2.1 Periodicity Flashcards
What is periodicity?
The repeating pattern of physical or chemical properties going across the periods.
How are elements classified in the periodic table?
As s, p, or d block, depending on which orbitals the highest energy electrons are in.
Which elements are in Period 2 and Period 3?
Period 2: Li, Be, B, C, N, O, F, Ne
Period 3: Na, Mg, Al, Si, P, S, Cl, Ar
What is the trend in atomic radius across a period?
It decreases from left to right.
Why does atomic radius decrease across a period?
Increased number of protons leads to greater nuclear attraction for electrons in the same shell with similar shielding.
What is the general trend of first ionisation energy across a period?
It increases.
Why does ionisation energy increase across a period?
Due to increasing number of protons while electrons are added to the same shell.
Why is there a small drop in ionisation energy between Mg and Al?
Mg has a 3s outer electron; Al starts filling the 3p subshell, which is higher in energy and easier to remove.
Why is there a small drop in ionisation energy between P and S?
S has electron pairing in the 3p orbital, leading to repulsion that makes it easier to remove one.
What causes similar drops in ionisation energy in period 2?
Be → B and N → O, due to subshell changes and electron pairing.
What type of bonding do Na, Mg, and Al exhibit, and how does it affect melting point?
Metallic bonding – strong due to more delocalised electrons; leads to higher melting points.
Why does Al have a higher melting point than Na or Mg?
Al has more delocalised electrons and a smaller, more highly charged ion.
What type of structure does Si have, and how does this affect its melting point?
Macromolecular with strong covalent bonds – very high melting point due to energy needed to break them.
What are Cl₂, S₈, and P₄ classified as, and what type of forces act between them?
Simple molecular substances – weak van der Waals forces.
Why does S₈ have a higher melting point than P₄?
S₈ has more electrons, creating stronger van der Waals forces.
What is the structure and melting point trend of Ar?
Monoatomic with weak van der Waals – very low melting point.
What is the trend in melting and boiling points across Period 3?
• Na → Al: Increase (metallic bonding)
• Si: Peak (macromolecular)
• P → Ar: Decrease (molecular → monoatomic)
