Chemical Level of Organisation

Hierarchical Structure of the Human Body

Atom → Molecule → Cell → Tissue → Organ → Organ System → Organism

Matter

Anything that has mass and takes up space.

Atom

The smallest stable unit of matter, consisting of protons, neutrons, and electrons.

Subatomic Particles Locations

Protons and neutrons are located in the nucleus; electrons orbit around the nucleus.

Importance of Electrons

Electrons determine chemical reactivity, form chemical bonds, and allow the formation of molecules and ions.

Element

A substance made of only one type of atom, e.g., Hydrogen (H) and Oxygen (O).

Atomic Number

The number of protons in the nucleus of an atom, which determines the element.

Fundamental Organic Elements

The five elements that make up biomolecules: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Phosphorus (P).

Most Abundant Element in the Body

Oxygen, which constitutes approximately 65% of body weight.

Molecule

Two or more atoms bonded together, which may be the same or different elements.

Compound

A molecule made of two or more different elements bonded together.

Difference Between Molecule and Compound

A molecule consists of the same atoms bonded (O₂); a compound consists of different atoms (CO₂).

Mixture

A combination of atoms, molecules, and compounds that are not chemically bonded together.

Ion Formation

An ion is formed when an atom gains electrons (negative ion) or loses electrons (positive ion).

Chemical Behavior Determinant

The electrons of an atom, particularly the number of outer shell electrons and their interaction.