Periodic Table Questions and Answers   Recently updated !

Periodic Table Questions and Answers

The periodic table is an important tool in chemistry, so there are many periodic table questions that people have. Here are some common questions, with answers in simple, down-to-Earth language that you can understand, even if you’re not a scientist.

Periodic Table Questions and Answers

What Is the Periodic Table?

Of course, the most basic question is “What is the periodic table?” The simple answer is that it is a chart that shows all of the chemical elements and basic facts about them, that orders the elements by increasing atomic number and common properties. The atomic number is the number of protons in every atom of the element. The number of neutrons in the atom changes its isotope, but not its element. Similarly, the number of electrons changes the ion, but not the element.

What Are Groups and Periods in the Periodic Table?

The way the periodic table organizes elements by properties is by putting them in rows, which are called periods, and columns, which are called groups. Elements in a period have the same outer electron shell, which gives them some common characteristics. Elements in a group have number of outer or valence electrons, again, giving them common properties.

What Are Periodic Table Trends or Periodicity?

Organizing the table with groups and periods makes certain trends in element properties apparent. In other words, the table displays periodicity (hence its name).

There are several periodic table trends in properties, but the key ones are atomic radius, electronegativity, electron affinity, and ionization energy:

  • Atomic radius is the size of an electrically neutral atom of an element. In increases moving down a group (column) because the atom gains a new electron shell. It decreases moving from left to right across a period (row) because adding protons (increasing atomic number) attracts and draws the electrons in more tightly.
  • Electronegativity is a measure of how easily an atom attracts electrons that can form a chemical bond. It increases moving left to right (except for the noble gases) and mostly decreases moving down a group.
  • Electron affinity is related to electronegativity. It is the energy change that occurs when a neutral atom accepts an electron. It increases moving across a period, but does not always decrease moving down a group.
  • Ionization energy is the energy required to remove an electron from an atom. It increases moving across a period and decreases moving down a group.

There are other also other trends, such as ionic radius, covalent radius, and metallicity.

Who Invented the Periodic Table?

While lots of scientists have made periodic tables over the years, the one that most closely resembles the table we use today was formulated by Dmitri Mendeleev. So, Mendeleev is considered the “inventor of the periodic table.” His 1869 table differed from the modern table in that it ordered elements by increasing atomic weight instead of atomic number. But, he made the table before protons were discovered. For the most part, using atomic weight instead of atomic number produces the same table.

Why Are the Noble Gases So Inert?

While the noble gases sometimes do participate in chemical reactions, they are mostly unreactive and are exceptions to periodic table trends. The reason is that atoms of elements of this group have stable valence electron shells. In other words, the noble gas atoms become less stable if they lose or gain electrons.

Why Are the Halogens So Reactive?

The halogens (fluorine, chlorine, iodine, etc.) are as reactive as the noble gases are stable. This group is right next to the noble gases, so why is it so reactive? The reason is that they are only one electron away from having a stable configuration. Forming chemical bonds gives the halogens this stability.

What Are the Periodic Table Groups?

While the periods of the periodic table just have numbers corresponding to their rows, the periodic table groups have both numbers and names. Probably the names arose because of the different numbering systems for the groups. The groups are the alkali metals, alkaline earth metals, transition metals, basic metals, metalloids, nonmetals, halogens, and noble gases. The lanthanide and actinide groups are actually a subset of the transition metals.

More Periodic Table Questions

Do you have unanswered periodic table questions? Leave a comment! If it’s a common question, I’ll add it to this article.


  • Bury, Charles R. (July 1921). “Langmuir’s Theory of the Arrangement of Electrons in Atoms and Molecules”. Journal of the American Chemical Society. 43(7): 1602–1609. doi:10.1021/ja01440a023
  • Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  • Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey (2002). General Chemistry: Principles and Modern Applications (8th ed.). Upper Saddle River, N.J: Prentice Hall. ISBN 978-0-13-014329-7.
  • Scerri, Eric. 2020. The Periodic Table, Its Story and Its Significance (2nd edition). New York: Oxford University Press. ISBN 978-0190914363.

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