Bohr Models Study Notes

Bohr Models

Learning Target

  • Students should be able to draw and interpret Bohr models of atoms.

Question of the Day

  • What are three prominent characteristics of the Bohr Model of the atom?

Characteristics of Bohr Model

  • The Bohr Model shows the internal structure of an atom.
  • Determines the number of energy levels corresponding to the periodic table.
  • Each energy level is represented in rows of the periodic table, with seven known energy levels (n).

Energy Levels

  • Definition: Principal energy levels (n) are the different layers of electrons in an atom.
  • As energy levels are further from the nucleus:
    • They become larger.
    • They can accommodate more electrons.
    • They possess higher potential energy.

Ground State of Electrons

  • Definition: Ground state refers to the lowest energy state of an atom.
  • Electrons are attracted to the nucleus and tend to remain as close as possible to it.
  • The limits on the number of electrons per orbital arise from:
    • Repulsions between electrons.
    • Available space in the orbitals.

Protons and Electrons

  • Definition: The atomic number of an element is the total count of protons within its nucleus.
  • The number of protons in an atom is equal to the number of electrons surrounding it.
  • Example: Carbon is represented as:
    • Atomic number: 6
    • Atomic mass (approximate): 12.011

Neutrons

  • Neutrons contribute to the mass number of an atom.
  • Mass number definition: The mass number is the sum of protons and neutrons in the nucleus.
  • To determine the mass number, round the atomic mass to the nearest whole number.
  • Formula to find the number of neutrons:
    • \text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}
  • Following this, for Carbon:
    • Atomic mass rounded: 12
    • Number of protons (atomic number): 6
    • Neutrons: 12 - 6 = 6

Drawing a Bohr Model

  1. Step 1: Determine the number of protons using a periodic table.
    • For Carbon: Protons = 6.
  2. Step 2: Identify the number of neutrons from the atomic mass.
    • For Carbon: Atomic mass (rounded) = 12; Neutrons = 12 - 6 = 6 .
  3. Step 3: Draw the nucleus, considering the number of energy levels.
    • Carbon is located in the second period, indicating it has two energy levels.
  4. Step 4: Fill in the electrons according to the energy levels and periodic table guidance:
    • First energy level can hold a maximum of 2 electrons. Thus:
      • Electrons in the first level: 2.
      • Remaining electrons for the second level: 4 (making total = 6 for Carbon).

Electron Configuration in Energy Levels

  • The number of elements in a row of the periodic table determines the maximum number of electrons that can fit in each energy level.
    • For example, the first energy level can hold up to 2 electrons while the second can hold up to 8 electrons.

Remember

  • Electrons are attracted to the positive charge of the nucleus and prefer to be close to it.
  • Always fill an energy level completely before adding electrons to the next level.