Abnormal electronic configuration of chromium and copper

Common misconceptions

• Cr = [Ar] 4s2 3d4 and Cu = [Ar] 4s2 3d9.

  That is the expected pattern, but the book writes Cr as [Ar] 4s¹\,3d⁵$4s^{1}3d^5$ and Cu as [Ar] 4s¹\,3d¹⁰$4s^{1}3d^{10}$. The atom has lower energy (extra stability) when 3d is half-filled (d⁵$d^5$) or completely filled (d¹⁰$d^{10}$).

  Explain in Egyptian Arabic

  لأ، ده توزيع القاعدة العامة، لكن الكتاب بيكتب الـ Cr كـ [Ar] 4s1 3d5 والـ Cu كـ [Ar] 4s1 3d10، عشان الذرة بتبقى طاقتها أقل (extra stable) لما الـ 3d يبقى half-filled (d5) أو completely filled (d10).

• Other elements also 'promote' an electron (e.g. Fe 4s1 3d7, Ni 3d10); only Cr and Cu do in this series.

  In this series, Cr and Cu are the two exceptions. Fe stays [Ar] 4s²\,3d⁶$4s^{2}3d^6$ and Ni stays [Ar] 4s²\,3d⁸$4s^{2}3d^8$ (book table): moving one 4s electron would not make their 3d half-filled (d⁵$d^5$) or completely filled (d¹⁰$d^{10}$).

  Explain in Egyptian Arabic

  مش صح

  في السلسلة دي مفيش غير الـ Cr والـ Cu اللي بينقلوا electron من الـ 4s للـ 3d. الـ Fe والـ Ni ماشيين على القاعدة العامة وبيحتفظوا بالـ 4s2، لأن نقل electron عندهم مش هيخلّي الـ 3d لا half-filled (d5) ولا completely filled (d10).