Atoms, ions, and molecules

Atoms are the smallest unit of matter that retain the chemical properties of an element. They are composed of three subatomic particles:

• Protons - Positively charged particles in the nucleus.
• Neutrons - Neutral particles in the nucleus.
• Electrons - Negatively charged particles orbiting the nucleus. The number of protons in an atom determines the element it belongs to, while the number of neutrons can vary, creating isotopes of the same element.

Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net positive or negative charge.

• Positively charged ions are called cations (e.g., Na⁺).
• Negatively charged ions are called anions (e.g., Cl^-).

Molecules are neutral groups of two or more atoms held together by covalent bonds. They can be composed of atoms of the same element (e.g., O₂) or different elements (e.g., H₂O). The specific arrangement of atoms in a molecule gives it unique properties.

Elements, compounds, and mixtures

Matter can be classified into three main categories: elements, compounds, and mixtures.

Elements are the simplest form of matter and cannot be broken down into simpler substances by chemical means. Each element is composed of only one type of atom.

Examples include carbon (C), oxygen (O), and iron (Fe).

Compounds are formed when atoms of different elements chemically bond together in a fixed ratio. The properties of a compound differ from those of its constituent elements due to the chemical bonds between atoms.

Examples include water (H_2_O) and sodium chloride (NaCl).

Mixtures contain two or more elements or compounds combined in variable proportions without chemical bonding. The components of a mixture retain their individual properties and can be separated using physical methods.

Examples include air (a mixture of gases) and salt water (a mixture of salt and water).

Properties of elements, compounds, and mixtures

Elements, compounds, and mixtures can be distinguished by their properties: