Classification Of Elements And Periodicity In Properties Chapter-Wise Test 1

Be (group 2, period 2) shows a diagonal relationship with Al (group 13, period 3) due to similar size and electronegativity, unlike Mg, Ca, or B.

Boiling points of group 16 hydrides increase with molecular weight, except for \(\ce{H2O}\) (hydrogen bonding). \(\ce{H2S}\) has the lowest boiling point among \(\ce{H2O}\), \(\ce{H2S}\), \(\ce{H2Se}\), and \(\ce{H2Te}\) due to weak intermolecular forces.

First ionization enthalpy decreases down a group due to increasing size. Among O, S, Se, and Te, Te (period 5) has the lowest value.

Metalloids lie along the metal-non-metal boundary. Si (group 14) is a metalloid, while Na (group 1), Mg (group 2), and S (group 16) are not.

Third ionization enthalpy peaks when removing an electron from a noble gas-like \(\ce{X^2+}\) ion. Ca (after losing two electrons, becomes \(\ce{Ca^2+}\) with \(1s^2 2s^2 2p^6 3s^2 3p^6\)) has the highest value.

Second ionization enthalpy for group 2 elements involves removing an electron from \(\ce{X+}\) (noble gas-like). Be⁺ (smallest size) has the highest value due to greater nuclear attraction.

Mendeleev predicted Eka-silicon below Si, later identified as Germanium (Ge), matching its properties like oxide formula \(\ce{GeO2}\).

s-block elements have outermost electrons in s-orbitals (groups 1 and 2). Na (group 1) is an s-block element, while B (group 13), Si (group 14), and P (group 15) are p-block elements.

Second ionization enthalpy is highest for Li (removing e⁻ from \(\ce{Li+}\) with \(1s^2\)) and decreases across period 2 as stability reduces: Li > Be > B > C.

Sixth ionization enthalpy peaks when removing an electron from a stable \(\ce{X^5+}\) ion. Te (after losing five electrons, becomes \(\ce{Te^5+}\) with \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6\)) has the highest value in period 5.