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What is a chemical bond? zBonds are forces that hold groups of atoms together and make them function as a unit
What do bonds tell us? zResponsible for physical properties like mp, bp, hardness, conductivity zBond Energy- energy required to break a bond
Sodium Chloride zIn sol’n it is Na + and Cl - zElectrons are transferred zWhen water evaporates, aggregate to form solid NaCl
Why?? zThe system can achieve the lowest possible energy by behaving this way!!
Ionic Bonding zSodium chloride is very stablemp = 800 o C zIonic substances- when an atom that loses e - easily reacts with an atom with a high affinity for e -
Ionic Compound zResults when a metal reacts with a nonmetal
Coulomb’s Law zCan be used to calculate the energy of interaction between a pair of ions zE = 2.31 x Jnm(Q 1 Q 2 /r) zQ 1 and Q 2 = charge of ions zr = distance b/w ion centers
Such as... zCalculate the energy of interaction (kJ/mol) b/w Mg 2+ and O 2- if the distance b/w them is.205 nm (2.05 A)
Notice! zThe answer is negative indicating that the pair is at lower energy zYou can also find the repulsion b/w like ions, but the sign will be positive
Bonding b/w like atoms zLet’s look at H atoms z2 unfavorable terms (e - e - repulsion and p + p + repulsion) and 1 favorable term (e - p + attraction)
What conditions favor bond formation?? zWhatever causes the H atoms to achieve the lowest possible total energy zBond length = when energy is at a minimum
The Diagram zThe energy terms involved are the net E p that results from the attractions and repulsions among the charged particles and the E K is due to e - motion
The Diagram zThe zero point of energy is defined with the atoms at infinite separation
The Diagram zAt very short distances the energy rises steeply because of the importance of the repulsive forces when the atoms are very close together
The Diagram zThe bond length is the distance at which the system has minimum energy
Covalent Bonding zThe type of bonding encountered in H 2 and any other molecules in which electrons are shared by nuclei
Two extremes zIonic bonding transfers electrons zCovalent bonding atoms share electrons equally
The Middle Ground zPolar covalent bond- atoms unequally share electrons zResults in partial positive and partial negative charge
When will this happen? zElectronegativity zthe ability of an atom in a molecule to attract shared electrons to itself
Linus Pauling ( ) zUS scientist zNoble Prizes for chem and peace zmethod for determining electronegativities
Electroneg Values zHave been determined for almost all elements zRange is 4.0 for F to 0.7 for Cs
Periodic Trend? You Bet! zIncreases going left to right across a period zIncreases going up a group
Put in order! zBased only on positions, place the following in order of increasing electronegativity zSr, Cs, Se, O, Ba
Were you correct? zLeast Most z Cs
Bond type relationship zElectroneg diff zZero zIntermediate zLarge z Bond Type z Covalent z Polar Coval z Ionic
Bond Polarity zUse tables of electroneg and calculate for each of the following bonds and then order from most covalent to most ionic
Try these... zNa-Cl zLi-H zH-C zH-F zRb-O
The answers... zNa-Cl2.1 zLi-H1.1 zH-C0.4 zH-F1.9 zRb-O2.7
The Ranking... zCovalentIonic zH-C, Li-H, H-F, Na-Cl, Rb-O
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