Periodic Table of the
Elements: Practice Problems
Group and Period
PTE Group
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The columns on the PTE are called groups.
Each group follows a pattern.
All the elements in a group have the same number of valence electrons.
All the elements in a group need to gain/lose/share the same number of
valence electrons to achieve ideal electron configuration.
• Group number (1-8) indicates the number of valence electrons.
• Group 1=1 valence electron
• Group 4=4 valence electrons
• To achieve ideal electron configuration, an element will gain/lose electrons
to achieve the number of electrons of the “nearest” Nobel Gas.
Valence Electron Problem 1:
• How many valence electrons does Silicon (Si) have?
• It is in group 4/14, so it has 4 valence electrons.
Valence Electron Problem 2:
• How many valence electrons does Barium (Ba) have?
• It is in group 2, so it has 2 valence electrons.
Valence Electron Problem 3:
• How many valence electrons does Iodine (I)have?
• It is in group (7/17), so it has 7 valence electrons.
Ideal Electron Configuration Problem 1:
• How must the number of electrons change for Nitrogen (N) to be
stable?
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Nitrogen is in Period 5/15.
It is three “spaces” away from Neon, the nearest Noble Gas.
It is five spaces away from Helium, the next closest Noble Gas.
It can either gain 3 electrons or lose 5 electrons to get an ideal electron
configuration.
• It is more likely it will gain 3 electrons.
Ideal Electron Configuration Problem 3:
• How must the number of electrons change for Carbon (C) to be
stable?
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Carbon is in Period 4/14.
It is four “spaces” away from Neon, the nearest Noble Gas.
It is four spaces away from Helium, the next closest Noble Gas.
It can either lose 4 electrons or gain 4 electrons to get an ideal electron
configuration.
• It is equally likely that it will gain or lose 4 electrons.
Ideal Electron Configuration Problem 3:
• How must the number of electrons change for Sulfur (S) to be stable?
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Sulfur is in Period 6/16.
It is two “spaces” away from Argon, the nearest Noble Gas.
It is six spaces away from Neon, the next closest Noble Gas.
It can either lose 6 electrons or gain 2 electrons to get an ideal electron
configuration.
• It is more likely it will gain 2 electrons.
Electron Configuration and Electron Shells
• As electrons get added, they start filling in available spaces in each
Electron Shell.
• There are 7 known electron shells, each containing several orbitals
that can hold electrons.
• When a shell is the valence (outer) shell, it will never hold more than
8 electrons.
• The number of electrons in each shell are sometimes indicated on the
PTE.
• The period (row) that an element is found in indicates which shell is
the valence shell.
Electron Shell Problem 1
• How many electron shells does Tin (Sn) have?
• It is in period 5, so it has 5 shells, the first 4 of which are full.
Electron Shell Problem 2
• How many electron shells does Silicon (Si) have?
• It is in period 3, so it has 3 shells, the first 2 of which are full.
Electron Shell Problem 3
• How many electron shells does Copper (Cu) have?
• It is in period 4, so it has 4 shells, the first 3 of which are full.
Valence Shells and Electrons Problem 1:
• An element has 3 valence electrons and 3 electron shells. What
element is it?
• If it has 3 valence electrons, it is probably from group 3/13.
• If it has 3 electron shells, it must be period 3.
• The matching element is Aluminum.
Valence Shells and Electrons Problem 2:
• An element has 7 valence electrons and 2 electron shells. What
element is it?
• If it has 7 valence electrons, it is from group 7/17.
• If it has 2 electron shells, it must be period 2.
• The matching element is Fluorine (F).
Valence Shells and Electrons Problem 3:
• An element has 5 valence electrons and 5 electron shells. What
element is it?
• If it has 5 valence electrons, it is from group 5/15.
• If it has 5 electron shells, it must be period 5.
• The matching element is Antimony (Sb).
Simple Problem 1:
• An element is in group 6/16 and period 4. What element is it?
• The matching element is Selenium (Se).
Simple Problem 2:
• An element is in group 3/13 and period 7. What element is it?
• Ununtrium
Simple Problem 3:
• How many electron shells and valence electrons does the element
Strontium (Sr) have?
• It is in period 5, so it has 5 electron shells.
• It is in group 2, so it has 2 valence electrons in its valence shell.
Tough Problem 1:
• An element has 12 neutrons in a typical isotope, and has an ideal
electron configuration identical to neon. What element is it?
• If its ideal electron configuration is the same as neon’s, it must be within 4
spaces of neon.
• Fluorine is not massive enough: it only has 10 neutrons.
• Looking at more massive elements, sodium has a mass of 23 and an atomic
number of 11. 23-11=12 neutrons. Sodium matches.
• Magnesium has a mass of 24 and 12 protons. 24-12=12 neutrons.
Magnesium matches.
Tough Problem 2:
• An element needs to gain or lose 2 electrons to gain ideal electron
configuration. It has 5 filled electron shells, and one partially filled
shell. What elements could it be?
• It must be in period 6.
• Barium could lose 2 electrons to become like Xenon, or Polonium could gain 2
electrons to become like Radon.
Tough Problem 3
• An element has 81 neutrons, and an ideal electron configuration
similar to Xenon. What element is it?
• It must be in period 5 or 6.
• Barium has an atomic mass of 137, and 56 protons. 137-56=81 neutrons.
• Barium must be the answer.