Problem 7 - Astronomy Journey to the Cosmic Frontier

Question

One atom has 14 protons and 12 neutrons in its nucleus. Another atom has 12 protons and 12 neutrons. Are these atoms different elements or different isotopes of the same element?

Step-by-Step Solution

Answer

The atoms are different elements (silicon and magnesium).

Step 1: Identify the Atomic Number

The atomic number of an atom is determined by the number of protons in its nucleus. For the first atom, there are 14 protons, so its atomic number is 14. For the second atom, there are 12 protons, meaning its atomic number is 12.

Step 2: Determine the Element

Each atomic number corresponds to a specific element on the periodic table. An atom with an atomic number of 14 corresponds to silicon (Si), while an atomic number of 12 corresponds to magnesium (Mg).

Step 3: Analyze the Neutron Count

Both atoms have 12 neutrons, but the number of neutrons does not change the element itself; it only changes the isotope of that element.

Step 4: Conclude Based on Atomic Numbers

Since the atomic numbers (and thus the number of protons) are different, these atoms are different elements: one is silicon and the other is magnesium. The presence of the same number of neutrons does not affect this determination.

Key Concepts

Protons

Protons are subatomic particles that are found in the nucleus of an atom. They carry a positive electric charge. The number of protons in an atom determines its atomic number, which is a unique identifier for an element on the periodic table.
Protons not only define the element but also heavily influence its chemical properties. For example:

• An atom with 14 protons is silicon (Si), making 14 its atomic number.
• An atom with 12 protons is magnesium (Mg), making 12 its atomic number.

Each element has a different number of protons, which is why the periodic table is organized by increasing atomic number. Understanding the role of protons helps determine the identity and characteristics of elements.

Neutrons

Neutrons are neutral subatomic particles, meaning they carry no electric charge. They are also found in the nucleus of an atom, alongside protons. Neutrons play a crucial role in adding mass to the atom and providing stability.
Although neutrons do not determine the chemical identity of the element (as protons do), they influence the isotope of an element. Isotopes are variants of a particular chemical element that have the same number of protons but a different number of neutrons. For instance:

• Both the atoms in our exercise have 12 neutrons, but different proton counts, making them different elements rather than isotopes.
• If another atom of silicon had a different number of neutrons, it would be a different isotope of silicon.

The presence, absence, or variance of neutrons can affect the stability of an atom and its nuclear properties.

Elements

Elements are pure substances that cannot be broken down into simpler substances by chemical means. Each element is defined by its number of protons, known as the atomic number, which gives each element its unique identity. The periodic table organizes elements by increasing atomic number.
Elements have differing properties largely because of how their electrons are arranged, but fundamentally, it is the protons that determine the type of element. Let's consider two elements from our exercise:

• Silicon (Si), with an atomic number of 14, is a metalloid, meaning it has properties of both metals and nonmetals.
• Magnesium (Mg), with an atomic number of 12, is a shiny metal that reacts with water.

These examples illustrate how elements can have vastly different characteristics due to their unique number of protons. Understanding the concept of elements is fundamental to the study of chemistry, as each element combines in distinct ways to form the diverse range of compounds and materials around us.