Question

Determine the mass number of (a) a fluorine atom with 11 neutrons, (b) a sulfur atom with 16 neutrons, (c) an arsenic atom with 45 neutrons, and (d) a platinum atom with 120 neutrons.

Short answer

Fluorine: 20, Sulfur: 32, Arsenic: 78, Platinum: 198.

Step-by-step solution

Understanding the Problem

The mass number of an atom is the sum of the number of protons and the number of neutrons in the nucleus. To find the mass number, you'll need the atomic number (which is the number of protons) from the periodic table and the number of neutrons.

Fluorine Atom

The atomic number of fluorine is 9, meaning it has 9 protons. With 11 neutrons, the mass number is calculated as follows: \[\text{Mass number of Fluorine} = \text{Number of protons} + \text{Number of neutrons} = 9 + 11 = 20\]

Sulfur Atom

The atomic number of sulfur is 16, so it has 16 protons. With the given 16 neutrons, the calculation is:\[\text{Mass number of Sulfur} = \text{Number of protons} + \text{Number of neutrons} = 16 + 16 = 32\]

Arsenic Atom

For arsenic, the atomic number is 33, indicating 33 protons. With 45 neutrons, the mass number is:\[\text{Mass number of Arsenic} = \text{Number of protons} + \text{Number of neutrons} = 33 + 45 = 78\]

Platinum Atom

Platinum has an atomic number of 78, which means it has 78 protons. With 120 neutrons at its core, the mass number calculation is:\[\text{Mass number of Platinum} = \text{Number of protons} + \text{Number of neutrons} = 78 + 120 = 198\]

Key concepts

Atomic Structure

At the heart of chemistry lies an understanding of atomic structure. Every atom consists of a nucleus and electrons cloud around it. The nucleus, which is the central core, is made up of protons and neutrons.
A proton is a positively charged particle, while a neutron carries no charge. Together, these particles determine much of an element's properties.
The electron cloud contains electrons, which are tiny, negatively charged particles that orbit the nucleus at various energy levels. These electrons participate in chemical reactions and bonding. Understanding atoms is essential because the atomic structure provides the foundation for explaining chemical reactions and physical properties of materials. Here's a simple breakdown of what constitutes atomic structure:

• Nucleus: Composed of protons and neutrons.
• Protons: Positively charged particles that define the atomic number.
• Neutrons: Neutral particles that along with protons, determine the mass number.
• Electrons: Negatively charged particles forming electron clouds.

Learning how these components interact helps us predict how atoms will react and bond in various chemical reactions.

Isotopes

Isotopes are fascinating variations of the same chemical element that have the same number of protons but a different number of neutrons in their nucleus. This results in different mass numbers for isotopes of the same element.
Isotopes share similar chemical properties because they have the same number of electrons and thus exhibit identical behavior in chemical reactions. However, their physical properties can vary significantly due to the difference in mass. Here's a closer look at isotopes:

• Same atomic number: Isotopes have identical numbers of protons.
• Different mass number: Due to differing numbers of neutrons.
• Example: Carbon has isotopes such as Carbon-12 and Carbon-14.

Understanding isotopes is crucial in fields such as medicine and archaeology. Radioactive isotopes, for example, are used in medical imaging and procedures to diagnose and treat various conditions. Similarly, isotopic analysis helps archaeologists determine the age of ancient artifacts.

Periodic Table

The periodic table is a vital tool in chemistry that organizes all known elements in a tabular arrangement based on their atomic number, electron configuration, and recurring chemical properties. Dmitri Mendeleev is credited with its creation, which has undergone several iterations since its inception in the 19th century.
The table's layout makes it simple to understand relationships among elements and predict chemical reactions. Elements are arranged in order of increasing atomic number from left to right, and elements with similar properties fall into the same column or family. Here’s how the periodic table is organized:

• Periods: Horizontal rows representing increasing atomic numbers.
• Groups: Vertical columns with elements having similar chemical properties.
• Metals, Nonmetals, Metalloids: These are broad categories of elements based on properties.

The periodic table is a gateway into understanding the chemical behavior of elements. It provides information on elemental properties and guides predictions in chemical interactions.

Neutrons and Protons

Neutrons and protons are subatomic particles found within an atom's nucleus. They are crucial as they account for most of an atom's mass and contribute to the mass number, which is the sum of these particles. Protons are positively charged and define the atomic number of an element. This is important because the atomic number determines the element's identity in the periodic table. Each element has a unique number of protons. Unlike protons, neutrons have no electrical charge. Their primary role is to add mass and stability to an atom's nucleus. Atoms with the same number of protons but different numbers of neutrons are called isotopes. The relationship between protons and neutrons is critical:

• Mass number: Calculated by adding the number of protons and neutrons.
• Stability: Neutrons help stabilize the nucleus, especially when protons repel each other.
• Isotopes: Variations in the neutron number among atoms of the same element.

Understanding these particles helps us grasp why certain elements behave the way they do and how they interact with other elements in nature.