Mammoth Memory

Properties of the alkali metals

Properties of alkali metals

There are three methods that you can choose to help you remember and understand the properties of the alkali metals.

 

Method 1. Understand and see the single electron in the outer shell.

 

Method 2. See and understand one of the most famous chemistry experiments.

 

Method 3. Learn a mnemonic story line.

 

Method 1

The reason why lithium (Li), sodium (Na) and potassium (K) react in a similar manner and so aggressively is because they all have only one electron in their outer shell. This means that they will not only react in a similar way but this single electron can very easily transfer to another atom.

Lithium has 2 shells the inner with 2 electrons and outer containing one with a mass of 3

Sodium has 3 shells, the inner and middle shells are full and the outer contains one electron, it has a mass of 11

Potassium has 4 shells the inner, second and third shells are full and the outer contains 1 electron

 

 

Method 2

If you take some lithium and drop it in water this famous experiment will teach you much about the properties of group 1 elements.

 

Lithium is very reactive

Group 1 metals are very reactive and one way that indicates that they are so reactive is they are stored in liquid keresone or mineral oil to prevent or limit their reaction with oxygen.

Alkali metals like to steal oxygen and form oxides:

Lithium stored in mineral oil

If we take the lithium out of the mineral oil you can see it is dull, grey and coated with a layer of the oxide.

Lithium

Lithium is very soft:

Cutting a bar of lithium with a knife

Group 1 metals are relatively soft and can be cut with a knife.

 

Lithium is not dull but actually shiny:

Bar of lithium cut in half

Lithium is a shiny metal, that is until it oxidises and turns dull grey.

Lithium is an excellent conductor of electricity:

Testing conductivity of lithium

Lithium floats:

Add lithium to water and you will notice it will float. Group 1 metals are less dense than water.

 

Lithium reacts rapidly with water:

We can also observe that lithium reacts rapidly with water.

 

Lithium reacts with water to give off hydrogen:

Lithium reacts with water producing lithium hydroxide and hydrogen. The lithium hydroxide is very water soluble and dissolves in water.  The hydrogen gas escapes. If we trap some of the gas in a test tube and test the flammability by bringing a lighted wooden splint you will hear a pop proving that it is hydrogen. 

 

Lithium hydroxide is a base:

Testing pH of lithium hydroxide

If you add an acid/base indicator in the beaker then the solution turns red/purple proving that lithium hydroxide is basic in solution.

 

Method 3

The third method involves giving you a mnemonic story that helps you to remember the properties of alkali metals.

Following a raid on the alley, where the alkies were lying down with their metal beer cans, the alkali metals (along with their electric robots*), were deemed dangerous and criminal.

They were put on the wanted list. The police issued the following statement, warning the public about alkali metals and their devious robots (electrons) and informing them of their properties.

 *Each alkali metal has a robot as their sidekick (they have a single electron in their outer shell). It is these robots (electrons) that cause the metals to behave how they do. The robots (electrons) are a bad influence and are responsible for the alkali metals’ unlawful reputation.

All alkali metals have one electron in there outer shell which makes them very reactive

NOTE: 

Alkali Metals (Group 1 in the periodic table) are entirely different from alkalis (which may be more easily remembered as alkali solutions). 

 

1. Alkali metals like to steal oxygen and form oxides

The police began by explaining that alkali metals had a long criminal history centred on the theft of oxygen.

Alkali metals like to steal oxygen and from oxides

For example:

Potassium + Oxygen → Potassium oxide

4K + O2            → 2K2O

 

Sodium + Oxygen → Sodium oxide

4Na + O2 → 2Na2O

 

Lithium + Oxygen → Lithium oxide

4Li + O2           → 2Li2O

 

2. Alkali metals react violently towards water

The public were warned not to approach an alkali metal and their robot, particularly in the presence of water, as they could be very violent and explosive.

Alkali metals react violently to water    

3. Alkali metals are less dense than water so they float on its surface

The police said that, like many criminals, the alkali metals believed they were better than others as they were smarter and less dense than water.

Alkali metals are less dense than water so floats on its surface

 

4. Alkali metals are soft and easily cut with a knife

Not wanting to inflate the alkali metal’s ego too much, the police went on to say they were soft and easily cut with a knife much like butter.

Alkali metals are soft and can be easily cut with a knife

 

5. Alkali metals react with water to form solutions called hydroxides

After reading the police statement, the alkali metals and their robots were worried, so their solution was to go and hide in a rock side (hydroxide).

Hydroxide solution is produced when alkali metals react with water

 

For example:

Potassium + water → potassium hydroxide + hydrogen

2K + 2H2O → 2KOH + H2

 

Sodium + water → sodium hydroxide + hydrogen

2Na + 2H2O → 2NaOH + H2

 

Lithium + water → lithium hydroxide + hydrogen

2Li + 2H2O → 2LiOH + H2 

  

6. Alkali metals have low melting points

However, this plan didn’t work as the alkali metals and their robot sidekicks soon began to melt under the heat from the police search.

Alkali metals have low melting points

 

To summarise, alkali metals:

  • Have one electron in their outer shell
  • Take oxygen atoms from other molecules to form oxides
  • React violently with water
  • Are less dense than water so they float
  • Are soft so can easily be cut with a knife
  • Form hydroxides when in a water solution
  • Have low melting points compared with other metals
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