2.1 Periodicity Flashcards
How are elements in the periodic table arranged?
Elements are arranged according to their proton number
What is a period on the periodic table?
The horizontal rows
What is a group on the periodic table?
The vertical columns
What does the group number indicate on the periodic table?
The number of outer electrons of an element
What are the 4 blocks of the periodic table?
S block
P block
D block
F block
What elements are in each block of the periodic table?
S block = groups 1 and 2
P block = groups 3 and 0
D block = transition metals
F block = radioactive elements
What is periodicity?
The study of trends within the periodic table. Often these trends are linked to elements’ electron configurations
What is the trend in atomic radius along a period
Along a period, atomic radius decreases
Why does atomic radius decrease along a period
Atomic radius decreases because nuclear charge increases for the same number of electron shells
This means that the outer electrons are pulled in closer to the nucleus because the charge produces a greater attraction
As a result the atomic radius is reduced
What is the trend in atomic radius going down a group
Going down a group, atomic radius increases
Why does the atomic radius increase going down a group
With each increment down a group, an electron shell is added
This increases the distance between the outer electrons and the nucleus, reducing the power of attraction
More shells also increases electron shielding, whereby the inner shells create a ‘barrier’ that blocks the attractive forces.
The nuclear attraction is reduced further and atomic radius increases
What is the trend in ionisation energy along a period?
Along a period, ionisation energy increases
Why does ionisation energy increase along a period
It increases because atomic radius decreases, hence nuclear charge increases
This means that the outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom
What is the trend in ionisation energy going down a group
Ionisation energy decreases
Why does ionisation energy decrease going down a group
The nuclear attraction between the nucleus and outer electrons reduces and shielding also increases. Both of these factors mean less energy is required to remove the outer electron
What does the melting point of period 3 elements depend on?
The structure of the element
The bond strength
What happens to melting points across period 3 between sodium and aluminium
Sodium magnesium and aluminium are all metals with metallic bonding. Their melting points increase due to greater positive charge of their ions (Na +1 Mg +2 Al +3)
This means more electrons are released in the form of free electrons
This increases the attractive electrostatic forces from Na to Al, therefore more energy is needed to break them
Why does the melting point increase dramatically for silicone in period 3
Silicon has a very strong covalent structure
So more energy is required to break the strong covalent bonds - giving it a very high melting point
Why does the melting point decrease in period 3 between phosphorous and chlorine
Phosphorus, sulphur and chlorine are all simple covalent molecules held with weak van der waals forces
Less energy is needed to overcome these weak intermolecular forces, so these molecule have relatively low melting points
Why does argon have an even lower melting point than chlorine
Argon is a noble gas that exists as individual atoms with a full outer shell of electrons
This makes the atom very stable and the van der waals forces between them very weak.
As a result less energy is needed to overcome these weak van der waals forces and so argon exists as a gas at room temperature
