02 Atomic Structure

Question 1

What is a mass spectrometer used for?

Answer 1

To measure the mass of individual atoms.

Question 2

How do you calculate atomic weight?

Answer 2

Atomic weights are weighted averages calculated by multiplying the RELATIVE ABUNDANCE of each isotope by its atomic mass and then summing up all the products.

Question 3

Recite the equation which relates wavelength and frequency.

Answer 3

c = λν

where c is the speed of light, λ is the wavelength, and ν is the frequency.

Question 4

How does an electron move into a higher energy level further away from the nucleus? What happens after that and what is produced?

Answer 4

An electron moves into a higher orbital be absorbing energy, thus reaching an EXCITED STATE. The excited state, however, is unstable, and the electron soon falls back into the stable GROUND STATE. When it does so, the energy that the electron emits is in the form of electromagnetic radiation – PHOTONS. One photon is released for each electron transition.

Question 5

How much energy is released when an electron falls from an excited state back to ground state?

Answer 5

The energy of the photon released equals the change in energy of the electron.

Question 6

The energy change of electrons, and hence the energy of photons, is also related by the Planck equation. State the Planck equation.

Answer 6

ΔEelectron = Ephoton

Planck equation:
Ephoton = h v

؞ ΔEelectron = h v
where h = Planck’s constant and v = frequency.

Question 7

Outline the evidence for QUANTIZATION.

Answer 7

Atoms emit photons of certain energies which give lines of certain frequencies, because electrons can only occupy one orbital at a time. The energy levels can be thought of as a staircase. The electron cannot change its energy in a continuous manner in the same way a person cannot stand between steps. The electron can only change its energy in DISCRETE AMOUNTS. Therefore the energy of the atom is QUANTIZED: if the energy were not quantized, the emission spectrum would be continuous.

Question 8

Define IONIZATION ENERGY.

Answer 8

Ionization energy is THE ENERGY NEEDED TO REMOVE AN ELECTRON FROM THE GROUND STATE OF AN ATOM in a mole of gaseous atoms, ions or molecules.

Question 9

Define FIRST IONIZATION ENERGY.

Answer 9

The first ionization energy of an element is the MINIMUM ENERGY needed to remove ONE MOLE OF ELECTRONS from ONE MOLE OF GASEOUS ATOMS in their GROUND STATE.

Question 10

When do electrons give out energy?

Answer 10

When they FALL INTO LOWER ENERGY LEVELS (high to low).

Question 11

Explain absorption spectra with regards to electron activity.

Answer 11

When an electron is excited from a lower to a higher energy level, energy is absorbed and a line in an absorption spectrum is produced.

Question 12

Explain emission spectra with regards to electron activity.

Answer 12

When an electron falls from a higher to a lower energy level, energy is released in the form of radiation (photons) and is represented by an electromagnetic wave. A line in an emission spectrum is therefore produced.

Question 13

What is the evidence for the existence of electron energy levels?

Answer 13

Emission spectra. Emission spectra manifest as discrete lines – proof of quantization. Therefore electron energy levels are discrete. The emission spectrum is not continuous, as it would be if electrons were not separated in energy levels.

Question 14

Describe an electron at n = ∞.

Answer 14

When an electron is at the HIGHEST energy n = ∞, IT IS NO LONGER IN THE ATOM AND THE ATOM HAS BEEN IONIZED.
IONIZED !!! When the atom has become an ion !!!

Question 15

Outline the two different ways that light can be described by.

Answer 15

Light can either be described as a WAVE (by way of frequency, v), or as a PARTICLE (energy of individual particles = E; called photons or quanta of light), which make up a beam of light.
Light’s WAVE and PARTICLE properties are related by the Planck equation E = h v.

Question 16

Both wave and particle models are needed to explain scientific phenomena. Neither on its own gives a true representation. Outline what the two different models can explain.

Answer 16

The DIFFRACTION, or spreading out of light, that occurs when light passes through small slits, can only be explained by the WAVE model.
The SCATTERING OF ELECTRONS which occurs when light is INCIDENT on a metal surface, is best explained using a PARTICLE model.

Question 17

State Heisenberg’s Uncertainty Principle.

Answer 17

HEISENBERG’S UNCERTAINTY PRINCIPLE states that we cannot know a electron’s position at any given time– we can only find the probability of where it is LIKELY to be.
Think of the possible positions of an electron as spread out in space in the same way that a wave is spread across a water surface.

Question 18

How were atomic orbitals found?

Answer 18

ATOMIC ORBITALS are the solutions to the wave equation when applied to multi-electron systems.
It was Schrödinger who proposed that a wave equation could be used to describe the behaviour of an electron in the same way that it can be used to describe the behaviour of light.
Because ∆Eelectron = Ephoton.

Question 19

Define atomic orbital.

Answer 19

An atomic orbital is a region around an atomic nucleus in which there is a 90% probability of finding an electron.

Question 20

What determines the SHAPE of an ATOMIC ORBITAL?

Answer 20

The energy of the electron. The higher the electron’s energy, the further it will be from the nucleus, and hence the higher the atomic orbital it will be in.

Question 21

First energy level?

Answer 21

One 1s orbital.

Question 22

Shape of the s-orbital?

Answer 22

SPHERICAL.

Question 23

Second energy level?

Answer 23

Split into TWO SUB-LEVELS, 2s and 2p.

Question 24

State the Aufbau Principle.

Answer 24

The AUFBAU PRINCIPLE states that electrons are placed into orbitals of lowest energy first.