Atomic orbitals, electronic configurations and the periodic table

Question 1

How can the discrete lines observed in atomic spectra be explained

Answer 1

The discrete lines observed in atomic spectra can be explained if electrons, like photons, also display the properties of both particles and waves.

Question 2

How do electrons behave

Answer 2

Electrons behave as standing (stationary) waves in an atom.

Question 3

What are standing (stationary) waves

Answer 3

These are waves that vibrate in time but do not move in space.

Question 4

What are orbitals

Answer 4

There are different sizes and shapes of standing wave possible around the nucleus, known as orbitals.

Question 5

What is the maximum number of electrons orbitals can hold

Answer 5

Orbitals can hold a maximum of two electrons.

Question 6

What different shapes are orbitals identified as

Answer 6

The different shapes of orbitals are identified as s, p, d and f (knowledge of the shape of f orbitals is not required).

Question 7

What is quanta

Answer 7

Electrons within atoms have fixed amounts of energy called quanta.

Question 8

It is possible to describe any electron in an atom using four quantum numbers:

Answer 8

• the principal quantum number
• the angular momentum quantum number
• the magnetic quantum number
• the spin magnetic quantum number

Question 9

The principal quantum number

Answer 9

the principal quantum number n indicates the main energy level for an electron and is related to the size of the orbital

Question 10

The angular momentum quantum number

Answer 10

the angular momentum quantum number l determines the shape of the subshell and can have values from zero to n − 1

Question 11

The magnetic quantum number

Answer 11

the magnetic quantum number ml determines the orientation of the orbital and can have values between −l and + l

Question 12

The magnetic quantum number

Answer 12

the magnetic quantum number ml determines the orientation of the orbital and can have values between −l and + l

Question 13

The spin magnetic quantum number

Answer 13

the spin magnetic quantum number ms determines the direction of spin and can have
valuesof +1/2 or −1/2

Question 14

Electrons within atoms are arranged according to

Answer 14

• the aufbau principle
• Hund’s rule
• the Pauli exclusion principal

Question 15

The aufbau principal

Answer 15

the aufbau principle — electrons fill orbitals in order of increasing energy (‘aufbau’ means ‘building up’ in German)

Question 16

Hund’s rule

Answer 16

Hund’s rule — when degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts

Question 17

The Pauli exclusion principal

Answer 17

the Pauli exclusion principle — no two electrons in one atom can have the same set of four quantum numbers, therefore, no orbital can hold more than two electrons and these two electrons must have opposite spins

Question 18

In an isolated atom what are the orbitals within each sub shell

Answer 18

In an isolated atom the orbitals within each subshell are degenerate.

Question 19

How can the relative energies corresponding to each orbital be represented

Answer 19

The relative energies corresponding to each orbital can be represented diagrammatically using orbital box notation for the first four shells of a multi-electron atom.

Question 20

What elements can electronic configurations be written for

Answer 20

Electronic configurations using spectroscopic notation and orbital box notation can be written for elements of atomic numbers 1 to 36.

Question 21

What four blocks is the periodic table divided into

Answer 21

The periodic table is subdivided into four blocks (s, p, d and f) corresponding to the outer electronic configurations of the elements within these blocks.

Question 22

What is associated with half filled and full sub shells

Answer 22

There is a special stability associated with half-filled and full subshells.

Question 23

The more stable the electronic configuration …

Answer 23

The more stable the electronic configuration the higher the ionisation energy

Question 24

What is VSEPR theory used for

Answer 24

VSEPR (valence shell electron pair repulsion) theory can be used to predict the shapes of molecules and polyatomic ions.

Question 25

The number of electron pairs surrounding a central atom can be found by:

Answer 25

• taking the total number of valence (outer) electrons on the central atom and adding one for each atom attached
• adding an electron for every negative charge
• removing an electron for every positive charge
• dividing the total number of electrons by two to give the number of electron pairs

Question 26

How are electron pairs arranged

Answer 26

Electron pairs are negatively charged and repel each other. They are arranged to minimise repulsion and maximise separation.

Question 27

The arrangement of electron pairs around a central atom is:

Answer 27

• linear for two electron pairs
• trigonal planar for three electron pairs
• tetrahedral for four electron pairs
• trigonal bipyramidal for five electron pairs
• octahedral for six electron pairs

Question 28

How are Shapes of molecules or polyatomic ions determined

Answer 28

Shapes of molecules or polyatomic ions are determined by the shapes adopted by the atoms present based on the arrangement of electron pairs. Electron dot diagrams can be used to show these arrangements.

Question 29

Electron pair repulsions decrease in strength in the order:

Answer 29

non-bonding pair/non-bonding pair > non-bonding pair/bonding pair > bonding pair/bonding pair