Deutsch: Atom / Español: Atomo / Português: Atomo / Français: Atome / Italiano: Atomo
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms. Atoms are very small; typical sizes are around 100 pm (a ten-billionth of a meter, in the short scale).

In the environmental context, "atom" refers to the basic building block of matter that cannot be further divided by chemical means. Here are some examples:

1. Carbon atom: Carbon is a common element found in living organisms, and it forms the basis of many important molecules such as DNA, proteins, and carbohydrates.

2. Oxygen atom: Oxygen is a gas that is essential for life, and it is a major component of the Earth's atmosphere.

3. Nitrogen atom: Nitrogen is a key element in the cycle of life, and it is an essential component of proteins and nucleic acids.

4. Hydrogen atom: Hydrogen is the most abundant element in the universe, and it is a key component of water and many other important molecules.

Other terms that are similar to "atom" in the environmental context include:

1. Molecule: This refers to a group of two or more atoms that are chemically bonded together, such as water (H₂O) and carbon dioxide (CO₂).

2. Element: This refers to a substance made up of only one type of atom, such as carbon (C) and oxygen (O).

3. Compound: This refers to a substance made up of two or more different types of atoms that are chemically bonded together, such as glucose (C₆H₁₂O₆) and methane (CH₄).

4. Isotope: This refers to a variation of an element that has a different number of neutrons in its nucleus, resulting in a different atomic mass. Some isotopes are radioactive and can be used in environmental monitoring and research.