Atoms, Molecules, Elements, and Compounds

Atoms, Molecules, Elements and Compounds

Core Concepts

• Atom: The smallest part of an element that can exist.

• Atomic Structure:

  • Central nucleus containing:

    • Positively charged protons

    • Neutrons with no charge

  • Negatively charged electrons revolving around the nucleus

• Element: A substance made of one type of atom (e.g., oxygen $O_2$, iron $Fe$).

• Molecule: A particle made of two or more atoms joined together (e.g., oxygen $O<em>2$, water $H</em>2O$).

• Diatomic Molecule: A molecule that consists of two atoms, often the same element (e.g., $O<em>2$, $Cl</em>2$).

• Chemical Symbol: A one or two-letter universal code for each element, found in the periodic table.

• Compound: A substance made of more than one type of atom chemically joined together (e.g., water $H<em>2O$, carbon dioxide $CO</em>2$).

• Chemical Formula: A formula that shows the number and type of atoms present in a molecule.

  • ide: A compound of only the named substances.

  • ate: A compound of the named substances and oxygen.

• Physical Change: Changes of state where no new substances are made.

• Chemical Change (Chemical Reaction): When atoms rearrange to make new substances.

• Metals: Generally found on the left side of the periodic table.

• Non-metals: Generally found on the right side of the periodic table.

Properties of Metals

• Good conductors of electricity.

• Good conductors of heat.

• Shiny.

• High density (heavy for its size).

• Malleable (can be hammered).

• Sonorous (makes a ringing sound when hit).

• Ductile (can be pulled into wires).

• High melting points (except mercury).

• Hard.

Properties of Non-metals

• Poor conductors of electricity.

• Poor conductors of heat.

• Dull.

• Low density (light for its size).

• Brittle (breaks easily).

• Non-sonorous (no ringing sound when hit).

• Low melting points.

Thermal Decomposition

• Definition: A chemical reaction where a compound breaks down into simpler substances when heated.

• Example: Copper carbonate ($CuCO<em>3$) breaks down into copper oxide ($CuO$) and carbon dioxide ($CO</em>2$) when heated.

• Chemical Equation: $CuCO<em>3(s) \rightarrow CuO(s) + CO</em>2(g)$

• Word Equation: Copper carbonate → Copper oxide + Carbon dioxide

Elements, Mixtures, and Compounds

Definitions

• Atom: A single particle.

• Molecule: One particle made of 2 or more atoms.

• Element: A collection of atoms that are all the same.

• Compound: Two or more different elements joined together.

• Mixture: Different substances mixed together but not joined.

Diagrams and Descriptions

• Atoms of an element.

• Molecules of an element.

• A mixture of 2 elements, both of which are made of atoms.

• A pure compound made of molecules.

Solutions

• Supersaturated Solution: Contains more solute than the maximum amount that can be dissolved at a given temperature. To add more solute:

  • Increase the temperature of the solution.

  • Add more solvent.

Mixtures and Separation Techniques

Distillation

• Used in desalination plants to obtain pure water from seawater.

Separation Techniques

Separating Sand and Salt from Water (Rock Salt)

1. Filtration:

   • Separate sand from the salt solution using a filter funnel and filter paper.

2. Evaporation:

   • Separate salt from water by evaporating the water, leaving the salt behind.

Apparatus for Distillation

• Components:

  • Flask

  • Liebig condenser (with water in and water out)

  • Beaker

  • Thermometer

  • Heat source

Separation Methods

1. Filtration:

   • To separate an insoluble solid (e.g., sand) from a suspension.

2. Evaporation:

   • To separate a soluble solid (e.g., salt) from a solution.

3. Chromatography:

   • To separate a mixture of colored compounds/pigments/dyes.

   • Uses chromatography paper (stationary phase) and a solvent (mobile phase).

   • bInvolves applying a sample spot and allowing the solvent to move up the paper.