Changes in Energy on the Molecular Level

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Matter Noun

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[mat-er]

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Matter

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Anything that has mass and takes up space, composed of fundamental particles such as atoms and molecules.

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Example: This image shows that matter, like water, can exist in different states—solid, liquid, and gas—by showing the arrangement of its particles.

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Atom Noun

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[at-uhm]

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Atom

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The smallest unit of an element that retains the chemical properties of that element and makes up all matter.

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Example: This diagram shows an atom's structure: a central nucleus with protons and neutrons, and electrons orbiting the nucleus in shells.

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Molecule Noun

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[mol-i-kyool]

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Molecule

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A group of two or more atoms chemically bonded together, representing the smallest unit of a chemical compound.

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Example: This image shows a single water molecule (H₂O), which is made of one oxygen atom and two hydrogen atoms bonded together.

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States of matter Noun

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[stayts uhv mat-er]

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States of matter

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The distinct physical forms that matter can exist in, primarily solid, liquid, and gas, also known as phases.

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Example: This diagram shows the three main states of matter—solid, liquid, and gas—and the names of the processes that change one state into another.

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Solid Noun

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[sol-id]

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Solid

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A state of matter characterized by a definite shape and volume, with particles packed tightly in a fixed arrangement.

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Example: This atomic-level model shows particles in a solid are packed tightly together in a fixed, repeating pattern called a crystal lattice.

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Liquid Noun

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[lik-wid]

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Liquid

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A state of matter that has a definite volume but no fixed shape, with particles that can flow past one another.

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Example: This diagram shows the particles in a liquid are close together but are not in fixed positions, allowing them to move past one another.

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Gas Noun

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[gas]

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Gas

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A state of matter with no definite shape or volume, where particles are far apart and move freely and randomly.

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Example: This image shows the particle arrangement for a gas on the right, where particles are far apart and not in a fixed pattern.

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Volume Noun

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[vol-yoom]

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Volume

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The amount of three-dimensional space that a substance or object occupies or contains, measured in cubic units.

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Example: This image shows a rectangular prism with its dimensions—length, width, and height—labeled, which are multiplied together to calculate the object's volume.

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Thermal energy Noun

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[thur-muhl en-er-jee]

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Thermal energy

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The internal energy of an object due to the kinetic energy of its atoms and molecules, related to temperature.

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Example: This diagram shows that thermal energy is the motion of particles. The red, 'hot' side has fast-moving particles (more thermal energy).

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Kinetic energy Noun

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[ki-net-ik en-er-jee]

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Kinetic energy

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The energy that a substance's molecules possess due to their constant, random motion and vibration.

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Example: A ball rolling down a ramp has kinetic energy because the arrow shows it is in motion.