Goals for the next 2 days: Draw simple representations of different types of solids that illustrate important aspects of their structure Analyze models of different solid types in order to explain the properties of these substances.

Chemistry of Solids Types of Solids

Intermolecular forces hold molecules together in a solid state

Chemistry of Solids Types of Solids

Covalent Network Solids: Composed of: Non-metal atoms attracted to one another via covalent bonds

Non-metal Non-metal Non-metal Non-metal Non-metal Non-metal Non-metal

Covalent Network Solids: Composed of: Non-metal atoms attracted to one another via covalent bonds There are NO DISTINCT MOLECULES!!!

Covalent Network Solids: Diamond: Every C atom is covalently bonded to 4 other C atoms

Covalent Network Solids: Graphite: Still C atoms, just arranged differently

Covalent Network Solids: Graphite: Still C atoms, just arranged differently The layers slide off easily from one another, making it great for writing with!

Covalent Network Solids: Composed of: Non-metal atoms attracted to one another via covalent bonds There are NO DISTINCT MOLECULES!!! If a formula is given, what does it probably represent? (SiC, silicon carbide for example)

Covalent Network Solids: Silicon carbide: SiC Ratio: 1 Si atom for every 1 C atom

Covalent Network Solids: Composed of: Non-metal atoms attracted to one another via covalent bonds There are NO DISTINCT MOLECULES!!! Formula’s for covalent network solids only represent the ratio between the atoms in the solid

Covalent Network Solids: How to ID them? There are very few common examples of covalent network solids … Look for substances with Si and/or C!!!

Covalent Network Solids: Melting Point: Remember  this is based on the strength of whatever force holds the solid together! (Intramolecular forces are always strongest) Extremely high melting points Carbon(diamond) has the highest melting point of any pure substance: 6,300oF

Covalent Network Solids: Electrical Conductivity: Remember  Free flowing charged particles are needed Covalent network solids are NOT predicted to conduct electricity Some do however …

Covalent Network Solids: Thermal Conductivity: Good thermal conduction = easy to increase the movement of the particles Very poor thermal conductors Since every atom is covalently bonded to many others, it is hard to increase movement between them

Covalent Network Solids: Thermal Conductivity: Covalent network solids are thermal insulators!

Covalent Network Solids: Hardness Scale: Hardness is the resistance to various kinds of permanent shape change Cov. network solids comprise the hardest substances known to man

Ionic Solids: Composed of: Ions attracted to one another via ionic bonds

Anion- Anion - Anion - Anion - Cation + Anion - Cation + Anion - Cation + Anion - Cation + Anion- Cation + Anion - Cation + Anion - Cation + Anion - Cation + Anion - Cation + Anion - Anion - Cation + Cation + Anion - Cation + Anion - Cation + Anion - Cation +

Ionic Solids: Composed of: Ions attracted to one another via ionic bonds How to ID them? Look for compounds made of metals and non-metals … Ex: NaCl, MgO, Al2S3

Melting points of ionic solids You have two competing factors here. As the charge increases on the ions the bonds get stronger. However, as the distance between atoms increases the bonds get weaker. Let's look at some data first: Melting Points MgO 2852 °C BaO 1923 °C NaCl 801 °C KCl 790 °C As you can see the +2 ions (Mg+2 and Ba+2) have much higher melting points than the +1 ions (Na+1 and K+1). Now if you compare the two +2 ions, magnesium has a much smaller radius than barium which appears further down on the periodic table. You would predict MgO to have a higher melting point than BaO for that reason (much higher because they are far apart on the table). Similarly, potassium has a larger radius than sodium which you can infer from its position on the periodic table. So NaCl has a higher melting point than KCl (but not by much as they are quite close on the table)

Generally higher compared to other solids Ionic Solids: Melting points: Generally higher compared to other solids mp = 801oC mp = 993oC

Generally higher compared to other solids Ionic Solids: Melting points: Generally higher compared to other solids lower higher

Electrical conduction: (solid, molten, dissolved) Ionic Solids: Electrical conduction: (solid, molten, dissolved) Solid Molten Dissolved No conduct! Conducts! Conducts!

Ionic Solids: Hardness: + - + - + - + - + - + - + - + - + - + - + - + - +

Ionic Solids: Hardness: - + - + When impacted, rows of ions re-align. + + - + - - - + - + + + - + - - - + - + +

Ionic Solids: Hardness: - + - + When impacted, rows of ions re-align. + - + - - + - + + - + - If like charges face each other, the entire row is repelled away - + - +

Ionic Solids: Hardness: - + - + Ionic compounds tend to be very brittle + - + - - + - + + - + - - + - +

Practice problems 1d-f, 2, 3 and 5

Practice problems 1d-f, 2, 3 and 5