Elements Review

Solid

A state of matter with a definite shape and volume; particles are tightly packed and vibrate in fixed positions.

Liquid

A state of matter with a definite volume that takes the shape of its container; particles are close together but can move around.

Gas

A state of matter with no definite shape or volume; expands to fill available space with widely dispersed and randomly moving particles.

Melting

The phase change from solid to liquid, occurring when temperature increases and particles gain enough energy to break free.

Freezing

The phase change from liquid to solid, occurring when temperature decreases and particles lose energy, forming a more ordered structure.

Boiling

The phase change from liquid to gas, occurring when temperature increases and particles gain enough energy to escape into the gas phase.

Condensation

The phase change from gas to liquid, occurring when temperature decreases and particles lose energy, slowing down and coming closer together.

Sublimation

The phase change from solid to gas, bypassing the liquid phase, such as dry ice turning into CO2 gas.

Deposition

The phase change from gas to solid, such as frost formation, when particles lose energy and form a solid structure.

Density

Mass per unit volume, defined by the formula ρ = m/V; solids are generally denser than liquids, which are denser than gases.

Compressibility

A measure of how much the volume of a substance decreases under pressure; gases are highly compressible, liquids are slightly compressible, and solids are nearly incompressible.

Thermal Expansion

The tendency of matter to change in volume in response to changes in temperature, with gases expanding more than liquids, and liquids expanding more than solids.

Kinetic Molecular Theory

The theory stating that matter is composed of particles in constant motion, with kinetic energy increasing with temperature.

Electron Shell

Regions around an atom's nucleus where electrons reside, with the formula 2n² indicating the maximum number of electrons each shell can hold.

Valence Electrons

Electrons in the outermost shell of an atom that determine its chemical properties and ability to bond with other atoms.

Pure Substance

Matter with a consistent composition and properties, which can be an element or a compound.

Mixture

A combination of two or more pure substances that can be homogeneous or heterogeneous.

Acid

A substance with a sour taste, sticky feel, that turns litmus paper red, and reacts with bases to form water and salt.

Base

A substance with a bitter taste, slippery feel, that turns litmus paper blue, and reacts with acids to form water and salt.

More Valence Electrons (Nearing Full Shell)

Atoms with nearly full valence shells tend to gain electrons, forming negative ions and becoming more stable.

Fewer Valence Electrons (Easily Lost)

Atoms with only a few valence electrons tend to lose them to form positive ions, achieving a stable electron configuration.

Formula for Maximum Electrons in a Shell

The formula 2n^2 determines the maximum number of electrons a shell can hold, where n is the principal quantum number (shell number).

Protons

Positive subatomic particles found in the nucleus.

Neutrons

Neutral subatomic particles found in the nucleus.

Electrons

Negative subatomic particles orbiting the nucleus.

Atomic Number

Represents the number of protons and electrons in an atom.

How do you find the number of neutrons in an atom?

Atomic Mass minus Atomic Number