AS - Unit 1 - The periodic table Flashcards
Give some advantages of Mendeleev’s table
Predicted the discovery of new elements
As a result their discovery did not disturb the organisation of the table
Indicated some accepted atomic weights were wrong
Give some disadvantages of Mendeleev’s table
Isotopes had not yet been discovered
Didn’t include any noble gases
What is a period?
A horizontal row of elements in the periodic table. Elements show trends in properties across a period
What is a repeating pattern of trends called?
Periodicity
What is each vertical column in the periodic table called?
A group
What does a group contain?
Elements with similar chemical properties
Atoms have the same number of outer shell electrons
What is periodicity?
A regular periodic variation of properties of elements with atomic number and position in the periodic table
What part of the atom is responsible for the chemical reaction?
The outer shell electrons
Why do elements in the same group react in very similar ways?
Each vertical group has the same number of electrons in its outer shell
And the same type of orbitals
Meaning they react in a similar way because they have similar electronic configurations
What factors affect ionisation energies?
Nuclear charge
Distance from the nucleus
Electron shielding
Why does ionisation increase across a period?
The number of protons increases, so the attraction between the nucleus and the outer electrons increases, so more energy is needed to remove an electron
this means the first ionisation energy increases across a period
Which was does a decrease in atomic radius occur?
Across a period, this is because the increased nuclear charge pulls the electrons in towards it
Starting the next period why is there a sharp decrease in first ionisation energy between the end of one period and the start of the next period?
It reflects the addition of a new shell, further from the nucleus which leads to:
increased distance of the outermost shell from the nucleus
increased electron shielding of the outermost electrons by the inner shells
What happens to first ionisation energies down a group?
It decreases because:
The number of shells increases
distance of the outer electrons from the nucleus increases
hence weaker forces of attraction on the outer electrons
there are more inner shells
so shielding effect on outer shells is greater
hence again, less attraction
There is a distinct change in boiling points between group 4 and 5, why is this?
the structure go from giant structures to simple molecular structures
from strong forces of attraction to wear forces of attraction
In metallic bonding, as ionic size increases, and thus attraction increases, what happens to the melting and boiling points?
They also increase
What physical properties do group 2 elements have?
Reasonably high melting and boiling points
light metals with low densities
form colourless compounds
Where are Group 2’s highest energy electrons?
In the S sub shell, along with group 1, they form the s-block of the Periodic table
What group in the periodic table contains strong reducing agents?
Group 2
What is the reactivity change in Group 2 of the periodic table?
It increases down the group, reflecting the increasing ease of losing electrons
What is the trend in ionisation energy in Group 2 of the periodic table?
Ionisation energy decreases down the group, due to the outer electrons being further away from the nucleus and therefore easier to remove from the atom
When calcium reacts with oxygen what is produced?
Calcium oxide
When calcium reacts with water what is produced?
Calcium hydroxide and hydrogen gas
Mg reacts very slowly with water, what happens with each metal as you move further down the group?
They react more vigorously with water as you move down the group
What two half equations have to be written when Calcium reacts with water to form calcium hydroxide and hydrogen gas?
Ca –> Ca2+ +2e-
and
2H2O + 2e- —–> 2OH- + H2
Acids neutralise bases to form what?
A salt and water
What do Group 2 oxides do when they react with water?
Produce a metal hydroxide
What is the typical pH of a metal hydroxide solution
10-12 pH
What do Group 2 hydroxides do when they are dissolved in water?
Form alkaline solutions
What happens to the solubility of Group 2 metal hydroxides as you move down the group?
Solubility in water increases down the group
What is thermal decomposition?
The breaking up of a chemical substance with heat into at least two chemical substances
What happens to alkalinity as you move down the Group 2 hydroxides?
It increases
What happens to the ease of thermal decomposition as you go down the Group 2 carbonates?
The ease of thermal decomposition of Group 2 metal carbonates decreases
When you thermally decompose a metal carbonate, what is produced?
Metal oxide and carbon dioxide gas
Give two uses of the alkaline group 2 elements which are used to combat acidity
Calcium hydroxide is used by farmers and gardeners as ‘lime’ to neutralise acid soils
Magnesium hydroxide is used in ‘milk of magnesia’ to relieve indigestion. Work by neutralising as excess acid in the stomach
Give two properties of Group 7 elements
Low melting and boiling point
Exist as diatomic molecules
As you move down Group 7, the number of electrons increases, what affect does that have on the Van Der Waals’ forces?
It increases the Van Der Waals’ forces between the molecules
What happens to the boiling points of molecules as you go down Group 7?
It increases
What is the trend in reactivity as you go down Group 7, and thus what is the trend in its oxidising power?
The halogen become less reactive as you go down the group and their oxidising power decreases
Which other halogens does Chlorine oxidise?
Bromine and Iodine
What other halogens(s) does bromine oxidise?
Iodine
What order do the three halogens (Cl, I and Br) go in to represent their oxidising powers?
Chlorine
Bromine
Iodine
What is a displacement reaction?
A reaction in which a more-reactive element displaces and less-reactive element from an aqueous solution of the latter’s ions
What is disproportionation?
The oxidation and reduction of the same element in a redox reaction
Give an example in everyday life where a disproportionation reaction takes place
Small amounts of chlorine are added to drinking water to kill bacteria and make the water safe to drink
Chlorine reacts with water to produce two acids: hydrochloric acid and chloric(I) acid
What happens to reactivity as you go down the Group 7 elements?
They become less reactive
What happens to the Group 7 halides when they form ionic bonds?
They react with metals to form ionic halides with an X- ion
Give two examples of how halide compounds are very stable and state how they are used in industry
Sodium fluoride is added to toothpaste to prevent tooth decay
Crystals of calcium fluoride CaF2 are used to make lenses to focus infrared light
Talk through the process of testing for halide ions
Unknown halide substance is dissolved in water
Silver nitrate is added AgNO3
The Ag+ ions react with the X- ions forming a silver halide precipitate. AgX (s)
Chlorine produces a white precipitate
Bromine produces a cream precipitate
Iodine produces a yellow precipitate
If you are unsure of the coloured precipitate formed with an unknown halide and Ag+ ions then what can you do the confirm your answer?
Add aqueous ammonia, different halide precipitates have different solubilities in aqueous ammonia
What is observed when chlorine is tested for in the unknown halide test?
A white precipitate at first then it also dissolves in dilute NH3 if you are unsure
What is observed when bromine is tested for in the unknown halide test?
A cream precipitate however it also dissolves in concentrated ammonia if you are unsure of the colour precipitate
What is observed when iodine is tested for in the unknown halide test?
A yellow precipitate, and if you are unsure of the colour of the precipitate then if you add concentrated ammonia, the precipitate should not dissolve. Then you know you have iodine
What is a precipitation reaction?
A formation of a solid from a solution during a chemical reaction. Often formed when two aqueous solutions are mixed together
