Overview
This lecture introduces the basics of chemical composition, focusing on elements, compounds, mixtures, and their properties, as well as key concepts like solubility and rates of dissolving.
Elements and the Periodic Table
- Elements are basic building blocks of all matter, living or non-living.
- An element cannot be broken down into simpler substances.
- Elements are listed with unique chemical symbols in the periodic table.
- Most elements are solids at room temperature.
Metals vs Non-metals
- Metals are shiny, malleable (can be shaped), ductile (can be drawn into wires), and good conductors; they have high melting/boiling points.
- Non-metals are dull, brittle (break easily), poor conductors, and have low melting/boiling points.
Compounds
- Compounds are substances formed from two or more different elements chemically combined.
- Compounds do not share the same properties as their constituent elements.
- Compounds form through chemical reactions and have elements in fixed proportions by mass.
- Compounds can only be separated into elements using chemical methods.
Mixtures
- Mixtures consist of two or more elements and/or compounds not chemically bonded.
- Mixtures retain the properties of their constituents and do not have fixed proportions.
- Mixtures can be separated by physical methods and do not require chemical reactions to form.
Types of Mixtures: Solutions and Suspensions
- Solutions: mixtures where one substance dissolves fully in another; particles are evenly mixed and cannot be seen or filtered out.
- Dilute solutions contain less solute; concentrated solutions contain more.
- Suspensions: mixtures of insoluble substances; particles settle over time and can be separated by filtration.
- Suspensions are heterogeneous; solutions are homogeneous.
Solubility and Rate of Dissolving
- Solubility is how well a solute dissolves in a given solvent.
- Factors affecting solubility: nature of solute, nature of solvent, and temperature (higher temperature increases solubility).
- Rate of dissolving depends on temperature, size of solid particles (smaller dissolves faster), and rate of stirring.
Distinguishing Elements, Compounds, and Mixtures
- Elements: single type of atom, cannot be separated, and occur naturally.
- Compounds: fixed ratio of different elements, can be separated chemically, formed by chemical reactions.
- Mixtures: any ratio, properties similar to components, separated physically, formed by physical changes.
Key Terms & Definitions
- Element — a substance that cannot be broken down into simpler substances.
- Compound — a substance formed by chemically combining two or more different elements in fixed proportions.
- Mixture — a combination of elements and/or compounds not chemically bonded.
- Malleable — able to be shaped or beaten into sheets.
- Ductile — able to be drawn into wires.
- Solute — the substance that dissolves in a solvent.
- Solvent — the substance in which a solute dissolves.
- Solution — a homogeneous mixture where a solute is dissolved in a solvent.
- Suspension — a heterogeneous mixture with insoluble particles that can settle or be filtered out.
- Residue — insoluble substance left on filter paper during filtration.
- Filtrate — liquid that passes through filter paper.
- Solubility — measure of how much solute can dissolve in a solvent.
- Rate of dissolving — speed at which a solute dissolves in a solvent.
Action Items / Next Steps
- Review the periodic table and memorise symbols for common elements.
- Prepare for further study on separation techniques in the next chapter.
- Revisit previous material on physical properties if needed.