QCM : Fundamentals of Atomic Structure and Periodic Trends — 14 questions

Explication

Dalton proposed that each element consists of identical atoms and that compounds form from atoms combining in simple whole-number ratios. The other options describe later atomic models.

Explication

Rutherford’s experiment showed that most alpha particles passed through the atom, but a few were strongly deflected, supporting a small dense positive nucleus. The uniform positive sphere is Thomson’s idea, not Rutherford’s.

Explication

Atomic number Z is defined as the number of protons in an atom. The total of protons and neutrons is the mass number, not the atomic number.

Explication

Isotopes are atoms of the same element, so they share the same atomic number and differ in neutron number. That means they have the same number of protons but different mass numbers.

Explication

The principal quantum number n labels the principal shell and corresponds to the electron energy level. It does not describe charge or spin.

Explication

Hund’s rule states that electrons fill degenerate orbitals singly before any pairing takes place. This minimizes repulsion and gives a more stable arrangement.

Explication

A large jump indicates that the next electron is being removed from a more inner principal quantum shell, where it is held much more strongly. The earlier smaller steps usually involve electrons from the same outer shell.

Explication

After each electron is removed, the remaining electrons feel a greater effective attraction from the nucleus, so each successive electron is harder to remove. The atom does not gain protons or lose neutrons in this process.

Explication

s-block elements are those whose last electron enters an s orbital, and this includes group 1 and group 2 elements, as well as hydrogen and helium. Group 13 to 18 are p-block elements.

Explication

An element is assigned to a block based on the subshell receiving its last electron: s, p, d, or f. Neutron number and ion charge do not define the block.

Explication

Noble gas notation shortens a configuration by replacing the filled inner shells with the nearest noble gas core in brackets. The other options describe box notation, dot notation, or an incomplete description of the method.

Explication

The notes state that Cr and Cu are exceptions because half-filled and fully filled subshells are energetically more stable than incomplete arrangements. The other choices contradict the stated exception or involve the wrong subshell.

Explication

A free radical is defined by having one or more unpaired electrons, and dot notation is used to show that unpaired electron. The other options describe unrelated particle properties or ordinary ions.

Explication

For d-block ions, the notes state that the outer electrons are removed first, and in Cr-type behavior the 4s electrons are lost before the 3d electrons. The other options do not match the ion-formation pattern described.