Question 1

Which scientist is credited with leaving empty spaces in the periodic table for elements that had not yet been discovered, and predicting their properties based on periodic trends?

Accepted Answer

Dmitri Mendeleev

Question 2

According to the Pauli exclusion principle, which statement is correct regarding electrons in an atom?

Accepted Answer

No two electrons in an atom can have the same four quantum numbers.

Question 3

Which of the following electron configurations represents the ground state of phosphorus (Z = 15)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^3$$

Question 4

Which of the following best explains why the 2s subshell is filled before the 2p subshell in multielectron atoms?

Accepted Answer

The 2s subshell has a lower energy due to greater penetration and effective nuclear charge.

Question 5

Which element has the following electron configuration: $$[Ar] 4s^1$ 3d^5$?

Accepted Answer

Chromium (Cr)

Question 6

What is the correct order of subshell energies for the third shell ($$n=3) in $$multielectron atoms?

Accepted Answer

$$3s \u003c 3p \u003c 3d$$

Question 7

Which of the following ions is isoelectronic with neon ($$Ne$$)?

Accepted Answer

$$O^{2-}$$

Question 8

Which trend is observed in atomic radius as you move across a period from left to right in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing effective nuclear charge.

Question 9

Which of the following elements has the highest first ionization energy?

Accepted Answer

Fluorine ($$F)$$

Question 10

Which statement best describes Hund's rule?

Accepted Answer

Electrons occupy orbitals singly before pairing in orbitals of equal energy.

Question 11

Which of the following ions has the largest ionic radius?

Accepted Answer

$$F^-$$

Question 12

Which of the following elements is most likely to form a cation with a +2 charge?

Accepted Answer

Magnesium

Question 13

Which of the following best describes the Aufbau principle?

Accepted Answer

Electrons fill the lowest energy orbitals first before filling higher energy orbitals.

Question 14

Which of the following elements has an 'unusual' electron configuration compared to the predicted pattern?

Accepted Answer

Chromium (Cr)

Question 15

What is the electron configuration for the $$Fe^{2+}$$ ion?

Accepted Answer

$$[Ar] 3d^6$

Question 16

Which of the following statements about effective nuclear charge ($$Z_{eff}) is $$correct?

Accepted Answer

$$Z_{eff}$$ increases as you move across a period due to increased nuclear charge and incomplete shielding.

Question 17

Which of the following is the correct noble gas notation for the electron configuration of calcium ($$Ca$$, Z = 20)?

Accepted Answer

$$[Ar] 4s^2$

Question 18

Which of the following best explains why transition metals often have multiple oxidation states?

Accepted Answer

Their d and s electrons are close in energy, allowing for variable electron loss.

Question 19

Which of the following elements has the electron configuration $$[Ne] 3s^2$ 3p^4$?

Accepted Answer

Sulfur (S)

Question 20

Which of the following statements about electron affinity is correct?

Accepted Answer

Electron affinity generally increases across a period from left to right.

Atomic Structure, Electron Configuration, and Periodic Trends

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