Fundamental Chemistry: Elements, Compounds, and Mixtures

Introduction to Chemistry and Matter

• Chemistry is defined as the study of matter.
• Matter is classified into three primary groups based on its composition:
  • Elements
  • Compounds
  • Mixtures

Elements

• An element is a pure substance that cannot be broken down into two or more simpler substances by chemical reactions or electricity.
• An element contains only one type of atom.
• There are 118 known elements in total.
  • $92$ elements occur naturally on Earth.
  • $26$ elements are man-made, created by scientists.
• Elements are the building blocks that combine with one another to form thousands of different compounds.

Chemical Symbols

• Chemists use unique chemical symbols to represent elements, consisting of one or two letters.
• Rules for symbols:
  • The first letter is always capitalized.
  • The second letter (if any) is always lowercase.
• Examples of elements and symbols:
  • Oxygen: $O$
  • Hydrogen: $H$
  • Iron: $Fe$
  • Copper: $Cu$
  • Gold: $Au$

Comparison of Elements and Simpler Substances

• Copper ($Cu$) is an element because it cannot be split into simpler substances.
• Water ($H_2O$) is not an element because it contains two different kinds of atoms: hydrogen and oxygen. Water can be broken down using electricity into hydrogen and oxygen.

Classification of Elements

Elements are divided into three groups: metals, non-metals, and metalloids.

Metals

• A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance.
• Metals conduct electricity and heat relatively well.
• Physical properties of metals:
  • Appearance: Shiny (lustrous).
  • Heat Conductivity: Good conductor.
  • Electricity Conductivity: Good conductor.
  • Malleability: Can be hammered into sheets.
  • Ductility: Can be drawn into wires.
  • State at room temperature: Mostly solids (with the exception of mercury).
  • Sound: Sonorous (they ring when struck).

Non-metals

• Non-metals lack metallic attributes and are good insulators of heat and electricity.
• Examples include carbon, sulphur, and phosphorus.
• Physical properties of non-metals:
  • Appearance: Dull.
  • Heat Conductivity: Poor conductor.
  • Electricity Conductivity: Poor conductor.
  • Malleability: Brittle if solid.
  • Ductility: Cannot be drawn into wires.
  • State at room temperature: Mostly gases, some solids; bromine is a liquid.
  • Sound: Not sonorous.

Metalloids

• Metalloids possess properties that are between those of metals and non-metals.
• They can conduct electricity better than non-metals but not as well as metals.

Compounds

• A compound is a pure substance formed when two or more different elements are chemically combined in a fixed ratio (fixed proportion).
• Elements in a compound are chemically bonded together.

Characteristics of Compounds

• It is a pure substance.
• It contains two or more different elements.
• Elements are chemically combined.
• It has a fixed chemical composition (fixed ratio of elements).
• It possesses properties that are entirely different from the elements that make it.
• Components cannot be separated by physical methods such as filtering or evaporation; they can only be separated by chemical reactions or electrolysis.

Formation of Magnesium Oxide ($MgO$)

• When magnesium ($Mg$) burns in oxygen ($O_2$), it reacts vigorously and produces a bright white flame.
• A new substance, Magnesium Oxide ($MgO$), is formed.
• Chemical equation:
  • $2Mg_{(s)} + O_{2(g)} \rightarrow 2MgO_{(s)}$
• Magnesium Oxide is classified as a compound because:
  • It contains two different elements (magnesium and oxygen).
  • The elements are chemically bonded.
  • Magnesium and oxygen combine in a fixed ratio.
  • Magnesium oxide has completely different properties from magnesium and oxygen.

Comparison of Properties

• Magnesium ($Mg$): Shiny metal, good conductor of electricity, burns easily.
• Oxygen ($O_2$): Colourless gas, poor conductor, supports burning.
• Magnesium Oxide ($MgO$): White solid powder, poor conductor when solid, does not burn.

Common Compounds and Their Elements

Mixtures

• A mixture is made by physically combining two or more substances without any chemical reaction taking place.
• Unlike compounds, the substances in a mixture are not chemically bonded.
• Each substance in a mixture keeps its own physical and chemical properties.
• The components of a mixture can be present in any proportion, meaning there is no fixed composition.

Characteristics of Mixtures

• Contains two or more substances.
• Formed by physical mixing, not chemical bonding.
• Has no fixed ratio of components.
• The substances involved retain their original properties.
• Can be separated by physical methods.
• May be homogeneous (uniform) or heterogeneous (non-uniform).

Common Examples of Mixtures

• Air: Nitrogen, oxygen, carbon dioxide, argon, water vapor, and other gases.
• Seawater: Water and dissolved salts (mainly sodium chloride).
• Crude oil: A mixture of organic compounds (mainly hydrocarbons).
• Ink: Water or alcohol mixed with coloured dyes and pigments.
• Gunpowder: Potassium nitrate, sulfur, and carbon.

Types of Mixtures Based on Components

1. Mixture of Two Elements

• Formed when two different elements are physically mixed without forming chemical bonds.
• They keep their physical/chemical properties and can be separated physically.
• Examples:
  • Iron and sulfur (before heating).
  • Nitrogen and oxygen (main gases in air).
  • Copper and zinc (forming the alloy brass).
• Note: If iron and sulfur are heated together, they react chemically to form iron sulfide ($FeS$), which is a compound.

2. Mixture of Two Compounds

• Formed when two different compounds are physically mixed without a chemical reaction.
• Each compound keeps its own properties and can be separated physically.
• Example: Sugar and salt mixed together.

3. Mixture of One Element and One Compound

• Contains one element mixed physically with one compound without chemical bonds.
• Examples:
  • Oxygen and water.
  • Iron and sulfuric acid (before any reaction).
  • Carbon and sugar.
• Note: If the element reacts chemically with the compound, it is no longer a mixture as new substances are formed.

Comparison: Compounds vs. Elements vs. Mixtures

Homogeneous Mixtures (Solutions)

• A homogeneous mixture is one in which the components are uniformly distributed throughout.
• The mixture has the same composition and appearance in every part.
• Individual components cannot be distinguished with the naked eye.
• It has only one visible phase.

Characteristics of Homogeneous Mixtures

• Uniform composition throughout.
• Components are evenly distributed.
• Appears as a single substance.
• Every sample taken has the same composition.
• Usually transparent or evenly coloured.

Examples of Homogeneous Mixtures

• Solutions: A solution is always homogeneous because the solute dissolves completely and spreads evenly among solvent particles.
• Salt Solution: Salt particles cannot be seen, and every part of the solution contains the same amount of salt.
• Sugar Solution: Produces a clear solution with the same composition throughout.
• Air: Gases ($N_2, O_2, CO_2, Ar$) are evenly distributed, making the air appear uniform.
• Vinegar: A solution of acetic acid dissolved uniformly in water.
• Brass: An alloy of copper and zinc where metals are evenly mixed.

Heterogeneous Mixtures

• A heterogeneous mixture is one in which the components are not evenly distributed.
• Different parts of the mixture have different compositions.
• Individual substances can often be seen or separated easily.
• It has two or more visible phases (different substances or layers).

Characteristics of Heterogeneous Mixtures

• Non-uniform composition.
• Components are not evenly distributed.
• Different substances can usually be seen.
• Different parts contain different amounts of each substance.
• Components can often be separated by physical methods like filtration, decantation, or sieving.

Examples of Heterogeneous Mixtures

• Sand and Water: Sand does not dissolve and settles at the bottom, forming a separate layer.
• Oil and Water: These are immiscible; oil floats on top of the water, forming two distinct layers.
• Soil: Contains unevenly mixed sand, clay, rocks, organic matter, water, and air.
• Granite: Made of different minerals like quartz, feldspar, and mica, which can be seen.
• Fruit Salad: Different fruits remain separate and can be easily identified.

Reasons for Heterogeneity

• Substances do not dissolve in each other (e.g., oil and water molecules remain separate).
• Components have different physical properties such as density or particle size.

Summary Comparison: Homogeneous vs. Heterogeneous