Modern Atomic Theory
6 Minutes
Modern atomic theory for students: learn about isotopes, isobars, transmutation, and chemical ratios to solve a cryptex. An English science lesson.
- What isotopes are using mass numbers and hydrogen examples
- What isobars are using carbon-14 and nitrogen-14
- Natural and artificial transmutation and chemical reaction ratios
What this lesson teaches
Modern atomic theory explains how the internal parts of atoms determine the identity of elements, how atoms change, and how they combine. It shows that while an element is defined by its protons, its mass can vary, atoms can transform into different elements, and electrons drive chemical bonding.
Understanding isotopes
The total number of protons and neutrons in an atom is its mass number, which can be written alongside the element name in hyphen notation like hydrogen-1. The number of protons fixes an element in the periodic table, so isotopes are atoms of the same element that keep the same proton count but have different neutron counts. For instance, hydrogen-1 has one proton, hydrogen-2 has one proton and one neutron, and hydrogen-3 has one proton and two neutrons. Boron-10 and boron-11 are another pair of isotopes that have different mass numbers.
Understanding isobars
Isobars are the exact opposite of isotopes. They are atoms of different chemical elements that share the same mass number. Because they are different elements, their proton counts differ, but the sum of their protons and neutrons remains identical. Carbon-14 and nitrogen-14 are isobars because both elements have a mass number of 14.
Natural and artificial transmutation
- Transmutation occurs when an atom splits into different atoms or when two different atoms join to create a new atom.
- Natural transmutation occurs in the sun at temperatures of about ten crore degrees Celsius, where hydrogen atoms join together to form helium.
- Artificial transmutation takes place on Earth in nuclear power plants, where large uranium-236 atoms are split into barium-144 and krypton-89.
- When atoms split, the total mass decreases, and the amount of mass lost is released directly as energy.
Chemical reactions and atomic ratios
A chemical reaction takes place when electrons from one atom interact with electrons from another atom. This interaction causes an atom to lose a tiny fraction of its mass, comparable to an elephant losing a single hair, which releases energy. When atoms react, they bond in specific proportions that can be either simple or complex. Water combines in a simple 2:1 ratio of hydrogen to oxygen, while glucose combines carbon, hydrogen, and oxygen in a complex 6:12:6 ratio.