Grade 8
The Human Knowledge Project
Unit 6 — Atomic Structure, Chemical Reactions, and the Foundations of Chemistry
Welcome to Grade 8 Science!
Chemistry is the study of matter and the changes it undergoes.
Everything around us—from the air we breathe to the stars in distant galaxies—is made of atoms.
Understanding how atoms combine, separate, and rearrange helps explain countless natural processes and modern technologies.
Today you will explore atomic structure, the periodic table, chemical reactions, and the conservation of matter.
Reviewing the Atom
Every atom contains three primary particles.
Protons
- positive electric charge
- located in the nucleus
Neutrons
- no electric charge
- located in the nucleus
Electrons
- negative electric charge
- move around the nucleus
The number of protons determines the identity of an element.
Atomic Number
Every element has a unique atomic number.
The atomic number equals:
- the number of protons
For a neutral atom:
- number of protons = number of electrons
The atomic number tells scientists which element they are studying.
Atomic Mass
The atomic mass depends primarily on:
- protons
- neutrons
Different atoms of the same element may contain different numbers of neutrons.
These different forms are called isotopes.
Most isotopes are stable, while some are radioactive.
The Periodic Table
The Periodic Table organizes elements according to their atomic number and properties.
Elements in the same column often share similar chemical behavior.
Major groups include:
- alkali metals
- alkaline earth metals
- transition metals
- halogens
- noble gases
The periodic table allows scientists to predict how many elements will behave.
Chemical Bonds
Atoms combine through chemical bonds.
The most common types include:
- ionic bonds
- covalent bonds
Ionic bonds form when electrons are transferred.
Covalent bonds form when electrons are shared.
Chemical bonds create compounds with new properties.
Chemical Reactions
A chemical reaction rearranges atoms to produce new substances.
During a reaction:
- atoms are not created
- atoms are not destroyed
- atoms are rearranged
This idea follows the Law of Conservation of Matter.
Chemical equations help describe these changes.
Indicators of Chemical Change
Common signs of a chemical reaction include:
- color change
- temperature change
- gas production
- formation of a solid (precipitate)
- light production
- odor change
Not every reaction shows all of these signs.
Scientists rely on careful observation and measurement.
Acids and Bases
Many common substances are classified as acids or bases.
Acids often:
- taste sour
- react with certain metals
- have a pH below 7
Bases often:
- feel slippery
- have a pH above 7
A pH of 7 is considered neutral.
The pH scale helps scientists describe the chemical properties of solutions.
Chemistry in Everyday Life
Chemistry affects many parts of daily life.
Examples include:
- cooking
- digestion
- batteries
- medicines
- agriculture
- water treatment
- manufacturing
- environmental protection
Modern chemistry has improved health, technology, and quality of life throughout the world.
Activity
Complete the following:
- identify the parts of an atom
- research five common elements
- classify elements using the Periodic Table
- identify examples of ionic and covalent compounds
- observe or research five chemical reactions
- measure the pH of several household substances using safe testing methods if available
Explain your observations and conclusions.
Practice
Answer these questions.
What particles make up an atom?
What does the atomic number represent?
What are isotopes?
How do ionic and covalent bonds differ?
What is the Law of Conservation of Matter?
What does the pH scale measure?
Review
Today you learned:
- atoms contain protons, neutrons, and electrons
- the atomic number identifies an element
- isotopes contain different numbers of neutrons
- the Periodic Table organizes elements by their properties
- chemical bonds form compounds
- chemical reactions rearrange atoms
- the Law of Conservation of Matter explains why matter is neither created nor destroyed in ordinary chemical reactions
- the pH scale measures acidity and basicity
Chemistry helps explain the composition of matter and the countless reactions that occur throughout nature, technology, and everyday life.
Looking Ahead
Next we will investigate forces, energy, electricity, magnetism, waves, and motion, exploring how the laws of physics govern the behavior of the universe.