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Attractions Between Particles

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Information about Attractions Between Particles
Education

Published on December 10, 2008

Author: lallen

Source: slideshare.net

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Attractions between Particles Chapter 6, Holt Modern Chemistry Lisa Allen

Chemical bond types Covalent bonds: Shared valence electrons Ionic bonds: Attractions between oppositely charged particles Metallic bonds: Bonds formed when atoms are held together by a shared “sea of electrons”

Covalent bonds: Shared valence electrons

Ionic bonds: Attractions between oppositely charged particles

Metallic bonds: Bonds formed when atoms are held together by a shared “sea of electrons”

Useful sites http://www.visionlearning.com/library/module_viewer.php?mid=55 http://www.chemtutor.com/compoun.htm

http://www.visionlearning.com/library/module_viewer.php?mid=55

http://www.chemtutor.com/compoun.htm

Covalent bonds Occurs between atoms of similar electronegativity (  <0.3) Molecules are formed by covalent bonds Equal sharing of electrons makes for strong bonds. Strong bonds are short bonds. Bond length and bond energy are inversely related

Occurs between atoms of similar electronegativity (  <0.3)

Molecules are formed by covalent bonds

Equal sharing of electrons makes for strong bonds.

Strong bonds are short bonds. Bond length and bond energy are inversely related

Covalent molecules

Covalent crystals? Diamonds are strong because they are covalently bonded, but they form a crystal. The carbon atoms in a diamond are bonded to 4 other carbon atoms in a “covalent network crystal” See page 340 for more explanation of this. Don’t let this confuse you! Most covalent bonds form simple molecules, like sugar; not covalent network crystals like diamonds!

Diamonds are strong because they are covalently bonded, but they form a crystal.

The carbon atoms in a diamond are bonded to 4 other carbon atoms in a “covalent network crystal”

See page 340 for more explanation of this.

Don’t let this confuse you! Most covalent bonds form simple molecules, like sugar; not covalent network crystals like diamonds!

Ionic bonds Occurs between atoms of very different electronegativity (  >1.7) Ionic compounds are formed from these bonds. There are MANY atoms in the compound. Unequal sharing of electrons makes for less strong bonds.

Occurs between atoms of very different electronegativity (  >1.7)

Ionic compounds are formed from these bonds. There are MANY atoms in the compound.

Unequal sharing of electrons makes for less strong bonds.

Ionic humor?

Vocabulary associated with ionic bonds Crystal lattice: Formula unit: Lattice energy: Dissociate: Conductivity:

Crystal lattice:

Formula unit:

Lattice energy:

Dissociate:

Conductivity:

Vocabulary associated with ionic bonds Crystal lattice: Structure of ionic compounds Formula unit: smallest ratio of ions that forms an ionic bonded compound Lattice energy: energy released when one mole of gaseous ions forms a mole of ionic crystal lattice Dissociate: breaking of bonds Conductivity: ability to transmit electrical charge

Crystal lattice: Structure of ionic compounds

Formula unit: smallest ratio of ions that forms an ionic bonded compound

Lattice energy: energy released when one mole of gaseous ions forms a mole of ionic crystal lattice

Dissociate: breaking of bonds

Conductivity: ability to transmit electrical charge

Ionic Solid: http://web.jjay.cuny.edu/~acarpi/NSC/salt.htm

What about  between .3 and 1.7? Polar covalent bonds Uneven sharing results in charged ends of molecules Water is an example of a polar covalent molecule. The charged ends of the molecule make water sticky, give it a high boiling point, and are the reason snowflakes are shaped the way they are

Polar covalent bonds

Uneven sharing results in charged ends of molecules

Water is an example of a polar covalent molecule. The charged ends of the molecule make water sticky, give it a high boiling point, and are the reason snowflakes are shaped the way they are

FYI: clarification! (not on the test!) Look at the electronegativity difference between boron and fluorine to predict the bond type in BF 3 . Predictions based on this “rule” say this should be an ionic compound, but in the lab, it has been determined that this bond is actually very polar covalent. The diagram on the left of page 176 is instructive. This suggests the  is actually not a fixed rule with a LINE to separate that .3 and 1.7, but rather a “shades of gray” (or blue and green!) situation. Conclusion? This is a guideline, but the lab is the only way to definitively establish bond type.

Look at the electronegativity difference between boron and fluorine to predict the bond type in BF 3 .

Predictions based on this “rule” say this should be an ionic compound, but in the lab, it has been determined that this bond is actually very polar covalent.

The diagram on the left of page 176 is instructive. This suggests the  is actually not a fixed rule with a LINE to separate that .3 and 1.7, but rather a “shades of gray” (or blue and green!) situation.

Conclusion? This is a guideline, but the lab is the only way to definitively establish bond type.

Intermolecular attractions between particles Dipole-Dipole forces: occur between polar molecules Hydrogen bonding: a type of dipole-dipole force in which a hydrogen atom in a polar bond is attracted to the electronegative end of another polar molecule London dispersion forces: instantaneous tiny dipoles created in collisions between non-polar molecules or noble gas atoms

Dipole-Dipole forces: occur between polar molecules

Hydrogen bonding: a type of dipole-dipole force in which a hydrogen atom in a polar bond is attracted to the electronegative end of another polar molecule

London dispersion forces: instantaneous tiny dipoles created in collisions between non-polar molecules or noble gas atoms

Comparing ionic and covalent bonds Ionic bonds dissociate in solution Ionic substances conduct when in solution or molten Covalent bonds are stronger than ionic bonds Covalent substances melt and boil at LOWER temperatures than ionic. WHY?

Ionic bonds dissociate in solution

Ionic substances conduct when in solution or molten

Covalent bonds are stronger than ionic bonds

Covalent substances melt and boil at LOWER temperatures than ionic. WHY?

Polyatomic ions A group of covalently bonded atoms working together as a single ion Example: the hydroxide ion, OH - The oxygen and hydrogen are covalently bonded, but together have 10 electrons and 9 protons, for a net charge of -1. They stick together, bonding as a single ion in compounds like KOH, an ionic compound. KOH dissociates into K + and OH - in solution. See chart on window wall for more polyatomic ions.

A group of covalently bonded atoms working together as a single ion

Example: the hydroxide ion, OH -

The oxygen and hydrogen are covalently bonded, but together have 10 electrons and 9 protons, for a net charge of -1. They stick together, bonding as a single ion in compounds like KOH, an ionic compound. KOH dissociates into K + and OH - in solution.

See chart on window wall for more polyatomic ions.

Metallic Bond

Metallic bonds Vocabulary: Sea of electrons How do the properties of metals result from the metallic bond? We usually don’t contrast metallic bonds with ionic and covalent; they could be generally considered a subgroup of covalent bonds due to their  , but they don’t form molecules. They’re just different. Be aware of them, but the ionic/covalent differences are of greater importance.

Vocabulary: Sea of electrons

How do the properties of metals result from the metallic bond?

We usually don’t contrast metallic bonds with ionic and covalent; they could be generally considered a subgroup of covalent bonds due to their  , but they don’t form molecules. They’re just different. Be aware of them, but the ionic/covalent differences are of greater importance.

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