Chemistry - Atomic structure and the periodic table - Group 1 alkali metals Flashcards
What are the properties of group one elements?(alkali metals)
-They have low melting points
-They are very soft and so can easily be cut with a knife
-They have low densities
What happens when group 1 elements react with water?
Hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group.
What are the key safety points for group 1 reactions?
-Use of a plastic safety screen
-Using small pieces of the metal
-Using a large volume of water
-Using tweezers to hold the metal
-Wearing thick rubber gloves
What happens when lithium is added to water?
When lithium is added to water, lithium floats. It fizzes steadily and becomes smaller, until it eventually disappears.
What happens when sodium is added to water?
When sodium is added to water, the sodium melts to form a ball that moves around on the surface. It fizzes rapidly before it disappears.
What happens when potassium is added to water?
When potassium is added to water, the metal melts and floats. It moves around very quickly on the surface of the water. The metal self-ignites, which also ignites the hydrogen gas. This results in sparks and a lilac flame. There is sometimes a small explosion at the end of the reaction.
How do you test for hydrogen gas?
-Collect the gas in an upside down test tube.
-Put the flame from a burning splint into the top of the test tube.
-The gas will burn quickly and give off a squeaky ‘pop’.
What does the metal do to the water after burned?
The hydroxides formed in all of these reactions dissolve in water to form alkaline solutions. These solutions turn universal indicator purple, showing they are strongly alkaline.
What is tarnishing?
When the alkali metals are cut, they initially appear shiny grey but quickly become dull and white as they react with oxygen in the air.
How does lithium tarnish?
Lithium tarnishes slowly due to its relatively slow reaction with oxygen.
How does sodium tarnish?
Sodium tarnishes quicker than lithium, which is further evidence for the greater reactivity of sodium when compared to lithium.
How does potassium tarnish?
Potassium tarnishes so quickly that it is difficult to see that potassium is actually a shiny metal. This is further evidence that potassium is a more reactive metal than both lithium and sodium.
What is combustion?
When any substance burns in oxygen it is called a combustion reaction.
What happens when alkali metals react with halogens?
When the alkali metals react with the different halogens, the group of compounds formed are known as the alkali metals halides.
What colour flames do sodium, potassium and lithium burn?
Sodium - Red
Potassium - lilac
Lithium - yellow
