Atomic Bonding and MoleculesChapter 15Bonding of atoms makes molecules• The Formation of Ions and Ionic Bonds• Types of bonds– Metallic Bonds– Covalent Bonds– Polar Covalent Bonds• Molecular Polarity and Molecular AttractionsCauses of bonding• Atoms bond together through their electrons• Electrons behave as though they are contained within a series of seven concentric shells• Outer shell electrons interact with electrons of other atoms• These are the VALENCE electronsElectron Shells• Maximum number of electrons in each shell is shown• Inner shell fills up before next shell begins to get electrons• Full shells are most stableFull electron shells• Outer electron shells of noble gases are fullIn Class Activity 1• Draw the electron shells for the sodium atom around the chemical symbol for sodium• What element has the electron structure that sodium would have if it lost one electron?Sodium Ion Formation• Ion: An atom that has lost or gained one or more electronsPeriodic tableElectrons shells in periodic table• First three periodsElectron Dot Structure• A notation showing only the valence electrons surrounding the atomic symbolElectron dot structure patternIn Class Activity 2• How are electron shell diagrams different from electron dot structure diagrams?• Do they both tell you about the valence electrons? • Which is easier to draw?In Class Activity 3• Draw the electron dot structure for sodium and chlorine atoms• What electron change do you imagine may occur so these elements bond?Molecular Ions• Typically formed by the loss or gain of a hydrogen ion, H+HOHH+Hydronium ion, H3O+H+Water Hydrogen ionIon• An atom, molecule, or compound with a different number of protons and electrons• More protons: positive CAT ION–THE t looks like a plus sign…• More electrons: negative AN ION– Negative has an N in the prefix• Both are all one word: anion, cationIon formation• Lose electrons– more protons than electrons– positive charge• Gain electrons– More electrons than protons– Negative charge• More than one can be lost or gained• Determine by position in periodic tableElectron dot structure patternTypical ions formedIn Class Activity 4• Draw the electron dot structure for a magnesium atom in area to right →• What is the charge of an ion that is formed from a magnesium atom?• Why does it have this sign and amount of charge?Ionic Bonds• Electrical force of attraction between oppositely charged ionsIonic Bond Ratios• Compounds form in ratios to neutralize chargesQuestion For Thought• Is the change of sodium and chlorine atoms to the ionic compound sodium chloride a physical or a chemical change?In Class Activity 5• Write the chemical formula for a compound made of magnesium ions, Mg2+, and oxygen ions, O2–• Write the chemical formula for a compound made of aluminum ions, Al3+, and oxygen ions, O2–• Write the chemical formula of the ionic compound calcium fluorideGroups of atoms forming ions• Polyatomic ions• Bonds within group are covalentMetallic Bonds• Nucleus of metal atoms only weakly hold outer electrons• Weak attraction allows the electrons to move from one atom to another quite freelyMetallic PropertiesMobility of electrons results in many properties of metals• Conductive—electrons move freely• Shiny—electrons vibrate and reflect light• Malleable—can move with respect to one another without breaking because electrons in constant motion• Alloys—electrons shared between unlike types of metal atomsMetallic Alloys• An alloy is a mixture of metallic elements.Metal Ores• Few metals naturally occur as elements– Gold, copper, mercury• Most occur as oxides and sulfides– Ionic compounds– Concentrations of these are ORECovalent Bonds• Atoms are held together by their mutual attraction for shared electrons• There are two electrons within a single covalent bondCovalent Bond Diagrams• The covalent bond is represented using a straight lineF — FF FCovalent Water• The number of covalent bonds an atom can form equals its number of unpaired valence electronsCovalent Ammonia• The number of covalent bonds an atom can form equals its number of unpaired valence electronsCovalent Methane• The number of covalent bonds an atom can form equals its number of unpaired valence electronsMultiple covalent bonds• are possible if atom has more than one unpaired valence electronNonpolar Covalent Bonds• Electrons are shared evenly when the two atoms are the same elementPolar Covalent Bonds• Shared unevenly when the bonded atoms are different elementsPolar covalent bonds• Closer together on the periodic table, less polar bond• Further apart on the periodic table, more polar bond• Molecules are called ‘dipoles’• Ionic bonds are extremely polar—but not covalentIn Class Activity 6• Rank these compounds in order from least polarity (1) to greatest polarity (4) by number below each compoundPF, SF, GaF, GeFMolecular PolarityMolecular Attractions• Electrical attractions between molecules that does not result in bonding–Ions–Polar molecules– Non-polar moleculesIon-dipole attraction• Water and salt– Ions of NaCl attract dipole of waterDipole-dipole attraction• Water and … water– Dipoles of water attract one anotherDipole-Induced dipole attractionsSome non-polar molecules can be distorted into dipoles by polar molecules--Oxygen and waterInduced dipole-induced dipole attractionsMolecules can develop induced dipoles especially if they are largeTeflon is nonstick• Because the fluorine atoms are non-polar and don’t readily become induced
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