Question

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: Count total electrons

The sum of exponents in the electron - configuration gives the total number of electrons, which is equal to the atomic number for a neutral atom.

Step2: Identify element

Use the periodic table to find the element with the corresponding atomic number.

Step3: Determine valence electrons

Valence electrons are the electrons in the outermost shell. For main - group elements, they are in the highest - numbered s and p orbitals. For transition metals, they include the outermost s and the d electrons involved in chemical bonding.

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

• Total electrons: $2 + 2+6 + 2+6 + 2+10 + 6+1=37$. The element is Rubidium (Rb). Valence electrons: 1 (the $5s^{1}$ electron).

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

• Total electrons: $2 + 2+6 + 2+6 + 2+6=24$. The element is Chromium (Cr). Valence electrons: 6 ($4s^{2}$ and $3d^{4}$, in Cr the electron configuration is $[Ar]4s^{1}3d^{5}$ for stability, but still the total valence electrons considering bonding are 6).

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

• Total electrons: $2 + 2+6 + 2+6 + 2+10 + 5=35$. The element is Bromine (Br). Valence electrons: 7 ($4s^{2}$ and $4p^{5}$).

1. (Same as 3, repetition) For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{5}$:

• Total electrons: 35, element is Bromine (Br), valence electrons: 7.

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

• Total electrons: $2 + 2+6 + 2+5=17$. The element is Chlorine (Cl). Valence electrons: 7 ($3s^{2}$ and $3p^{5}$).

Answer:

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