Structure of the Atom
Understanding the internal components of the atom and how they interact
The atom is composed of three fundamental particles: protons, neutrons, and electrons. Their arrangement and interactions determine the properties of all matter.
1. Subatomic Particles
Proton
p⁺+1
Nucleus
Role: Determines element identity
Neutron
n⁰0
Nucleus
Role: Provides nuclear stability
Electron
e⁻-1
Electron cloud
Role: Chemical bonding
Particle Explorer
Click on a particle button to learn more:
2. Relative Mass and Charge
Key Point: Protons and neutrons have approximately the same mass (1 amu). Electrons are ~1840 times lighter - their mass is negligible in atomic mass calculations. This is why 99.9% of the atom's mass is in the nucleus.
Atomic Mass Calculator
Protons + Neutrons = Atomic Mass
3. The Nucleus
Characteristics
- Extremely small and dense
- Contains most of the atom's mass
- Positively charged (due to protons)
- If an atom were a stadium, the nucleus would be a pea!
Composition
The nucleus is made up of nucleons:
The number of protons = atomic number (identifies the element).
Mass Center: Almost 100% of the atom's mass is concentrated here.
Scale Comparison
If the nucleus were the size of this dot •
The electron cloud would be the size of a football stadium!
This shows how much empty space is in an atom.
4. The Electron Cloud (Orbitals)
Electron Cloud Visualization
The dots represent the probability of finding an electron in that region.
Characteristics
- Occupies most of the atom's volume
- Not a fixed structure - a probability region
- Electrons are in constant motion
Electrostatic Attraction
The atom is held together by the attraction between:
Opposites attract - this keeps electrons near the nucleus.
5. Neutral Atoms vs. Ions
Neutral Atom
Equal protons and electrons
Net charge = 0
Cation
More protons than electrons
Lost electron(s)
Anion
More electrons than protons
Gained electron(s)
Ion Formation
A neutral sodium atom has 11 protons and 11 electrons. It loses 1 electron. What is the result?
Test Your Understanding
1. Which subatomic particle has a positive charge?
2. Where is most of the mass of an atom located?
3. What is the relative mass of an electron compared to a proton?
4. A cation forms when an atom:
Key Terms
Key Takeaways
- Protons (+): In nucleus, determine element, mass = 1 amu
- Neutrons (0): In nucleus, provide stability, mass = 1 amu
- Electrons (-): In electron cloud, mass = 1/1840 amu (negligible)
- Nucleus: Tiny, dense, contains >99.9% of atom's mass
- Electron cloud: Occupies most volume, probability region for electrons
- Neutral atom: Equal protons and electrons (charge = 0)
- Cation: Loses electrons → positive charge
- Anion: Gains electrons → negative charge
