REVIEWTOPIC 2/12: ATOMIC STRUCTURE
A. KEY DEFINITIONS (MEMORIZE!)
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Mass number(A) - the number of protons and neutrons in an atom
Atomic number(Z) - the number of protons in an atom (also equal to the number of electrons in an atom).
Isotopes - atoms of the same element with the same atomic number but different mass numbers
B. YOU SHOULD KNOW:
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the following details about subatomic particles:
Subatomic Particles
Relative Mass
Proton
1
Neutron
1
Electron
5 x 10-4
Relative Charge
+1
0
-1
a mass spectrometer is used to determine relative atomic masses by comparing the masses of atoms to the mass of
12
C
the main stages in the operation of a mass spectrometer are: Vapourization, Ionization, Acceleration, Deflection, and
Detection (VIADD)
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ultraviolet (UV) light has a higher frequency and shorter wavelength than visible light
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visible light has higher frequency and shorter wavelength than infrared (IR) light
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Position in Atom
In nucleus
In nucleus
In energy levels(shells)
orbiting nucleus
a continuous spectrum will contain all possible wavelengths within a range (e.g. the ‘rainbow’ seen in the visible range of
the spectrum)
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a line (i.e. emission or absorption spectrum) only contains single (discrete) lines
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lines converge towards high frequency
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each energy level contains sub-levels and these sub-levels contain orbitals
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the orbitals within an energy level increase in energy as s<p<d<f
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orbitals can hold a maximum of two electrons
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an s sub-level holds 2 electrons, a p-sublevel holds 6 electrons, a d sub-level holds 10 electrons, and an f sub-level holds
14 electrons
Energy Level
Sub-levels
Orbitals Present
n=1
s
1xs
n=2
s, p
1x s ; 3 x p
n=3
s, p, d
1x s ; 3 x p ; 5 x d
n=4
s, p, d, f
1xs;3xp;5xd;7xf
 Aufbau principle – electrons fill lower energy levels first
 Hund’s Rule – orbitals in the same sub-level are filled singly before the electrons pair up
 Pauli Exclusion Principle – no two electrons can occupy the same orbital unless they have opposite spins
C. YOU SHOULD BE ABLE TO:
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Work out which isotope is present from the mass and atomic numbers
Calculate the number of protons, neutrons, and electrons in atoms and ions
Work out the relative atomic mass given the masses and abundances of isotopes
Compare the properties of isotopes – remember that chemical properties are the same and physical properties vary
Draw an energy level diagram to show the transitions between energy levels in an atom
Explain that lines in the emission spectrum relate to these energy level transitions
Explain that the evidence from the first ionization energies of elements show that there are main energy levels and sublevels in atoms
Explain how successive ionization energies(removing one electron at a time until all removed) are related to electron
configuration
Work out the electron arrangement of atoms [e.g. Sodium, Na is (2,8,1)]
Work out full electron configurations [e.g. Calcium, Ca, Z = 20: 1s22s22p63s23p64s2]
Write the abbreviated electron configurations of atoms from the nearest noble gas [e.g. Scandium, Sc is [Ar]4s23d1 ]
D. BE PREPARED
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The data booklet contains the equations E = hf and c=fλ, which can be used to answer questions. That is, be able to solve
problems using these formulas.
You should be able to write full configurations up to Z = 36 of both atoms and ions. Always make sure the superscripts
add up to the atomic number. Remember that electrons are removed from the highest energy level first, so Ni2+ is
[Ar]3d8 NOT [Ar]4s23d6.
Remember the EXCEPTIONS to orbital filling that occur with COPPER,1s22s22p63s23p64s13d10 (NOT
1s22s22p63s23p64s23d9) and CHROMIUM, 1s22s22p63s23p64s13d5 (NOT 1s22s22p63s23p64s23d4), as these arrangements are
more stable. This is because filled sub-levels and half-filled sub-levels are more stable.
You need to know how to draw orbital box diagrams. Like the one below for Fe 3+ = [Ar]3d5.
[Ar]
3d5
PROBLEM SET #2 (TOPIC 2/12: ATOMIC STRUCTURE)
1. MULTIPLE CHOICE: Consider the composition of the species W, X, Y and Z below. Which species is an anion? (1)
SPECIES
NUMBER OF PROTONS
NUMBER OF NEUTRONS
NUMBER OF ELECRONS
W
9
10
10
X
11
12
11
Y
12
12
12
Z
13
14
10
2. (a) Use the Aufbau Principle to write the full electron configuration of an atom of germanium.
(b) MULTPLE CHOICE: Energy levels for an electron in a hydrogen atom are:
A. evenly spaced
C. closer together near the nucleus
B. farther apart near the nucleus D. arranged randomly
(c) MULTIPLE CHOICE: How many orbitals are there in the n=3 level of an atom?
A. 3
B. 5
C. 7
D. 9
3. Strontium exists as four naturally-occurring isotopes. Calculate the relative atomic mass of strontium to two decimal places
from the following data.
Isotope
Percentage Abundance
Sr-84
0.56
Sr-86
9.90
Sr-87
7.00
Sr-88
82.54
4. The graph of the first ionization energy plotted against atomic number for the first twenty elements shows periodicity(i.e.
patterns at regular intervals).
(i) Define the term first ionization energy. (1)
(ii) Explain how information from this graph provides evidence for the existence of main energy levels and sub-levels within
atoms. (4)
(iii) State what is meant by the term second ionization energy.(1)
(iv) Sketch an explain the shape of the graph obtained for the successive ionization energies of potassium using a logarithmic
scale for ionization energy on the y-axis against number of electrons removed on the x-axis.(4)