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Molecules and Atoms


"The Atom"

Molecules and Atoms - Atoms
Definition: Atoms are composed of three kinds of smaller particles, called protons, neutrons and electrons. The number of protons, the number of neutrons and the number of electrons an atom has determines what an element it is.

Molecules and Atoms - Definition of a Molecule
What is a Molecule? Definition: A molecule is the smallest amount of a chemical substance that can exist. A molecule is capable of independent existence and can consist of one or more atoms.

Molecules and Atoms
Only a few atoms are capable of independent existence, therefore only a few atoms are molecules. A single helium (symbol He) atom is capable of independent existence so Helium is a molecule as well as an atom.

A molecule may consist of atoms of a single chemical element such as with Helium (He), or of different elements, as with water (H2O - Hydrogen and Oxygen) which is called a compound.

Molecules and Atoms - Compounds
A compound is a molecule that contains at least two different elements, refer to Examples of Compounds. The molecule is the building block of a compound, just like the atom is the building block of the element. In gases (like air) the molecules just fly around. In liquids (like water - H2
O) the molecules are stuck together but they can still move. In solids (like salt -  NaCl) the molecules can only vibrate.

Molecules and Atoms - Compounds and Molecules
Compounds and Molecules:

  • A molecule is formed when two or more atoms join together chemically

  • A compound is a molecule that contains at least two different elements

  • All compounds are molecules, but not all molecules are compounds

Molecules and Atoms - Bonded Molecules
Bonded Molecules. Molecules are made up of atoms that have bonded and are stuck together in a particular shape or form. For a molecule to exist, atoms have to stick together. If a molecule were split into smaller pieces, it would be a different substance.

Molecules and Atoms - Molecule Bonding
Molecule Bonding. Molecule Bonding happens when two atoms share electrons. Instead of circling just one atom, the electron now circles around two. This is called bonding and the shared electrons are called 'bonds'.

Molecules and Atoms - Covalent Bond
A covalent bond is formed when electrons are shared between atoms.

Molecules and Atoms - Ionic Bond
An ionic bond is formed when electrons are exchanged from one atom to the other.

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