Electronic Structure in Chemistry

Question 1

What does the dual nature of matter theory state about electrons? What does this reveal for atoms?

Answer 1

That they exist as waves, as well as particles.

Properties are derived from their wave function and energy.

The wave functions and their geometric representations are referred to as the atomic orbitals.

Question 2

What does the square of the wave function associated with a given state of energy tell you?

Answer 2

The probability to find the electron, which is in that same state of energy, at any given point in space at any given time.

Question 3

What are the four quantum numbers?

Answer 3

The labels of the possible states that an electron can occupy in an atomic orbital.

• n (principal quantum number)
• / (angular momentum quantum number)
• mi (the magnetic quantum number)
• ms (the spin quantum number)

Question 4

What is the principal quantum number? (n)

Answer 4

An integer, which represents the energy of the state

Eg. K (n=1), L (n=2), M (n=3) etc.

Higher value = higher energy

Question 5

What is the angular momentum quantum number? (/)

Answer 5

It defines the shape of the atomic orbital

/ takes all possible integer values between 0 and n-1

Eg. for a state with n=0, there is only one possible shape of the orbital, it is defined by /=0. For n=3, there are three possible orbital shapes defined by /, /=0, 1 and 2

Question 6

List the atomic orbital shapes defined by /

Answer 6

/=0 s (spherical)

/=1 p (dumbbell)

/=2 d

/=3 f

for / larger than 3, the corresponding series correlates to alphabetical order

Question 7

What is the magnetic quantum number?

Answer 7

It defines the orientation of the orbital of a given shape (defined by /)

mi can take the value between -/ and +l, for example, if /=1 then mi can = -1, 0, 1

It denotes the possible orientations along the x, y and z axis of a coordinate system. /=1 (p) orbitals can fall under npx, npy and npz states. These are the 3D volumes where there is 90% chance to find an electron.

Question 8

What is the spin quantum number (ms)?

Answer 8

Denotes a value +1/2 or -1/2 for an electron.

Question 9

What is Pauli’s exclusion principle and Hund’s rule?

What do these two rules ensure?

Answer 9

PEP: If two electrons around the same atom have the same n, / and mi quantum numbers, than their ms (spin number) have to be of opposite signs.

HR: When filling orbitals, they are filled in sequence. Each orbital in a subshell is filled with one electron first until all orbitals are filled, than they are paired according to Pauli’s exclusion principle.

These rules ensure that orbitals are filled to produce an atom in its lowest overall state of energy (the ground state)

Question 10

For a given n (given shell), how many electrons are allowed?

Answer 10

2n^2

Question 11

For a given /, how many electrons are allowed?

Answer 11

4(/) + 2

Question 12

For a given mi (orbital orientation), how many electrons are allowed?

Answer 12

2

Question 13

When writing the electronic configuration of a polyelectronic atom, how are orbitals filled? List 22 of the first lowest energy state orbitals that can be filled.

What is the common notation for representing the orbitals of an element?

Answer 13

In order of increasing energy. (see page CHM-17)

Eg. 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 5g, 6f, 6g, 6h

Common notation includes a superscript 1 or 2, to denote how many electrons are in an orbital (eg. 1s^2, 2s^2 for Be)

Question 14

What happens to electrons in the ground state when an external disturbance inputs energy into the atom?

Answer 14

They go into an excited state configuration. Which includes promotion to higher unoccupied (or partially occupied) orbitals

Question 15

How can you use the periodic table to discern information about the valence electrons of an element? (4)

Answer 15

1. The row (or period) number gives the ‘n’ of the valence electrons of any given element of the period
2. The first two columns (or groups) and helium (He) are referred to as ‘s’ block. The valence electrons of elements in these groups are ‘s’ electrons.
3. Groups 3A to 8A (13th to 18th) columns are the ‘p’ group. Elements belonging to these groups have their ground state electronic configurations ending with ‘p’ electrons.
4. Elements in groups 3B to 2B (columns 3 to 12) are called transition elements. Their electronic configurations end with (n-1)d^x, where n is the period number and x=1 for column 3, x=2 for column 4 and x=3 for column 5 etc. (this can vary, however)

Question 16

Element Sc is in the fourth period, in the IIIB group. What is its electronic configuration?

Answer 16

4s^2, 3d^1

The 3d^1 is a little special, because it is a transition element (calculated by (n-1)d^x, where n is period and x is 1 for column 3, 2 for column 4 etc.).

Question 17

Describe ionization energy, and how it has a periodic trend.

Answer 17

It is the energy required to remove one of the outermost electrons from an atom in its gaseous state (also known as ionization potential)

The IP increases from bottom left to top right on the periodic table

Question 18

Describe second ionization energy (ie 2nd IP) and its trend on the periodic table.

Answer 18

The trend for first IP can be used (increasing from bottom left to top right), if the relationship between 1st and 2nd ionization processes of an atom are taken into consideration.

Question 19

Describe electron affinity (EA) and its trend on the periodic table.

Answer 19

Electron affinity (EA) is the energy change that accompanies the following process for an atom of element X:

X(gas) + 1 e- = X-(gas)

This property measures the ability of an atom to accept an electron. Halogens have a very negative EA, because they have a great tendency to form negative ions. Alkaline earth metals have very large EAs, and tend to form cations.

EAs become more negative from left to right on the periodic table.

Question 20

Describe the trend for atomic radius in the periodic table.

Answer 20

Increases from top right to bottom left

Largest is on bottom left of table

Question 21

Describe electronegativity and its trend on the periodic table

Answer 21

EN is a parameter that measures the ability of an atom, when engaged in a bond, to pull or repel the bond electrons. It is determined from the first ionization potential (1st IP) and electron affinity of a given atom.

EN increases from bottom left to top right on the periodic table (same as first IP)

Question 22

When do elements with similar electronegativity form stronger bonds than those with differing electronegativities?

Answer 22

The bond is shared more equally and thus more stability when EN is more equal between elements

Question 23

Why does nickel (II) give off a green colour?

Answer 23

Nickel (II) ion has unfilled d orbitals and the electrons in the lower energy d orbitals absorb visible light to move to the higher energy d orbitals.

Question 24

What are precipitation reaction of mixing aqueous solutions of cations and anions called? Why?

Answer 24

Metathesis reactions

The precipitation reactions are the result of mixing aqueous solutions of cations and anions. The ionic compounds switch the ions with which they are paired. These are reactions of the type AB + CD = AD + CB, where one of the products is a precipitate. This type of reactions is a metathesis reaction.

Question 25

What are two requirements to form hydrogen bonds?

Answer 25

1. ONe of the interacting molecules must have a hydrogen atom attached to an electronegative atom.
2. The other molecule must have its own electronegative atom, with an available lone pair of electrons.

the presence of hydrogen atoms in a molecule is not sufficient for it to participate in hydrogen bonding.

Question 26

What is the geometrical shape of SO2?

Answer 26

It has a dipole moment, so instead of being linear, it is bent.