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Chemistry Review: Atoms ➲ ➲ Atoms are made up of a nucleus containing protons and neutrons and orbitals containing electrons (2, 8, 8,...). The outermost electrons are known as valence electrons. Ions ➲ Ion: Valence electrons are lost or gained in order to have a full outer shell. This results in a charge. ➲ Metals lose electrons to form cations. ➲ Nonmetals gain electrons to form anions. Intramolecular Bonds ➲ Ionic Bonds: A force of attraction between a cation and an anion (aka a transfer of electrons). ➲ Ex. NaCl Intramolecular Bonds ➲ ➲ Covalent Bonds: neither atom is willing to give up electrons so the electron pairs are shared (i.e. two non-metals). ex. H2 (g) , CH4 (g) Intramolecular Bonds ➲ Double and triple bonds can result if 2 or 3 pairs are shared. ex. O2, N2, CH2CH2 Number of bonds • Non metals always make a certain number of covalent bonds (based on their need for valence electrons). Electronegativity ➲ ➲ ➲ Elements have varying electronegativity (EN) or the affinity (want for) electrons. Non-polar covalent bond: the atoms involved have similar electronegativities, so the electrons are shared equally. (ex. C-H). Electronegativity ➲ ➲ Polar covalent bonds: the atoms involved have different electronegativities so there is uneven sharing of electrons. This results in a separation of charge. (ex. O-H) Electronegativity ➲ the more electronegative atom (often O, N, S) will pull the electron pair towards it more often and gain a partial negative charge. ➲ The electrons spend more time away from the more electropositive atom (often H), so it has a partial positive charge. Polar Covalent Molecules ➲ If the molecule is asymmetrical and has a polar covalent bond, the molecule will also be polar. ➲ ex. H2O, CH3OH Non-polar Covalent Molecules • Non polar molecules occur when a molecule has non polar covalent bonds OR because of the symmetrical arrangement of polar covalent bonds. Intermolecular Bonds ➲ ➲ The partial charges on polar covalent molecules result in attraction between molecules. Ex. Hydrogen bonds: the attractive force between an electronegative atom and an electropositive hydrogen atom that is bonded to either nitrogen, oxygen, or fluorine. Organic Compounds ➲ ➲ ➲ Organic compounds: “chemicals of life”, contain a lot of Carbon ex. C6H12O6 (usually also hydrogen, but not always) Hydrocarbons: only contain C and H, ex. CH4 Inorganic compounds do not contain Carbon ex. HCl Organic Compounds ➲ Carbon atoms attach to each other to form chain and ring structures that are the backbones of the major biological molecules (carbohydrates, lipids, proteins, and nucleic acids). Functional Groups ➲ ➲ Other elements attach to the carbon backbone of organic compounds. These groups are more reactive and give certain chemical properties to the molecule. Functional Groups • ex. -OH, -COH, -CO and -COOH are polar because of the highly electronegative oxygen atom, making compounds that contain them (alcohols and sugars) highly soluble in water. Water ➲ Water is inorganic (no Carbon) but is an important chemical to life because it comprises a large part of living organisms. Water ➲ ➲ ➲ It is polar covalent, which makes it a versatile solvent. Like dissolves like: Other polar molecules/functional groups are hydrophilic and will dissolve, Nonpolar molecules/functional groups are hydrophobic and will not.