2.1 Periodicy
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How are the elements in the periodic table arranged ?
By 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 represent on the periodic table ?
The outer electrons of an elements .
What are the 4 blocks of the periodic table ?
• s block (group 1 and 2) • p block (group 3 to 8) • d block (transition metals) • f block (bottom rows)
What is periodicy ?
The study of trends within the periodic table, often these are linked with electron configuration.
What is the trend in atomic radius across a period ?
Atomic radius decreases across a period.
Why does atomic radius decrease across a period ?
• The protein number increases across a period, meaning there is a greater attraction between the nucleus and outer electrons • Because there is the same number of shielding electrons in a period, this results in the outer electrons being pulled closer to the nucleus.
What is the trend in atomic radius going down a group ?
It increases.
Why does atomic radius increase going down a group ?
• As you go down a group, more electrons are added to each element • These electrons are organised into orbitals which come at increasingly large distances from the nucleus due to electrons negative repulsion • The additional protons in the nucleus have no substantial effect as there are additional shielding electrons present in each step down a group.
What is the trend in ionisation energy across a period ?
Along a period, first ionisation energy increases.
Why does ionisation energy increase across a period ?
• It increases as atomic radius decreases, hence nuclear charge increases • This means that each electron requires more energy to displace.
What is the trend in ionisation energy going down a group ?
It decreases.
Why does the ionisation energy decrease down a group ?
• The atomic radius of elements increases down a group, which means the attractive force is weaker for the outermost electrons as you progress down a group • This means less energy is required to displace electrons further down a group.
What does the melting point of period 3 elements depend on ?
• The structure of the element • The bond strength.
What happens to the melting points of period three metals (sodium to aluminium) as you progress through the period ?
• The melting point of each metal increases • This is because of the greater positive charge of their ions (Na+ / Al3+) • The additional electrons which are delocalised and the greater positive charge of the ion in Al results in a greater attractive force , meaning more energy is required to break the bonds of Al compared to Na.
What is the trend in melting points from Na to Al ?
• The melting points of the period three metals increase as you progress • This is because the ions formed by the metals have increasingly large charges (Na+ / Al3+) • This means that more electrons are delocalised and the nucleus has a greater positive charge, resulting in a greater electrostatic force in Al compared to Na’s metallic bonding • The stronger electrostatic force requires more energy to overcome, resulting in a higher mpt.
Why does the melting point increase dramatically for Silicon in period 3 ?
• Silicon has a very strong covalent structure • Therefore more energy is required to break the covalent bonds compared to van der waals, giving a higher mpt.
Why does the melting point decrease in period three for phosphorus, sulphur and chlorine ?
• These molecules exist as simple covalent molecules held together by weak van der waals • These bonds are easily broken so these molecules have a relatively low mpt.