Introductory Chemistry

1
Atoms the building blocks of matter
University of Lincoln presentation
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Whats so special about atoms?

• All matter is made of atoms
• When 2 surfaces touch each other, atoms from one
  surface are transferred to the other
• TRACE EVIDENCE

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The Locard Principle of Exchange
Prof Edmond Locard (1877-1966) When objects
come into contact there is a transfer of
particles.
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For example

• FIREARM DISCHARGE RESIDUE
• When a firearm is discharged, traces of lead,
  antimony and barium are deposited onto the hand
  holding the gun.

• IDENTIFYING SITE OF BULLET PENETRATION
• Uncoated lead bullets and copper-coated
  bullets discharged from firearms and penetrating
  wood, fabric, paper, etc., leave behind 0.1 100
  micron particles of metallic lead or copper

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What you Need to Know

• Structure of the atom proton, neutron and
  electron
• Electron orbitals s- and p-orbitals, principal
  quantum numbers and energy
• Electronic configurations noble gas
  configurations, core electrons and valence
  electrons
• Drawing energy level diagrams putting electrons
  into orbitals and pairing electrons

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6
Atomic Structure
Direction of electron motion
Electron
Nucleus
The Bohr atom
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Make-up of the Atom

• The NUCLEUS
• Two particles make up the nucleus
• PROTON
• NEUTRON
• A third particle, the ELECTRON, moves around the
  nucleus in ORBITALS

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The three atomic particles
PROTON NEUTRON ELECTRON
Charge (C) 1.602x10-19 0 -1.602x10-19
Charge number 1 0 -1
Rest mass (kg) 1.673x10-27 1.675x10-27 9.109x10-31
Relative mass 1837 1839 1
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Orbitals

• Consider the moon orbiting the earth
• We always know where the moon is because we can
  see it its position and motion can be defined
  EXACTLY
• For an e- with a tiny mass, this is not the case
  it is impossible to know, exactly, both its
  position and momentum at the same instant in
  time.
• This is known as Heisenbergs uncertainty
  principle

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Orbitals

• If we cant determine exactly where the electron
  is, we must consider the probability of finding
  the electron in a given volume of space. This
  volume of space is called an ORBITAL
• Probabilities are calculated mathematically, and
  in this case are defined by the
• Schrödinger wave equation

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11
Why do we need to know where the electrons are?
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Periodic Table of the Elements
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The first 20 elements
Element Number of protons (Atomic number Z) Number of electrons
Na 11 11
Mg 12 12
Al 13 13
Si 14 14
P 15 15
S 16 16
Cl 17 17
Ar 18 18
K 19 19
Ca 20 20
Element Number of protons (Atomic number Z) Number of electrons
H 1 1
He 2 2
Li 3 3
Be 4 4
B 5 5
C 6 6
N 7 7
O 8 8
F 9 9
Ne 10 10
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Where are these electrons?

• According to Schrödinger, there are 4 different
  types of orbital in an atom (each type has a
  different shape)

Orbital label No. orbitals No. e-s per orbital Total no. e-s
s 1 2 2
p 3 2 6
d 5 2 10
f 7 2 14
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Shapes of Orbitals (s p)
S-orbital
P-orbitals
Px
Py
Pz
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Shapes of Orbitals (d)
dyz
dxy
dxz
Note change of axis
dz2
dx2 y2
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Electron Orbitals

1s 2s 3s 4s 5s 6s 7s
2p 3p 4p 5p 6p
3d 4d 5d
4f 5f
The number is called the principal quantum number
(n) and indicates the size of the orbital (1 is
the smallest 7 the largest)
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The Principal Quantum Number
1s
2s
3s
4s
The increase in size of atomic orbitals
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Position of Orbitals Around Nucleus
4pr2R(r)2
Energy increase
1s
2s
3s
Nucleus
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Relationship Between Principal Quantum Number and
Energy
0
n 8
Energy levels become closer together
Energy, E
n 6
n 5
n 4
n 3
n 2
n 1
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Comparing the Energy for n3
4pr2R(r)2
Energy increase
3d
3p
3s
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The Energy of Orbitals
3d
Energy
3p
3s
N 3
2p
Link to Energy level diagrams video
2s
N 2
1s
N 1
Each orbital will hold 2 electrons
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How do the electrons fill these orbitals?

• Groundstate electronic configurations
• In order for an element to be stable, it has to
  house its electrons in such a way that its
  overall energy is as low as possible
• The electrons will therefore occupy the lowest
  energy orbitals available

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Orbitals in energy order
1s 2s 3s 4s 5s 6s 7s
2p 3p 4p 5p 6p
3d 4d 5d
4f 5f
1s lt 2s lt 2plt 3s lt 3p lt 4s lt 3d lt 4p lt 5s lt 4d lt
5plt 6s lt 4f ? 5d lt 6p lt 7s lt 5f
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Electronic Configuration
Atomic number Element Symbol Electronic configuration Atomic number Element Symbol Electronic configuration
1 H 1s1 11 Na 1s22s22p63s1
2 He 1s2 12 Mg 1s22s22p63s2
3 Li 1s22s1 13 Al 1s22s22p63s23p1
4 Be 1s22s2 14 Si 1s22s22p63s23p2
5 B 1s22s22p1 15 P 1s22s22p63s23p3
6 C 1s22s22p2 16 S 1s22s22p63s23p4
7 N 1s22s22p3 17 Cl 1s22s22p63s23p5
8 O 1s22s22p4 18 Ar 1s22s22p63s23p6
9 F 1s22s22p5 19 K 1s22s22p63s23p64s1
10 Ne 1s22s22p6 20 Ca 1s22s22p63s23p64s2
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Three things to remember

• 1. For principal quantum numbers gt1 there is both
  an s- and a p-orbital. This means 8 electrons are
  needed to fill these two orbitals. If the
  orbitals are all filled, the element is extra
  stable. These elements are the NOBLE gases
• 2. CORE electrons are those electrons sitting in
  filled orbitals. These usually correspond to the
  noble gas configurations (He, Ne, Ar etc.)
• 3. VALENCE electrons are the electrons outside
  the core electrons. It is these electrons that
  define the chemistry of the element

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Noble gases Group 18
H
He
Be
Li
Ne
B
C
N
O
F
Na
Mg
Ar
Al
Si
P
S
Cl
Noble gases All orbitals are filled
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Kr
Ga
Ge
As
Se
Br
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Xe
Sb
Te
I
Cs
Ba
La
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Fr
Ra
Ac
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
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Energy Level Diagrams - Arrangement of Electrons
in Orbitals
Work out the number of electrons that are
present, and then start filling the lowest energy
orbitals first
C
Li
He
Energy
2s
1s
Electrons remain unpaired when they can (i.e.
when there is more than 1 orbital of the same
energy)
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How do electrons pair up?
Incorrect
Correct
In order to pair up, electrons have to spin in
different directions
ve spin -ve spin
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Summary

• Structure of the atom proton, neutron and
  electron
• Electron orbitals s- and p-orbitals, principal
  quantum numbers and energy
• Electronic configurations noble gas
  configurations, core electrons and valence
  electrons
• Drawing energy level diagrams putting electrons
  into orbitals and pairing electrons

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Acknowledgements

• JISC
• HEA
• Centre for Educational Research and Development
• School of natural and applied sciences
• School of Journalism
• SirenFM
• http//tango.freedesktop.org

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