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.
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!
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!Alkali metals also have low melting points. For example, cesium has a melting point of 83 degrees F, so it would be hard to have a cesium ice-cream cone on a hot, summer day! They also have low boiling points; cesium boils at 1,240 degrees F. You might be thinking, 1,240 degrees sounds really hot! But if you compare that to other metals, it actually isn’t.
Uses of Alkali Metals
Now that we know a little more about the alkali metals, let’s look at a few more examples other than bananas, batteries, and salt. Sodium is the sixth most abundant element on earth and potassium is the seventh, so you can find them in more places than salt and bananas! Sodium is in all sorts of things, from cleaners to baking soda. It is also utilized in film development, paper making and glass making.
Potassium also has quite a few commercial uses, like as an ingredient in fireworks and fertilizers. It also makes up 2.4% of the earth’s crust and is found as salt in the oceans. Lithium isn’t used as much as the first two alkali metals, but it still has its commercial uses in addition to batteries, such as a major ingredient in medication, like those used to treat bipolar disorders.You don’t hear as much about rubidium, cesium, and francium.
There’s no such thing as a cesium ice-cream cone, but cesium is actually used in video equipment. Rubidium and francium are used in scientific research and don’t have much commercial use.
So, what do a +1 cation, a battery, and one valence electron have in common? They’re all examples or properties of alkali metals! Although that doesn’t sound very exciting, alkali metals are extremely important! In fact, you need some to survive, and others are important ingredients in the products you use.
Let’s quickly review some of the main properties that distinguish alkali metals from other elements:
- They are located in group 1A on the periodic table
- They have one valence electron
- They form a +1 cation and ionic bonds
- They are soft and bendable
- They are reactive
- They form bases when added to water
- They have low melting and boiling points
So, they might not make good joke material, but they are explosively important (get it?).
After watching this lesson, you should be able to:
- Define what alkali metals are
- Identify properties of alkali metals that separate them from other elements