Constructing a Modified Bohr Model

Let’s look at an example to build your skills on reading information from the periodic table and using it to construct a modified Bohr model. Click on the video to watch a teacher work through this example.

Draw a modified Bohr diagram for an atom of phosphorus-31.
 


On the periodic table, look up the atomic number of phosphorus. This is the number of protons and will be placed in the nucleus.

B2.43 phosphorus from the periodic table


Determine the number of neutrons by subtracting the number of protons (atomic number) from the mass number.
Number of Neutrons = Mass Number – Atomic Number
Number of neutrons = 31 – 15
Number of neutrons = 16
Place the number of neutrons in the nucleus.
Determine the number of electrons. Recall that atoms are neutral, so the number of electrons equals the number of protons. For this atom, it will have 15 electrons.

Draw in the first energy level and place two electrons at the top. Recall that the first energy level can hold a maximum of two electrons.
There are still 13 more electrons to place. Place one electron in each orbital of the second energy level. If there are more than four electrons, start to pair up electrons to a maximum of eight electrons.
There are still five more electrons to place. Place one electron in each orbital of the third energy level. Since there are more than four electrons, pair up electrons on the top orbital.


  Read This

Please read pages 33 to 34 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on information about the structure of elements that are located on the periodic table. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Which subatomic particle determines the identity of an element?

    The protons determine the identity. Each element has a unique number of protons. This relates to the atomic number on the periodic table. For example, if you know that a certain element has 16 protons, that element must be sulfur.
  2. How many electrons and protons are in an atom of chlorine?

    There are 17 protons and 17 electrons. This number is on the periodic table; it is the atomic number for chlorine.
  3. Identify the number of protons, electrons, and neutrons in an atom of magnesium-26.

    protons = 12, electrons = 12, and neutrons = 14. To determine the number of protons, look up the atomic number for magnesium on the periodic table. For this isotope, the mass number is 26, so to determine the number of neutrons, subtract the atomic number from the mass number: 26 – 12 = 14
  4. Write the isotope symbol for calcium-44.

    «math xmlns=¨http://www.w3.org/1998/Math/MathML¨» «mstyle mathsize=¨24px¨» «mmultiscripts» «mo»§#160;«/mo» «mprescripts»«/mprescripts» «mrow» «mi»atomic«/mi» «mo»§#160;«/mo» «mi»number«/mi» «/mrow» «mrow» «mi»mass«/mi» «mo»§#160;«/mo» «mi»number«/mi» «/mrow» «/mmultiscripts» «mi»element«/mi» «mo»§#160;«/mo» «mi»symbol«/mi» «/mstyle» «/math»

    «math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mstyle mathsize=¨24px¨»«mmultiscripts»«mo»§#160;«/mo»«mprescripts»«/mprescripts»«mn»20«/mn»«mn»44«/mn»«/mmultiscripts»«mi»Ca«/mi»«/mstyle»«/math»

    Remember that you need to include the mass number for this specific isotope. The atomic number is on the periodic table.
  5. Draw a modified Bohr diagram for an atom of chlorine-37.

    Remember that in an atom, the number of electrons is equal to the number of protons, which is the atomic number listed on the periodic table. Remember that electrons are placed two in the first energy level, a maximum of eight in the second energy level, and the remaining seven in the third energy level. Remember to place each electron separate, one per orbital for the first four electrons, then pair them up. Neutrons are determined by taking the mass number for this isotope and subtracting the atomic number. Protons and neutrons are placed in the nucleus.
  6. Write the isotope name for the isotope represented by this modified Bohr diagram.