chem wa2

• An atom is the smallest component of the element which still has the chemical properties of the element
• Atom


  • Made up of smaller subatomic particles
  • Subatomic particles do not have the chemical properties of the element
• Nucleus


  The central portion of an atom that contains protons and neutrons
• Electron shells


  Contain electrons
• Protons and neutrons have almost similar mass, while electrons are much lighter (about 1/1840 the mass)
• Protons have a positive charge, electrons have a negative charge, and neutrons have no charge
• In a neutral atom, the number of protons equals the number of electrons
• If an atom has a net charge, it is called an ion (positive ion = cation, negative ion = anion)
• Rutherford gold foil experiment

  1. Alpha particles fired at gold foil

  2. Most particles pass through (atom is mostly empty space)

  3. Some particles deflected (due to positive charge of nucleus)

  4. Some particles bounce back (collide with nucleus)
• Lighter particles (electrons)

  Deflected more in electric field than heavier particles (protons)
• Mass number

  Number of protons and neutrons in the nucleus
• Atomic number


  Number of protons in the nucleus (equal to number of electrons in a neutral atom)
• Isotopes


  Atoms of the same element with different numbers of neutrons
• Isotopes have the same chemical properties but different physical properties (e.g. boiling point)
• Hydrogen isotopes


  • Protium (1 proton, 0 neutrons)
  • Deuterium (1 proton, 1 neutron)
  • Tritium (1 proton, 2 neutrons)
• Tritium is radioactive and formed in nuclear reactors, not found naturally
• Deuterium forms "heavy water" when combined with oxygen
• Isotopes are identified by their mass number (protons + neutrons)
• Finding the particle with the greatest mass

  1. Scan through the nucleon number (number of protons plus neutrons)

  2. Electron mass is negligible and not considered
• Atom D has the greatest mass
• Isotopes


  Atoms with the same number of protons but different number of neutrons
• Atoms A and C are isotopes of each other
• Electronic structure of an atom

  The arrangement of electrons in an atom
• Rules for electronic structure

  • First shell (n=1) can hold max 2 electrons
  • Second shell (n=2) can hold max 8 electrons
  • Third shell (n=3) can hold max 18 electrons
  • The formula 2n^2 gives the max number of electrons in each shell
• Drawing the electronic structure of hydrogen

  1. Draw the nucleus with 1 proton

  2. Draw the first shell with 1 electron
• Drawing the electronic structure of helium

  1. Draw the nucleus with 2 protons and 2 neutrons

  2. Draw the first shell with 2 electrons
• Drawing the electronic structure of lithium

  1. Draw the nucleus with 3 protons and 4 neutrons

  2. Fill the first shell with 2 electrons, the remaining 1 electron goes in the second shell
• Drawing the electronic structure of carbon

  1. Draw the nucleus with 6 protons and 6 neutrons

  2. Fill the first shell with 2 electrons, the remaining 4 electrons go in the second shell
• Drawing the electronic structure of magnesium

  1. Draw the nucleus with 12 protons and 12 neutrons

  2. Fill the first shell with 2 electrons, the second shell with 8 electrons, the remaining 2 electrons go in the third shell
• Drawing the electronic structure of nitrogen

  1. Draw the nucleus with 7 protons and 7 neutrons

  2. Fill the first shell with 2 electrons, the second shell with 5 electrons
• Drawing the electronic structure of neon

  1. Draw the nucleus with 10 protons and 10 neutrons

  2. Fill the first shell with 2 electrons, the second shell with 8 electrons
• Drawing the electronic structure of argon

  1. Draw the nucleus with 18 protons and 22 neutrons

  2. Fill the first shell with 2 electrons, the second shell with 8 electrons, the third shell with 8 electrons
• Valence shell


  The outermost shell of an atom, furthest from the nucleus
• Electronic configuration


  The numerical expression representing the arrangement of electrons in an atom
• The periodic table arranges elements based on proton number, which also determines the number of electrons in a neutral atom
• Trends in the periodic table

  • Elements in the same group have the same number of valence electrons
  • Elements in the same period have the same number of electron shells
• Ion


  An atom or group of atoms that has an electrical charge, either positive or negative
• Formation of positive ions


  Atom loses valence electrons to attain the stable electronic configuration of a noble gas
• Formation of negative ions

  Atom gains valence electrons to attain the stable electronic configuration of a noble gas
• Atoms can also share valence electrons without forming ions