Electronic structure of atoms

Question 1

The atomic theory:

Answer 1

States that matter consists of atoms

Question 2

What is the structure of the atom?

Answer 2

• Consists of a central positive nucleus, containing protons and neutrons
• Surrounded by electrons which exist in orbits

Question 3

Atomic mass (A)

Answer 3

number of neutron and protons

Question 4

Atomic number (Z)

Answer 4

number of protons

Question 5

• 2n^2 rule

- flame test

Answer 5

• maximum number of electrons

- metals ions produce distinctive colours when their salts are volatile in a blue bunsen burner

Question 6

The Bohr Model

Answer 6

• atom consists of a positive nucleus, surrounded by electrons orbiting in certain stable energy level
• Bohr proposed that electron in atoms are bound to certain discrete energy levels/ states
• Electrons may undergo transitions between these states by absorbing or releasing energy

Question 7

What happens when an electron absorbs a ‘quantum of energy’?

Answer 7

• Electrons get excited, they go to a higher energy level temporarily
• Electrons release energy as light with a particular frequency when they return to the ‘ground state’

Question 8

What gives an atom a unique emission spectrum?

Answer 8

Atoms of each element have unique energy levels

Question 9

Absorption spectrum:

Answer 9

When light is passed through the atoms of one element and then a prism, a unique absorption spectrum is obtained.

Electrons of an element which are in the ground state may absorb incident energy in order to reach a higher energy state. The frequencies of light transmitted through this substance, with dark bands showing absorbed light, constitute the absorption spectrum of the substance.

Question 10

Emission spectrum:

Answer 10

When an excited sample of atoms emit light that is passed through a prism a unique emission spectrum is obtained.

When a quantum of energy is given to an element, the electrons of its atoms accept the energy and go to higher energy levels. However, these electrons have to emit energy in order to return to their ground state, since the excited state is unstable. The frequencies of light emitted in such a case constitute the emission spectrum. When an electron comes down from an excited state to the ground state, it emits a photon of energy. The energy of this photon depends on the difference between the energy levels of the excited state and ground state of that electron.

Question 11

What are Bohr Model limitations?

Answer 11

• Provides poor spectral predictions for systems with more than one electron
• Electrons moving in a circular motion should emit electromagnetic radiaition and lose enrgy

Question 12

Evidence that electrons are particles:

Answer 12

They have a mass

Question 13

Evidence that electrons are waves:

Answer 13

Waves extend a reigion of space

Question 14

Atomic orbital:

Answer 14

Reigion of space occupied by an electron 90% of the time

Question 15

Aufbau principle:

Answer 15

orbitals are filled in order of increasing energy

Question 16

Pauli exclusion principle:

Answer 16

An orbital can hold a maximum of 2 electrons, each with opposite spins

Question 17

Hund’s rule:

Answer 17

For a set of degenerate orbitals in a sub-shell, electrons will occupy the orbitals one at a time to maximise parallel spins until force to pair up by the lack of additional orbitals.