Shielding or screening occurs when one electron is blocked from the full effects of the nuclear charge so that the electron experiences only a part of the nuclear charge. penetration occurs when an electron penetrates the electron cloud of the 1s orbital and now experiences the full effect of the nuclear charge. penetration occurs when one electron is blocked from the full effects of the nuclear charge so that the electron experiences only a part of the nuclear charge. shielding or screening occurs when an electron penetrates the electron cloud of the 1s orbital and now experiences the full effect of the nuclear charge. shielding and penetration are essentially the same thing and occurs when an electron penetrates the electron cloud of the 1s orbital and now experiences the full effect of the nuclear charge. shielding and penetration are essentially the same thing and occurs when one electron is blocked from the full effects of the nuclear charge so that the electron experiences only a part of the nuclear charge.