Question 1

Which principle states that electrons fill the lowest energy orbital available before occupying higher energy orbitals?

Accepted Answer

Aufbau principle

Question 2

What is the ground-state electron configuration for phosphorus (atomic number 15)?

Accepted Answer

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

Question 3

Which of the following elements has a higher first ionization energy: sodium (Na) or chlorine (Cl)? Explain using periodic trends.

Accepted Answer

Chlorine, because it is further to the right and has a higher effective nuclear charge

Question 4

Which rule explains why electrons in degenerate orbitals (orbitals of the same energy) will first fill each orbital singly before pairing up?

Accepted Answer

Hund's rule

Question 5

What is the electron configuration for the vanadium atom (atomic number 23) in its ground state?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^6$$ $$4s^2$$ $$3d^3$$ \,	ext{or}\, [Ar]$$4s^2$$ $$3d^3$

Question 6

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

Accepted Answer

$$Na^+$$

Question 7

Why does atomic radius decrease across a period from left to right?

Accepted Answer

Because effective nuclear charge increases, pulling electrons closer

Question 8

Which element would you expect to have the most negative electron affinity?

Accepted Answer

Fluorine ($$F)$$

Question 9

What happens to the size of an atom when it forms a cation?

Accepted Answer

It decreases because the outer shell is removed

Question 10

Which of the following best describes the Pauli exclusion principle?

Accepted Answer

No two electrons in an atom can have the same set of quantum numbers

Question 11

Why do the first ionization energies generally decrease as you move down a group in the periodic table?

Accepted Answer

Because the atomic radius increases and outer electrons are held less tightly

Question 12

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$Si)$$

Question 13

A neutral atom of chlorine ($$Cl) $$has 17 electrons. What is its ground-state electron configuration?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^6$$ $$3s^2$$ $$3p^5$$

Question 14

Which of the following is an exception to the expected electron configuration due to near-degenerate orbitals?

Accepted Answer

Copper ($$Cu)$$

Question 15

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

Accepted Answer

Core electrons shield the nucleus, reducing the attraction felt by valence electrons

Question 16

Which element has the largest atomic radius among the alkali metals?

Accepted Answer

Cesium ($$Cs)$$

Question 17

If an atom has the electron configuration $$1s^2$$ $$2s^2$$ $$2p^6$$, what is the element and what is its charge if it is an ion?

Accepted Answer

Neon ($$Ne$$), neutral atom

Question 18

Which of the following best explains why the bonding atomic radius is smaller than the nonbonding atomic radius?

Accepted Answer

Bonding atomic radius is half the distance between nuclei in a bonded pair, where attractive forces overcome repulsion

Question 19

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

Accepted Answer

Helium ($$He)$$

Question 20

Which of the following statements about electron affinity is correct?

Accepted Answer

A more negative electron affinity means the atom more readily accepts an electron

Chapter 9: Periodic Properties of the Elements – Structured Study Notes

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