Question

1. radium

10.iodine
determine what elements are denoted by the following electron configurations:
11.1s² 2s² 2p⁶ 3s² 3p⁴
12.1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰4p⁶ 5s¹
13.kr 5s² 4d¹⁰5p³
explain what is wrong with the following electron configurations:
14.1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4d¹⁰4p⁶
15.1s² 2s² 2p⁶ 3s³ 3d⁵
identify the element and determine the valence electrons.

electron configuration	element symbol	valence electrons
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰4p⁶ 5s¹
1s²2s²2p⁶3s²3p⁶4s²3d⁶
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁵
1s² 2s² 2p⁶ 3s² 3p⁵

Explanation:

Step1: Recall electron - configuration rules

The number of electrons in an atom is equal to its atomic number. The order of filling orbitals is $1s<2s < 2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p$.

Step2: Determine element for $1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}$

Count the electrons: $2 + 2+6 + 2+4=16$. The element with atomic number 16 is sulfur (S).

Step3: Determine element for $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{1}$

Count the electrons: $2+2 + 6+2+6+2+10+6 + 1=37$. The element with atomic number 37 is rubidium (Rb).

Step4: Determine element for $[Kr]5s^{2}4d^{10}5p^{3}$

The electron - configuration of Kr is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$. Adding $5s^{2}4d^{10}5p^{3}$ electrons, we have $36+2 + 10+3=51$. The element with atomic number 51 is antimony (Sb).

Step5: Analyze $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4d^{10}4p^{6}$

The error is that after filling the $4s$ orbital, the next orbital to be filled is $3d$ not $4d$. The correct configuration should be $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}$.

Step6: Analyze $1s^{2}2s^{2}2p^{6}3s^{3}3d^{5}$

The $s$ sub - shell can hold a maximum of 2 electrons. So, $3s^{3}$ is incorrect. The correct configuration might be something like $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{5}$ (following the Aufbau principle).

Step7: For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{1}$

Element symbol: Rb. Valence electrons: 1 (the electron in the $5s$ orbital).

Step8: For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{6}$

Element symbol: Fe. Valence electrons: 8 ($2$ in $4s$ and $6$ in $3d$).

Step9: For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$

Element symbol: I. Valence electrons: 7 ($2$ in $4s$, $10$ in $3d$ and $5$ in $4p$, but valence electrons are the outermost electrons, so $7$ from $4s^{2}4p^{5}$).

Step10: For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$

Element symbol: Cl. Valence electrons: 7 ($2$ in $3s$ and $5$ in $3p$).

Answer:

1. Element: S
2. Element: Rb
3. Element: Sb
4. Error: Incorrect orbital - filling order, should fill $3d$ before $4d$.
5. Error: $3s$ sub - shell cannot have 3 electrons.

For the table:

Electron Configuration	Element Symbol	Valence Electrons
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{6}$	Fe	8
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$	I	7
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$	I	7
$1s^{2}2s^{2}2p^{6}3s^{2}3p^{5}$	Cl	7