What is an Atom?
An atom is the basic unit of matter. It is the smallest particle of an element that retains the properties of that element. Atoms are made up of three subatomic particles: protons, neutrons, and electrons.
Structure of an Atom
The center of an atom is called the nucleus, which contains protons and neutrons. The protons have a positive charge, while neutrons have no charge (they are neutral). Surrounding the nucleus are the electrons, which have a negative charge and orbit the nucleus in energy levels or shells.
Protons, Neutrons, and Electrons
- Protons: Positively charged particles found in the nucleus of an atom.
- Neutrons: Neutral particles found in the nucleus of an atom.
- Electrons: Negatively charged particles that orbit the nucleus in energy levels.
Atomic Number and Mass Number
The atomic number of an atom is the number of protons it contains. The mass number is the sum of the protons and neutrons in the nucleus. The number of electrons is equal to the number of protons, giving the atom a neutral charge overall.
Study Guide
- What is the basic unit of matter?
- What are the three subatomic particles that make up an atom?
- Where are protons and neutrons located within an atom?
- What is the charge of protons, neutrons, and electrons?
- What is the atomic number of an atom?
- Define mass number and explain how it is calculated.
[Atom] Related Worksheets and Study Guides:
.◂Science Worksheets and Study Guides Third Grade. Relationships among living things
Study Guide
Relationships among living things 
Activity Lesson
Relationships Among Living Things Worksheet/Answer key
Relationships among living things Worksheet/Answer key
Relationships among living things Worksheet/Answer key
Relationships among living things Worksheet/Answer key
Relationships among living things Vocabulary/Answer key
Relationships among living things Vocabulary/Answer key
Relationships among living things
Activity LessonWorksheet/Answer keyWorksheet/Answer keyWorksheet/Answer keyWorksheet/Answer keyVocabulary/Answer keyVocabulary/Answer keyThe resources above cover the following skills:
LIFE SCIENCE
From Molecules to Organisms: Structures and Processes
Create representations to explain the unique and diverse life cycles of organisms other than humans (e.g., flowering plants, frogs, butterflies), including commonalities such as birth, growth, reproduction, and death.
Unity and Diversity
Construct an argument from evidence to explain the likelihood of an organism’s ability to survive when compared to the resources in a certain habitat (e.g., freshwater organisms survive well, less well, or not at all in saltwater; desert organisms survive well, less well, or not at all in woodlands).
Create models that illustrate how organisms and their habitats make up a system in which the parts depend on each other.