Periodicity Flashcards
How are elements in the periodic table arranged?
Arranged according to their proton number
What does the group number indicate on the periodic table?
The number of electrons in the outer shell of an element
What elements are in each block of the periodic table?
S block= grpup 1 & group 2
P block= groups 3 to 0
d block= transition metals
f block= radioactive elements.
What is the trend in atomic radius along a period?
Atomic radius decreases.
why does atomic radius decrease along a period?
Due to an increased nuclear charge 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?
Atomic radius increases
why does atomic radius increase as you go down a group?
An electron shell is added each time. This increases the distance between the nucleus and the outer electrons, reducing the attraction. More shells= increased electron shielding which blocks attractive forces to the nucleus. The nuclear attraction is reduced further and atomic radius decreases.
What is the trend in ionisation energy across a period?
Ionisation energy increases
Why does ionisation energy increase across a period?
Atomic radius decreases, hence nuclear charge increases.
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?
Nuclear attraction between nucleus and outer shell electrons is reduced and shielding is increased. Therefore, it requires less energy to remove and ionise an electron from the outer shell.
What does the melting point of period 3 elements depend on?
Structure of element
bond strength
What happens to melting points across period 3 between sodium and aluminium?
Na, Mg, Al all have 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 melting point increase dramatically in period 3 for silicone?
Has a very strong covalent structure
More enrgy 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?
Phosphorous, sulphur and chlorine are all simple covalent molecules hed by weak van der waals forces .
Less energy is needed to overcome these weak intermolecular forces, so they have relatively low melting points.
