Question 1

Why was hydrogen used in the Hindenburg airship, and what property made it dangerous?

Accepted Answer

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

Question 2

What makes helium gas inert compared to hydrogen?

Accepted Answer

Helium has a completely filled 1s orbital, resulting in a stable electron configuration.

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 statement best describes the Bohr model of the atom?

Accepted Answer

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

Question 5

Why was the Bohr model replaced by the quantum-mechanical model?

Accepted Answer

The Bohr model could not predict the emission spectra of elements 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 ($$n) $$and what does it specify?

Accepted Answer

It specifies the principal shell and the energy level of an orbital.

Question 8

What is the ground state of a hydrogen atom?

Accepted Answer

The electron is in the $$1s$$ orbital, the lowest energy state.

Question 9

Which of the following statements about orbital shapes is correct?

Accepted Answer

Orbitals in the $$s$$ subshell have a spherical shape.

Question 10

How many subshells are present in the principal shell with $$n = 3$$?

Accepted Answer

Three subshells: $$3s$$, $$3p$$, and $$3d$$

Question 11

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 12

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

Accepted Answer

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

Question 13

Which of the following best describes valence electrons?

Accepted Answer

Electrons in the outermost principal shell (highest $$n$$ value)

Question 14

How many valence electrons does silicon have?

Accepted Answer

4

Question 15

Which element would have the electron configuration $$[Ne] 3s^2$ 3p^5$?

Accepted Answer

Chlorine

Question 16

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

Accepted Answer

Atomic size decreases.

Question 17

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

Accepted Answer

Ionization energy decreases.

Question 18

Which of the following statements about metallic character is correct?

Accepted Answer

Metallic character increases as you move down a group.

Question 19

Why are alkali metals (Group 1A) highly reactive?

Accepted Answer

They have one valence electron and can easily lose it to achieve noble gas configuration.

Question 20

Which of the following best explains why elements in the same group have similar chemical properties?

Accepted Answer

They have the same number of valence electrons.

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

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