1. Periodicity
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What is periodicity?
The term used to describe repeating patterns in the properties of elements in the periodic table
What determines the properties of elements?
Electronic structure
What is the position of any element in the periodic table determined by?
Proton number
What does it mean, if an element is in the s block?
Their highest energy electrons are in the s block
What is a definition of the atomic radius?
The distance between the centre of the nucleus of an atom to its outer most electrons
Why is atomic radius measured in a bonded pair of atoms?
As there is no clear end to an electron cloud
What is the atomic radii specifically measured using?
A bonded pair of atoms, and therefore half the distance between the centres of a pair of atoms
What happens to the atomic radius of atoms across period 3?
It decreases
Why does the atomic radii of elements across period three decrease?
• proton number ↑ so nuclear charge ↑ • shielding is constant • so attraction between outer electrons and nucleus ↑
What happens to forces in a substance when it melts?
Some of the ‘forces’ are broken or loosened
What happens to forces in a substance when it boils?
All of the ‘forces’ are broken
What factors increase melting/boiling points in ionic compounds?
• higher charge → stronger electrostatic forces of attraction • smaller ions → stronger attraction as can sit more closely to other ions
What factors increase melting/boiling points in metallic compounds?
Higher charge on ion → more delocalised electrons → stronger attraction
What factors increase melting/boiling points in simple molecular compounds?
• larger molecule → increase van der waal’s forces * bigger difference in electronegativity
What factors increase melting/boiling points in giant covalent compounds?
• more/all covalent bonds → harder to break graphite - IMFs between layers, diamond - all covalent
How is the pattern of melting/boiling points across period 3 elements?
Irregular
How can the trend in period 3 melting/boiling points be explained?
The structure of each element is different
Why does the melting and boiling point increase from sodium to aluminium, when looking at period 3 elements?
• Na forms 1+ ion; Al forms 3+ ion • stronger electrostatic forces between electrons and ions in Al • so Al has a higher m.p. and b.p.
Why does silicon have the highest melting point in period three?
• silicon is macromolecular • so it has many covalent bonds and no IMFs • and therefore takes more energy to break its bonds
Why does silicon have a higher melting point than aluminium but a lower boiling point, when looking at period 3 elements?
• when silicon is melted most covalent bonds are already broken • so there are not very many bonds left to break when boiling • whereas Al has a lot of bonds left to break
Why is the boiling point from phosphorous to argon lower than from sodium to silicon, when looking at period 3 elements?
• P and Ar - P has IMFs and so does Ar • Na has metallic bonds and Si is macromolecular - no IMFs • IMFs are easier to break
Why, when looking at period 3 elements, does the boiling point generally decrease from phosphorous to chlorine?
• Cl is a smaller molecule (Cl₂) • P₄ • weaker VDWs between Cl₂ as there are fewer contact forces due to smaller SA
Why, when looking at period 3 elements, does sulphur have a higher boiling point than phosphrous?
• S₈ • P₄ • weaker VDWs between P₄ as it is a smaller molecule → fewer contact forces due to smaller SA
Why does Argon have the lowest boiling point in period 3?
• it is a noble gas so unreactive * VDWs only → little energy required to break