CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES
Frequently Asked Questions
It is the systematic arrangement of elements so that similar properties recur periodically with atomic number.
The properties of elements are periodic functions of their atomic numbers \(Z\).
The modern periodic table is based on Moseley’s atomic number concept.
There are 7 horizontal periods.
There are 18 vertical groups.
It is the number of protons in the nucleus, denoted by \(Z\).
Regular repetition of properties after fixed intervals of atomic number.
Elements belonging to groups 1, 2, and 13–18.
Elements of d-block (groups 3–12).
f-block elements: lanthanoids and actinoids.
\(Z_{eff}=Z-\sigma\)
Half the distance between nuclei of two bonded atoms.
Decreases left to right.
Increases top to bottom.
Energy required to remove outermost electron from gaseous atom.
\(X(g)\rightarrow X^+(g)+e^-\)
It increases.
It decreases.
Energy change when electron is added to gaseous atom.
Chlorine.
Tendency of atom to attract shared electrons.
Pauling scale.
Increases.
Decreases.
Combining capacity of an element.
Usually -1 or +1.
Tendency to lose electrons.
Decreases.
Increases.
Inner electrons reduce attraction between nucleus and valence electrons.
s<p<d<f
Volume occupied by one mole of atoms.
Similarity between elements diagonally placed (e.g. Li–Mg).
They have stable electronic configuration \(ns^2np^6\).
\(1s^22s^22p^6\)
Species having same number of electrons.
\(O^{2-},F^-,Ne,Na^+,Mg^{2+}\)
Apparent charge assigned to atom in compound.
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Systematic variations of properties with atomic number.
Deviation of first element from group trend.
Small size and high charge density.
Half distance between nuclei of bonded atoms.
Radius of ion in crystal lattice.
Na is larger than Na+.
Cl- is larger than Cl.
Higher positive charge ? smaller radius.
Groups 1 and 2 elements.
Groups 13–18 elements.
Division based on subshell being filled.
Gradual decrease in size from La to Lu.
Poor shielding of 4f electrons.
Predicts properties of unknown elements.
Ionization enthalpy and electronegativity.
Small size causes repulsion in F.
Fluorine.
Horizontal row.
Vertical column.
Cs (practically).
Helium.
Helium.
d-block.
Aufbau principle: filling by increasing energy.
\(1s<2s<2p<3s<3p<4s<3d\)
Lower energy due to penetration.
It organizes trends for prediction and synthesis.
