Bohr’s Atomic Model
In 1913, Neils Bohr, a Dane, proposed his model of the atom. It was a modification of the Rutherford model. Bohr however put the electrons in certain circular orbits called shells or principal energy levels (PEL’s). + 1 st shell (2 electrons max.) 2 nd shell (8 electrons max.) 3 rd shell (18 electrons max.) Nucleus Empty space The “planetary” model
Protons and neutrons are found in the nucleus. Electrons orbit the nucleus in various shells. Everything else is empty space. + 1 st shell (2 electrons max.) 2 nd shell (8 electrons max.) 3 rd shell (18 electrons max.) Nucleus Empty space The “planetary” model Bohr’s Atomic Model
Q:What are the Bohr models for the neutral atoms of the three isotopes of hydrogen? A:Step-1 Draw a box to represent the nucleus. Step-2 Determine the number of protons and neutrons and place them in the nucleus. Step-3 Draw one circle around the nucleus to represent the electron shell and then place the one electron in the shell. H-1H-2H-3 1p 0n 1p 1n 1p 2n e-e- e-e- e-e- Bohr’s Atomic Model
Q:What are the Bohr models for the neutral atoms of the two isotopes of carbon? A:Step-1 Draw a box to represent the nucleus. Step-2 Determine the number of protons and neutrons and place them in the nucleus. Step-3 Draw two circles around the nucleus to represent the electron shells and then place the six electron in the shells as indicated by the electron configuration. C-12C-14 6p 6n 6p 8n e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Bohr’s Atomic Model
Q:What are the Bohr models for the neutral atom 27 Al and the ion 23 Na 1+ ? A:Step-1 Draw a box to represent the nucleus. Step-2 Determine the number of protons and neutrons and place them in the nucleus. Step-3 As indicated by the electron configuration, draw arcs to represent the electron shells and place the electron on them. 27 Al 23 Na 1+ 13p 14n 11p 12n 2e - 8e - 3e - 2e - 8e - 0e - Bohr’s Atomic Model
Q:What are the Bohr models for the ion 37 Cl 1- and the neutral atom of calcium-42? A:Step-1 Draw a box to represent the nucleus. Step-2 Determine the number of protons and neutrons and place them in the nucleus. Step-3 As indicated by the electron configuration, draw arcs to represent the electron shells and place the electron on them. 37 Cl 1- Calcium-42 17p 20n 20p 22n 2e - 8e - 2e - 8e - 2e - Bohr’s Atomic Model
The last shell holding electrons is called the valence. Electrons in the last shell are called valence electrons. Q: How many valence electron are there in 37 Cl 1- ? A: 8 Q: Which shell in a neutral atom of calcium-42 is the valence? A: 4 th 37 Cl 1- 17p 20n 2e - 8e - Calcium-42 20p 22n 2e - 8e - 2e - Bohr’s Atomic Model