Fundamentals C: Compounds

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University of California - Irvine
Ramesh D Arasasingham

Chemical Principles: The Quest for Insight bthAtkins and Jones 5 Edition Study Guide by Gigi :D Fundamentals C Compounds Compounds  compound: an electrically neutral substance; two or more different elements with their atoms present in a characteristic, definite ratio  binary compounds have 2 elements  organic compounds contain carbon (often hydrogen as well) ◦ these are extracted from living organisms (plant tissue, flesh, ect.)  all other compounds are inorganic and do not contain carbon ◦ they are often classified in terms of the elements or groups of elements that they contain  some very simple carbon compounds are grouped as inorganic ◦ examples: carbonates, cyanides, carbides, ect.  intermetallic compounds: inorganic compounds formed when two metal atoms bond in specific proportions ◦ Examples: NiTi (nitinol), FeCo ◦ they ofter differ discontinuously in structure from that of their base metals  atoms in a compound are bonded in a specific way due to a chemical change ◦ results in a substance with different properties (physical and chemical) from the elements that formed it  atoms can bond to form molecules or can be present in compounds as ions ◦ molecule – a discrete group of atoms bonded together in a specific way ◦ ion – a positively or negatively charged atom or molecule  cation – positively charged atom, denoted with a plus (+) sign  anion – negatively charged atom, denoted with a minus (–) sign  ionic compound – a compound made of ions in a ratio that results in overall electrical neutrality  molecular compound – a compound made of electrically neutral atoms  In general: ◦ binary compounds of two nonmetals are molecular (water, H2O) ◦ binary compounds with a metal and a nonmetal are ionic (sodium chloride, NaCl) Molecules and Molecular Compounds  chemical formula – represents the composition of a compound with chemical symbols  molecular formula – chemical formula; shows how many atoms of each element are present in a single molecule of a compound  diatomic molecule – molecule that has 2 atoms ◦ except noble gases, all elements that are gases at standard temperatures are diatomic ◦ all halogens and nitrogen exist as diatomic molecules  structural formula – indicates how atoms are linked together ◦ does not show their 3-dimensional arrangement in space ◦ represents chemical bonds with dashes ◦ represents atoms with their symbols  structural formulas are often condensed to simply their atom groupings (CH4, C2H6) ◦ atoms in these formulas often have subscripts to indicate the atoms connected to the preceding element ◦ groups of atoms are set off with parentheses such as HC(CH3)3  carbon atoms nearly always form four bonds ◦ however, they can form chains and rings of nearly limitless variety  in structural formulas: ◦ a single line for a single bond – atoms share one electron pair ◦ a double line for a double bond – two electron pairs ◦ triple line for a triple bond – three electron pairs  line structures represent chains of carbon atoms with zig-zag lines ◦ each short line indicates a bond and the end of the line represents a carbon atom ◦ atoms other than carbon and hydrogen shown by their symbols ◦ double lines for double bonds and triple lines for triple bonds ◦ because carbon always forms four bonds in organic compounds, C–H bonds are not shown explicitly ◦ the correct number of hydrogen atoms must be filled in mentally Models of Molecular Compounds  space-filling model ◦ atoms – colored spheres (not representative of atom colors) ◦ radii of atoms determined by calculation ◦ because atoms do not have hard surfaces, the surface shown uses a chos
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