Question 1

Why was hydrogen used in 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 completely filled outer electron shell, making it stable and unreactive.

Question 3

According to the Bohr model, how do electrons move around the nucleus?

Accepted Answer

Electrons travel in circular orbits at specific, fixed distances from the nucleus.

Question 4

What is a key limitation of the Bohr model of the atom?

Accepted Answer

It cannot predict the emission spectra of elements with more than one electron.

Question 5

How does the quantum-mechanical model describe the location of electrons in an atom?

Accepted Answer

As probability maps (orbitals) showing where an electron is likely to be found.

Question 6

Which statement best describes the difference between a Bohr orbit and a quantum-mechanical orbital?

Accepted Answer

A Bohr orbit is a fixed path, while a quantum-mechanical orbital is a probability map.

Question 7

What does the principal quantum number $$n$$ specify in the quantum-mechanical model?

Accepted Answer

The principal shell and energy level of the orbital.

Question 8

Which of the following best describes the shape of an s orbital?

Accepted Answer

Spherical

Question 9

What is the ground state of an atom?

Accepted Answer

The lowest energy state of the atom, with electrons in the lowest possible orbitals.

Question 10

According to Hund's rule, how do electrons fill orbitals of equal energy?

Accepted Answer

Electrons fill orbitals singly first, with parallel spins.

Question 11

Which of the following is the correct electron configuration for a ground-state carbon atom?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^2$$

Question 12

Which of the following statements about valence electrons is correct?

Accepted Answer

Valence electrons are in the outermost principal shell and are involved in chemical bonding.

Question 13

What is the trend in atomic size as you move from left to right across a period in the periodic table?

Accepted Answer

Atomic size decreases.

Question 14

Which element would have the highest ionization energy?

Accepted Answer

Neon ($$Ne)$$

Question 15

Which of the following best explains why alkali metals are highly reactive?

Accepted Answer

They have one valence electron, which they can easily lose to achieve a noble gas configuration.

Question 16

Which of the following is the correct noble gas core notation for sodium ($$Na$$)?

Accepted Answer

$$[Ne] 3s^1$

Question 17

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

Accepted Answer

Atomic size increases, ionization energy decreases, and metallic character increases.

Question 18

Which of the following best describes the relationship between wavelength and frequency for light?

Accepted Answer

Wavelength and frequency are inversely proportional.

Question 19

A transition metal in the first row of the d block is filling which orbital?

Accepted Answer

$$3d$$ orbital

Question 20

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

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

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