Trends in atomic size (radius) Definition of atomic radius: Covalent radius:  The covalent bond length in H 2 molecule is the distance between the two nuclei.  Assuming that the two hydrogen atoms are two balls in contact with each other, the radius of each ball would be then half the bond length. Bond Length BL= r H +r H Similarly for other elements, Cl 2, Br 2 …. BL can be measured experimentally: BL → covalent atomic radius II/

Factors affecting the atomic size: n of the outermost electrons Attraction force exerted by nucleus on outermost electrons Effective nuclear charge Z eff : charge of nucleus felt by outermost electrons. Electron doesn’t feel the total charge of nucleus because it is screened by inner shells electrons. Thumb rule: Z eff = Z - no. of core electrons 3+ n=1 2e - n=2 1e - Valence electrons: electrons in outermost shell (last n) Core electrons: the remaining electrons. In Li : Z eff =3-2=+1 II/

Z eff constant n ↑ r ↑ n constant Z eff ↑ r ↓ II/

Ionic radius Li : 1s 2 2s 1 Li + : 1s 2 Highest energy electron removed 3+ 2e - 1e - F : 1s 2 2s 2 2p 5 F - : 1s 2 2s 2 2p e - 7e - Electron added in next vacant orbital e - Increased repulsion between electrons Electrons more apart from each other Increased volume Metals tend to lose electrons forming cations. Non-metals tend to gain electrons forming anions. II/

 Cations are smaller than corresponding atoms.  Anions are larger than corresponding atoms. II/

Due to increased attraction Larger nuclear charge II/

Transition metal cations s-electrons removed before the d-electrons!!!!!! Sc 3+ : Ti 2+ : V 3+ : Cr 3+ : Mn 2+ : Fe 3+ : Co 3+ : Ni 2+ : Cu + : Zn 2+ : Find the electron configuration for: Cu 2+, Ti 4+, Fe 2+, V 2+, Co 2+, Cr 2+, Mn 3+. II/