Classification of Elements and Periodicity in Properties
Test 2

Among alkali metals (group 1), melting point decreases down the group due to weaker metallic bonding with increasing size. Li, being smallest, has the highest melting point.

In period 4 d-block (Sc to Zn), ionization enthalpy increases across due to increasing nuclear charge, with Zn (\(3d^{10} 4s^2\)) having the highest due to its full d-subshell stability.

Diagonal relationships lead to similar oxide properties. C (period 2) and Si (period 3) both form acidic oxides (\(\ce{CO2}\), \(\ce{SiO2}\)) with covalent character, unlike other pairs.

For \(Z=117\): 1 (un), 1 (un), 7 (sept) → ununseptium (before being named Tennessine).

Ionic character increases with larger electronegativity difference. F (highest electronegativity, 4.0) forms the most ionic compounds with group 1 elements (e.g., \(\ce{NaF}\)) compared to Cl, Br, or I.

F has less negative electron gain enthalpy than Cl due to electron repulsion in its compact 2p orbitals, an anomaly in group 17 trends where Cl > Br > I.

Ionic radius increases down group 17. Among \(\ce{F^-}\), \(\ce{Cl^-}\), \(\ce{Br^-}\), and \(\ce{I^-}\), \(\ce{I^-}\) (from I, period 5) has the largest radius.

Second ionization enthalpy for group 1 elements involves removing an electron from \(\ce{X+}\) (noble gas configuration). Cs⁺ (largest size) has the lowest value due to reduced nuclear attraction.

Hydration energy increases with smaller cation size and higher charge density. Be²⁺ (smallest) has the highest hydration energy among Be, Mg, Ca, and Sr.

Melting point in group 14 decreases from C (covalent network) to Sn and Pb (metallic), with Sn having the lowest among C, Si, Ge, and Sn due to weaker metallic bonding.