Particles Study Guide

Atoms are the fundamental building blocks of all matter. Despite their small size, atoms are not indivisible; they are composed of even smaller particles called subatomic particles. The three main subatomic particles are protons, neutrons, and electrons. Each of these particles has characteristic properties, including an electrical charge and an approximate relative mass, which are crucial for understanding the behavior of atoms and chemical reactions.

Protons are found in the central part of the atom, called the nucleus. They carry a positive electrical charge, which is assigned a relative value of +1. Protons also have a significant mass, which is approximated as 1 atomic mass unit (amu). Neutrons are also located in the nucleus alongside protons. Unlike protons, neutrons are electrically neutral, meaning they have no charge (a relative charge of 0). They have virtually the same mass as protons, so their approximate relative mass is also 1 amu. The sum of protons and neutrons in an atom's nucleus accounts for almost all of the atom's mass.

Electrons are found orbiting the nucleus in specific energy levels or shells. They carry a negative electrical charge, assigned a relative value of -1, which is equal in magnitude but opposite in sign to the charge of a proton. What distinguishes electrons significantly from protons and neutrons is their mass. Electrons are exceedingly light; their approximate relative mass is considered to be 1/1836 amu, or often simply approximated as 0 for most calculations concerning the atom's overall mass. This negligible mass means that electrons contribute very little to the overall mass of an atom, even though they play a crucial role in chemical bonding. The balance between positive protons and negative electrons determines the overall charge of an atom or ion.

The particle model is a fundamental concept in chemistry that helps us understand the properties of solids, liquids, and gases. It states that all matter is made up of tiny particles (atoms, ions, or molecules) that are constantly in motion. The arrangement, movement, and energy of these particles determine the state of matter.

In a solid, particles are arranged in a fixed, regular pattern (a lattice). They vibrate around fixed positions but do not move past each other. This gives solids a definite shape and volume. They cannot be easily compressed because the particles are already very close together.

In a liquid, particles are close together but are randomly arranged. They can move past each other, allowing liquids to flow and take the shape of their container. Liquids have a definite volume but no definite shape. They are also difficult to compress because their particles are still relatively close.

In a gas, particles are far apart and move randomly and rapidly in all directions. They have high kinetic energy. Gases have no definite shape or volume and will fill any container. They can be easily compressed because there is a lot of empty space between the particles.

Changes of state occur when a substance gains or loses energy. When a solid is heated, its particles gain kinetic energy and vibrate more vigorously. If enough energy is supplied, the particles overcome the forces holding them in fixed positions and start to move past each other, turning into a liquid (melting). Continued heating increases the particles' kinetic energy further. When particles have enough energy to completely overcome the forces of attraction and escape from the liquid surface, the liquid turns into a gas (boiling/evaporation).

The reverse processes also involve energy changes. When a gas is cooled, its particles lose kinetic energy and move less rapidly. They come closer together, forming a liquid (condensation). Further cooling causes the liquid particles to lose more energy, settle into fixed positions, and form a solid (freezing).