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2p
x
2p
y
2p
z
2s
1s
→
→
→
→
→
→
→
→
→
→
1s 2s
2p
Neon atom
Electron Arrangement
You can represent an atom’s electron configuration using one of two
convenient methods: orbital diagrams or electron configuration
notation.
Orbital diagrams
As mentioned earlier, electrons in orbitals can be represented by
arrows in boxes. Each box is labeled with the principal quantum
number and sublevel associated with the orbital. For example, the
orbital diagram for a ground-state carbon atom, shown below, contains
two electrons in the 1s orbital, two electrons in the 2s orbital, and one
electron in two of three separate 2p orbitals. The third 2p orbital
remains unoccupied.
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2s
→
→
→
→
1s
→
→
2p
Electron configuration notation
The electron configuration notation designates the principal energy level and energy
sublevel associated with each of the atom’s orbitals and includes a superscript
representing the number of electrons in the orbital. For example, the electron
configuration notation of a ground-state carbon atom is written 1s
2
2s
2
2p
2
.
Orbital diagrams and electron configuration notations for the elements in periods one and
two of the periodic table are shown in
Table 4. Figure 19
illustrates how the 1s, 2s, 2p
x
,
2p
y
, and 2p
z
orbitals illustrated earlier in
Figure 17
overlap in the neon atom.
Table 4
Electron Configurations and Orbital Diagrams for
Elements 1–10
Element
Atomic
Number
Orbital Diagram
1s 2s 2p
x
2p
y
2p
z
Electron Configuration
Notation
Hydrogen
1
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2s
→
→
→
→
1s
→
→
2p
1s
1
Helium
2
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2s
→
→
→
→
1s
→
→
2p
1s
2
Lithium
3
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
1
Beryllium
4
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
2
Boron
5
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
2
2p
1
Carbon
6
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
2
2p
2
Nitrogen
7
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
2p
1s
2
2s
2
2p
3
Oxygen
8
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
2
2p
4
Fluorine
9
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
2p
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2s
→
→
→
→
1s
→
2p
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2s
→
→
→
→
1s
→
→
2p
1s
2
2s
2
2p
5
Neon
10
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
→
2p
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2s
→
→
→
→
1s
→
2p
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2s
→
→
→
→
1s
→
2p
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2s
→
→
→
→
1s
→
2p
1s
2
2s
2
2p
6
Figure 19
The 1s, 2s, and 2p
orbitals of a neon atom overlap.
Determine
how many electrons a
neon atom has.
128
Module 4 • Electrons in Atoms