What are the Characteristics of the Particles of Matter?

The particles that make up matter are so infinitesimally small that they cannot be seen even with a standard powerful microscope. For example, a single small drop of water contains approximately 10²¹ (one sextillion) particles of water. Their microscopic size was famously demonstrated by dissolving a tiny crystal of potassium permanganate in water, which colors a massive volume of water, proving the crystal must break down into millions of tiny particles.

The particles in matter are not tightly packed without gaps; there are empty spaces between them called intermolecular spaces.

• In solids, these spaces are very small.
• In liquids, the spaces are larger.
• In gases, the spaces are the largest. This is why sugar or salt dissolves and 'disappears' in water—the tiny sugar particles slip into the empty intermolecular spaces between the water particles.

Particles of matter are never at rest. They possess kinetic energy and are constantly in motion.

• In solids, they only vibrate about their fixed positions.
• In liquids, they move and slide past one another.
• In gases, they move randomly at high speeds. As temperature increases, the kinetic energy of the particles increases, causing them to move faster. This continuous movement is the reason behind diffusion (like the smell of incense spreading across a room).

There is an invisible force acting between the particles of matter that keeps them together. This is called the intermolecular force of attraction. The strength of this force varies by state:

• Maximum in solids (making them rigid and hard to break).
• Moderate in liquids (allowing them to flow but remain together).
• Minimum or negligible in gases (allowing them to expand infinitely).