Niels Bohr won the Nobel Prize in Physics in 1922 for his ‘services in the investigation of the structure of atoms and of the radiation emanating from them’.
Atomic Structure Learning Intentions
In this topic we are learning to: zz
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Develop a model to help explain the basic structure of an atom. Reflect on the contribution of Niels Bohr to atomic theory.
Electronic Configuration
Danish scientist Niels Bohr came up with the idea of electron shells to explain atomic structure.
The first shell (the one closest to the nucleus) has space for 2 electrons. The second shell has space for up to 8 electrons. The third shell also has space for up 8 electrons. The electrons fill up the shells from the inner shells out.
Electron shells are the spaces where electrons orbit. The shells are also called energy levels. z z
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Describing the location of electrons in an atom is called the electronic configuration. Figure 10.3.2 shows the Bohr atomic models for nitrogen and sodium. Nitrogen
Fig. 10.3.1 Niels Bohr
14 7
N Sodium
23 11
z Fig. 10.3.2
Bohr models of nitrogen and sodium
There are 11 electrons in total: 2 in the first shell, 8 in the second shell and 1 in the third shell.
Scientists do not draw a model of an atom every time. They use a shorthand version of the electronic configuration showing the number of electrons in each shell, working outwards from the nucleus.
178 178
For example, the shorthand versions of nitrogen and sodium are: zz zz
Nitrogen: N: 2, 5 Sodium: Na: 2, 8, 1
Na
11 protons 11 electrons
12 neutrons (23 – 11 = 12)
12 N 11 P
7 protons 7 electrons
7 neutrons (14 – 7 = 7) There are 7 electrons in total: 2 in the first shell and 5 in the second shell.
