Chemistry 101: How to Find Valence Electrons

how to find valence electronsChemistry, it’s what makes stuff! That may be a bit simplistic, but really, we’re talking about the elements and molecules and bonds and reactions and explosions and things Neil deGrasse Tyson talks about.

When we talk about chemistry, we are talking about the building blocks of the universe as we know it. All the elements act like Lego bricks, joining one to another until they’ve made something more than the sum of its parts, like metals, water, chemical compounds, even living things. Sometimes, they don’t stick together so well and fall apart or explode, deteriorating into its most basic forms. It’s these bonds and reactions that make up the universe as we know it and see it and experience it.

If all that seems fascinating enough, then there’s a great place to start here in Chemistry 101- Principles of Chemistry. That class will build your foundation for further learning. It even covers the point of this article about the electrons that are part of what make it all happen, the so-called valence electrons.

Atoms

Lets start with atoms. Atoms are made up of protons (positively charged particles), electrons (negatively charged particles) and neutrons (no charge). The nucleus is where the protons and neutrons reside, giving the atom its weight. These are the most basic forms we deal with in chemistry.

Shells

The electrons in an atom live in orbits, moving like blindingly fast planets in a cloud around the nucleus. These orbits have different energy levels, depending on their distance from the nucleus, and are called shells. Each shell has a specific number of electrons that it can have and these increase by a fixed number. As the level of the shell increases, the energy of the shell increases because of the extra electrons. Each shell also has subshells, the number of which also increases as the number of the shell increases. So the first shell has one subshell and it’s labelled as 1s. The next subshell is 2 and contains two subshells, 2s and 2p. The third is numbered, you guessed it, 3 and has subshells s, p, and d. The next shell has four subshells and they are labelled s, p, d, and f.

This talk of shells actually begins to touch on quantum mechanics, a different and more confusing topic altogether. If this got your interest piqued, and you’d like to move beyond basic chemistry and dive into the weird world of quantum mechanics, you can check out this class: Quantum Physics: an overview of a weird world. You’ll be introduced to the mind-bending possibilities that make up the physical world around us. Heady stuff, for sure.

Finding Valence Electrons

So what’s the easiest way to find those electrons? By checking out an element’s place on the periodic table. At first glance, the periodic table seems like someone just put things in some odd assortment, using colors to differentiate things and then numbered them. But there is a method to that madness. For our purposes, we will be looking at the columns, numbered 1-18 in the table. Remember, columns go up and down.

These columns represent groups, or families, of elements. They are related through the similarity of the electrons in their outer shell, which is where valence electrons are located. These groups get their names either by the group number or the element at the top of the column (the exception being the lithium group). Though you may hear other names for some of these groups, you can’t go wrong sticking with the numbers or their element labels.

These columns are numbered 1-18. For the purpose of finding the valence electrons, we ignore the columns 3-12. Those guys are “transition metals” and their properties of finding the valence electrons are different than the other elements. So going from left to right, number 1-8 for groups 1-2 and 13-18, remembering that even though Helium hangs out on the far end, it only has 2 valence electrons, instead of the maximum number of 8 like the other elements in its group.

Looking at the table, we can see by counting over and skipping the transition metals that the element phosphorus (P) has 5 valence electrons. There you go.

Periodic Table

from Wikimedia

For the transition metals (groups 3-12), figuring out the valence electrons is more complicated. Their atomic structure is such that their d subshell is incomplete. This means that a shell that sits lower than the outer shell will be where the valence electrons react. It gets complicated.

But not all “valence shells” will actually have valence electrons! Sometimes these shells will be filled, or closed, which means that they have no electrons available to interact with. These atoms will not react or form bonds and so are called inert (you can call someone who sits on the couch and watches TV all day inert as well, but this has nothing to do with chemistry). All the noble gases in group 18 fall are inert.

A way to find valence electrons without the periodic table is using the atomic number and drawing a diagram. The atomic number is how many protons and electrons the atom has. That means an atomic number of 8 (oxygen), has 8 protons and 8 electrons.

Let’s draw it out as a simple diagram. Imagine the atom is a set of circles, with a dot in the middle. That dot will be the nucleus and the circles its shells. The first of the elements is hydrogen (H) and it has an atomic number of 1. It has 1 proton in its nucleus and 1 electron floating around out there in its shell. It would look like this:

hydrogen
The since it’s in group 1, we can figure out that that one electron is the valence electron for H and that its a highly reactive element.

That was easy enough with just one electron to deal with. What about oxygen? With 8 electrons to account for, then that’s more to figure out. As was mentioned before, the shells can only have certain amounts of electrons. The first can only have 2 and the next can have up to 8 (2 for subshell s and then 6 more for subshell p). Starting with the inner shell, we can fill in those 2 and then the remaining 6 go on the next one.

oxygen

Since that shell can carry a maximum of 8, it’s not inert and has 6 valence electrons. If you check the periodic table, and count the groups, you see it falls into group 6, which matches the above diagram.

There you have it: some basic pointers to help you find those valence electrons.

If you’re in the UK and need a refresher for the GCSE Edexcel Science Exam (or just want to brush up), then we’ve got a class for you! The aptly named GCSE Chemistry: Edexcel C1 will help you grasp what you need to know for the first half of the Science unit.

For a more specialized look at chemistry with serious practical applications, we have this class to meet your needs: Physical Metallurgy I. This class delves into the basics beyond what we’ve covered here, but also how it all relates to metals in industry and metalwork.

Best of luck!