Lewis Structures, VSEPR Shapes, & Polarity Test Study Guide

what are sigma bonds?

this is the strongest type of covalent bond that is created by the head-on overlap of atomic orbitals between the two atoms involved in the bond. any single covalent bond between atoms is a sigma bond. in a double bond, one of the two bonds is a sigma bond. in a triple bond, one of the three bonds is a sigma bond.

what are pi bonds?

this is the weaker type of covalent bond that is created by the parallel overlap of atomic orbitals between the two atoms involved in the bond. pi bonds only exist in double and triple covalent bonds. in a double bond, one of the two bonds is/are a pi bond. in a triple bond, two of the three bonds is/are a pi bond.

can you have three pi bonds between two atoms?

no, because a triple bond is the maximum covalent bond type that has 1 sigma bond so it can only have 2 pi bonds.

why are pi bonds important in molecules?

sigma bonds allow the two atoms to rotate/spin in relation to one another. if pi bond(s) exist, they prevent this rotation and stabilize locations of the atoms within the molecule. a good way to remember it is that “S”igma bonds can spin while “P”i bonds prevent spinning.

what is bond order?

the number of bonding pairs of electrons between the atoms. it is used as a measure of the length/strength of a bond. if the covalent bond has more electron pairs shared between the atoms, the bond will be shorter. if the covalent bond has less electron pairs shared between the atoms the bond will be longer.

bond order length (longest —> shortest)

single, double, triple

what are resonance structures?

if a central atom has multiple of the same element covalently bonded but some are single bonded and some are double bonded, the electrons from the pi bond(s) will resonate between the atoms of the same type. this means the pi bonds will move back and forth between bonding locations. resonance can only occur between atoms of the same element bonded to the central atoms. when resonance conditions exist, you need to draw all of the possible resonance structures.

linear (no lone pairs)

BP: 2 / LP: 0 / 180 symmetrical = non-polar

triangular planar

BP: 3 / LP: 0 / 120 symmetrical = non-polar

bent (one lone pair)

BP: 2 / LP: 1 / less 120 asymmetrical = polar

tetrahedral

BP: 4 / LP: 0 / 109.5 symmetrical = non-polar

trigonal pyramidal

BP: 3 / LP: 1 / less 109.5 asymmetrical = non-polar

bent (two lone pairs)

BP: 2 / LP: 2 / less 109.5 asymmetrical = polar

trigonal bipyramidal

BP: 5 / LP: 0 / 90 (between atom up and horizontal) and 120 (between the two horizontal on one side) symmetrical = non-polar

unsymmetrical tetrahedral (see saw)

BP: 4 / LP: 1 / 90 (between atom up and horizontal) and 120 (between the two horizontal on one side) asymmetrical = polar

t-shaped

BP: 3 / LP: 1 / 90 (corners of the T) and 180 (along the BP when going around the LPs) asymmetrical = polar

linear (three lone pair)

BP: 2 / LP: 3 / 180 symmetrical = non-polar

octahedral

BP: 6 / LP: 0 / 90 symmetrical = non-polar

square pyramidal

BP: 5 / LP: 1 / 90 asymmetrical = polar

square planar

BP: 4 / LP: 2 / 90 symmetrical = non-polar

what is a polar covalent bond?

the unequal sharing of electrons as a result of the differences in electronegativities between the atoms (the atom with the larger electronegativity has the electron for more time)

what is a polar molecule?

a molecule that has a net dipole as a result of opposing charges (slightly positive or negative) from polar bonds, arranged asymmetrically

what is a non-polar molecule?

a molecule that has no net dipole as a result of covalent bonds or polar covalent bonds, that oppose each other equally, canceling out the net dipole, arranged symmetrically

how can you tell if a two atom molecule is polar or non-polar?

if a diatomic molecule has two atoms of the same element, it is non-polar. if both atoms are different, it is likely polar

what is a solution

a homogeneous mixture with two (or more) substances mixed evenly with only one phase visible

what is the difference between the two components of a solution?

solvent: major component of a solution (can only be one)

solute: lesser component(s) of a solution (can be more than one)

when is the one situation you cannot tell the solute from the solvent?

when there is an equal amount of two components 50/50

what do we call it when two substances can form a solution in any possible ratio (you can mix as much of either substance together)?

“miscible” = can mix in any proportion of solute+solvent (ex. alcohol into water)

what is solubility?

it measures how much solute can dissolve into a solvent to form a solution

if we say one substance is soluble in another substance, what are we actually saying?

it dissolves easily to a great extent in the solvent

if we say one substance is insoluble in another substance, what are we actually saying?

it does not dissolve well or to any great extent in the solution

is any substance completely insoluble in another substance?

no, everything dissolves at least a little bit (to some limited extent)

why are polar substances able to dissolve (soluble) in other polar substances?

polar substances have slightly positive and negative ends that can attract the opposite ends on another molecule

why are non-polar substances not able to dissolve (insoluble) in polar substances?

they do not have slightly positive and negative ends. the non-polar regions attract one another

what will you observe if you try to mix a polar liquid with a non-polar liquid in a beaker?

the two substances will separate into two layers with the less dense layer on top

Beryllium

When Be is the central atom in a molecule, it can be satisfied with 4 electrons.

Family 3A

When an atom from the Boron family is the central atom in a molecule, it can be satisfied with 6 electrons.

Family 4A

When an atom from the Carbon family (not including Carbon) is the central atom in a molecule, it can be satisfied with 6 electrons.

Family 5A

When an atom from the Nitrogen family (not including Nitrogen) is the central atom in a molecule, it can be satisfied with 10 electrons.

Family 6A

When an atom from the Oxygen family (not including Oxygen) is the central atom in a molecule, it can be satisfied with 12 electrons.

Halogen and Noble Gas Atoms

Can have extra lone pairs of electrons when they are the central atom