Because of the shielding effect, when an atom has more than one electron shell, each electron feels electric repulsion from the other electrons as well as electric attraction from the nucleus.
bɪkˈʌz ʌvðə ʃˈiːldɪŋ ɪfˈɛkt, wˌɛn ɐn ˈæɾəm hɐz mˈoːɹ ðɐn wˈʌn ᵻlˈɛktɹɑːn ʃˈɛl, ˈiːtʃ ᵻlˈɛktɹɑːn fˈiːlz ᵻlˈɛktɹɪk ɹᵻpˈʌlʃən fɹʌmðɪ ˈʌðɚɹ ᵻlˈɛktɹɑːnz æz wˈɛl æz ᵻlˈɛktɹɪk ɐtɹˈækʃən fɹʌmðə nˈuːklɪəs.