Periodic Table With Valence Electrons (+ Lewis Dot Structures)

In a lot of cases, you will need a periodic table with valance electrons (this is also referred to as the Lewis dot structure of atoms). Some periodic systems include ion charges (photo below), but valance electron period tables are exceedingly rare to find. That’s why we created a period system with Lewis dot structures for the first 20 elements in the period table (from H to Ca).

periodic table with oxidation number for calcium atom
Some period tables include oxidation numbers for atoms (Example: Calcium has a +2 oxidation number), but you almost never get a period table with valence electrons.

Here is the mentioned period table with valance electrons for the first 20 elements (explanation and CaCl2, Al2O3, AlCl3, NH3 Lewis dot structure examples below):

Periodic Table With Valence Electrons
Labeled valence electrons periodic table.

Based on this, we can construct Lewis dot structures for different molecules. We will look at a few examples, including CaCl2 (calcium chloride), aluminum oxide (Al2O3), aluminum chloride (AlCl3), and ammonia (NH3).

Valence Electrons By Group In Periodic System

From this period table with valance electrons, we can see that:

  • Group 1 atoms (alkali metals such as H, Li, Na, K) have 1 valence electron. They can form ions with a +1 oxidation number. Examples: Na1+, Li1+, K1+.
  • Group 2 atoms (alkaline earth metals such as Be, Mg, Ca) have 2 valence electrons. They can form ions with a +2 oxidation number. Examples: Be2+, Mg2+, Ca2+. We will see this in effect in our calcium chloride Lewis dot structure example
  • Group 3 atoms (B, Al) have 3 valence electrons. They can form ions with a +3 oxidation number. Al3+ ion will help us understand the Lewis dot structure for aluminum oxide and aluminum chloride.
  • Group 4 atoms (such as C and Si) have 4 valence electrons. They can form quite a lot of different molecules exactly because of these 4 valence electrons.
  • Group 5 atoms (such as N and P) have 5 valence electrons. These elements like to receive 3 additional electrons to make an octet; we will look at the ammonia Lewis dot structure to see this in effect.
  • Group 6 atoms (such as O and S) have 6 valence electrons. They usually have an oxidation number of -2; that is, oxygen and sulfur atoms like to receive 2 additional electrons to form a bond. Aluminum oxide is one such example.
  • Group 7 atoms (such as F and Cl) have 7 valence electrons. They always form bonds by accepting 1 additional electron (-1 oxidation number). This will become evident in the calcium chloride and aluminum chloride examples.
  • Group 8 atoms (noble gases such as He, Ne, Ar) have 8 valence electrons. Since they already have a full octet, they almost never form bonds with other atoms.

We can see that, for a great majority of elements in the period table, group number tells you exactly how many valence electrons an atom has:

Group Number = Number Of Valence Electrons

Let’s have a look a these 4 examples we mentioned along the way:

Calcium Chloride Lewis Structure (CaCl2)

If we check the periodic table with valence electrons, we see the following:

  • Calcium atom has 2 valence electrons. It usually wants to donate these 2 electrons to get a full octet (like Argon).
  • Chlorine atom has 7 valence electrons. To get a full octet, chlorine atoms like to receive 1 additional electron.

In a molecule of calcium chloride, we have 1 calcium atom that donates 2 valence electrons into the molecule. Each chlorine atom can accept only 1 valence electron, thus we need 2 chlorine atoms in this structure. That’s why the molecular formula for calcium chloride is CaCl2.

You can draw a Lewis dot structure where the calcium atom donates 1 valence electron to each of the 2 chlorine atoms. Here is the CaCl2 Lewis dot structure with valence electrons:

calcium chloride lewis structure

We see that calcium donates both of the 2 valence electrons in two Ca-Cl bonds.

Aluminum Oxide Lewis Dot Structure (Al2O3)

Alright, when you want to create aluminum oxide, we have to be aware of the following things from the periodic table:

  • Aluminum atom (Al) has 3 valence electrons. To form a bond, it prefers to donate these 3 valence electrons into a bond.
  • Oxygen atom (O) has 6 valence electrons. Since its goal is to get a full octet (8 valence electrons), the oxygen atom wants to receive 2 additional valence electrons.

We can’t have 1 Al atom donating 3 electrons to only 1 oxygen atom since oxygen atom can only accept 2 valence electrons. Thus, we need 2 aluminum atoms donating 6 elections in total to 3 oxygen atoms that can accept 6 elections in total.

Hence, the molecular formula for aluminum oxide is Al2O3. Here is the Lewis dot structure:

aluminum oxide lewis dot structure

For aluminum to form a bond with oxygen, each aluminum atom donates 3 electrons into the common bond, and each oxygen readily accepts 2 electrons. In the Al2O3, we see that 6 valence electrons in total are put inside the 3 separate bonds.

Aluminum Chloride Lewis Dot Structure (AlCl3)

We already know that an aluminum atom wants to donate 3 valence electrons when forming a bond. When aluminum forms a bond with chlorine, we need to be aware that the chlorine atom wants to receive 1 valence electron to form a full octet (it has 7 valence electrons to behind with; 1 electron from the Al atom is needed).

Therefore, we need 3 chlorine atoms to accept 1 valence electron each so that the aluminum atom can donate all 3 of its valence electrons. Hence the molecular formula for aluminum chloride is AlCl3. Here is the AlCl3 Lewis dot structure:

alcl3 lewis dot structure with valence electrons

We can see that 1 aluminum atom forms a bond with 3 chlorine atoms.

Ammonia Lewis Dot Structure (NH3)

Ammonia is a molecule made out of nitrogen (N) and hydrogen (H) atoms. Here’s how these atoms want to form a bond:

  • Nitrogen has 5 valence electrons (you can check the periodic table with valence electrons above). To get to the full octet, it needs 3 additional electrons to form a full octet (8 valence electrons).
  • Hydrogen only has 1 valence electron (its only electron, actually). It will readily donate it to form a bond.

In ammonia, 1 nitrogen atom forms a bond with 3 hydrogen atoms. Thus, ammonia has a molecular formula of NH3. Understanding this, we can draw the following Lewis dot structure for ammonia:

ammonia lewis structure nh3

Each of the 3 hydrogen atoms in ammonia donates its only valence electron into the bond, while nitrogen readily receives all 3 of them.

We hope that the period table with valence electrons will help you when drawing the Lewis dot structure. It provides an additional understanding of atoms in the period table that is lacking in so many periodic tables.

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