APCE Atomic Structure & Periodicity

Question 1

What is the atomic number of an element?

Accepted Answer

The number of protons in the nucleus.

Answer

The atomic number of an element is defined by the number of protons found in the nucleus of an atom of that element. This number is unique to each element and determines its identity and position on the periodic table. For example, all carbon atoms have 6 protons, so carbon's atomic number is 6.

Question 2

What does the periodic table’s periodicity refer to?

Accepted Answer

The repetition of chemical properties in groups of elements.

Answer

The periodic table's periodicity refers to the recurring trends and patterns in the chemical and physical properties of elements. As elements are arranged by increasing atomic number, elements with similar properties appear at regular intervals, forming groups or families. This repetition allows scientists to predict the properties of elements based on their position in the table.

Question 3

What is the electron configuration of oxygen (O)?

Accepted Answer

1s² 2s² 2p⁴.

Answer

Oxygen (O) has an atomic number of 8, meaning a neutral oxygen atom has 8 electrons. Following the Aufbau principle, these electrons fill the lowest energy orbitals first: 2 electrons in the 1s orbital, 2 in the 2s orbital, and the remaining 4 electrons in the 2p orbital. Therefore, its electron configuration is 1s² 2s² 2p⁴.

Question 4

How does atomic radius change across a period in the periodic table?

Accepted Answer

It decreases across a period.

Answer

Across a period, the number of protons in the nucleus increases, leading to a stronger positive charge. This increased nuclear charge pulls the valence electrons closer to the nucleus, effectively reducing the atomic radius. Although electrons are added to the same principal energy level, the increasing nuclear pull dominates, causing the atoms to shrink.

Question 5

What is ionization energy?

Accepted Answer

The energy required to remove an electron from an atom or ion.

Answer

Ionization energy is a fundamental property that quantifies the energy needed to overcome the attraction between the nucleus and an electron. Specifically, it's the minimum energy required to remove the most loosely held electron from a gaseous atom or ion in its ground state. This process results in the formation of a cation.

AP Practice Test

AP Practice Test

APCE Atomic Structure & Periodicity