Question

After Moseley's discovery in \(1913,\) the periodic law stated that physical and chemical properties tend to repeat periodically when elements are arranged according to what trend?

Short answer

The properties repeat periodically when elements are arranged by increasing atomic number.

Step-by-step solution

Understand Moseley's Contribution

In 1913, Henry Moseley discovered that the properties of elements are better explained and ordered by their atomic numbers rather than their atomic masses. This was a significant shift from the old Periodic Law based on atomic mass.

Define Atomic Number

The atomic number of an element is defined as the number of protons in the nucleus of an atom of that element. This number gives the element its identity and unique properties.

The Revised Periodic Law

After Moseley's discovery, the Periodic Law was revised. It stated that the physical and chemical properties of elements tend to repeat periodically when they are arranged in order of increasing atomic number, not atomic mass.

Recognize the Periodic Trend

By arranging elements by atomic number, the groupings and periods of the periodic table align more accurately with recurring characteristics and chemical behaviors of elements. This same trend helps predict and explain the properties of new or undiscovered elements.

Key concepts

Henry Moseley

Henry Moseley was a pioneering figure in the field of chemistry whose work dramatically transformed our understanding of the organization of the periodic table. Before Moseley's research, elements were arranged primarily by atomic mass, which sometimes resulted in inconsistencies in the periodic pattern due to isotopic variations. In 1913, Moseley revealed a more coherent order by introducing the concept of atomic number.

Moseley's experiments involved studying the X-ray spectra of various elements. He discovered that each element produces X-rays of a distinctly unique frequency. This frequency, he found, was directly proportional to the square of the atomic number—essentially, the number of protons in the nucleus. His influential work established that the atomic number, rather than atomic mass, should be the guiding thread for the periodic table.

Moseley's findings cleared up previous discrepancies and validated the periodic law as a fundamental principle in chemistry, leading to a more accurate and predictable system for arranging elements.

Atomic Number

The atomic number of an element is a key identifier and is defined as the number of protons found in the nucleus of an atom. It is a unique and intrinsic property of each element, ensuring that no two elements share the same atomic number. The atomic number not only defines the identity of an element, but also determines its place in the periodic table.

This representation is significant because it dictates the chemical properties of the element, as the number of protons also equals the number of electrons in a neutral atom. These electrons are responsible for chemical bonding and interactions.

• For instance, hydrogen has an atomic number of 1, meaning it has one proton in its nucleus.
• Carbon, with an atomic number of 6, has six protons.
• Oxygen, with an atomic number of 8, has eight protons.

Understanding atomic numbers helps chemists predict common chemical behaviors and properties, enabling the identification and organization of elements in a systematic manner.

Periodic Table

The periodic table is a structured chart organizing all known chemical elements based on increasing atomic number. With Moseley's refinement, the periodic table became far more reliable and easier to interpret. Arranging elements in order of increasing atomic number ensures that elements with similar chemical characteristics are aligned in columns, known as groups. Each group shares similar valence electron configurations, which often dictate similar reactivity and bonding patterns among them.

In the rows, known as periods, elements demonstrate a gradual shift in properties as their atomic numbers increase. This shift is predictable and aligns well with recurring periodic trends, such as increasing electronegativity, ionization energy, and atomic radius.

• Metals are typically found on the left side and center of the table.
• Nonmetals are located on the right side of the table.
• Metalloids, which have properties of both metals and nonmetals, are usually found along a zigzag line dividing metals and nonmetals.

The periodic table is not just a tool for organizing elements, but a predictive framework for understanding chemical reactions and properties, even for elements yet to be discovered or synthesized.