Identifying Atoms — Reading Comprehension

Atoms make up all matter, from the air we breathe to the gold in a ring. Each atom has a unique identity, which scientists determine by looking closely at its structure. The most important feature is the atomic number, which tells us how many protons are in the atom’s nucleus. Since protons carry a positive charge and never change for a given element, the atomic number acts like an atom’s fingerprint. For example, every atom with 6 protons is always carbon, while every atom with 8 protons is always oxygen. The periodic table arranges elements in order of increasing atomic number, making it a powerful tool for identifying atoms.

How Atomic Number and Mass Number Work

The atomic number, found above each element’s symbol on the periodic table, is the key to identifying which element an atom is. However, atoms also contain neutrons (neutral particles) and electrons (negatively charged particles). The total number of protons and neutrons in the nucleus is called the mass number. To find the number of neutrons, you subtract the atomic number from the mass number. For example, carbon-12 has 6 protons (atomic number 6) and a mass number of 12. That means it has 12 – 6 = 6 neutrons. Electrons are not included in the mass number because they are much lighter than protons or neutrons.

Real-World Applications and Examples

Let’s look at three examples. First, carbon-12, the most common form of carbon, has 6 protons and 6 neutrons. Next, oxygen-16 has 8 protons (atomic number 8) and 8 neutrons (mass number 16). Finally, gold-197 has an atomic number of 79 and a mass number of 197. This means a gold-197 atom has 79 protons and 197 – 79 = 118 neutrons. By knowing these numbers, scientists can predict how atoms will interact, what isotopes exist, and how elements behave in nature or technology.

Why It Matters in Science and Society

Understanding atomic structure helps explain important scientific principles, such as chemical reactions, stability, and radioactivity. For example, knowing the mass number is essential in medicine, where specific isotopes are used for imaging or treatment. In environmental science, the identification of isotopes helps trace pollution or understand climate change. The periodic table, with its organization based on atomic number, reflects patterns in element properties and guides research in chemistry, physics, and even biology. These connections show that the way we identify atoms is not just a detail—it’s foundational to all of science.

Interesting Fact:
There are over 100 different elements, but every atom of a given element has the same number of protons, no matter where it is found in the universe!

What does the atomic number of an atom tell you?

How do you find the number of neutrons in an atom?

Which of the following is always true for atoms of the same element?

What is the mass number of an atom that has 8 protons and 8 neutrons?

What does the periodic table organize elements by?

In the passage, what is an isotope?

Why is the atomic number considered the 'fingerprint' of an atom?

If a gold-197 atom has 79 protons, how many neutrons does it have?

True or False: Electrons are included in the mass number of an atom.

True or False: The periodic table can be used to predict how atoms interact.