ochem 1 Flashcards
What is stronger a sigma bond or a pi bond? Why?
sigma is stronger. allow for electron density to be concentrated to a much larger degree between 2 nuclei. pi bond weaker because the bond is in a higher energy state
the first bond formed between two elements is a __ bond
sigma
As the radius of either atom increase, the p orbitals are ___ ___, resulting in less __. leading to a ___ pi bond
spread apart, overlap, weaker.
are sigma bonds or pi bonds more reactive?
pi bonds
What is hybridization?
Atoms, when bonded, hybridize (i.e., mix) their higher and lower energy valence electron orbitals to form “hybrid orbitals” with intermediate energy
How to determine hybridization
count number of electron densities and minus 1
What is the percent of s character of the hybrid oxygen orbital in water?
sp3, 25% s character
What is the Valence Shell Electron Pair Repulsion Theory?
The theory that predicts which shape molecules will take
due to the repulsion of lone pairs of electrons
name the shapes and bond angles of sp, sp2, sp3, sp3d, sp3d2 orbitals
sp= Linear [180 ̊]
sp2= Trigonal Planar or Bent [120 ̊]
sp3 = Tetrahedral, Trigonal Pyramidal, or Bent [109.5 ̊]
sp3d=Trigonal Bipyramidal, Seesaw, T-Shaped, or Linear [90 ̊/120 ̊or180 ̊]
sp3d2= Octahedral, Square Pyramidal, or SquarePlanar [90 ̊]
order the types of bonds (single, double, triple) in decreasing bond length
single, double, triple
Rank the bonds (single, double, triple) according to increasing stability
single, double, triple
Rank the bonds (single, double, triple) according to increasing reactivity.
single, triple, double
Rank the bonds (single, double, triple) according to increasing bond strength.
single, double, triple
Describe the forces responsible for the strength of a bond. What is the relationship between potential energy and bond length?
A chemical bond is a balance of electrostatic forces. We know that species with opposite charges (i.e., nuclei and electrons) will be attracted to each other with a force given by Coulomb’s Law: F = K(qq/r2). However, remember that there are also repulsive forces between the two nuclei and between electrons. The bond is formed at a sort of “sweet spot” where potential energy is lowest. Increasing bond length or decreasing it would raise the energy of the bond and therefore weaken it.
Which atom is the most electronegative?
fluorine
Which atom is the least electronegative?
francium
How to calculate dipole moment?
u= sigma(d)
sigma = charge d = distance between charges
molecules with __ or more dipole moments can have NO __ __ when their geometric orientation causes the dipole moments to __ each other out
2, net dipole, cancel
energy is always __ when a bond is formed, and ___ when a bond is broken
released, required
The less stable the bond, the ___ the heat of combustion
greater
the more stable the bond, the ___ the heat of combustion
lower
What is a coordinate covalent bond?
bond which both electrons shared in the bond are donated by one atom.
What is the octet rule?
atoms of low atomic number (<20) tend to gain or lose electrons to obtain exactly 8 electrons in their valence shell
exceptions to octet rule
1) Hydrogen and Helium: Stable with only two electrons in their valence shells (e.g., H2)
2) Boron and Beryllium: Stable with only six electrons in their valence shells (e.g., BF3)
3) Atoms from the third period or higher can accept more than eight electrons. Common MCAT examples include: PCl5, SF6, PO43- and SO42-.