Question

12 multiple choice 1 point which of the following best explains why mendeleevs periodic table was organized according to atomic mass rather than atomic number? atomic mass varies among the isotopes of an element. atomic mass is unaffected by chemical reactions. atomic number is more closely related to reactivity. atomic number had not yet been discovered. 13 multiple choice 1 point what is the identity of the element with the electron configuration of ( 1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 4 s^{2} 3 d^{10} )? p ca zn cd

Explanation:

12.

Step1: Analyze each option for question 12

• Option 1: Atomic mass varies among isotopes. This is a fact but not the reason for Mendeleev's table organization.
• Option 2: Atomic mass is unaffected by chemical reactions. While true, it's not relevant to why he used atomic mass over atomic number.
• Option 3: Atomic number is related to reactivity. But Mendeleev didn't know about atomic number's relation at that time.
• Option 4: Atomic number had not been discovered. Mendeleev worked in the 19th century. Atomic number (proton number) was discovered later (by Moseley in 1913). So he used atomic mass as the organizing principle.

13.

Step1: Calculate the number of electrons for question 13

The electron configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}\).
Sum the electrons: \(2 + 2+6 + 2+6 + 2+10=28\)

• For \(P\) (phosphorus), atomic number \(Z = 15\) (number of electrons \(=15\)).
• For \(Ca\) (calcium), \(Z = 20\) (number of electrons \(=20\)).
• For \(Zn\) (zinc), \(Z = 30\). But in the electron - filling order, after \(4s^{2}\), we fill \(3d\) orbitals. The total electrons in the given configuration: \(2+2 + 6+2+6+2+10=28\) (but for \(Zn\), the full electron configuration is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}\), atomic number \(Z = 30\). Wait, recalculate: \(2+2+6+2+6+2 + 10=28\) (error in previous sum). Correct sum: \(2+2+6+2+6+2+10=28\) (no, \(1s^{2}(2)+2s^{2}(2)+2p^{6}(6)+3s^{2}(2)+3p^{6}(6)+4s^{2}(2)+3d^{10}(10)\)

\(2+2 + 6+2+6+2+10=30\). Zinc (\(Zn\)) has atomic number \(Z = 30\).

• For \(Cd\) (cadmium), \(Z=48\)

Answer:

1. Atomic number had not yet been discovered.
2. \(Zn\)