Matter, Atoms, and the Periodic Table
What Matter Is Made Of
From particles to properties
Matter is made of atoms, which combine into molecules and extended structures. The arrangement of particles helps determine whether a substance is a gas, liquid, solid, or plasma, and why it behaves the way it does.
Atomic structure
Why the periodic table works
Elements are arranged by increasing atomic number. Similar outer-electron configurations create similar chemical behavior.
Atoms, ions, and isotopes
Atom
- Neutral overall
- Has equal numbers of protons and electrons
- Basic unit of an element
Ion
- Has a net charge
- Forms when electrons are gained or lost
- Important in salts and biological processes
What determines the identity of an element?
Changing the number of protons changes the element itself.
Correct answer: Number of protons
Why do elements in the same group often have similar chemical properties?
Valence electrons drive bonding and many reaction patterns.
Correct answer: Because they have similar valence electron configurations.
Particle locations
| Particle | Location | Charge |
|---|---|---|
| Proton | Nucleus | |
| Neutron | Nucleus | |
| Electron | Electron cloud |
An ion with more electrons than protons is:
Extra electrons create a net negative charge.
Correct answer: Negative
What is the main reason atomic masses are usually not whole numbers on the periodic table?
Natural elements often exist as mixtures of isotopes.
Correct answer: They are weighted averages of isotopes.