2.1 Periodicity Flashcards
(17 cards)
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)
