Worksheet 2: ELECTRONIC STRUCTURE OF THE ATOM
Name ___________________________
1.
The number and arrangement of electrons in the energy levels of the atom determine what type of compounds the
element will form. To determine the number of electrons in an atom, we consult the periodic chart of the elements in
your text book. The chart lists the atomic number, symbol, and atomic weight of each element. The element potassium,
for example, is listed as follows.
The atomic number represents the number of protons in the atom. (It is not necessary to discuss the atomic weight at this
time.)
Use the periodic chart to find the name and symbol for the following elements.
6
12.0
a.
b.
a.
b.
50
118.7
2.
Use the periodic chart to find the atomic numbers of the following elements.
Iron
Gold
Fe
Au
55.8
a
196.97
a
3.
The atomic number tells how many _____ are present in the atom.
4.
If an element has an atomic number of 79, there are _____ protons in an atom of
that element.
5.
The atomic number represents the number of protons in an atom, which is also the number of electrons since there are an
equal number of protons and electrons in every atom.
Example:
Element
Atomic Number
Number of Protons
Number of Electrons
Ne
10
10
10
Fill in the needed information below.
Element
Atomic Number
Cl
Number of Protons
Number of Electrons
Sc
Cr
Pb
U
6.
The next task is to determine how many electrons go into each of the seven energy levels. We can do this by using the
mathematical formula 2n2, where n is the number of the energy level.
Example:
Energy Level = n
Substituted for
Maximum Number
n in Formula
of Electrons in Level
1
2n2
2 (1 x 1) = 2
2
2n2
2 (2 x 2) = 8
3
5
6
7
7.
To arrange the electrons in the energy levels, we use our ability to find the total number of electrons an atom has and our
ability to find the maximum number of electrons in each energy level. Except for a limitation that will be explained later,
the energy levels fill from the first one on out. The first level of any atom can hold maximum of two electrons and the
second level can hold a maximum of eight.
Example:
Element
Number of Electrons
Arrangement of Electrons in Energy Levels
1
2
3
4
F
9
2
7
The fluorine atom has a total of nine electrons to distribute in the seven levels. The first level took two of the nine
electrons, leaving only seven for the second level even though it could hold eight.
Complete the following.
Element
a)
Number of Electrons
Arrangement of Electrons in Energy Levels
1
2
3
4
S
b) P
c)
Mg
d) Ca
8.
All atoms are neutral. This means that there is always an equal number of positive and negative charges in an atom.
Because protons are positively charged and electrons are negatively charged, there must therefore be an equal number of
electrons and protons in an atom.
An element with 29 electrons per atom must also have ____ protons per atom.
What element is this?
9.
Ions on the other hand have an imbalance of protons and electrons. This means that there are always an unequal number
of electrons to protons. The proton amount is fix however, based on the identity of the element, therefore the number of
electrons must vary in order to account for charge of the atom (ion). If a chloride anion has a charge of –1, then the
number of proton is fix at 17 (the atomic number or the number of protons). The number of electrons therefore must be
18. The 17 positive proton and the 18 negative electrons adds up to –1 net charge. Write out the electron and protons
each of the ions (or atom) below posses.
ion or atom
3Li
+
15P
-3
14Si
21Sc
+3
32Ge
-4
34Se
-1
No. of p+ / e -
10. The electron configuration of an atom is the nomenclature illustrating how electrons are distributed among the various
atomic orbitals. The atom hydrogen has one electron found in the 1s orbital. H has the electron configuration 1s1. The
atom carbon has the electron configuration C = 1s22s22p2, or it can also be written C = [He]2s22p2 where [He]
represents the electron configuration 1s2. Complete the electron configuration for the following atoms. The filling
sequence is 1s-2s-2p-3s-3p-4s-3d-4p-5s-4d-5p-6s-4f-5d-6p
Atom
i.e. Kr
electron-configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
Atom
He
P
Ar
Ca
Mg
Li
Ge
electron-configuration
11. The electron configuration of an ion is determine in the same manner as that for an atom except that the number of
electron must be adjusted based on the charge of the ion. An atom with the same number of electron as an ion will have
the same electron configuration. From the above example, the carbon atom has six electrons and has an electron
configuration of C = [He]2s22p2. A nitrogen +1 cation will also have the exact electron configuration N+ = [He]2s22p2.
Note that the nitrogen atom has an electron configuration of N = [He]2s22p3 but the +1 ion has one less electron, 6
instead of 7. Similarly, O+2, F+3, B-1 all have six electrons and therefore all have the electron configuration,
[He]2s22p2. Complete the electron configuration for the following atoms.
Atom
i.e. 32
Ge-4
15P
Atom
-1
34Se
-3
20Ca
10.
electron-configuration
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
21Sc
+2
15N
electron-configuration
+3
-3
Orbital box diagrams are used to show the location of electrons in the outer shell. Inner (“core”) electrons are those
that correspond to the nearest noble gas and are not typically represented. So iron, which has an electron
configuration of [Ar] 4s2 3d6 would have an orbital box diagram that looks like
4s
3d
The presence of unpaired electrons will cause the species to be paramagnetic; if ALL the electrons are paired it is
said to be diamagnetic.
Write out the electron configurations for the following atoms and ions. Determine the number of unpaired electrons
in the ground state. (continue on back if needed)
22Ti
+3
25Mn
+2
15P
65Tb
+4
78Pt
+2
11.
List all elements beginning with the letter "R" (with Z < 88) which are diamagnetic and write their electron
configuration.
12.
Assign all possible values for the quantum numbers n, l, ml for the following orbitals (assume that there is no
specific spatial assignment based on the ml value):
2pz
3dz2
3fxyz
4s