Chemistry · StudentHub Lesson
Atomic Structure
The structure of atoms including protons, neutrons, electrons, and electron configuration.
What you will learn
- Identify subatomic particles and their charges
- Explain atomic number and mass number
- Describe electron shells and configuration
- Explain isotopes
- Relate electron arrangement to chemical behavior
Watch the lesson
Electron Configuration - Basic introduction · The Organic Chemistry Tutor
Watch on YouTubeTopic notes
Main Idea
Atoms are made of protons, neutrons, and electrons arranged in a specific structure that determines an element's chemical properties.
Key Concepts
- Protons and neutrons are in the nucleus; electrons orbit around it
- Atomic number = number of protons
- Electron configuration shows how electrons fill energy levels
Definitions
- Proton: positively charged particle in the nucleus
- Neutron: neutral particle in the nucleus
- Electron: negatively charged particle orbiting the nucleus
- Isotope: atoms of the same element with different neutron numbers
Processes
Electrons fill orbitals in order of increasing energy (1s, 2s, 2p, 3s, 3p...), following the Aufbau principle.
Examples
Carbon (atomic number 6) has electron configuration 1s2 2s2 2p2.
Common Mistakes
- Confusing atomic number with mass number
- Forgetting electrons determine chemical bonding
- Miscounting electrons in ions
Key concepts
Important terms
- Proton
- Positively charged subatomic particle found in the nucleus.
- Isotope
- Atoms of the same element with different numbers of neutrons.
- Valence electron
- An electron in the outermost shell involved in bonding.
Worked examples
Problem
Write the electron configuration for oxygen (atomic number 8).
- 1. Oxygen has 8 electrons
- 2. Fill 1s orbital: 1s2
- 3. Fill 2s orbital: 2s2
- 4. Fill 2p orbital with remaining 4 electrons: 2p4
Answer: 1s2 2s2 2p4
Quick revision
- Protons and neutrons are in the nucleus
- Electrons orbit the nucleus
- Atomic number = protons
- Mass number = protons + neutrons
- Isotopes differ in neutron number
- Electron configuration follows Aufbau principle
- Valence electrons determine reactivity
Check your understanding
Question 1 · Multiple choice
What determines an element's atomic number?
Question 2 · Multiple choice
What are isotopes?
Question 3 · True or false
Electrons are located in the nucleus of an atom.
Question 4 · Short answer
What subatomic particle has a negative charge?
Question 5 · Short answer
What is the mass number of an atom with 6 protons and 6 neutrons?
Done with Atomic Structure?
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