Question

How is the mass number related to the number of protons and neutrons an atom has?

Short answer

The mass number (A) of an atom is directly related to the number of protons (Z) and neutrons (N) it contains, and can be expressed as: \(A = Z + N\). Here, A is the total number of protons and neutrons in the nucleus, Z is the number of protons (atomic number), and N is the number of neutrons.

Step-by-step solution

Understanding the Mass Number

The mass number (also called atomic mass number or nucleon number) is the total number of protons and neutrons in the nucleus of an atom. It is denoted by the symbol 'A' and is always a whole number. The mass number can help us determine the mass of an atom since protons and neutrons are the primary contributors to an atom's mass.

Understanding Protons and Neutrons

Protons and neutrons are subatomic particles found in the nucleus of an atom. Both have a similar mass, which is much larger than the mass of electrons. Protons are positively charged particles, and their number in an atom determines the atomic number (Z) and the element's identity. Neutrons have no electric charge and help to stabilize the nucleus of an atom.

Establishing the relationship

The mass number (A) is simply the sum of the number of protons (Z) and the number of neutrons (N) in the nucleus of an atom. Mathematically, we can express this relationship as: \[A = Z + N\] Here, A represents the mass number, Z is the number of protons (atomic number), and N is the number of neutrons. This equation shows that the mass number of an atom is directly related to the number of protons and neutrons it contains. By knowing any two of these values, we can solve for the third one using this relationship.

Key concepts

Protons

Protons are one of the fundamental building blocks of an atom, alongside neutrons and electrons. They are positively charged particles found in the nucleus of an atom. The charge of a proton is exactly equal in magnitude but opposite in sign to that of an electron, making them crucial for the balance of an atom's charge.

Protons play a key role in defining an element's identity. The number of protons in the nucleus of an atom, known as the atomic number, determines which element the atom represents. For instance:

• Hydrogen atoms have 1 proton.
• Carbon atoms have 6 protons.

The atomic number is unique for each element and is fundamental in organizing elements in the periodic table.

Besides defining the element, protons contribute significantly to the atom's mass. Though much smaller, electrons orbiting around the nucleus do not contribute as notably to the mass. This makes protons and neutrons key players when calculating mass number.

Neutrons

Neutrons are neutral particles found in the nucleus of an atom. They have no electric charge, distinguishing them from the charged protons and electrons. Like protons, they are essential components of atomic structure and significant contributors to the mass number - significantly impacting the overall mass of an atom.

Neutrons are responsible for adding stability to the nucleus. The nucleus is a dense region where positively charged protons exist in close proximity. Without neutrons, these protons would repel one another due to their like charges. By mediating these strong forces, neutrons help maintain nuclear cohesion.

The number of neutrons can vary even among atoms of the same element, leading to different isotopes. Isotopes have the same number of protons but differ in neutron count. For example, carbon-12 and carbon-14 are both carbon isotopes, with 6 protons but different numbers of neutrons. Understanding isotopes is crucial in areas like radiocarbon dating and nuclear physics.

Atomic Structure

The atomic structure describes how subatomic particles are arranged in an atom. At the center of an atom lies the nucleus, a dense core containing protons and neutrons. Surrounding this core are electrons, which move in defined spaces called orbitals or energy levels. This structure is not just important for the identity but also for the chemical properties of an element.

The nucleus's composition is reflected not only in atomic interactions but also in the mass number, which is the sum of protons and neutrons in the nucleus. Meanwhile, electrons, albeit smaller, play a pivotal role in chemical bonding and reactions as they are involved in interactions when atoms come close together.

The arrangement of electrons around the nucleus influences an atom's chemical behavior, reactivity, and placement in the periodic table. Understanding atomic structure provides insights into:

• Why elements bond in certain ways
• How chemical reactions occur
• The trends observed in the periodic table

Atomic structure is a fundamental concept in chemistry and physics, underpinning crucial scientific principles that explain the natural world.