Download Rdg: Electron Configuration

Mr. Scharff
Intro to Chemistry
Name __________________
Date ______________ Pd. _
State of Ohio GLI
 PS 9.1. Recognize that all atoms of the same element contain the same number of protons, and elements with the same number of protons
may or may not have the same mass. Those with different masses (different numbers of neutrons) are called isotopes.
 PS 9.2. Illustrate that atoms with the same number of positively charged protons and negatively charged electrons are electrically neutral.
Rdg: Electron Configuration
The electron configuration of an atom is a form of notation which shows how the electrons are distributed among the
various atomic orbital and energy levels. The format consists of a series of numbers, letters and superscripts such as 1s2.
Here we see the electron configuration for the element helium. This electron configuration provides us with the following
information:



The large number "1" refers to the principle quantum number "n" which stands for the energy level. It tells us that
the electrons of helium occupy the first energy level of the atom.
The letter "s" stands for the angular momentum quantum number "l". It tells us that the two electrons of the helium
electron occupy an "s" or spherical orbital.
The exponent "2" refers to the total number of electrons in that orbital or sub-shell. In this case, we know that there
are two electrons in the spherical orbital at the first energy level.
I. Principle Quantum Number (n) and Sublevels
The number of sublevels that an energy level can contain is equal to the principle quantum number of that level. So, for
example, the second energy level would have two sublevels, and the third energy level would have three sublevels. The
first sublevel is called an s sublevel. The second sublevel is called a p sublevel. The third sublevel is called a d sublevel
and the fourth sublevel is called an f sublevel. Although energy levels that are higher than 4 would contain additional
sublevels, these sublevels have not been named because no known atom in its ground state would have electrons that
occupy them.
II. Sublevels and Orbitals
An orbital is a space that can be occupied by up to two electrons. Each type of sublevel holds a different number of
orbitals, and therefore, a different number of electrons. s sublevels have one orbital, which can hold up to two electrons. p
sublevels have three orbitals, each of which can hold 2 electrons, for a total of 6. d sublevels have 5 orbitals, for a possible
total of 10 electrons. f sublevels, with 7 orbitals, can hold up to 14 electrons. The information about the sublevels is
summarized in the table below:
Orbital and Electron Capacity for the Four Named Sublevels
Sublevel
# of orbitals
Maximum number of electrons
s
1
2
p
3
6
d
5
10
f
7
14
III. Total Number of Orbital and Electrons per Energy Level
An easy way to calculate the number of orbitals found in an energy level is to use the formula n2. For example, the third
energy level (n=3) has a total of 32, or nine orbitals. This makes sense because we know that the third energy level would
have 3 sublevels; an s sublevel with one orbital, a p sublevel with 3 orbitals and a d sublevel with 5 orbitals. 1 + 3 + 5 = 9,
so the formula n2 works!
IV. Total Number of Electrons per Energy Level
An easy way to calculate the total number of electrons that can be held by a given energy level is to use the formula 2n2.
For example, the fourth energy level (n=4) can hold 2(4)2 = 32 electrons. This makes sense because the fourth energy
level would have four sublevels, one of each of the named types. The s sublevel hold 2 electrons, the p sublevel holds 6
electrons , the d sublevel holds 10 electrons and the f sublevel holds 14 electrons. 2 + 6 + 10 + 14 = 32, so the formula 2n2
works! We can summarize this information in the table below:
Orbitals and Electron Capacity of the First Four Principle Energy Levels
Principle energy
level (n)
Type of sublevel
Number of orbitals
per type
1
s
1
s
1
p
3
s
1
p
3
d
5
s
1
p
3
d
5
f
7
2
3
4
Number of orbitals Maximum number of
per level(n2)
electrons (2n2)
1
2
4
8
9
18
16
32
V. Order of Filling Sublevels with Electrons
The next thing that you need to recall is the fact that the energy sublevels are filled in a specific order that is shown by the
arrow diagram seen below:
Remember to start at the beginning of each arrow, and then follow it all of the way to the end, filling in the sublevels that it
passes through. In other words, the order for filling in the sublevels becomes; 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s,
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