atomic structure and periodic table

• Plum pudding model


  An atom is a ball of positive charge with negative electrons embedded in it
• Alpha scattering experiment


  1. Scientists took a piece of gold foil

  2. Fired tiny positive alpha particles at the gold foil

  3. Most alpha particles passed straight through the gold foil

  4. Some alpha particles were deflected

  5. Some alpha particles bounced straight back
• Most alpha particles went straight through the gold foil


  Atoms are mainly empty space
• Some alpha particles were deflected


  The center of the atom must have a positive charge
• Some alpha particles bounced straight back


  The center of the atom must contain a great deal of mass
• Nuclear model


  Most of the atom is empty space, with a tiny positive nucleus containing most of the mass, and negative electrons around the edge
• The nuclear model replaced the plum pudding model based on the results of the alpha scattering experiment
• Nuclear model of atomic structure

  Most of an atom is empty space, with a positive nucleus containing most of the mass, and negative electrons at the edge
• Nuclear model


  • Electrons orbit the nucleus at specific distances (energy levels/shells)
  • Positive charge in nucleus due to protons
  • Nucleus also contains neutral particles called neutrons
• Radius of an atom is around 0.1 nanometer
• Radius of the nucleus is approximately 1 * 10^-14 m
• Nearly all the mass of the atom is found in the nucleus
• Relative charge


  Charge of one particle compared to another particle
• Relative charge of particles

  • Protons: +1
  • Neutrons: 0
  • Electrons: -1
• Atoms have no overall charge because the number of electrons equals the number of protons
• Relative mass


  Mass of one particle compared to another particle
• Relative mass of particles

  • Protons: 1
  • Neutrons: 1
  • Electrons: much smaller than 1
• Relative atomic mass


  The weighted average of the mass numbers of an element's isotopes, based on their abundance
• Calculating relative atomic mass

  1. Mass number of isotope 1 x percent abundance of isotope 1

  2. + Mass number of isotope 2 x percent abundance of isotope 2

  3. / 100
• Relative atomic mass of boron calculated using the formula is 10.8, but rounded up to 11 on the periodic table
• Relative atomic mass of magnesium calculated using the formula is 24.3, but rounded down to 24 on the periodic table
• Atomic number


  The smaller of the two numbers, tells us the number of protons in the nucleus
• Neutral atom


  The number of electrons is the same as the number of protons
• Electron energy levels


  • Also called electron shells
  • Each energy level can hold a maximum number of electrons before the next energy level starts filling
• Maximum electrons per energy level

  • First energy level: 2
  • Second energy level: 8
  • Third energy level: 8
• Assigning electrons into energy levels

  1. Place electrons in first energy level until full

  2. Then place electrons in second energy level until full

  3. Then place electrons in third energy level
• Number of electrons in outer energy level

  Tells us the group number of that element in the periodic table
• Groups in the periodic table

  • Group 0 (noble gases)
  • Group 1
  • Group 2
  • Group 3
  • Group 4
• Helium and neon have a full outer energy level and are found in group 0
• Sodium has 2 electrons in the first energy level, 8 in the second, and 1 in the third energy level, and is in group 1
• Periodic table


  Arranged into columns called groups
• Groups in the periodic table

  • Group 1
  • Group 2
  • Transition elements
  • Group 3
  • Group 4
  • Group 5
  • Group 6
  • Group 7
  • Group 0
• Periodic


  Occurring at regular intervals
• Elements in a group

  • Have similar chemical properties
  • React in a similar way
  • Have the same number of electrons in their outer energy level
• Triads


  Groups of three elements with similar chemical properties
• Triads


  • Lithium, sodium, potassium
  • Chlorine, bromine, iodine
• Law of octaves

  Every eighth element reacts in a similar way
• Newland's law of octaves had problems as it did not always group elements correctly</b>
• Mendeleev's periodic table

  • Arranged elements in order of increasing atomic weight
  • Switched order of specific elements to fit patterns
  • Left gaps for undiscovered elements
• Mendeleev's predictions of undiscovered elements were correct