What are valence electrons? For representative elements, the number of valence electrons of an e

What are valence electrons? For representative elements, the...

Key Concepts

Periodic Table Group Number

The periodic table is organized into vertical columns called groups, and for many representative elements, the group number corresponds to the number of valence electrons. This relationship is foundational in understanding the periodic trends in reactivity and bonding characteristics among these elements.

Valence Electrons

Valence electrons are the electrons located in the outermost energy level of an atom. They are significant because they are the electrons involved in chemical bonding and reactions. Their arrangement and number largely determine an element's chemical properties and reactivity.

Representative Elements

Representative elements, also known as main-group elements, are the elements found in the s-block and p-block of the periodic table. These elements generally have valence electron counts that correlate directly with their group numbers, which simplifies the prediction of their chemical behavior.

Electron Configuration

Electron configuration describes the distribution of electrons among an atom’s orbitals. It explains how electrons are arranged in different energy levels and sublevels, particularly highlighting the electrons in the outermost shell that are designated as valence electrons. This concept is key to predicting and understanding an element's chemical properties.

Transcript

00:02 Hello.

00:03 Today we're going to be talking about valence electrons and how they kind of relate to an element group number.

00:11 So first, let's talk about what are valence electrons.

00:17 So valence electrons are the electrons located in the outermost shell of an element.

00:30 Okay, so these are going to be the very, very outside electrons.

00:38 And when we say groups on the periodic table, those are columns of the periodic table.

00:45 So like this first column right here, this is all group 1a.

00:52 Now for representative elements, the number of valence electrons of an element is equal to its group number.

01:00 So just to review really quickly, a representative element is an element that has a partially filled outer shell.

01:16 All right.

01:17 So basically, this is going to be everything except our noble gases.

01:24 And the noble gases are the elements located here.

01:29 And the last group on the periodic table, group 8a, these are our noble gases.

01:39 So this is a rule of thumb.

01:42 Let's kind of prove it.

01:45 All right, let's look at a few examples.

01:48 First, let's look at aluminum here.

01:52 So let's write out the electron configuration for aluminum.

01:57 So aluminum, you can see, is in the third row.

02:02 So that means we're going to be on the third level of all of our shells.

02:06 Our outermost shells are going to be level three.

02:08 So obviously our first shell is 3s.

02:13 Now, how many electrons does aluminum have in its outer shell? well, basically, we just count its position in the row.

02:20 So we've got sodium, magnesium, aluminum.

02:24 So it's going to have three electrons in its outermost shell.

02:27 Now, the s orbital can only hold two electrons, so it's going to be 3s2, 3p1.

02:36 Now, if we go up and look at aluminum's group number, it is in group number 3a.

02:42 So it's got three electrons in that valence shell, and it's in group 3a.

02:48 Let's look at a number example.

02:51 Why don't we do strontium? so, again, we look at the row number, strontium.

02:58 Is in row number five.

03:02 So we know we're going to start in the 5s orbital.

03:07 And then we, again, we just count its place in the row, one, two.

03:13 So it's going to have two electrons.

03:15 So its electron configuration is just going to be 5s2.

03:19 If we go to the top, there it is, group 2a.

03:26 Let's look at another example.

03:28 How about potassium here? so potassium is in the fourth row.

03:38 So we're going to start in the 4s orbital...

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