Chemistry: Substances and Their Classification

Definition and Classification

• A substance is a material or a mixture of materials that has a specific chemical composition and properties.
• Substances can be classified into:
  • Elements: substances that consist of only one type of atom (e.g. hydrogen, oxygen)
  • Compounds: substances that consist of two or more different elements (e.g. water, salt)
  • Mixtures: substances that consist of two or more different substances, but not in a fixed ratio (e.g. air, soil)

Properties of Substances

• Physical properties:
  • Color
  • Odor
  • Texture
  • Melting and boiling points
  • Solubility
• Chemical properties:
  • Reactivity
  • Flammability
  • pH level
  • Reactivity with other substances

States of Substances

• Solid: particles are closely packed and have a fixed shape
• Liquid: particles are close together but can move freely
• Gas: particles are widely spaced and can move freely
• Plasma: high-energy state of matter, where atoms are ionized

Changes of Substances

• Physical changes:
  • Changes in state (e.g. melting, freezing)
  • Changes in shape or form
• Chemical changes:
  • Changes in chemical composition (e.g. burning, rusting)
  • Formation of new substances

Importance of Substances

• Substances are the building blocks of matter and make up everything around us
• Understanding substances is crucial in various fields, such as:
  • Chemistry
  • Biology
  • Physics
  • Engineering
  • Medicine

Definition and Classification

• A substance is a material or mixture with a specific chemical composition and properties.
• Substances can be classified into three main categories: elements, compounds, and mixtures.
• Elements consist of only one type of atom (e.g. hydrogen, oxygen).
• Compounds consist of two or more different elements (e.g. water, salt).
• Mixtures consist of two or more different substances, but not in a fixed ratio (e.g. air, soil).

Properties of Substances

Physical Properties

• Color
• Odor
• Texture
• Melting and boiling points
• Solubility

Chemical Properties

• Reactivity
• Flammability
• pH level
• Reactivity with other substances

States of Substances

• Solid: particles are closely packed and have a fixed shape.
• Liquid: particles are close together but can move freely.
• Gas: particles are widely spaced and can move freely.
• Plasma: high-energy state of matter, where atoms are ionized.

Changes of Substances

Physical Changes

• Changes in state (e.g. melting, freezing).
• Changes in shape or form.

Chemical Changes

• Changes in chemical composition (e.g. burning, rusting).
• Formation of new substances.

Importance of Substances

• Substances are the building blocks of matter and make up everything around us.
• Understanding substances is crucial in various fields, such as chemistry, biology, physics, engineering, and medicine.