Ch. 6 Bonding Section 4: Metallic Bonding

Bonding of Metals the highest energy level for most metal atoms only contains s electrons. the highest energy level for most metal atoms only contains s electrons. usually have empty p and d blocks usually have empty p and d blocks these vacant overlapping orbitals allow outer electrons to roam freely around the entire outer electron cloud these vacant overlapping orbitals allow outer electrons to roam freely around the entire outer electron cloud the electrons are delocalized – are not with one specific atom the electrons are delocalized – are not with one specific atom

Bonding of Metals these roaming electrons these roaming electrons form a sea of electrons around the metal atoms metal nuclei are packed in a crystal lattice (like ionic compounds) metal nuclei are packed in a crystal lattice (like ionic compounds) metallic bonding – bonding that results from the attraction between metal nuclei and sea of electrons metallic bonding – bonding that results from the attraction between metal nuclei and sea of electrons

Properties of Metals conductive (heat, electricity, sound) conductive (heat, electricity, sound) caused by the freedom of electrons to move around the atoms (electrons can carry the message) caused by the freedom of electrons to move around the atoms (electrons can carry the message) luster (shininess) luster (shininess) contain many orbitals with only small differences in energy contain many orbitals with only small differences in energy remember the photoelectric effect? remember the photoelectric effect? Because of the tons of orbitals at similar energy levels, many different frequencies of light are capable of making metal shine Because of the tons of orbitals at similar energy levels, many different frequencies of light are capable of making metal shine

Properties of Metals malleable and ductile malleable and ductile moveable electrons enable metal nuclei to slide past each other if hit or pulled (like ball bearings) moveable electrons enable metal nuclei to slide past each other if hit or pulled (like ball bearings)

Bond Strength depends on the nuclear charge (how many protons) depends on the nuclear charge (how many protons) depends on the number of electrons in the “sea” depends on the number of electrons in the “sea” More protons &/or electrons = stronger bond More protons &/or electrons = stronger bond Measured using the heat of sublimination – amount of heat required to turn solid, bonded metal atoms into gaseous individual atoms Measured using the heat of sublimination – amount of heat required to turn solid, bonded metal atoms into gaseous individual atoms

Comparison of Bond Types All bonds are considered to be “strong” All bonds are considered to be “strong” metallic bonds are strong and flexible making them useful in the real world metallic bonds are strong and flexible making them useful in the real world ionic bonds connect ALL ions together tightly, so there is no flexiility. Ionic compounds are most useful in solutions (more on that MUCH later) ionic bonds connect ALL ions together tightly, so there is no flexiility. Ionic compounds are most useful in solutions (more on that MUCH later) molecules (covalent bonds) are more easily pulled apart because the attraction btwn molecules (intermolecular force) is weak. The attraction within molecules (intramolecular force) is very strong. molecules (covalent bonds) are more easily pulled apart because the attraction btwn molecules (intermolecular force) is weak. The attraction within molecules (intramolecular force) is very strong.

Comparison of Bond Types Molecular Compounds: Molecular Compounds: low melting and boiling points low melting and boiling points many are gases at room temperature many are gases at room temperature Remember, intermolecular forces of the molecules are weak so they are easily separated

Comparison of Bond Types Ionic Compounds: Ionic Compounds: higher melting and boiling points higher melting and boiling points all are solid at room temperature all are solid at room temperature hard: Because of the strong connecting bonds, it is difficult for one layer of ions to move past another hard: Because of the strong connecting bonds, it is difficult for one layer of ions to move past another brittle: if one layer is moved, the layers come apart completely brittle: if one layer is moved, the layers come apart completely

Comparison of Bond Types Metallic Compounds: Metallic Compounds: high melting and boiling points high melting and boiling points all but Hg are solid at room temperature all but Hg are solid at room temperature hard: Because of the strong attractions btwn nuclei & sea of electrons, metals are very tough hard: Because of the strong attractions btwn nuclei & sea of electrons, metals are very tough flexible: if one layer is moved, the other layers can slide over the sea of electrons and the whole sample can change shape. flexible: if one layer is moved, the other layers can slide over the sea of electrons and the whole sample can change shape.

Comparison of Bond Types Metallic Compounds: Metallic Compounds: great conductors in solid & liquid states because of the mobile electrons. great conductors in solid & liquid states because of the mobile electrons. Ionic Compounds: Ionic Compounds: good conductors in liquid state because ions are free to move and carry charge good conductors in liquid state because ions are free to move and carry charge poor conductor in solid state poor conductor in solid state because ions are fixed in place good conductors when in solution b/c ions can move around in water good conductors when in solution b/c ions can move around in water Molecular compounds: Molecular compounds: poor conductors in any state because there are no ions poor conductors in any state because there are no ions