What does the Group number and Period number tell you?

The group number tells you the total number of electrons present in the outermost orbit of an atom.

In other words, group number tells you the number of valence electrons of an atom.

For example,

Let us consider group 1 of the Periodic table.

What does the Group number and Period number tell you (How many valence electrons does hydrogen, lithium, sodium, potassium have)

Group 1 indicates that the elements lying in that group have only 1 electron in its outermost orbit.

In other words, group 1 elements have 1 valence electron.

how many valence electrons are in lithium, sodium, potassium, rubidium, cesium and francium

Similarly, consider group 2 of the periodic table.

how many valence electrons are in beryllium, magnesium, calcium, strontium, barium and radium

Group 2 represents that the elements lying in that group have 2 electrons in the outermost orbit.

Or we can say that these elements of group 2 have 2 valence electrons. 

valence electrons in beryllium, magnesium, calcium, strontium, barium and radium

Similarly, also remember that;

Group 13 elements have 3 valence electrons, not 13.

valence electrons in boron, aluminium, gallium, indium and thallium.

Group 14 elements have 4 valence electrons, not 14.

valence electrons in carbon, silicon, germanium, tin and lead

Group 15 elements have 5 valence electrons, not 15.

valence electrons in nitrogen, phosphorous, arsenic, antimony and bismuth

Group 16 elements have 6 valence electrons, not 16.

valence electrons in oxygen, sulfur, selenium, tellurium and polonium

Group 17 elements have 7 valence electrons, not 17.

valence electrons in fluorine, chlorine, bromine, iodine and astatine

Group 18 elements have 8 valence electrons, not 18.

valence electrons in helium, neon, argon, krypton, xenon and radon

(Side Note: d-block elements and f-block elements do not show the same number of valence electrons as that of their group number.
For example, group 3 elements of d-block should have 3 electrons in outermost orbit. But they have 2 electrons in outermost orbit.
Similarly, group 4 elements of d-block should have 4 electrons in outermost orbit, but they also have 2 electrons in outermost orbit. 
This is because the d-block elements have outermost electrons in s-orbitals as well as d-orbitals. 
Plus these d-block elements have incomplete d-orbitals. 
Thus electrons of both s-orbitals as well as d-orbitals participate in chemical reaction.
Similarly, f-block elements have incomplete f-orbitals.
And here also, the electrons of both s-orbitals and f-orbitals participate in chemical reaction.
Hence d-block and f-block elements have variable valency or different valence electrons other than the group number.)

Confused?? Checkout Interactive Periodic table (where you will find the arrangement of electrons for each element.)

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What does the period number tell you?

The period number on the Periodic table tells you the total number of orbits that the atom will have.

In other words, the period number indicates the number of energy levels (or energy orbit) of an atom.

For example,

1st period indicates that these elements possess 1 energy shell (or energy orbit).

what does the period number on the periodic table tells you

2nd period indicates that these elements possess 2 energy shells.

how many shells does lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon have

3rd period indicates that these elements possess 3 energy shells.

how many shells does sodium, magnesium, aluminium, silicon, phosphorous, sulfur, chlorine and argon have

4th period indicates that these elements possess 4 energy shells.

what do period 4 elements have in common

5th period indicates that these elements possess 5 energy shells.

energy shells in period 5 elements

6th period indicates that these elements possess 6 energy shells.

energy shells in period 6 elements

And lastly,

7th period indicates that these elements possess 7 energy shells.

energy shells in period 7 elements

Final words

The groups and periods are very important on the Periodic table

The elements are arranged according to their atomic number on the modern periodic table.

The elements which are in the same groups have the same number of electrons in outermost orbit (i.e 1st group has 1 electron in outermost orbit, 2nd has 2 electrons in outermost orbit, 13th group has 3, 14th has 4, and so on…)

Also, the periods of periodic table indicates the number of energy orbits or energy shells of an atom.

Elements of period 1 have 1 energy shell, elements of period 2 have 2 energy shells, and so on…

This is it for this topic.

I hope now you know what group number and period number tells you about the atom on a Periodic table.

If you have any doubts, feel free to ask me in the comments below.

Also let me know, has this article helped you or not?

Bonus Gift for you: Interactive Periodic Table

Let me tell you how this Interactive Periodic Table will help you in your studies.


1).
You can effortlessly find every single detail about the elements from this single Interactive Periodic table.

(For Interactive Periodic table, view on laptop/desktop for better experience. If you are on mobile device, then use a “Desktop site mode” to see interactive periodic table)

2). You will get the detailed information about the periodic table which will convert a newbie into pro.

3). You will also get the HD images of the Periodic table (for FREE).

Checkout Interactive Periodic table and download it’s high resolution image now (It’s FREE)

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