Atomic orbitals, electronic configurations and the periodic table

Question 1

How can the discrete lines 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

Describe the nature of electrons

Answer 2

Electrons behave as standing (stationary) waves in an atom. These are waves that vibrate in time but do not move in space. There are different sizes and shapes of standing wave possible around the nucleus, known as orbitals. Orbitals can hold a maximum of two electrons.

Question 3

Name all the atomic orbitals

Answer 3

The different shapes of orbitals are identified as s, p, d and f

Question 4

Electrons within atoms have?

Answer 4

Electrons within atoms have fixed amounts of energy called quanta.

Question 5

Describe the four quantum numbers, the values they can have and what they describe about any electron

Answer 5

It is possible to describe any electron in an atom using four quantum numbers:
 the principal quantum number n indicates the main energy level for an electron and is related to the size of the orbital
 the angular momentum quantum number l determines the shape of the subshell and can have values from zero to n − 1
 the magnetic quantum number ml determines the orientation of the orbital and can have values between −l and + l
 the spin magnetic quantum number ms determines the direction of
spin and can have values of + 1/2 or − 1/2

Question 6

Description of principal quantum numbers of each shell

Answer 6

1. Principal Quantum Numbers (n)
    Each electron shell has a principal quantum number n
   n = 1 is the 1st shell, n = 2 is the 2nd shell, n = 3 is the 3rd shell, etc

N=1-1s
N=2-2s,2p
N=3-3s,3p,3d
N=4-4s, 4p, 4d, 4f 5s, 5p, 5d, 5f 6s

Question 7

Describe the values for each subshell, Angular Momentum Quantum Number (l)

Answer 7

Each shell has up to four subshells: s, p, d and f

l = 0: s block
l = 1:p block
l = 2:d block
l = 3:f block

Question 8

Describe what the magnetic quantum number ml tells you

Answer 8

the magnetic quantum number ml tells you how many pairs of wlwcteons can fit in a sub-shell and can have values from.values from -l…0…+l

Question 9

Describe aufbau’s principle

Answer 9

the aufbau principle — electrons fill orbitals in order of increasing energy

Question 10

Describe Hunds Rule

Answer 10

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

Question 11

Describe Paulis exclusion Law

Answer 11

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 12

The orbitals within each subshell in an isolated atom are

Answer 12

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

Question 13

Evidence for electronic configurations.

Answer 13

The variation in first, second and subsequent ionisation energies with increasing atomic number for the first 36 elements can be explained in terms of the relative stability of different subshell electronic configurations. This provides evidence for these electronic configurations. Anomalies in the trends of ionisation energies can be explained by considering the electronic configurations

Question 14

Decribe the stability associated with half-filled and full sub-shells and how this affects the ionisation energy

Answer 14

There is a special stability associated with half-filled and full subshells. The more stable the electronic configuration, the higher the ionisation energy.

Question 15

Hat can VSEPR be used to predict?

Answer 15

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

Question 16

Describe how the electrons surrounding the arom can be found using VSEPR

Answer 16

The number of electron pairs surrounding a central atom can be found by:
 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 17

Describe how electron pairs are distributed

Answer 17

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

Question 18

Decribe the arrangement of electron pairs around a central atom

Answer 18

The arrangement of electron pairs around a central atom is:
 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 19

Describe how shapes of molecules or polyatomic ions are determined

Answer 19

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 20

Decribe the strength in electron pair repulsions in decreasing order

Answer 20

Electron pair repulsions decrease in strength in the order:
non-bonding pair/non-bonding pair > non-bonding pair/bonding pair > bonding pair/bonding pair