An atom is the smallest particle of an element that keeps the chemical properties of that element.
Atoms are the basic building blocks of all matter.
What Are Atoms Made Of?
Atoms contain three main subatomic particles:
- protons
- neutrons
- electrons
These particles have different charges and positions inside the atom.
Structure of an Atom
Atoms have:
- a nucleus in the centre
- electrons moving around the nucleus
The nucleus contains:
- protons
- neutrons
Electrons move in energy levels around the nucleus.
Subatomic Particles in an Atom
| Particle | Charge | Relative Mass | Location |
|---|
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | -1 | Very small | Shells |
What Are Protons?
Protons are positively charged particles found in the nucleus of an atom.
The number of protons determines the element.
For example:
- Hydrogen has 1 proton
- Carbon has 6 protons
- Oxygen has 8 protons
What Are Neutrons?
Neutrons are neutral particles found in the nucleus. They help make atoms more stable. Different numbers of neutrons create isotopes.
What Are Electrons?
Electrons are negatively charged particles that move around the nucleus in shells or energy levels.
Electrons are involved in:
- chemical reactions
- bonding
- electricity
What is an atomic number?
Atomic number is the number of protons in an atom. Every element has a unique atomic number.
| Element | Atomic Number |
|---|---|
| Hydrogen | 1 |
| Carbon | 6 |
| Oxygen | 8 |
| Sodium | 11 |
What Is Mass Number?
Mass number is the total number of:
- protons
- neutrons
inside the nucleus.
Mass Number Formula
Example of Mass Number
A carbon atom contains:
- 6 protons
- 6 neutrons
Calculation
The mass number is 12.
How Atoms Form Elements
An element contains only one type of atom.
For example:
- All oxygen atoms have 8 protons
- All carbon atoms have 6 protons
Changing the number of protons changes the element completely.
Atoms and Chemical Reactions
Chemical reactions happen when atoms rearrange and form new substances.
During reactions:
- atoms are not destroyed
- bonds break and form
- new products form
This follows the Law of Conservation of Mass.
Easy Way to Remember Subatomic Particles
| Particle | Charge |
|---|---|
| Proton | Positive |
| Neutron | Neutral |
| Electron | Negative |
Common Confusion About Atoms
| Incorrect Idea | Correct Explanation |
|---|---|
| Electrons are in the nucleus | Electrons move around the nucleus |
| Atomic number equals neutrons | Atomic number equals protons |
Common Exam Questions
State the Charge of a Proton.
A proton has a positive charge.
State Where Protons and Neutrons Are Found.
Protons and neutrons are found in the nucleus of an atom.
Why Atoms Are Neutral Overall.
Atoms are neutral because they contain equal numbers of protons and electrons.
Calculate the Mass Number of an Atom with 8 Protons and 8 Neutrons.
8 + 8 = 16
The mass number is 16.
Why Electrons Have Very Little Mass Compared to Protons and Neutrons.
Electrons are much smaller subatomic particles with significantly lower relative mass.
Why Atomic Number Identifies an Element?
The atomic number identifies an element because it shows the number of protons in the nucleus.
Why Isotopes Have Different Mass Numbers
Isotopes contain different numbers of neutrons, which changes the mass number.
Why Electrons Are Important in Chemical Reactions
Electrons are involved in bond formation and determine how atoms react chemically.
Common Student Mistakes
Students often:
- confuse mass number with atomic number
- think neutrons have a charge
- forget electrons move in shells
- mix up protons and electrons
These mistakes can reduce marks in exams.
Read More Physical Change vs Chemical Change
FAQs
What Is an Atom?
An atom is the smallest particle of an element that keeps the properties of that element.
What Are Atoms Made Of?
Atoms contain protons, neutrons, and electrons.
Where Are Protons Found?
Protons are found in the nucleus of an atom.
What Charge Does an Electron Have?
Electrons have a negative charge.
What Is Atomic Number?
Atomic number is the number of protons in an atom.
What Is Mass Number?
Mass number is the total number of protons and neutrons in an atom.
Why Are Atoms Neutral?
Atoms are neutral because they contain equal numbers of protons and electrons.
What Is the Difference Between Protons and Neutrons?
Protons have a positive charge, while neutrons have no charge.