Atoms, Elements, Compounds & Mixtures

Atom: The smallest unit of an element that can exist. Atoms are the fundamental units that make up everything around us.
Element: A substance made up of only one type of atom.
- Elements can exist in different states: solid, liquid, or gaseous.
- Examples:
  - The Sodium element is composed solely of sodium atoms; its chemical formula is $Na$ .
  - The Hydrogen element is composed only of hydrogen atoms; its chemical formula is $H_2$ .
Compound: A substance made up of two or more different atoms that are chemically bonded together.
- Examples:
  - Water: $H_2O$ (consists of Hydrogen and Oxygen atoms).
  - Carbon dioxide: $CO_2$ (consists of Carbon and Oxygen atoms).
Mixture: Formed when two or more substances are physically combined but not chemically bonded.
- They can be separated by physical methods.
- Examples:
  - Salt and water.
  - Sand and sugar.

Elements are categorized into two primary groups based on their position on the Periodic Table:
- Metals: Located on the left side of the stepped line.
- Non-Metals: Located on the right side of the stepped line.
Example Reference: Carbon ( $C$ ) has an atomic mass of $12.01$ .

Solution: A specific type of mixture where a solute and a solvent are combined.
Solute: The substance that is being dissolved.
Solvent: The substance that dissolves the solute. Common examples include water or ethanol.

All substances possess unique chemical and physical properties that allows for their identification.
Chemical Properties: Describe how a substance behaves during a chemical reaction.
- Reactivity: How vigorously or slowly a substance reacts.
- Reaction Partners: Identifying what a substance can react with (e.g., water or acid).
- Observable Changes: The formation of colored compounds.
Physical Properties: Characteristics that can be observed or measured without changing the substance's identity.
- Appearance: Including color, shininess, or dullness.
- State of Matter: The substance's state at room temperature (solid ( $s$ ), liquid ( $l$ ), or gas ( $g$ )).
- Thermal Constants: Melting points and boiling points.

Magnesium metal (Element, $Mg$ ):
- Physical Properties: Shiny; grey solid at room temperature; malleable.
- Chemical Properties: Reacts with acid to form hydrogen gas.
Magnesium carbonate (Compound, $MgCO_3$ ):
- Physical Properties: White powder.
- Chemical Properties: Reacts with acid to form carbon dioxide.

Definition: An alloy is a mixture consisting of two or more metals (e.g., Element X mixed with Element Y).
Properties of Alloys:
- Alloys possess different chemical and physical properties compared to their constituent elements.
- Hardness: Alloys are generally harder than pure metals. This is because the different-sized atoms disrupt the regular arrangement, making it harder for particles to slide over each other.
Common Alloys, Compositions, and Uses:
- Bronze:
  - Composition: Copper ( $Cu$ ) and Tin ( $Sn$ ).
  - Uses: Bells, cymbals.
- Brass:
  - Composition: Copper ( $Cu$ ) and Zinc ( $Zn$ ).
  - Uses: Electric plugs, ornaments.
- Steel:
  - Composition: Iron ( $Fe$ ) and Carbon ( $C$ ).
  - Uses: Car bodies.
- Stainless Steel:
  - Composition: Iron ( $Fe$ ), Nickel ( $Ni$ ), and Chromium ( $Cr$ ).
  - Uses: Knives, forks, spoons, kitchen sinks.

General Worksheet Tasks (Reference: Textbook pages 67-88):
1. Define atom, element, compound, and mixture.
2. Represent elements, compounds, and mixtures using the particle model.
3. Provide two examples each for an element, compound, and mixture.
Specific Textbook Exercises:
- Answer questions 5-8 on page 87 of the textbook.
- Answer end-of-chapter questions on page 75.
- Answer end-of-chapter questions on page 88.
Alloy Research Project: Construct a mini-poster that includes:
- The definition of the term "alloy."
- The names and compositions of four researched alloys.
- The specific uses for each of the four alloys selected.