The Structure of Matter Compounds and Molecules

What are Compounds? Compounds are 2 or more elements chemically bonded together

Mixtures Physical Blend of two or more pure substances Elements and compounds

Examples of Molecular Substances Many examples

Compounds Chemical Bonds are forces that hold compounds together A compound always has the same chemical formula H2O NaCl KNO3 CO2

Reading Chemical Formulas Chemical formulas tell us a lot. The subscripts tell us how many atoms or ions are in the compound A compound always has the same chemical formula H2O NaCl KNO3 CO2 HCl

Chemical Structure-shows how compounds atoms or ions are connected Positions of Atoms 1) Bond Length- is the distance between nucleus 2) Bond Angle- is the orientation in space

Models of Compounds Ball and Stick model Structural Formula shows structures, how they are built. H--------O---------H Space Filling Models shows the space filled up by the atoms

How does Structure affect Properties? States (solids, liquids, gases) Melting points Boiling points Freezing Points

Network Structures Arrangement of ions or atoms continues throughout the substance More rigid Strong solids Bonded ions Metal and a non-metal bonded Example Sodium Chloride (NaCl), salt

Molecules Sugar C6H22 O11 Some compounds are made of molecules Two non-metals bonded together Structures vary Not as strongly bonded

Network vs. Molecules Network Solids Molecules Properties Properties Compound State @ 25C Melting Pt.(C) Boiling Pt. (C) Silicon Dioxide Solid 1700 2230 Magnesium Fluoride 1261 239 Sodium Chloride 801 1413 Compound State @ 25C Melting Pt.(C) Boiling Pt. (C) Sugar Solid 185-186 ------------------ Water Liquid 100 Hydrogen sulfide Gas -86 -61

Special Water Attractions Attractions between water molecules are called hydrogen bonds Not as strong as the bonds between hydrogen and oxygen atoms in the water molecule itself