Atomic number, mass number, and isotopes | Chemistry | Khan Academy

Summary

This educational video script explores the concept of atomic number, isotopes, and the structure of atoms. It uses hydrogen as an example to explain that isotopes of an element have the same number of protons but differ in neutron count, affecting their mass. The script introduces protium, deuterium, and tritium, illustrating how to represent them with symbols that denote atomic and mass numbers. It further explains how to calculate the number of protons, neutrons, and electrons in atoms, using carbon and uranium as additional examples, and introduces the hyphen notation for representing isotopes.

Takeaways

• 🔬 The atomic number (Z) represents the number of protons in an atom's nucleus and can be found on the periodic table.
• 💧 Hydrogen, with an atomic number of one, has one proton in its nucleus and, in a neutral state, one electron to balance the charge.
• 🌐 The Bohr model, though an oversimplification, is a helpful starting point for visualizing the structure of an atom like hydrogen.
• 🔍 Isotopes are variants of a single element that differ in the number of neutrons within their nuclei.
• 🚀 Protium, deuterium, and tritium are isotopes of hydrogen, distinguished by having zero, one, and two neutrons respectively.
• ⚖️ Isotopes have different masses due to the varying number of neutrons, but share the same atomic number.
• 📊 The mass number (A) is the sum of protons and neutrons in an atom's nucleus and is symbolized by A = Z + N, where Z is the atomic number and N is the number of neutrons.
• 📝 Chemical symbols for isotopes include the element symbol, a subscript for the atomic number, and a superscript for the mass number.
• 📚 For example, protium is represented as ^1H, deuterium as ^2H, and tritium as ^3H, using the mass number in the superscript.
• 📉 To find the number of neutrons in an atom, subtract the atomic number from the mass number.
• 📘 The script provides examples using carbon and uranium isotopes to illustrate how to determine the number of protons, electrons, and neutrons.

Q & A

What is the atomic number symbolized by?

The atomic number is symbolized by 'Z' and it refers to the number of protons in a nucleus.

Where can you find the atomic number for an element?

You can find the atomic number on the periodic table.

What is the atomic number of hydrogen?

The atomic number of hydrogen is one, indicating there is one proton in the nucleus of a hydrogen atom.

How does the number of protons relate to the number of electrons in a neutral atom?

In a neutral atom, the number of protons is equal to the number of electrons, as the positive charges of the protons balance the negative charges of the electrons, resulting in no overall charge.

What is the name of the most common isotope of hydrogen?

The most common isotope of hydrogen is called protium.

What is the difference between protium, deuterium, and tritium?

Protium, deuterium, and tritium are isotopes of hydrogen that differ in the number of neutrons in their nuclei: protium has zero neutrons, deuterium has one, and tritium has two.

What is the term used to describe atoms of a single element that differ in the number of neutrons?

Isotopes are atoms of a single element that differ in the number of neutrons in their nuclei.

What is the mass number and how is it represented in atomic symbols?

The mass number is the combined number of protons and neutrons in a nucleus, represented by the symbol 'A'. It is shown as a superscript in atomic symbols.

How can you determine the number of neutrons in an atom?

The number of neutrons in an atom can be determined by subtracting the atomic number (number of protons) from the mass number.

What is the difference between the isotopes of carbon with mass numbers 12 and 13?

The isotopes of carbon with mass numbers 12 and 13 differ in the number of neutrons: the former has six neutrons while the latter has seven.

What is the hyphen notation used for representing isotopes?

The hyphen notation is used to represent isotopes by writing the name of the element followed by a hyphen and the mass number, e.g., carbon-13.

How many protons, electrons, and neutrons are in an atom of uranium with an atomic number of 92 and a mass number of 235?

An atom of uranium with an atomic number of 92 and a mass number of 235 has 92 protons and 92 electrons in a neutral state, and 143 neutrons (calculated by subtracting the atomic number from the mass number).