3: Atomic orbitals and the periodic table

Question 1

what is the relationship between the speed of light (c), frequency (ν), and wavelength (λ)

Answer 1

c = v x λ

Question 2

What is a spectral line?

Answer 2

absorption or emission of a particular wavelength; the image formed by the spectrometer is one of a set of stripes, separated horizontally by their frequency

Question 3

What is Planck’s constant

Answer 3

h=6.626E−34 J s

Question 4

What is the principal quantum number of ground state?

Answer 4

n=1

Question 5

What is relationship between the difference in energy, Planck’s constant, and frequency

Answer 5

ΔE=hν

Question 6

Different wavelengths are emitted as the electron falls from a higher to a lower energy level. The lines are grouped into series by …

Answer 6

their common lower energy level

Question 7

What are the n=1 and n=2 series in Hydrogen called?

Answer 7

n=1 : Lyman series
n=2 : Balmer series

Question 8

What is the Rydberg formula used for?

Answer 8

To calculate the wavelength of light emitted by these transitions in hydrogen

Question 9

Why is the emission spectrum of Na more complex than that of H?

Answer 9

Due to the presence of subshells

Question 10

What is the Aufbau principle?

Answer 10

Also called the building-up principle. This states that the electrons fill atomic orbitals in order of increasing energy.

Question 11

What is the Pauli principle?

Answer 11

This principle states that a maximum of two electrons may occupy each orbital. Spin (the rotation of an electron on its own axis) may take one of two values called “spin-up” and “spin-down”. The two electrons in a single orbital must have paired, or opposite, spins.

Question 12

What is Hund’s rule?

Answer 12

applies where orbitals have equal energy, such as the 3 orbitals in the 2p subshell. This rule states that each electron must first go into a separate orbital with parallel spins before a second electron is added to any orbital.

Question 13

What do atomic orbitals show?

Answer 13

The atomic orbitals show the probability of finding an electron in a particular region of space.

Question 14

What does the shape of an orbital represent?

Answer 14

The shape of an orbital represents the boundary that encloses 90% of the electron density.

Question 15

Why does the trend in atomic radius in period 4 become flat in the middle?

Answer 15

Because the 3d subshell is being filled and the radial distribution function for the 4s and 3d subshells show that the 3d subshell lies within the 4s.

Question 16

What is the first ionisation energy?

Answer 16

The first ionisation energy is the energy required to remove one electron from an isolated atom in the gas phase

Question 17

Why is there a decrease in the first ionisation energy from group II to III?

Answer 17

On moving from G2 to G3 the 3s orbital has been filled, and the next electron goes into a 3p orbital. This 3p electron is further from the nucleus so requires slightly less energy to remove it during ionisation.

Question 18

Why is there a decrease in the first ionisation energy from group V to group VI?

Answer 18

The 3p electrons in G5 all occupy separate orbitals. The fourth electron added on moving to G6 must then enter an already occupied orbital, resulting in greater electron-electron repulsion and a lower ionisation energy.

Question 19

Why is the overall trend in ionisation energy across the d-block elements much smaller than s- or p-block?

Answer 19

This is because an electron is lost from the outer s orbital, rather than the partially filled d orbital. For example, the electron configuration of scandium is [Ar]3d1 4s2, and that of nickel is [Ar]3d8 4s2. Both elements lose a 4s electron on ionisation, so the energies are similar.