Trends in the Effective Nuclear Charge across the 3rd Period

Trends in Z_eff across the 3^rd period of the Periodic Table

Experimental Observation of the Atomic properties of the 3^rd period atoms tells us that the effective nuclear charge increases with Z but exhibits shielding by inner shell electrons and only partial shielding of the electrons within the same shell.

Atom Electron
Config
IP₁
(eV)
Covalent
Radius (A)
Z_eff
(Radius)
Z_eff
(IP)

Na [Ne]3s 5.14 1.86 1.71 1.84

Mg [Ne]3s² 7.64 1.60 1.98 2.25

Al [Ne]3s²3p 5.99 1.43 2.22 1.99

Si [Ne]3s²3p² 8.15 1.17 2.71 2.32

P [Ne]3s²3p³ 10.49 1.10 2.89 2.63

S [Ne]3s²3p⁴ 10.36 1.04 3.05 2.62

Cl [Ne]3s²3p⁵ 12.96 0.99 3.21 2.93

Ar [Ne]3s²3p⁶ 15.76 - - 3.23

The following formula were used

Atom	Electron Config	IP₁ (eV)	Covalent Radius (A)	Z_eff (Radius)	Z_eff (IP)
Na	[Ne]3s	5.14	1.86	1.71	1.84
Mg	[Ne]3s²	7.64	1.60	1.98	2.25
Al	[Ne]3s²3p	5.99	1.43	2.22	1.99
Si	[Ne]3s²3p²	8.15	1.17	2.71	2.32
P	[Ne]3s²3p³	10.49	1.10	2.89	2.63
S	[Ne]3s²3p⁴	10.36	1.04	3.05	2.62
Cl	[Ne]3s²3p⁵	12.96	0.99	3.21	2.93
Ar	[Ne]3s²3p⁶	15.76	-	-	3.23