The atom

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Lesson notes

Scientific Models

A **scientific model** is a simplified version of an object or phenomenon, making it easier to understand while still representing key features.
The **particle model** is one example; it explains and predicts the behaviour of solids, liquids and gases.
Models are changed and updated over time as new evidence emerges.

Dalton Model of the Atom

The **Dalton model** described atoms as **indivisible** – they could not be broken down into anything smaller.
This was the earlier model before sub-atomic particles were discovered.

Current Model of the Atom

The atom is made of three **sub-atomic particles**: protons, neutrons and electrons.
**Protons** have a **positive charge** and are found in the **nucleus**.
**Neutrons** are **neutral** (no charge) and also in the nucleus.
**Electrons** have a **negative charge** and **orbit** around the nucleus.
Most of the atom's **mass** is in the nucleus; protons and neutrons have about **2000 times more mass** than an electron.
Overall, an atom is **neutral** because it has equal numbers of protons and electrons.

Peer Review

**Peer review** is when other scientists examine new evidence to decide if it is **valid**.
It prevents incorrect models and theories from being spread.
After peer review, research can be published and other scientists may try to **reproduce** the results to check **repeatability**.

Bohr model of a sodium atom showing the nucleus (11 protons, 12 neutrons) and electron shells (2,8,1).

Particle arrangement in solids, liquids and gases.

Slides

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Practice questions

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1.What is the Dalton model of the atom?
Easy
- AAtoms are indivisible and cannot be broken down into anything smaller.
- BAtoms are made of protons, neutrons and electrons.
- CAtoms have a nucleus with electrons orbiting.
- DAtoms are mostly empty space.
2.Where is the nucleus of an atom located?
Easy
- AIn the centre of the atom.
- BOrbiting the atom.
- COutside the electron shells.
- DScattered throughout the atom.
3.Which two sub-atomic particles are found in the nucleus?
Easy
- AProtons and neutrons.
- BProtons and electrons.
- CNeutrons and electrons.
- DProtons, neutrons and electrons.
4.Which sub-atomic particle orbits around the nucleus?
Easy
- AElectron
- BProton
- CNeutron
- DPositron
5.What is the charge on a proton?
Easy
- APositive
- BNegative
- CNeutral
- DNo charge
6.What is the charge on an electron?
Easy
- ANegative
- BPositive
- CNeutral
- DNo charge
7.What is the charge on a neutron?
Easy
- ANeutral
- BPositive
- CNegative
- DNo charge
8.Which sub-atomic particle has the least mass?
Easy
- AElectron
- BProton
- CNeutron
- DNucleus

Revision notes

## The Atom - Revision Notes ### Scientific Models - A **scientific model** is a simplified version of an object or phenomenon, making it easier to understand while representing key features. - Models are changed and updated over time as new evidence emerges. ### Dalton Model (Old Model) - Atoms were thought to be **indivisible** (could not be broken down into anything smaller). ### Current Model of the Atom - Atoms are made of **sub-atomic particles** (smaller than the atom itself). - Three sub-atomic particles: 1. **Protons** – positive charge, located in the **nucleus** (centre of atom). 2. **Neutrons** – neutral (no charge), also in the nucleus. 3. **Electrons** – negative charge, **orbit** around the nucleus. - Most of the mass is in the nucleus; protons and neutrons have ~2000 times more mass than an electron. - Overall atom is **neutral** because number of electrons = number of protons. ### Peer Review - **Peer review** is when other scientists examine new evidence to decide if it is valid. - Prevents incorrect models/theories from spreading. - After peer review, research can be published; other scientists may try to **reproduce** the results to check if they are repeatable. ### Key Differences: Dalton vs Current Model - Dalton: atoms are indivisible. - Current: atoms are made of protons, neutrons, and electrons.

Scientific model: A simplified version of an object or phenomenon, used to explain and predict behaviour while representing key features.
Dalton model: An early atomic model stating that atoms are indivisible and cannot be broken down into smaller parts.
Sub-atomic particle: A particle smaller than an atom; includes protons, neutrons, and electrons.
Proton: A positively charged sub-atomic particle found in the nucleus of an atom.
Neutron: A neutral (no charge) sub-atomic particle found in the nucleus of an atom.
Electron: A negatively charged sub-atomic particle that orbits the nucleus of an atom.
Nucleus: The centre of an atom, containing protons and neutrons, and most of the atom's mass.
Peer review: A process where other scientists examine new evidence to decide if it is valid before publication.

Flashcards

What is a scientific model?

A simplified version of an object or phenomenon that makes it easier to understand while still representing key features.

What is the particle model used for?

To explain and predict the behaviour of solids, liquids and gases.

What was the Dalton model of the atom?

The Dalton model stated that atoms were indivisible (could not be broken down into anything smaller).

Why are subatomic particles called subatomic?

Because they are smaller than the atom itself.

Name the three subatomic particles in the current model of the atom.

Protons, neutrons, and electrons.

What is the charge of a proton?

Positive.

Where are protons located in an atom?

In the nucleus (centre of the atom).

What is the charge of a neutron?

Neutral (no charge).

Where are neutrons located?

In the nucleus.

What is the charge of an electron?

Negative.

Where do electrons orbit?

Around the nucleus.

Which part of the atom contains most of its mass?

The nucleus (protons and neutrons have about 2000 times more mass than an electron).

Why is an atom overall neutral?

Because it has equal numbers of electrons and protons.

Which subatomic particle has the least mass?

Electron.

What is peer review?

When other scientists examine new evidence to decide whether it is valid.

Why is peer review important?

To prevent incorrect models and theories from being spread.

What happens after peer review?

New research can be published, and other scientists may try to reproduce the results to check repeatability.

How do scientific models change over time?

They are updated based on new evidence and research.

What is the nucleus of an atom?

The centre of the atom, containing protons and neutrons.

What is the difference between the Dalton model and the current model of the atom?

Dalton thought atoms were indivisible; the current model shows atoms are made of subatomic particles (protons, neutrons, electrons).

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