C3 - The Periodic Table Flashcards
Outline the development of the early periodic table
John Newlands > 1865
First person to use a pattern
He used the atomic mass
Noticed every 8th element was similar (Law of Octaves)
But only worked for first 15 elements
He assumed all the elements have been discovered
Dimitri Mendeleev > 1869
He also used the atomic mass number
He put similar elements in columns
Left gaps for undiscovered elements
What radically changed the periodic table?
The discovery of protons, neutrons and electrons.
Describe the trends in the modern periodic table.
It arranges elements according to proton number.
All elements are in groups which all have the same number of electrons in their outermost shell.
Each row (period) gets gradually filled up with electrons. i.e.
2
2, 8
2, 8, 1
2, 8, 8, 1
Describe the properties of the group 1 alkali metals.
They are metals with low density (lithium, potassium and sodium are less dense than water and float)
They react with non metals to form ionic compounds.
They react with water to release hydrogen gas and forms a metal hydroxide which gives an alkaline solution.
eg.
Sodium + Water -> Hydrogen + Sodium Hydroxide
2Na + 2H20 -> H2 + 2NaOH
Why is it the further you go down the group the more reactive it is and the lower the melting and boiling point?
Down the group, an extra shell of electrons is added.
This means the outer electrons are further away from the nucleus.
The pull from the nucleus is therefore less.
It is easier for them to give an electron away which makes them more reactive.
Describe the properties of the group 7 (halogens) elements.
They react with metals to form ionic compounds.
The halide ion has a -1 charge.
More reactive halogens can displace less reactive halogens from an aqueous solution of it’s salt.
eg. Chlorine + Potassium Bromide -> Potassium Chloride + Bromine
Why is it the further down the group you go the less reactive they become and the melting and boiling points increase?
As you go down the group an extra shell of electrons is added.
The outer electrons are therefore further away from the nucleus and they have less attraction from the nucleus.
This makes it harder to gain another electron which makes the element less reactive.
Describe the properties of the transition metals. (5 ideas)
High melting points (apart from mercury) High densities Strong and hard Useful as catalysts Form coloured compounds
