In chemistry, Valence electrons are the electrons that are in the last electron layer of an element. Knowing how to find the number of valence electrons for a given atom is an important skill for chemists, as this information determines the chemical bonds it can form. Fortunately, all you need to find an element's valence electrons is a standard periodic table.
Find out the valence electrons with a periodic table
For elements other than transition metals
Find a periodic table of the elements. The periodic table is a color-coded table that contains several different images and shows all of the chemical elements known to man. The periodic table shows a great deal of information about the elements. You will use some of this information to determine the number of valence electrons for the atom you want to study. You can usually find this table on the cover of chemistry books. You can also find an excellent interactive table available online at this page.
Label each column of the Periodic Table of the Elements from 1 to 18. Typically, all of the elements in a single vertical column in a periodic table have the same number of valence electrons. If your periodic table doesn't have every numbered column, assign each one a number, starting with 1 for the far left and 18 for the far right. In scientific terms, these columns are known as "Groups" of elements.For example, if you are working with a periodic table in which the groups are not numbered, you need to write a 1 over the hydrogen (H) one, a 2 over beryllium (Be) and so on 18 over helium (He).
Find your item in the table. Now look for the element for which you want to find the valence electrons in the table. You can do it by its chemical symbol (the letters that appear in each box), its ordinal number (the number that is in the top left of each box), or any other information available in the table.As an example, you can look for valence electrons for a very common element: the carbon (C). This element has an atomic number of 6. It is in the upper part of group 14. In the next step we will explain how to find its valence electrons.This subsection does not take into account the transition metals that are the elements of the block with a rectangle from groups 3 through 12. These elements are slightly different from the rest, so the steps in this section will not work with them. You can see how to work with them in the next subsection.
Use the group numbers to determine the number of valence electrons. You can use the group number of elements other than transition metals to find the number of valence electrons an atom of that element has. The Units that are in the group number is the number of valence electrons in an atom of these elements. In other words:Group 1: 1 valence electronGroup 2: 2 valence electronsGroup 13: 3 valence electronsGroup 14: 4 valence electronsGroup 15: 5 valence electronsGroup 16: 6 valence electronsGroup 17: 7 valence electronsGroup 18: 8 valence electrons (except helium, which has 2)For example, since the element belongs to group 14, it can be said that there is a carbon atom four valence electrons.
For transition metals
Find an item from Groups 3 to 12.
As already mentioned, the elements of groups 3 to 12 are called "transition metals" and they behave differently from the other elements in terms of their valence electrons. In this section we will explain how to some extent these atoms often cannot be assigned valence electrons.
- As an example, let's take tantalum (Ta), which is element 73. In the next few steps we're going to find (or at least find) its valence electrons we will try).
- Remember that transition metals are the lanthanide and actinide series (also known as "rare earth"). These are the two series of items that are usually below the rest of the table and begin with Lanthanum and Actinium. All of these elements belong to the Group 3 of the periodic table.
Understand that transition metals do not have valence electrons "traditionally". To understand why transition metals aren't really "they work", just like the rest of the periodic table, you need a brief explanation of how electrons behave in atoms. If you want to take a quick look at this topic or ignore it to go straight to the answers, read the next few sections.When electrons are added to an atom, they are arranged in different orders "orbitals," which are basically different areas around an atom in which electrons collect. In general, the valence electrons are the atoms that make up the last layer. In other words, they are the last atoms added.For reasons that are somewhat complex to explain in this article, when the atoms are added to the last layer of a transition metal (discussed in more detail below), the first atoms in the layer in the area tend to act as valence electrons of normal but after that, they stop and electrons orbiting other layers sometimes act as valence electrons instead. This means that an atom can have multiple numbers of valence electrons depending on how they are manipulated.For a more in-depth explanation, read this excellent page from Clackamas Community College on valence electrons.
Determine the number of valence electrons based on the group number. Again, the group number of the element you are going to study can indicate its valence electron number. For transition metals, however, there is no pattern to follow. The group number usually corresponds to a number of possible amounts of valence electrons. These are:Group 3: 3 valence electronsGroup 4: 2 to 4 valence electronsGroup 5: 2 to 5 valence electronsGroup 6: 2 to 6 valence electronsGroup 7: 2 to 7 valence electronsGroup 8: 2 or 3 valence electronsGroup 9: 2 or 3 valence electronsGroup 10: 2 or 3 valence electronsGroup 11: 1 or 2 valence electronsGroup 12: 2 valence electronsFor the example of tantalum, as it belongs to group 5, it can be said that, depending on the situation, it has between 2 and 5 valence electrons.
Search for valence electrons by their electronic configuration
Learn to read the electronic configuration.
Another way to find an element's valence electrons is through something called an "electronic configuration". This may seem complicated at first, but it's just one way of representing the electron orbitals of an atom with letters and numbers. Once you understand what you are seeing, it will be easy for you.
- See the example of the electronic configuration of the element sodium (Na):
- Note that this electronic configuration is just a repeating string formed this way:
- (Number) (letter) (number) (letter) ...
- ... and so on. The first fragment of (Number) (letter) is the name of the orbital of the electron and is the number of electrons in that orbital. That's it!
- So, for the example above, sodium could be said to have 2 electrons in the 1s orbital more 2 electrons in the 2s orbital more 6 electrons in the 2p orbital more 1 electron in the 3s orbital. That's a total of 11 electrons. Sodium is the eleventh element so it makes sense.
Find the electronic configuration for the item you want to investigate. Once you know your electronic configuration, finding your valence number is very easy (except for transition metals, of course). If they give you the configuration from the first moment, you can ignore the next step. If you need to find it by yourself, read on:Here you have the complete electronic configuration of the ununoctio (Uuo), which is element 118:
Now that you have this, all you have to do is complete this pattern from the beginning until there are no electrons left to find the electronic configuration of another atom. It's easier than it sounds. For example, if you want to do the chlorine orbital diagram (Cl), item 17, with 17 electrons, you should do it like this:
Note that the number of electrons 17: must add 2 + 2 + 6 + 2 + 5 = 17. All you have to do is change the number in the last orbital. The rest is the same as the orbitals preceding the last one are completely filled.To learn more about electronic configurations, also read this article.
They bind electrons to the orbital planes with the octet rule. When electrons are added to an atom, they fall into multiple orbitals in the order listed above. The first two go to the 1s orbital, the next two go to the 2s orbital, the next six go to the 2p orbital, and so on. When working with atoms that are not transition metals, these orbitals should form "layers of orbitals" around the atom and each subsequent layer is further away than the previous one. In addition to the first layer, which can only hold two electrons, each layer can have eight electrons (except, let's repeat, when working with transition metals). This is known as the octet rule.Suppose you want to examine the boron element (B). Since its atomic number is 5, you know that it has 5 electrons and that its electronic configuration is: 1s2s2p. Because the first orbital plane only has two electrons, you know that boron has two layers: one with two 1s electrons and one with three electrons in the 2s and 2p orbitals.As another example, an element like chlorine has three layers of orbitals: one with two electrons 1s - another with two electrons 2s and six electrons 2p - and another with two electrons 2s and five electrons 3p.
Find the number of electrons in the last layer. Now that you know the element's electron layers, it's easy to find its valence electrons: just use the number of electrons in the last layer. When the last layer is full (in other words, if you have 8 electrons, or 2 if it is the first layer) the element is inert and does not react easily with other elements. But we repeat: these rules may not be met for transition metals.For example, if you are working with boron since you have three electrons in the second layer, you can say that boron has three Valence electrons.
Use the rows in the table as links to determine how many levels you have. The horizontal lines of the periodic table are known as "Periods" of the elements. Starting from the top of the table, each period corresponds to the number of Electron layers that the atoms of this period have. You can use this number as an abbreviation to determine how many valence electrons an element has. Just start from the left side of the period if you want to count electrons. Again, with this method you have to ignore the transition metals.For example, you know that the selenium element has four orbital planes because it is in the fourth period. Since it is the sixth element on the left in the fourth period (ignore the transition metals), you know that the fourth most distant layer has six electrons and therefore has the selenium six valence electrons.
- Note that electronic configurations can be written in abbreviated form using the noble gases (Group 18 elements) to replace the orbitals at the beginning of the configuration. For example, the electronic configuration of sodium can be written as [Ne] 3s1. It is essentially the same as the neon, but with one more electron in the 3s orbital.
- Transition metals can have valence sublayers that are not completely filled. In order to be able to determine the exact number of valence electrons for transition metals, the fundamentals of quantum theory must be known, which are beyond the scope of this article.
- Note that periodic tables are different in different countries. So make sure you are using the correct one to avoid confusion.
- Periodic table of the elements
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