Click image to open full size
Atomic Structure
Protons, Neutrons, Electrons, Orbitals, and Atomic Number
Related Tools
Related Labs
Atomic structure explains how all matter is built from a small set of subatomic particles. Every atom contains protons, neutrons, and electrons arranged in a specific way. This structure determines an element's identity, mass, and chemical behavior. Understanding atomic structure is the foundation for chemistry, electricity, bonding, and nuclear science.
Protons and neutrons are packed tightly in the nucleus, while electrons occupy regions around the nucleus called energy levels or shells. The number of protons sets the atomic number and tells which element the atom is. Neutrons change the isotope of an element without changing its identity. Electrons control how atoms interact, gain charge, and form chemical bonds.
Key Facts
- Atomic number = number of protons
- Mass number = protons + neutrons
- Number of neutrons = mass number - atomic number
- In a neutral atom, number of electrons = number of protons
- Charge of atom = protons - electrons
- Proton charge = +1, neutron charge = 0, electron charge = -1
Vocabulary
- Atom
- The smallest unit of an element that still keeps the chemical properties of that element.
- Nucleus
- The dense central region of an atom that contains protons and neutrons.
- Proton
- A positively charged particle in the nucleus that determines the element's identity.
- Neutron
- A neutral particle in the nucleus that adds mass and can change the isotope of an element.
- Electron
- A negatively charged particle found in energy levels around the nucleus.
Common Mistakes to Avoid
- Confusing atomic number with mass number, because atomic number counts only protons while mass number counts protons and neutrons together.
- Assuming neutrons determine the element, which is wrong because the number of protons is what defines the element.
- Forgetting that ions are not neutral, which leads to wrong electron counts because gained or lost electrons change the atom's charge.
- Drawing electrons inside the nucleus, which is wrong because electrons occupy regions outside the nucleus in energy levels.
Practice Questions
- 1 An atom has 11 protons, 12 neutrons, and 11 electrons. What are its atomic number, mass number, and net charge?
- 2 A magnesium ion has 12 protons and 10 electrons. What is its charge, and how many neutrons does it have if its mass number is 24?
- 3 Two atoms each have 6 protons, but one has 6 neutrons and the other has 8 neutrons. Explain how they are similar and how they are different.