Grade 8 · Atoms, Elements and the Periodic Table · Atomic Structure
Inside the Atom
Protons, neutrons, electrons and how we model the atom.
Learning objectives
- Identify the three subatomic particles and their charges.
- Explain why an atom is normally neutral.
- Use atomic number and mass number to describe an atom.
NGSS alignment
HS-PS1-1
Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
MS-PS1-1
Develop models to describe the atomic composition of simple molecules and extended structures.
HS-PS1-8
Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
MYP criteria
- Criterion A — Knowing and Understanding
ENGAGE
What is inside an atom?
EXPLAIN
Subatomic particles
| Particle | Location | Relative charge | Relative mass |
|---|---|---|---|
| Proton | Nucleus | 1+ | 1 |
| Neutron | Nucleus | 0 | 1 |
| Electron | Shells around nucleus | 1- | 1/1836 |
- Atomic number = number of protons = the element identity.
- Mass number = protons + neutrons.
- Neutral atom: protons = electrons.
Watch
Atomic Structure Explained
TED-Ed · 5:20
It builds the atom piece by piece so you can see where mass and charge come from.
Before you watch: Before watching: what do you think is inside an atom?
- What are the three main subatomic particles?
- Which particle determines the element?
- Why is an atom normally electrically neutral?
Interactive simulation · PhET
Isotopes and Atomic Mass
Build different isotopes of the same element and compare their masses.
While you explore
- What changes between isotopes of one element?
- Why is atomic mass not a whole number?
Key vocabulary
- Atomic number
- The number of protons in an atom - it tells you which element it is.
Practice questions
0/2 correct
Level 1
Which subatomic particle has a negative charge?
Level 2
An atom has 17 protons and 18 neutrons. What is its mass number?
Reflect & track
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