2.1 - Group 1 Flashcards
What are the Group 1 elements?
The elements in Group one of the periodic table are called the alkali metals.
What are the physical properties of the Group 1 metals?
The melting point and boiling point of the elements are very low for metals, and get lower moving down the group.
Their densities tend to increase down the group although not regularly, Lithium, sodium and pottasium are less than water so will float on it.
The metals are also very soft and are easily cut with a knife, becoming softer as they move down the group. They are shiny and silver when freshly cut but tarnish very quickly on exposure of air
What are the concerns with storage and handling of the Group 1 metals?
All these metals are extremely reactive as you go down the group. They all react quickly with oxygen in the air form oxides, and react quickly with water to form strong alkaline solutions of the metal hydroxide.
To stop the metals reacting with oxygen or water vapour in the air, lithium, sodium and pottasium stored under oil caesium are so reactive that they have to be stored u a sealed glass tubes to stop possibility of oxygen getting at them.
Must not be touched with bare fingers.
What are the chemical properties of the Group 1 elements?
They all react with water in the same way to form a hydroxide with the formula MOH
They react with oxygen to form an oxide with the formula M20
They react with halogens to form compounds
Chemical properties depend on the number of electrons in the outer shell. Group 1 elements react in a similar way because of the same number of electrons on the outer shell.
How do the Group 1 elements react with water?
All metals in Group1 react in the same way with water to produce a metal hydroxide and hydrogen
Alkali metal + water > Alkali metal hydroxide + Hydrogen
The main difference between the reactions is how quickly they happen.
Moving down the group the metals become more reactive and reactions occour more rapidly
How does sodium’s reaction occour with water?
2Na + 2H20 > 2NaOH + H2
Sodium floats because it is less dense than water
The sodium melts into a ball because its melting point is low and a lot of heat is produced by the reaction
There is a fizzing because hydrogen gas is produced
The sodium moves around the surface of the water. Because the hydrogen isn’t given off symmetrically around the ball sodium pushed on the surface of the water
The peice of sodium gets smaller and eventually disappears the sodium is used up in the reaction
If test the solution that is formed with universal indicator solution see that the universal indicator goes blue, indicating an alkaline slution been formed Metal hydroxide is alkaline solution OH-
How does Lithium react with water?
2Li + 2H2O > 2LiOH + H2
This reaction is very similar to sodium’s except it is slower lithium’s melting point is higher and the heat is not produced so quickly so the lithium does not melt.
How does Potassium react with water?
2K + 2H2O > 2KOH + H2
Potassium reacts faster than sodium’s. Enough heat is produced to ignite the hydrogen, which burns with a lilac flame. Reaction often ends with the potassium spitting around exploding.
How does Rubidium and caesium react with water?
These reacts even more violently than potassium and the reaction can be explosive. Rubidium hydroxide and caesium hydroxide are formed.
How does the reactivity change in Group 1?
As moving down the groups, metals become more reactive. Metal atoms are losing electrons and forming metal ions in these solutions
The differences between the reactions depend on how easily the outer electron of the metal is lost in each case. That depends on how strongly it is attracted to the nucleus in the original atom. Nucleus of an atom is positive because it contains protons and so attracts the negative electrons
Moving down the group the atoms have more shells of electrons and get bigger; a sodium atom is bigger than a lithium and pottasium as atoms get bigger outer electrons which is lost one in the reaction, is further from the nucleus because it is further from the nucleus not as easily attracted to the nucleus and therefore more easily lost.
How do the alkali metals react with air?
Lithium sodium and pottasium all stored in oil they react with air. When sodium has been taken out it has a crust on the outside. It is not shiny unless it has been freshly cut
When the piece of sodium is cut the fresh surface is shin but it tarnishes rapidly as the exposed sodium reacts with oxygen in the air. When lithium tarnishes it does so more slowly as it reacts more slowly than sodium. Metals react
with oxygen to form an oxide
When heating the metals in the air using Bunsen burner more vigorous reaction more difficult to see which metal is most reactive because the reaction occours so quickly
Lithium burns with a red flame e to form lithium oxide
Sodium burns with yellow flame to form sodium oxide
Pottasium burns with lilac flame to form pottasium oxide
Forms a white powder
What are compounds of the alkali metals?
All Group 1 metal ions are colourless. Means compounds will be colourless or white unless they are combined with a coloured negative ion. Potassium dichromate is orange because the dichromate ion is orange and potassium magnate is purple because ion is purple they are typically ionic solids and mostly soluble in water
Summarise the main the features of the Group 1 elements?
Are metals
Are soft with melting point and densities which are very low for metals
Have to be stored out of contact with air and water
React rapidly with air to for coatings of the metal oxides
Increase in reactivity as you go down the group
Forms compounds in which the metal has a +1 ions
Have mainly white/colourless compounds which dissolve to produce colourless solutions
How would we predict the properties of Francium?
Moving down the group in the periodic table to properties lf the elements change. Knowing the properties of most of the elements in a given group should be able to predict th properties of elements hat dont know. Able to predict the properties of Francium using properties of other alkali metals:
It is very soft
Melting point around room tempreture
Has density just over 2g/cm3
Will be a silvery metal, but tarnish almost instantly in air
Will react violently with water to give francium hydroxide and hydrogen
Will be more reactive than caesium
Will have a hydroxide francium hydroxide which the formula FROH which was soluble in water to form a strong alkane solution
Will form compounds that are white and colourless and dissolve in water to give colourless solution.
