CHEMISTRY NOTES BONDING & ELECTROPLATING

 Chemists call the attraction that holds atoms together a chemical bond. Several types of bonds exist, and they all involve electrons in some way.  We’ve seen that most substances can be divided into four categories based on their physical properties. These categories can be explained by different models of bonding. You can see these in the table on the previous page. BONDING

Carbon dioxide exists as separate CO 2 molecules; silicon dioxide exists as a network of silicon and oxygen.

 Some properties are directly related to the type of bonds the atoms in the substances have. Therefore, it is possible to match the bonding with the physical properties observed in different substances. BONDS AND PROPERTIES

 Conduction requires the movement of charged particles.  Ionic substances in aqueous solution contain free-moving cations and anions, so they conduct electricity.  Metallic substances conduct electricity because their valence electrons are free to move within the solid.  Network covalent substances and molecular covalent substances do not contain ions or transfer electrons, so they do not conduct electricity.

 Melting point depends on the attractive forces between the particles.  The higher the melting point, the stronger the attractive forces.

SubstanceType of Bond Soluble in water? Conducts electricity? Electrons are… Description Magnesium chloride, MgCl 2 Rubbing alcohol, C 3 H 8 O Packet 3 Example 2: Identifying Types of Bonds Determine the type of bond in each of the following substances. Then decide the physical properties each substance would have. Ionic (metal + nonmetal) Yes Yes—when dissolved in water Transferred Brittle solids Molecular covalent (C, H, and O) YesNoShared between atoms Liquid

 Most metals are dug out of the ground as ionic compounds (ores); in other words, they cannot be found in nature in their pure forms. Through the ages, people have struggled to extract the pure metals from these ores; some are easier to purify than others. ELECTROPLATING METALS This is a piece of gold ore— obviously, it’s not pure gold. Gold and other metals can be extracted from ores using a variety of methods.

 Despite being the third most common element in Earth’s crust, aluminum was one of the most difficult metals for scientists to isolate. It was first purified in 1827 by a German chemist named Friedrich Wöhler. Processing aluminum was still difficult and inefficient, making it more expensive per ounce than gold for quite some time. ALUMINUM This is bauxite, the ore aluminum can be extracted from.

 Napoleon III famously let only his favorite guests use his aluminum cutlery, while the rest had to use gold.  The Washington Monument was also capped with aluminum which (at the time) was as expensive as silver.  It was not until the advent of electrolysis (running an electric current through aluminum ore), that the isolation of aluminum became more efficient, therefore dropping the price of aluminum.

 Electricity can be used to extract metal from compounds by “giving” electrons back to metal ions, which converts them to neutral metal atoms. This process is called electroplating.  Ex. Copper metal can be extracted from a copper sulfate solution by running an electrical current through the solution. ELECTROPLATING

ELECTROPLATING WITH GOLD