Topic 6 - groups in the periodic table Flashcards
How are element arranged in the periodic table?
Ordered by increasing atomic number
Elements in the same group have the same number of outer shell electrons
Elements in the same period have the same number of electron shells
How many electrons are in the outer shell of a group 1 element?
1
Why do elements in the same group have similar chemical properties?
They have the same number of electrons in the outer shell
What group of the periodic table are the alkali metals?
Group 1
List two properties of alkali metals
Soft
Relatively low melting points
Why are group 1 elements called the alkali metals?
They react with water to form alkaline solutions
Why should alkali metals be stored in oil?
To prevent them reacting with water vapour and oxygen in the air
What is the order of reactivity of the first 3 alkali metals with water?
Lithium
Sodium
Potassium
Predict the reactivity trend down group 1
Increases down group 1
Why does reactivity increase down group 1?
The number of electron shells increases so there is more electron shielding
There is a weaker attraction between the positive nucleus and outer shell electrons so it is easier to remove an outer shell electron to form a positive metal ion
What groups are the halogens in? Why?
Group 7 because they have 7 outer shell electrons
What is the colour and state of chlorine at room temperature?
Pale green gas
What is the colour and state of bromine at room temperature?
Red-brown liquid
What is the colour and state of iodine at room temperature?
Black solid
Why are the halogens at different states at room temperature? What is the trend down the group?
Chlorine is gas, bromine is liquid and iodine is solid because they have different melting points
As you go down, the melting and boiling points increase
Why does melting and boiling point increase down group 7?
The molecules get bigger so there are more intermolecular forces to overcome during melting/boiling so more energy is required
What is the chemical test for chlorine?
Damp litmus paper placed into a test tube of gas. If chlorine is present, the litmus paper will turn red then white due to the bleaching effect of chlorine
What does diatomic mean?
Substances that form molecules consisting of 2 atoms
What charge does a halide ion Carry? Why?
-1
They gain one electron to have a stable electron configuration
What is produced when a halogen reacts with a metal?
Metal halide salt
Describe the trend in reactivity of the halogens
It decreases down group 7
What is formed when a halogen reacts with hydrogen?
Hydrogen halides
What is formed when a hydrogen halide dissolves in water?
An acidic solution. Hydrogen ions dissociate, making the solution acidic
When does a halogen displacement occur?
When a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
Why does reactivity decrease down group 7?
As you go down group 7, the outer shell is further from the nucleus and electron shielding increases
Attraction between the nucleus and outer electrons decreases so it is harder for the atom to gain an electron meaning reactivity decreases
What colours are solutions of chlorine, bromine and iodine?
Chlorine water - colourless
Bromine water - orange
Iodine solution - brown
What is a redox reaction?
A reaction where oxidation and reduction take place at the same time
WhT name is used to describe the elements in group 0 of the periodic table?
Noble gases
How many electrons do the noble gases have in their outer shell?
0
What does chemically inert mean?
Not chemically active
Why are the noble gases chemically inert?
They have full outer electron shells
What is the trend in boiling points down group 0?
Boiling point increases down group 0 because the relative atomic mass increases so there are more intermolecular forces between atoms
What is the trend in density down group 0?
Density increases down the group
What are the products when an alkali metal reacts with water?
Metal hydroxide and hydrogen
What would be observed when lithium reacts with water?
Bubbles of hydrogen produced
Doesn’t melt
Slowest reaction
What would be observed when sodium reacts with water?
Faster reaction than lithium
Floats of the surface of water
Bubbles of hydrogen are produced, causing the sodium to whizz around the surface of the water
Melts as enough energy is given out to meet sodium’s melting point
What would be observed when potassium reacts with water?
More violent reaction than sodium
Bubbles of hydrogen produced, causing the potassium to whizz around the surface of the water
Melts into a shiny ball
Burns with lilac flame
Which group 1 element would you expect to rea t most violently with water?
Francium
Chlorine reacts with hydrogen in the presence of sunlight but bromine requires a flame. Why?
Reactivity decreases down the group so bromine requires more energy for the reaction to occur
Why will halogen A only be displaced by halogen B if B is above A in group 7
The most reactive halogen (B) will displace the less reactive halogen (A) to become part of the ionic compound. Reactivity increases as you go up the group so B must be higher than A
What would you observe when chlorine is added to potassium bromide?
Colour change from colourless to orange
Are halogen displacement reactions redox reactions? Why?
Yes because the halide ion is oxidised to form a halogen atom and the halogen is reduced to form a halide ion
What properties of helium makes it suitable for use in balloons?
It is less dense than air and does not burn
Why is argon used to fill electric light bulbs?
It is very chemically inert so will not react when the light bulb gets hot. It is non-flammable
Why is argon used for welding?
It provides an inert welding atmosphere
Is more dense than air so keeps air away from the metal
