AP Chemistry Lessons & Study Guide

## What Is an Atom? Atoms are the tiny building blocks of all matter. Every object you see, touch, or even breathe is made up of atoms! Each atom contains a nucleus, made of protons and neutrons, surrounded by a cloud of electrons zipping around in different energy levels. ### Parts of an Atom - **Protons:** Positively charged particles found in the nucleus. - **Neutrons:** Neutral particles (no charge), also in the nucleus. - **Electrons:** Negatively charged particles, found in shells or orbitals outside the nucleus. The number of protons defines the element (for example, all hydrogen atoms have 1 proton). ## The Periodic Table Connection The atomic number (Z) is the number of protons in the nucleus. The mass number (A) is the sum of protons and neutrons. - **Isotopes** are atoms of the same element with different numbers of neutrons. ## Why Does It Matter? Understanding atomic structure helps us predict how elements will behave in chemical reactions, and even why certain materials conduct electricity or react explosively! ### Real-World Impact - Medicine: Isotopes are used in medical imaging. - Energy: Nuclear reactors rely on manipulating atomic nuclei.