Atoms are often referred to as the building blocks of matter. Each element on the periodic table is composed of one type of atom and cannot be broken down into a simpler substance.
Atoms contain a nucleus surrounded by an electron cloud that consists of one or more energy levels.
- Nucleus - Small, dense, positively charged center of the atom which contains most of the atom’s mass
The nucleus contains the following subatomic particles: - The nucleus contains the following subatomic particles:
- Protons - positively (+) charged particles
- Neutrons - particles that have no charge (neutral), but contribute to the atom’s mass
- Electron cloud - an area around the nucleus where electrons are likely to be found orbiting the nucleus in several energy levels
- The electron cloud contains several energy levels
Multiple energy levels in the electron cloud completely surround the nucleus. - Multiple energy levels in the electron cloud completely surround the nucleus.
- Electrons follow a specific order to fill the energy levels.
- The electrons in the outermost energy level are called valence electrons
- We will go into more detail about the importance of valence electrons in our next unit.
The number of protons in the nucleus is the atomic number of that atom. Protons are used to identify elements. The atomic number represents the number of protons (+) and is equal to the number of electrons (-).
The atomic mass is the mass of the protons plus the mass of the neutrons. The atomic mass is the mass of the protons plus the mass of the neutrons. - Atomic mass is recorded in the SI units: atomic mass units (amu).
- Protons and neutrons each are given an amu of 1.
- Electrons have a mass of nearly zero.
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