Periodic table

This is the first lesson where you will meet the periodic table. You will see how atoms are structured in the periodic table depending on their electron orbital configuration.

This lesson is a part of MEL Chemistry VR. Learn more →

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At present, sci­en­tists have dis­cov­ered more than one hun­dred chem­i­cal el­e­ments.

All the el­e­ments are ar­ranged in the mod­ern pe­ri­od­ic ta­ble in the or­der of their atom­ic num­ber.

What is the atom­ic num­ber of an el­e­ment? It's the num­ber of pro­tons in­side a nu­cle­us.

There is a re­la­tion­ship be­tween the el­e­ment's elec­tron con­fig­u­ra­tion and its place­ment in the pe­ri­od­ic ta­ble. Let's see how it works.

Each atom has a cer­tain num­ber of pro­tons in the nu­cle­us and an equal num­ber of elec­trons.

Elec­trons in an atom oc­cu­py or­bitals that are ar­ranged in lev­els and sub-lev­els ac­cord­ing to the di­a­gram on the right.

Let's dis­trib­ute the atoms ac­cord­ing to their elec­tron con­fig­u­ra­tions. First, we copy this di­a­gram.

Then flip it.

As you know, each or­bital may con­tain up to two elec­trons. So, we di­vide each square in two.

Now we will ar­range our atoms by a num­ber of elec­trons. We start with hy­dro­gen — the small­est atom, which con­sists of one pro­ton and one elec­tron on the 1s or­bital.

The next is he­li­um. Two pro­tons in the nu­cle­us and two elec­trons on the 1s or­bital.

Now the first row is filled, go to the sec­ond one. There come el­e­ments with elec­trons on the 2s or­bital.

…and on the 2p or­bitals.

The next row con­tains el­e­ments whose elec­trons fill the 3s or­bital.

…and the 3p or­bitals.

Look care­ful­ly, the next row be­gins with el­e­ments whose elec­trons oc­cu­py the 4s or­bital, but then there are el­e­ments whose elec­trons fill the 3d-or­bital.

Next, the el­e­ments with elec­trons on the 4p or­bital.

The fol­low­ing rows are filled in the same way.

Now you see that we have groups of el­e­ments in col­ored squares: red, blue and green.

Re­mem­ber that we use col­or to dis­play what or­bital the last elec­tron in the atom oc­cu­pies - s, p or d.

Let's group the el­e­ments un­der the col­ors in each row. Look at the first pe­ri­od (the rows in the pe­ri­od­ic ta­ble are called pe­ri­ods).

Did you see he­li­um? It has a com­plet­ed elec­tron shell. That is why it is a no­ble gas that does not re­act with oth­er atoms. Like ar­gon and neon.

So it makes sense to put it in the group of no­ble gas­es.

Re­mem­ber, the el­e­ments are ar­ranged in the mod­ern pe­ri­od­ic ta­ble in the or­der of their atom­ic num­ber - the num­ber of pro­tons in the nu­cle­us.

But the place of the atom gives you in­for­ma­tion about the elec­tron con­fig­u­ra­tion of this atom.

Teacher's notes


el­e­ment, atom, atom­ic num­ber, nu­cle­us, pro­tons, elec­trons, elec­tron con­fig­u­ra­tion, shell, s-or­bital, p-or­bital, d-or­bital, pe­ri­ods, no­ble gas­es

Stu­dents will

  • Learn that there are 118 dif­fer­ent chem­i­cal el­e­ments dis­cov­ered at the mo­ment
  • Learn what el­e­ments are ar­ranged in the Pe­ri­od­ic Ta­ble ac­cord­ing to their atom­ic num­ber
  • Study that the atom­ic num­ber is the num­ber of pro­tons in an atom’s nu­cle­us, which is equal to the num­ber of elec­trons in the atom
  • Learn that rows in the Pe­ri­od­ic Ta­ble cor­re­spond to an elec­tron­ic lev­el, as soon as the lev­el is full, new el­e­ments ap­pear on the next row (lev­el)
  • Find out that the rows of the Pe­ri­od­ic Ta­ble are called pe­ri­ods
  • See that neon is the el­e­ment with a com­plet­ed elec­tron shell and is sim­i­lar to oth­er no­ble gas­es
  • Learn that the po­si­tion of the el­e­ment in the Pe­ri­od­ic Ta­ble pro­vides the in­for­ma­tion about the elec­tron con­fig­u­ra­tion of the atom

Com­mon mis­con­cep­tions

The el­e­ments on the pe­ri­od­ic ta­ble are ar­ranged by in­creas­ing atom­ic mass

Hands-on ac­tiv­i­ties

Be­fore VR

  1. The aim is to give stu­dents an idea that el­e­ments in groups have sim­i­lar chem­i­cal and phys­i­cal prop­er­ties be­cause they have sim­i­lar num­bers of elec­trons in their out­er shell. Show stu­dents how Li, Na and K re­act with wa­ter.
  2. The aim is to show stu­dents how they can cat­e­gories dif­fer­ent ob­jects sim­i­lar in prop­er­ties. Ask stu­dents to sort a set of bolts and nuts in dif­fer­ent sizes (3-4) made out of plas­tic, stain­less steel, and brass (dis­cuss that they can be cat­e­go­rized by size or by ma­te­ri­al).

His­to­ry and sources of knowl­edge

  • Ear­ly at­tempts to find out nat­u­ral laws ex­plain­ing the prop­er­ties of el­e­ments.
  • Dal­ton and New­lands ideas.
  • Mendeleev break­through: ta­ble ar­range­ment show­ing pe­ri­od­ic­i­ty in prop­er­ties.
  • Pre­dic­tion of new el­e­ments.

Top­ics to dis­cuss

  • Good sci­en­tif­ic ex­pla­na­tion not only de­scribes ob­ser­va­tions but makes pre­dic­tions.
  • Out­er elec­tron shell as a source of pe­ri­od­ic­i­ty.
  • Out­er elec­tron shell de­ter­mines chem­i­cal prop­er­ties.
  • Group 0, group 1 and group 7 elec­tron con­fig­u­ra­tion and chem­i­cal prop­er­ties.

Fun facts and quotes

  • There were ap­prox­i­mate­ly 50 el­e­ments at the time when Mendeleev cre­at­ed the Pe­ri­od­ic Ta­ble. He left some box­es emp­ty, ex­pect­ing that new el­e­ments would be dis­cov­ered and pre­dict­ed their prop­er­ties. And they ac­tu­al­ly were dis­cov­ered and the pre­dic­tion of prop­er­ties matched per­fect­ly.
  • New el­e­ments are dis­cov­ered reg­u­lar­ly, all of them un­sta­ble.
  • The only let­ter not in the pe­ri­od­ic ta­ble is the let­ter J.
  • Al­most 75% of all el­e­ments in the Pe­ri­od­ic Ta­ble are met­als.
  • Of all 118 known el­e­ments, only two of them are liq­uid at room tem­per­a­ture: bromine and mer­cury.


  • What is a pe­ri­od in the pe­ri­od­ic ta­ble?
  • What is a group in the pe­ri­od­ic ta­ble?
  • Why do el­e­ments in groups have sim­i­lar prop­er­ties?
  • What are no­ble gas­es?
  • How many elec­trons does ni­tro­gen have?
  • How many el­e­ments are in the sec­ond pe­ri­od and why?