1b- Atomic orbitals, electronic configurations and the periodic table

Question 1

How can the discrete lines observed in atomic spectroscopy be explained?

Answer 1

If electrons, like photons, also display the properties of both particles and waves

Question 2

How do electrons behave in an atom?

Answer 2

As standing (stationary) waves

Question 3

Electrons behave as standing (stationary) waves in an atom. What are these waves called and how do they act?

Answer 3

These waves are known as orbitals, they vibrate in time but do not move in space. There are different sizes and shapes of these standing waves around the nucleus.

Question 4

How many electrons can an orbital hold?

Answer 4

A maximum of two

Question 5

What can the different shapes of orbitals be identified as?

Answer 5

s, p, d and f

Question 6

Electrons within atoms have fixed amounts of energy called what?

Answer 6

Quanta

Question 7

What can be used to describe any electron in an atom?

Answer 7

The electrons four quantum numbers

Question 8

What are the four quantum numbers?

Answer 8

• the principal quantum number (n)
• the angular momentum quantum number (l)
• the magnetic quantum number (m)
• the magnetic spin quantum number (s)

Question 9

What does the principal quantum number indicate?

Answer 9

The main energy level for an electron (this is related to the size of the orbital)

Question 10

What does the angular momentum quantum number determine and what values can it have?

Answer 10

The shape of the subshell and can have values from zero to n-1

Question 11

What does the magnetic quantum number determine and what values can it have?

Answer 11

The orientation of the orbital and and can values between -l and +l

Question 12

What does the spin magnetic quantum number determine and what two values can it have?

Answer 12

The direction of spin and can have values of +1/2 or -1/2

Question 13

What are the three ways electrons are arranged according to?

Answer 13

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

Question 14

What does the aufbau principle state?

Answer 14

Electrons fill orbitals in order of increasing energy

Question 15

What does Hund’s rule state?

Answer 15

When degenerate orbitals are available, electrons fill each singly, keeping their spins parallel before spin pairing starts

Question 16

What does the Pauli exclusion theory state?

Answer 16

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 electrons must have opposite spins

Question 17

In an isolated atom the orbitals within each subshell are said to be degenerate. What does this mean?

Answer 17

Degenerate orbitals have the same energy (all p orbitals have the same energy)

Question 18

The periodic table can be subdivided into four blocks (s, p, d and f) corresponding with what?

Answer 18

The outer electronic configurations of the elements within these blocks

Question 19

The variation in first, second and subsequent ionisation energies with increasing atomic number for the first 36 elements can be explained in terms of what?

Answer 19

The relative stability of different subshell electronic configurations

Question 20

What is the relationship between the electronic configuration and the ionisation energy?

Answer 20

The more stable the electronic configuration, the higher the ionisation energy

Question 21

What can VSEPR (valence shell electron pair repulsion) be used to predict?

Answer 21

The shapes of molecules and polyatomic ions

Question 22

What are the steps when finding out the number of electron pairs surrounding a central atom?

Answer 22

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

Question 23

Electron pairs are negatively charged and repel each. In which way are they arranged?

Answer 23

To minimise repulsion and maximise separation

Question 24

What three things are needed to work out the shape of a molecule?

Answer 24

1. the number of electron pairs
2. how many of the electron pairs are bonded to other atoms and how many are
   non-bonded
3. the number of atoms attached to the central atom

Question 25

What are the arrangements of electron pairs around a central atom for two, three, four, five and six electron pairs?

Answer 25

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

Question 26

Electron pair repulsions decrease in strength in what order?

Answer 26

non-bonding pair/non-bonding pair (most repulsion)
non-bonding pair/bonding pair
bonding pair/bonding pair (least repulsion)