Welcome to our beginner’s guide on atomic structure! Whether you’re just starting your AQA A-level Chemistry course or need a refresher, this guide will help you grasp the fundamental concepts of atomic structure. This topic is essential for understanding more complex areas in chemistry, so let’s dive in.
The Key Subatomic Particles
1. Protons
o Charge: Positive (+1)
o Location: Nucleus
o Mass: 1 atomic mass unit
o Protons determine the atomic number, which is unique to each element. The number of protons in an atom’s nucleus is like its "ID," identifying it as a particular element.
2. Neutrons
o Charge: Neutral (0)
o Location: Nucleus
o Mass: 1 atomic mass unit
o The number of neutrons can vary among atoms of the same element, leading to isotopes.
3. Electrons
o Charge: Negative (-1)
o Location: Surrounding the nucleus in electron shells
o Mass: Negligible (about 1/1836 of the mass of a proton)
o Electrons are arranged in shells around the nucleus and are responsible for chemical reactions. They are involved in forming bonds with other atoms. Which determine an atomic chemical properties.
Atomic Number and Mass Number
Every element has:
• Atomic Number: The number of protons in the nucleus. This defines the element.
• Mass Number: The sum of protons and neutrons in the nucleus.
For example, carbon has an atomic number of 6 (six protons) and a common mass number of 12 (six protons + six neutrons).
Isotopes are atoms with the same atomic number but different mass numbers. This is caused by the atom having the same number of protons but a different number of neutrons. For instance, Carbon-12 and Carbon-14 are both carbon isotopes, but Carbon-14 has two extra neutrons.
Electron Shells and Configuration
Electrons surround the nucleus in distinct energy levels or shells. The arrangement of these electrons determines an atom’s chemical properties and reactivity. These energy shells are the rings we used at GCSE. However each shell is further broken down in to the Subshells s,p and d depending on the shell. Each of these subshells contains orbitals the number of orbitals depends on the type of subshell.
Key Principles to Remember
1. Pauli Exclusion Principle: An orbital can hold a maximum of two electrons with opposite spins.
2. Aufbau Principle: Electrons occupy the lowest available energy levels first.
3. Hund’s Rule: Electrons fill orbitals singly before pairing up in the same sub-shell, helping to minimize repulsion.
Check out our videos on YouTube all about Atomic Structure.
