it an overall positive charge
• Ionic bonding


  Forms a massive lattice, not just one-to-one bonding
• Properties of ionic compounds

  • High melting point, high boiling point, only conduct when molten or dissolved
• Covalent bonding


  Sharing of electrons between two nonmetals