Question

Which of the following statements is(are) true? a. Dalton was the first to theorize that atoms consist of smaller particles called electrons, protons, and neutrons. b. Dalton's atomic theory didn't account for isotopes. c. All particles in the nucleus of an atom are charged.

Short answer

Statement b is true: Dalton's atomic theory didn't account for isotopes, as the existence of isotopes was not known during his time.

Step-by-step solution

Statement a - Analyzing Dalton's contribution to atomic theory

Dalton was known for introducing the atomic theory in chemistry, but he didn't specifically theorize about electrons, protons, and neutrons as the smaller particles within atoms. It was actually J.J. Thomson who discovered the electron, Ernest Rutherford who discovered the proton, and James Chadwick who discovered the neutron. So, statement a is false.

Statement b - Analyzing Dalton's atomic theory and isotopes

Dalton's atomic theory consisted of the idea that elements are made of atoms, which are indivisible particles, and that the atoms of a given element are identical to each other with the same mass. However, the existence of isotopes was not known at that time. Isotopes are atoms of the same element with a different number of neutrons, which results in different atomic masses. Therefore, statement b is true, as Dalton's atomic theory didn't account for isotopes.

Statement c - Analyzing charges in the nucleus of an atom

The nucleus of an atom consists of protons and neutrons. Protons carry a positive charge, while neutrons carry no charge (they are neutral). Since not all particles in the nucleus are charged (neutrons are not charged), statement c is false.

Key concepts

Dalton's Atomic Theory in Chemistry

John Dalton's atomic theory laid the groundwork for our modern understanding of atoms. Dalton postulated that matter is composed of small, indivisible particles called atoms. He claimed atoms of a single element are identical in size, mass, and other properties, whereas atoms of different elements vary in these respects. Although his theory was revolutionary, it wasn't entirely accurate. It was limited by the scientific knowledge available at the time.

Dalton's theory did not include the subatomic particles—electrons, protons, and neutrons—because they were discovered much later. Electrons were identified by J.J. Thomson in 1897 and the proton by Ernest Rutherford in 1917. Lastly, James Chadwick discovered the neutron in 1932. These discoveries challenged the indivisibility of atoms and brought forward the concept of atomic structure that involved a nucleus and orbiting electrons.

Despite Dalton's focus on the atomic differences between elements, even atoms of the same element can have variations—this concept was not accounted for in Dalton's original theory but later became known through the discovery of isotopes.

Understanding Atomic Structure

Atomic structure delves into the composition of atoms, which are the smallest units of matter that retain the identity of an element. An atom is composed of a central nucleus that contains protons and neutrons, surrounded by a cloud of electrons. Protons, having a positive charge, and neutrons, which are neutral, compose the nucleus, while electrons, which are negatively charged, orbit around this nucleus.

The arrangement of electrons in their respective energy levels, or electron shells, influences an atom's reactivity and its ability to form chemical bonds. These subatomic particles—their numbers and arrangements—define the chemical behavior and properties of the element. Understanding the complexities of atomic structure provides the essential foundation for explaining why different materials exhibit different properties and how they interact in chemical reactions.

The Concept of Isotopes

Isotopes are variants of a particular chemical element that share the same number of protons but differ in the number of neutrons. This results in atoms of the same element with different mass numbers. Isotopes have nearly identical chemical properties because they have the same electron configuration, but their physical properties, such as melting point and density, can vary.

Some isotopes are stable, while others are unstable (radioactive), decaying over time and emitting radiation. The study of isotopes is crucial in various scientific fields. For instance, carbon dating utilizes the known half-lives of isotopes to determine the age of archaeological finds. In medicine, certain isotopes are used for diagnostic imaging and cancer treatment. The nuanced understanding of isotopes extends the fundamental concepts of Dalton's atomic theory, highlighting the diversity within atoms of a single element.