Halogens (Group 7A Elements): Definition & Properties

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  • 0:01 The Halogens: Group 7A
  • 0:56 Properties Halogens Share
  • 5:30 Individual Elements…
  • 8:15 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

The halogens are a group of non-metals that share several properties. This lesson will examine these properties and will also look at the many uses of these group 7A elements.

The Halogens: Group 7A

In the distance, you can see it. A dark shadow slowly approaching. It's here to take something from you, but what? As it gets closer, it slowly comes into focus, and it's terrifying. You rub your eyes to make sure you're seeing it correctly. It's in focus, so you can see it now. It's.... fluorine, and it's here to take your.... electrons?

Yeah, you got me. Fluorine really isn't lurking in dark, shadowy places trying to steal your electrons. But it is extremely electronegative, meaning it really wants electrons (but we'll delve into that definition later in the lesson).

Fluorine is a halogen, which is a group of non-metals located on the right side of the periodic table that includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Most halogens are electron-hungry, like fluorine. Halogens can also be referred to as group 7A, group 17, or group VIIA elements. All mean the same thing.

Properties Halogens Share

So, we know halogens are a group of non-metal, electronegative elements located on the right side of the periodic table. Nonmetals have certain properties that distinguish them from the metals or metalloids, including being poor conductors of electricity or heat, brittle (if it's a solid), and not having a metallic luster.

Elements are placed into groups because they share similar properties, and the halogens have quite a few properties in common. So, let's take a look at some of the properties and trends within this group. All of the halogens have seven valence electrons, which are the electrons farthest from the center of the atom. Valence electrons help determine the properties of the element, as well as who the atom can bond, or attach, with.

Atoms bond, or stick together, in a couple of different ways. Some atoms share electrons in what is called a covalent bond. Sometimes atoms transfer electrons, which is called an ionic bond. Valence electrons are often represented as dots around the element, and you can see here that chlorine (Cl) has seven dots:

Structure of chlorine
chlorine structure

This is because chlorine is a halogen, with seven valence electrons.

In this image, sodium (or Na's) electrons are being transferred to chlorine:

Ionic bond
sodium and chlorine structures

This is an ionic bond. Halogens tend to form ionic bonds when they attach to other elements.

Having seven valence electrons makes the halogens extremely reactive. Atoms are stable when they have eight valence electrons, so the halogens really want another element's electrons to make eight. Since electrons are negative, and halogens gain an electron from another atom, they tend to form a -1 anion, or an atom with a negative charge. You may also hear charges referred to as oxidation states. For example, halogens typically form a -1 oxidation state.

But notice I used the word 'typically.' It's not always the case that halogens form a -1 anion. But don't worry; I'll give you more information on that when we examine the individual elements. So, we know that halogens are nonmetals, have seven valence electrons, usually form a -1 anion, and form ionic bonds. But what about that shadowy, electron-hungry fluorine we talked about earlier? Well, as you go up the group, the halogens become more electronegative, so fluorine is the most electronegative out of the group. In fact, fluorine is the most electronegative element on the periodic table!

When elements are bonded together, one element may want the electrons in the bond a little more. Most of the halogens are electronegative, so they tend to hog the bonded electrons. Remember the definition for ionic bond? Electrons are transferred from one atom to another. Well, because halogens hog these electrons, the electrons are transferred to the halogen, hence the ionic bond. So, when an atom is electronegative, it just means they attract electrons when they are in a bond.

So, what else do the halogens have in common? Well, the halogens often form salts with the metals on the periodic table. For example, the group 1A metals, also known as alkali metals, really want to get rid of their extra valence electron, and the halogens are happy to take it!

In fact the name 'halo' is Greek for salt, so halogens get their name because they bond, or attach, to metals to make salts. Here's an example for you: chlorine is a greenish-yellowish gas, but when it combines with the metal sodium, you get table salt! Chlorine can also bond to the alkaline Earth metals, like calcium to make calcium chloride, a salt used as a de-icer on slippery roads.

Another property this group shares is they're all toxic, but many are useful when combined with other elements. For example, chlorine gas can cause symptoms such as fluid in the lungs, blurred vision, and nausea and vomiting. But as we just saw, when chlorine is combined with sodium, you get table salt!

One last thing before we take a brief look at the individual halogens. This group is pretty neat in that it is the only group of elements on the periodic table where you can find elements that are gases, liquids, and solids at room temperature. Chlorine and fluorine are gases, bromine is a liquid, and iodine and astatine are solids.

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