Question

determine what elements are denoted by the following electron configurations:

1. \t1s²2s²2p³

1. \tar 4s²3d⁴

1. \txe 6s²5d⁹

Explanation:

Problem 7: $1s^22s^22p^3$

Step1: Calculate total electrons

Sum the exponents: $2 + 2 + 3 = 7$.

Step2: Identify element

Atomic number = 7, so element is Nitrogen (N).

Problem 8: $[\text{Ar}] 4s^23d^4$

Step1: Electrons in Ar

Argon has 18 electrons.

Step2: Add outer electrons

Add $2 + 4 = 6$ to 18: $18 + 6 = 24$.

Step3: Identify element

Atomic number 24 is Chromium (Cr).

Problem 9: $[\text{Xe}] 6s^25d^9$

Step1: Electrons in Xe

Xenon has 54 electrons.

Step2: Add outer electrons

Add $2 + 9 = 11$ to 54: $54 + 11 = 65$.

Step3: Identify element

Atomic number 65 is Terbium (Tb)? Wait, no: Wait, 54 (Xe) + 2 (6s) + 9 (5d) = 65? Wait, no, 54 + 2 + 9 = 65? Wait, no, 54 + 2 is 56, plus 9 is 65? Wait, no, 54 (Xe) has atomic number 54. Then 6s² is 2, 5d⁹ is 9. So total electrons: 54 + 2 + 9 = 65. Wait, but element 65 is Terbium? No, wait, 5d⁹: Wait, no, maybe I made a mistake. Wait, Xenon is 54. 6s² is 2, so 54 + 2 = 56 (Barium). Then 5d⁹: so from Ba (56), add 9: 56 + 9 = 65. Element 65 is Terbium? Wait, no, Terbium is 65? Wait, no, 65 is Terbium? Wait, no, 64 is Gadolinium, 65 is Terbium? Wait, no, actually, the electron configuration for Gold is [Xe] 6s¹4f¹⁴5d¹⁰, but no. Wait, no, let's check again. Wait, the electron configuration given is [Xe] 6s²5d⁹. So total electrons: 54 (Xe) + 2 + 9 = 65. Atomic number 65 is Terbium? Wait, no, 65 is Terbium (Tb). Wait, but maybe I messed up. Wait, no, 5d⁹: let's count the atomic numbers. Xe is 54. 6s²: 54 + 2 = 56 (Ba). Then 5d orbitals: starting from La (57) which is 5d¹, so 57 (La): [Xe] 6s²5d¹, 58 (Ce): [Xe] 6s²4f¹5d¹, but maybe for d-block, after Ba (56), the next is La (57) with 5d¹, then Ce (58) with 4f¹5d¹, but maybe the problem is simpler. Wait, the electron configuration [Xe] 6s²5d⁹: total electrons 54 + 2 + 9 = 65. So element 65 is Terbium? Wait, no, 65 is Terbium (Tb). Wait, but maybe the problem is about Copper? No, Copper is [Ar] 4s¹3d¹⁰. Wait, no, let's check the periodic table. Atomic number 65: Terbium (Tb) is a lanthanide, but its electron configuration is [Xe] 4f⁹6s². Oh! Wait, I made a mistake. The electron configuration for Terbium is [Xe] 4f⁹6s², not 5d⁹. So where is 5d⁹? Wait, element 79 is Gold: [Xe] 4f¹⁴5d¹⁰6s¹. Wait, no, 5d⁹: element 78 is Platinum: [Xe] 4f¹⁴5d⁹6s¹? No, Platinum is [Xe] 4f¹⁴5d⁹6s¹? Wait, no, Platinum is 78: [Xe] 4f¹⁴5d⁹6s¹? Wait, no, 78: 54 (Xe) + 14 (4f) + 9 (5d) + 1 (6s) = 78? No, 54 +14=68, +9=77, +1=78. So Platinum is [Xe] 4f¹⁴5d⁹6s¹. But the given configuration is [Xe] 6s²5d⁹. So that would be 54 + 2 + 9 = 65, but that's not matching. Wait, maybe the problem has a typo, or I misread. Wait, the problem says [Xe] 6s²5d⁹. Let's recalculate: 54 (Xe) + 2 (6s) + 9 (5d) = 65. But element 65 is Terbium, which has [Xe] 4f⁹6s². So maybe the problem intended 4f⁹ instead of 5d⁹? Or maybe I made a mistake. Alternatively, maybe it's Copper? No, Copper is 29. Wait, no, let's check again. Wait, the electron configuration [Xe] 6s²5d⁹: total electrons 65. So atomic number 65 is Terbium, but its electron configuration is [Xe] 4f⁹6s². So there's a mistake here. But assuming the problem is correct, maybe it's a different element. Wait, no, maybe I messed up the subshell order. The correct order of filling is 6s, then 4f, then 5d. So after 6s², the next is 4f, not 5d. So the electron configuration [Xe] 6s²5d⁹ is incorrect for a real element, but maybe in the problem's context, we just calculate the total electrons: 54 + 2 + 9 = 65, so element 65 is Terbium, even though the configuration is wrong. Alternatively, maybe it's a typo and should be 4f⁹, which is Terbium. So we'll go with that.

Answer:

1. Nitrogen (N)
2. Chromium (Cr)
3. Terbium (Tb) (Note: The electron configuration [Xe] 6s²5d⁹ is non - standard; the correct configuration for Terbium is [Xe] 4f⁹6s², but following the given configuration's electron count, it is Terbium.)