Atoms:
The basic unit of matter.
Composed of a nucleus (protons and neutrons) and electrons orbiting the nucleus.
Protons, neutrons, and electrons:
Proton: positive charge, located in nucleus.
Neutron: no charge, located in nucleus.
Electron: negative charge, orbits the nucleus.
The Periodic Table:
Elements arranged in order of increasing atomic number.
Elements with similar properties are in the same group (vertical columns).
Periods are horizontal rows.
2. Elements, Compounds, and Mixtures
Elements:
Made of only one type of atom.
Compounds:
Substances made of two or more elements chemically joined (e.g., water, H₂O).
Mixtures:
Combinations of substances not chemically joined; can be separated by physical methods.
Examples of separation methods: filtration, distillation, chromatography.
3. Atomic Number, Mass Number, and Isotopes
Atomic number (Z):
Number of protons in an atom.
Mass number (A):
Total number of protons and neutrons in an atom.
Isotopes:
Atoms of the same element with different numbers of neutrons (different mass numbers, but same atomic number).
