2.1 Periodicity
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Periodicity
A repeating pattern of properties shown across the different periods
General trend of ionisation energy across a period
Increases - Electrons being removed from same shell (similar sheilding) - Increasing number of protons - Greater nuclear attraction, so more energy required to remove an electron
Trend in atomic radius across a period
Decreases - Same shells (similar sheilding) - Increases protons number - Greater nuclear attraction, so electrons held more tightly
Atomic radius –> Ionic radius
Positive ions: smaller - Same protons attracting fewer electrons Negative ions: larger - Same protons attracting more electrons
Trend in electronegativity across a period
Increases - Increasing protons - Same shells (similar sheilding) - So pair of electrons more strongly attracted
Structure and bonding Na to Al
Structure: Giant mettalic lattice Bonding: Mettalic bonding
Trend in melting and boiling points Na to Al
Increases - Charge on the ions increases - Number of delocalised electrons increases - Metallic bond gets stronger, so more energy required
Structure and bonding of Si
Structure: Giant covalent structure Bonding: Covalent bonds
Melting and boiling point of Si
Very high - Strong covalent bonds must be broken
Structure of P₄, S₈, Cl₂
Simple molecular - Weak van der Waal’s forces between molecules
Melting and boiling point order of phosphorus, sulfur and chlorine
Cl₂<P₄<S₈ - Larger molecules have more electrons - So they have stronger van der Waal’s forces
Structure of Ar
Simple molecular - very weak van der Waal’s forces
Why does period 2 have higher first ionisation energy than period 3?
• P2 has fewer shells and less sheilding • So stronger nuclear attraction to outer electron
Why does Al have a higher m.p than Mg?
Aluminium ions have a larger charge and more delocalised electrons (forming stronger mettalic bonds)
Which has a higher melting point? Al or Si
Si
Which has a higher boiling point? Al or Si
Al