Energy and matter

UNIT 8.- MATTER AND ENERGY

The Universe can be described in terms of matter and energy. A material system is any kind of matter whose limits are undefined due to its nature or to its size; on the other hand, a body has defined limits.

Characteristics of matter:

• It has dimensions: matter occupies space, that is, it has volume.
• It has inertia: this property keeps the body still or in motion, and it is related to the mass.
• It causes gravitational attraction: bodies attract each other because of gravity.

Scales of observation:

• Macroscopic scale: to measure things that can be perceived using our senses.
• Microscopic scale: to measure things like cells, viruses, atoms, etc.

Composition of matter:

All matter is made up of very tiny particles called atoms, which are the smallest part of any substance.

Pure substances:

A pure substance is a type of matter which has specific properties and a chemical constant composition. Pure substances can be classified as:

• Elements: these have only one type of atom that cannot be broken down further (C, H, O, N, P, S, Fe, Na, Cl, I….).
• Compounds: these have 2 or more different atoms joined together (H₂O, CO₂, C₆H₁₂O₆, H₂SO₄…).

Forms of pure substances:

• Atomic substances: here the basic unit is the atom.
• Molecular substances: atom join together to form molecules. Molecules can be formed by atoms of the same element or by atoms of diferent elements.
• Ionic substances: here the basic unit is the ion. Ions are atoms that have lost or gained electrons (Na⁺, Cl^-, Fe²⁺…).

Energy and changes in material systems:

A change is any transformation that can be measured. Material systems and bodies change when they interact with another material system, another body or with itself. In a change, an exchange of energy occurs between a material system (or a body) and its surroundings.

Classification of material systems:

• Open systems: they can exchange matter and energy with their surroundings.
• Closed systems: they can only exchange energy with their surroundings.
• Isolated systems: systems that cannot exchange energy or matter with their surroundings.

Types of changes:

• Physical changes: these changes affect some properties of matter, but no new substance is produced. The mos usual are:
  • Changes in movement
  • Thermal changes
  • Electrical changes
  • Changes due to light and sound
    
    
• Chemical changes: produce new substances. Pure substances, called reactants, are transformed into different substances called products.