Matter and its Physical and Chemical Changes

Introduction to Matter

Everything around us is made up of matter. It is anything that has mass & takes up space. Matter exists in different forms—solids, liquids, and gases. It can undergo changes, which are classified as physical changes or chemical changes.

Substances or Matter

• Everything around us is made of matter. Matter is any substance that has mass & occupies space. All substances can be classified as either pure or impure.

• Pure substances consist of either atoms or molecules. Atoms are the smallest unit of matter. Atoms have only one kind of particle, having a definite set of properties. Molecules, on the other hand, have more than one kind of particle combined in a fixed ratio by mass. Both elements and compounds are pure substances. They have a fixed composition and a definite set of properties.

• Impure substances are obtained by combining two or more substances (elements, compounds, or both) without any change in their chemical properties. Impure substances are also called mixtures. Mixtures are of two types: homogeneous and heterogeneous. They do not have a fixed composition & a definite set of properties, but they retain the properties of their constituents.

 

Classification of Matter

Elements

• The most basic & fundamental form of matter that cannot be broken down into simpler substances.

• Consisting of but one type of atom.

• Indicated as a chemical formula (E.g., O for Oxygen, H for Hydrogen).

Types of Elements:

• Metals: (Iron (Fe), Gold (Au), Silver (Ag))

• Non-metals: (Oxygen (O), Carbon (C), Sulfur (S))

• Metalloids: (Silicon (Si), Boron (B))
  
  

Compounds

• A compound is formed when two or more elements combine in a fixed ratio.

• This is also represented using chemical formulae (e.g., H₂O for Water, CO₂ for Carbon Dioxide)

• It can only be separated through chemical reactions.

Examples of Compounds:

• Water (H₂O) → Hydrogen + Oxygen

• Carbon Dioxide (CO₂) → Carbon + Oxygen

• Sodium Chloride (NaCl - Common Salt) → Sodium + Chlorine
  
  

Mixtures

• Two or more substances that are physically combined.

• Ease of separation by physical methods such as filtration, evaporation, or distillation

Types of Mixtures:

1. Homogeneous Mixtures (Composition is uniform)

• Example: Air (Oxygen, Nitrogen, Carbon Dioxide), Saltwater

2. Heterogeneous Mixtures (Non-uniform composition)

• Example: Oil & Water, Sand & Iron Filings
  
  

Chemical Symbols

Every element is designated by a chemical symbol — a one- or two-letter abbreviation of its name. They assist in constructing chemical equations and formulas.
Here are a few examples:

• H for Hydrogen

• O for Oxygen

• Na for Sodium

• Cl for Chlorine

• Fe for Iron

Each symbol stands for one atom of the element. Ionic compounds are chemically represented by a specific symbol such as NaCl, which indicates a compound composed of chloride & sodium ions (Na+ and Cl-).

Chemical Formulae

A chemical formula indicates the number and kind of atoms that exist in a compound. The formula is made of elements' symbols in the compound & subscripts showing how many atoms there are. Here’s how they work:

• Water (H₂O): 2 hydrogen atoms + 1 oxygen atom.

• Carbon dioxide (CO₂): 1 carbon atom + 2 oxygen atoms.

• Sodium chloride (NaCl): 1 sodium atom + 1 chlorine atom.

Formulas that can represent the ratio of atoms in compounds. For instance, In CO₂, one carbon atom bonds to two oxygen atoms to make one carbon dioxide molecule.

Chemical Reactions

A chemical reaction transforms one set of chemical substances into another. Chemicals consist of two or more atoms that bind together, but when a chemical reaction occurs, the bonds break and reform to add to or remove from an existing molecule. Energy (heat, light, or electricity) always accompanies this process.

Signs of a Chemical Reaction:

• Color change: For example, an apple turns brown due to oxidation.

• Gas formation: Some reactions produce gas, like when baking soda meets vinegar & releases carbon dioxide gas.

• Precipitate formation: When two clear liquids mix to make a solid (e.g., when mixing silver nitrate & sodium chloride to create silver chloride precipitate).

• Energy change: The reaction can be either exothermic (releases heat) or endothermic (absorbs heat).
  
  

Example of a Chemical Reaction:

When Hydrogen (H₂) reacts with Oxygen (O₂), water (H₂O) is formed: 2H2 + O2 → 2H2O

Physical Changes

Physical Change: the state, size, or appearance of a substance changes, but no new substance is formed. A physical change does not alter the chemical structure of a substance, instead only its physical properties.

Characteristics of Physical Changes:

• Reversible: Many changes are irreversible. This can be in arrays, graphs, etc.

• No new substance: It does not alter the substance into something new. For example, cutting a sheet of paper.

• State changes: Physical change includes a change in the state of matter. For example, Water can crystallize into ice or vaporize into steam.
  
  

Examples of Physical Changes:

• Melting: Ice melting to form water.

• Freezing: Water freezes to form ice.

• Boiling: Water boiling to form steam.

• Dissolving: Salt dissolving in water.
  
  

Chemical Changes

A chemical change is a change in the configuration of the compound or mixture that creates a new material with unique characteristics. Chemical changes, unlike physical changes, are generally not reversible.

Characteristics of Chemical Changes:

• Formation of new substances: The original substance becomes one or more new substances. For example, burning wood leaves behind ash & gas.

• Energy change: Chemical changes release or consume energy, such as in the form of heat, light, or sound.

• Irreversible: Once a chemical reaction has taken place, it cannot be reversed easily or at all. Example: Cooking an egg.
  
  

Examples of Chemical Changes:

• Burning: When wood burns in a fireplace, it combines with oxygen, resulting in carbon dioxide & vaporized water.
  Wood + Oxygen → Carbon Dioxide + Water

• Rusting: Rusting is the reaction of iron with oxygen in the air to form iron oxide, commonly known as rust.
  Iron + Oxygen → Iron Oxide (Rust)

• Digestion: This process is known as digestion, which is when the food we consume undergoes chemical reactions in our body to break down into simpler substances.

Examples of Physical and Chemical Changes Together

In many real-world processes, both physical & chemical changes occur at the same time.

 

Fun Facts

1. The most malleable metal, gold, can be pulled out into a thread thousands of metres long.

2. Water is the only substance that occurs in all three states of matter — solid (ice), liquid (water) & gas (steam) — under natural Earth conditions.

3. Water (H₂O) is a compound that constitutes 70% of the human body.

4. Sodium is so highly reactive that exposure to water causes it to catch fire.

Things you have learned!

• Understand that matter is anything that has mass and occupies space. It exists in the form of solids, liquids, and gases.
• Classify substances as pure (elements and compounds) or mixtures (homogeneous and heterogeneous).
• Identify physical changes as changes in state, size, or shape that do not produce a new substance.
• Recognize chemical changes as changes that result in the formation of a new substance and are usually irreversible.
• Observe that certain processes, such as burning a candle, involve both physical and chemical changes.