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Alkali Metals (Group 1A Elements): Definition & Properties

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  • 0:00 Alkali Metals
  • 1:26 Properties
  • 4:32 Uses of Alkali Metals
  • 5:43 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.

Elements that can explode when put into water? Metals that can be cut with a knife? These are just some of the properties alkali metals share. This video will describe more properties and give some uses of these interesting metals.

Alkali Metals

What do batteries, table salt, and bananas have in common? No, this isn't the first line to a bad joke, unless the punch line is 'these items contain one element from the alkali metals'. But that would make a really bad joke. So, you might be thinking, what is an alkali metal? Or, how can batteries, bananas, and table salt have anything in common?

Alkali metals belong to group 1A of the periodic table, which includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Even though hydrogen is in the same column, it doesn't belong.

Groups, by the way, are the vertical columns on a periodic table, and group 1A is on the far left. Sometimes you'll see group 1A written with a Roman numeral, or group IA. It's a good idea to get used to seeing it both ways.

All of the alkali metals are in the same group because they share similar properties, so it might not appear that batteries, bananas, and table salt have a whole lot in common, but the elements that make them up (lithium, potassium, and sodium) sure do!

Properties

Let's take a look at some of these similarities. Valence electrons are the outermost electrons and give elements a lot of their properties. All of the elements in group 1A have one valence electron, so that should be easy to remember! Having one valence electron makes alkali metals extremely reactive, meaning they desperately want to bond (or attach) to other elements.

As you go down the group, the alkali metals become more reactive, meaning potassium is much more reactive than sodium. When exposed to water, the alkali metals actually cause an explosion! In addition to causing an explosion, these elements form an alkaline substance when they react with water, hence the name alkali metal. Alkaline substances are also called bases and are substances who have a pH greater than seven.

You might not know it, but you are familiar with some alkali metals that have combined with water. For example, hair relaxers, shaving creams, hair-removing creams, and drain cleaners all contain at least a small amount of a base that was formed from the reaction of an alkali metal with water.

Let's talk a little bit more on how alkali metals bond, or attach to other elements. Do you remember when I said alkali metals have one valence electron? The valence electrons are gained, lost, or shared when elements bond together.

Having just one valence electron makes alkali metals unstable, so when they come into contact with an element that needs some electrons, it gives up its one electron and becomes a cation, or a positively charged atom. Electrons are negatively charged, so if an element gives up an electron, it becomes positively charged. So, since alkali metals lose one electron, they have a +1 charge. Since they give up an electron, they tend to form ionic bonds, or bonds that are formed when one atom gives its electrons to another atom.

So, we know that alkali metals have one valence electron, are reactive, can form bases when added to water, form a +1 cation, and bond using ionic bonds, but what other similarities does this group share? Well, all of the elements in this group are soft and bendable. When you think of a metal, you usually don't envision being able to cut it into pieces with a knife or bend it, but alkali metals are so soft and bendy, you can do just that!

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