Question 1

Why was hydrogen used to fill the Hindenburg airship, and what property of hydrogen contributed to the disaster?

Accepted Answer

Hydrogen is less dense than air and highly reactive, making it flammable and prone to ignition.

Question 2

Modern blimps use helium instead of hydrogen. What makes helium inert compared to hydrogen?

Accepted Answer

Helium has a full outer electron shell (two electrons in the 1s orbital), making it stable and nonreactive.

Question 3

According to Mendeleev's periodic law, what happens when elements are arranged by increasing atomic number?

Accepted Answer

Certain sets of properties recur periodically.

Question 4

Which model of the atom introduced the concept of electrons traveling in fixed circular orbits around the nucleus?

Accepted Answer

Bohr model

Question 5

Why did the Bohr model fail to predict the emission spectra of elements other than hydrogen?

Accepted Answer

It could not account for electron-electron interactions in atoms with more than one electron.

Question 6

In the quantum-mechanical model, what does an orbital represent?

Accepted Answer

A probability map showing where an electron is likely to be found.

Question 7

What is the principal quantum number ($$n) $$for the lowest-energy orbital in the quantum-mechanical model?

Accepted Answer

$$n = 1$$

Question 8

What is the shape of an orbital in the 's' subshell?

Accepted Answer

Spherical

Question 9

What happens to the energy of an orbital as the principal quantum number ($$n) $$increases?

Accepted Answer

The energy increases.

Question 10

Which rule states that orbitals of identical energy are first occupied singly by electrons with parallel spins before pairing occurs?

Accepted Answer

Hund's rule

Question 11

What is the electron configuration for a ground-state helium atom?

Accepted Answer

$$1s^2$$

Question 12

How many valence electrons does silicon have, and in which principal shell are they found?

Accepted Answer

4 valence electrons in the $$n = 3$$ shell

Question 13

Which of the following elements is most likely to form a $$+1$$ cation to achieve noble gas configuration?

Accepted Answer

Sodium (Na)

Question 14

As you move to the right across a period on the periodic table, what happens to atomic size?

Accepted Answer

Atomic size decreases.

Question 15

What is ionization energy?

Accepted Answer

The energy required to remove an electron from an atom in the gaseous state.

Question 16

Which trend is observed for metallic character as you move down a group in the periodic table?

Accepted Answer

Metallic character increases.

Question 17

What is the electron configuration for sodium (Na) using noble gas core notation?

Accepted Answer

$$[Ne] 3s^1$

Question 18

Which subshell is being filled for the transition metals in the first row of the transition series?

Accepted Answer

$$3d$$

Question 19

Why are elements close to noble gases on the periodic table highly reactive?

Accepted Answer

They can attain noble gas configuration by gaining or losing a small number of electrons.

Question 20

Which principle states that no more than two electrons can occupy the same orbital, and they must have opposite spins?

Accepted Answer

Pauli exclusion principle

Electrons in Atoms and the Periodic Table: Models, Orbitals, and Periodic Trends

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