Basic Chemistry Concepts
Matter is anything that has mass and takes up space—like solids, liquids, and gases. The most basic unit of matter is the atom, which consists of three key subatomic particles: protons (positive charge in nucleus), neutrons (neutral charge in nucleus), and electrons (negative charge orbiting in shells).
Electrons orbit the nucleus in orbital shells, following the octet rule which states that atoms prefer to have eight electrons in their outer shell. Remember this crucial point: the number of protons determines what element an atom is. In a neutral atom, the number of protons equals the number of electrons.
The atomic number tells you how many protons an element has, while atomic mass represents the average number of protons and neutrons. When you have the same element with different numbers of neutrons, you have isotopes. When an atom gains or loses electrons, it becomes an ion with a positive or negative charge.
💡 Quick Tip: To find the number of neutrons in an atom, just subtract the atomic number from the rounded atomic mass. For example, if an element has an atomic mass of 23 and an atomic number of 11, it has 12 neutrons!
