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Transcript of Types of What is a chemical bond? zBonds are forces that hold groups of atoms together and make them...
What is a chemical bond?
Bonds are forces that hold groups of atoms together and make them function as a unit
What do bonds tell us?
Responsible for physical properties like mp, bp, hardness, conductivity
Bond Energy- energy required to break a bond
Sodium Chloride
In sol’n it is Na+ and Cl-
Electrons are transferredWhen water evaporates, aggregate to form solid NaCl
Ionic Bonding
Sodium chloride is very stable mp = 800oC
Ionic substances- when an atom that loses e- easily reacts with an atom with a high affinity for e-
Coulomb’s Law
Can be used to calculate the energy of interaction between a pair of ions
E = 2.31 x 10-19Jnm(Q1Q2/r)
Q1 and Q2 = charge of ionsr = distance b/w ion centers
Such as...
Calculate the energy of interaction (kJ/mol) b/w Mg2+ and O2- if the distance b/w them is .205 nm (2.05 A)
Notice!
The answer is negative indicating that the pair is at lower energy
You can also find the repulsion b/w like ions, but the sign will be positive
Bonding b/w like atoms
Let’s look at H atoms2 unfavorable terms (e- e- repulsion and p+ p+ repulsion) and 1 favorable term (e- p+ attraction)
What conditions favor bond formation??
Whatever causes the H atoms to achieve the lowest possible total energy
Bond length = when energy is at a minimum
The Diagram
The energy terms involved are the net Ep that results from the attractions and repulsions among the charged particles and the EK is due to e- motion
The Diagram
At very short distances the energy rises steeply because of the importance of the repulsive forces when the atoms are very close together
Covalent Bonding
The type of bonding encountered in H2 and any other molecules in which electrons are shared by nuclei
The Middle Ground
Polar covalent bond- atoms unequally share electrons
Results in partial positive and partial negative charge
When will this happen?
Electronegativitythe ability of an atom in a molecule to attract shared electrons to itself
Linus Pauling (1901-95)
US scientistNoble Prizes for chem and peace
method for determining electronegativities
Put in order!
Based only on positions, place the following in order of increasing electronegativity
Sr, Cs, Se, O, Ba
Bond Polarity
Use tables of electroneg and calculate for each of the following bonds and then order from most covalent to most ionic