Among the second period elements the actual ionization enthalpies are in the order $Li < B < Be < C < O < N < F < Ne$. Explain why (ii) $O$ has lower $\Delta_{i} H$ than $N$ and $F$?

Assign the position of the element having outer electronic configuration (ii) $(n-1)d^{2}ns^{2}$ for $n=4$, and

Write the atomic number of the element present in the third period and seventeenth group of the periodic table.

Predict the formulas of the stable binary compounds that would be formed by the combination of the following pairs of elements. (b) Magnesium and nitrogen

Photoelectric effect explain by

Assign the position of the element having outer electronic configuration (i) $ns^{2}np^{4}$ for $n=3$

What is the basic theme of organisation in the periodic table?

Which one of the following statements is incorrect in relation to ionization enthalpy?

The first ($\Delta_{i}H_{1}$) and the second ($\Delta_{i}H_{2}$) ionization enthalpies (in kJ $mol^{-1}$) and the ($\Delta_{eg}H$) electron gain enthalpy (in kJ $mol^{-1}$) of a few elements are given below:
Elements $\Delta H_{1}$ $\Delta H_{2}$ $\Delta_{eg}H$
I 520 7300 –60
II 419 3051 –48
III 1681 3374 –328
IV 1008 1846 –295
V 2372 5251 +48
VI 738 1451 –40
Which of the above elements is likely to be : (a) the least reactive element.

In the modern periodic table, the period indicates the value of :

Write the general outer electronic configuration of $s$-, $p$-, $d$- and $f$- block elements.

Energy of an electron in the ground state of the hydrogen atom is $-2.18 imes 10^{-18}J$. Calculate the ionization enthalpy of atomic hydrogen in terms of $J mol^{-1}$.

On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.

Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

Considering the elements $B$, $C$, $N$, $F$, and $Si$, the correct order of their non-metallic character is :

The increasing order of reactivity among group 1 elements is $Li < Na < K < Rb < Cs$ whereas that among group 17 elements is $F > Cl > Br > I$. Explain.

What does atomic radius and ionic radius really mean to you?

Describe the theory associated with the radius of an atom as it (b) loses an electron

Which of the following statements related to the modern periodic table is incorrect?

Considering the elements $B$, $Al$, $Mg$, and $K$, the correct order of their metallic character is :