Week 1 Textbook Reading

Question 1

what does each orbital describe

Answer 1

Each orbital describes a different distribution of the probabilities of finding an electron in the space about the nucleus

Question 2

Why is there a greater likelihood of finding a 2s electron at larger distances from the nucleus than a 1s electron?

Answer 2

Both the 1s and 2s atomic orbitals are spherical, but the 2s orbital is larger than the 1s orbital

Question 3

nodal plane

Answer 3

The region in space where a 2p orbital changes phase is a nodal plane: the place where the value of the orbital is exactly zero and as a result, the probability of finding the electron in that plane is exactly zero

Question 4

degenerate atomic orbitals

Answer 4

orbitals that have the same energy

Question 5

valence orbitals vs electrons

Answer 5

Less stable orbitals known as valence orbitals
Electrons that occupy them called valence electrons

Question 6

electrostatic attraction

Answer 6

The force holding atoms together in all molecules is electrostatic attraction
The bonds holding atoms together are the result of the attraction b/w positive and negative charges
2 types of bonds that hold atoms together: ionic bonds and covalent bonds
Resulting compounds from an ionic bond → salt

Question 7

formal charge in lewis structure

Answer 7

Some atoms in lewis structures carry a formal charge

(# valence electrons) - (# bonds) - (# non-bonded electrons)

Can be some exceptions to the octet rule where some atoms have an incomplete octet
These structures are often unstable and contribute to reactivity

Question 8

what do covalent bonds result from

Answer 8

Covalent bonds result from the overlap of atomic orbitals between atoms to form new orbitals of electrons surrounding both nuclei
Atomic orbitals may overlap and share electrons in 2 ways: either head-on or side-by-side
The mode of orbital overlap is controlled by the type of atomic orbitals involved in forming the bond

Question 9

sigma bonds

Answer 9

Orbitals with s character overlap head-on to form sigma bonds
This is when the overlap takes place along the axis connecting the 2 nuclei
Since the orbitals point directly at each other, there is a high probability that the bonding electrons will be found in the region b/w the nuclei

Question 10

what makes the sigma bond strong

Answer 10

When the orbitals overlap, they do so in phase (the phases of the overlapping orbital lobes match)
Result is a direct sharing of the 2 valence electrons b/w the 2 nuclei, and this makes the sigma bond strong

Question 11

pi bond

Answer 11

Side by side overlap forms a pi bond → the orbitals are oriented perpendicular to the axis through the nuclei
This bond is formed by mixing p atomic orbitals (in more complex metals, other orbital types may be involved)
The p orbitals must overlap in-phase in order to produce a bonding pi orbital
The result is that the greatest likelihood of finding the shared electrons of a pi bond lies equally on each side of this axis
This equal probability above and beneath the line together constitutes one pi bond

Question 12

difference b/w pi bond and sigma bond in terms of probability

Answer 12

In contrast to the sigma bond, there is zero probability of finding the bonding electron pair along the axis through the nuclei (a node lies along the plane b/w the lobes having opposite phases)

Question 13

Why is a pi bond a weaker covalent bond than a sigma bond?

Answer 13

Because the p orbitals that contribute to the pi bond are not pointing directly at each other, the overlap achieved in a pi bond is generally less than that of a sigma bond and results in a poorer sharing of electrons

Question 14

electronegativity

Answer 14

Electronegativity: the ability of an atom to pull electrons toward itself from the surrounding atoms to which it is bonded
The greater the electronegativity, the greater the ability of the atom to draw electrons from its neighbours

Question 15

bond dipole

Answer 15

a dipole created across a chemical bond. It is the result of differences in electronegativity b/w the nuclei involved
E.g. the oxygen pulls more strongly in CH3OH since it’s more electronegative, creating a bond dipole

Question 16

Polar covalent bond:

Answer 16

a bond that has a substantial dipole due to the unequal sharing of electrons

Question 17

When covalently bonded, carbon atoms have 3 possible structural geometries/shapes →

Answer 17

tetrahedral, trigonal planar and linear

Question 18

Tetrahedral:

Answer 18

pyramid arrangement around the central carbon atom and has bond angles of 109 degrees between the atoms

Question 19

Trigonal planar:

Answer 19

the carbon is surrounded by 3 atoms (2 H and 1 O), which all lie in the same plane as carbon, bond angle 120 degrees

Question 20

Linear: x

Answer 20

the 2 atoms bonded to each carbon are 180 degrees from each other, in a straight line

Question 21

vsepr theory

Answer 21

VSEPR: the groups of valence electrons around each atom are arrayed as far away from each other as possible to minimize electron-electron repulsions b/w them

Question 22

what can repulsions b/w groups of valence electrons around an atom dictate…

Answer 22

its geometry

Question 23

dark vs hashed bonds

Answer 23

Bonds that point towards the reader, out of the page, are shown using dark wedges

Bonds that point away from the reader, into the page, are drawn using hashed

The hashed bond(shows 3D orientation) and wedged bond are always drawn next to each other and in the wider space around the carbon atom
-Dashed bond (partial bond)

Question 24

valence bond model

Answer 24

Valence bond model extends the idea that a covalent bond involves the sharing of 2 spin-paired electrons through the overlap of atomic orbitals b/w atoms
-Specifically each atom contributes 1 orbital
and 1 electron to form the bond

Question 25

localized bonds

Answer 25

Localized bonds: involves the sharing of 2 electrons by means of the overlap of 2 atomic orbitals on 2 adjacent atoms, confined to the region b/w the 2 atoms The better the orbital overlap, the better the sharing of electrons and the stronger the bond

Question 26

what does each line in a lewis structure represent?

Answer 26

Each line in a lewis structure represents a localized bond in which the probability of finding the electron pair is confined to the regions b/w the atoms

Question 27

Hybrid orbitals:

Answer 27

atomic orbitals, formed by a suitable mixing of the 2s and 2p orbitals on a single atom, that have geometries corresponding to the bonding geometries of organic molecules

Question 28

orbital hybridization

Answer 28

a math combination of atomic orbitals on a single atom that makes new orbital geometries that correspond to the observed bonding geometry New atomic orbitals created called hybrid orbitals (sp^3, sp^2, sp)

Question 29

Tetrahedral geometries require sp^3 hybrid orbitals

Answer 29

Requirement for a tetrahedral distribution of bonds is resolved by the generation of hybrid orbitals 4 tetrahedrally distributed atomic orbitals of carbon can be generated by hybridizing one 2s orbital and three 2p orbitals on the same atom Results in a set of 4 hybrid orbitals and since each hybrid is composed of one part 2s and three parts 2p, each of the 4 hybrid orbitals are called sp^3 orbitals

Question 30

Trigonal planar geometries require sp^2 hybrid orbitals

Answer 30

This trigonal arrangement of orbitals is attained by sp^2 hybridization of the valence orbitals of the carbon atom, in which the 2s orbital and 2 of the 2p orbitals of the atom are mixed Because each hybrid consists of one part 2s and two parts 2p, each of these 3 hybrid orbitals are designated as sp^2 orbitals These orbitals overlap in a side-by-side manner to form a pi bond that projects above and below the plane of the molecule

Question 31

Linear geometries require sp hybrid orbitals

Answer 31

The linear arrangement of 2 electron groups around an atom requires a linear arrangement of 2 valence orbitals at that atom This can be achieved only by hybridizing the atoms 2s orbital with one of its 2p orbitals The resulting sp hybrid orbitals of each carbon are then directed for a head-on overlap to form a sigma bond with each other

Question 32

sigma bonds of all geometries require...

Answer 32

hybrid orbitals(either sp^3, sp^2, or sp hybrids) so they point in the direction of the surrounding atoms

Question 33

how do pi bonds arise

Answer 33

Pi bonds arise from the overlap between unhybridized p orbitals Hybrid orbitals are not involved in pi bonding

Question 34

The sum of the superscripts in hybrid orbital designations is equal to...

Answer 34

the number of groups of electrons that surround the hybridized atom E.g. sp^2 is “1 s orbital” + “2 p orbitals” = 3 groups of electrons→ trigonal planar