Transcript Introductory Chemistry - University of Lincoln

Atoms – the building blocks
of matter
University of Lincoln
presentation
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What’s 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 (18771966)
“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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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:
o PROTON
o NEUTRON
A third particle, the ELECTRON, moves
around the nucleus in ORBITALS
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The three atomic particles
Charge (C)
Charge
number
Rest mass
(kg)
Relative mass
PROTON
NEUTRON
ELECTRON
+1.602x10-19
0
-1.602x10-19
+1
0
-1
1.673x10-27
1.675x10-27
9.109x10-31
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 Heisenberg’s uncertainty principle
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Orbitals
If we can’t 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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Why do we need to know where the
electrons are?
Element
Matter made up of
identical atoms
Atoms
Protons
Neutrons
The element is defined
by the
number of protons it has
Electrons
The number of electrons
= the number of protons
Position of the electrons
within the atom defines
the chemistry of the
element
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Periodic Table of the Elements
Hydrogen
and s – block
elements
H
Li
p – block elements
He
d – block elements
Be
Na Mg
K
Ca
Sc
Ti
V
Rb
Sr
Y
Zr
Nb Mo Tc
Cs
Ba
La
Hf
Ta
W
Fr
Ra
Ac
Ce
Th
Lanthanoids
Actinoids
Cr
Mn Fe
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Re
Os
Ir
Pt
Au
Hg Tl
Pb
Bi
Po
At
Rn
Pr
Nd Pm
Sm
Eu
Gd Tb
Dy
Ho
Er
Tm Yb
Lu
Pa
U
Np Pu
Am
Cm
Cf
Es
Fm
Md No
Lr
Bk
f - block elements
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The first 20 elements
Element
Number of
protons
(Atomic
number = Z)
Number of
electrons
Element
Number of
protons
(Atomic
number = Z)
Number of
electrons
H
1
1
Na
11
11
He
2
2
Mg
12
12
Li
3
3
Al
13
13
Be
4
4
Si
14
14
B
5
5
P
15
15
C
6
6
S
16
16
N
7
7
Cl
17
17
O
8
8
Ar
18
18
F
9
9
K
19
19
Ne
10
10
Ca
20
20
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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
s
p
1
3
2
2
2
6
d
5
2
10
f
7
2
14
Total no. e-s
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Shapes of Orbitals (s & p)
z
S-orbital
y
x
P-orbitals
z
z
z
y
x
Px
y
y
x
x
Py
Pz
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Shapes of Orbitals (d)
z
z
z
y
y
x
x
x
dyz
y
dxy
dxz
Note change of axis
z
z
y
x
dz2
y
x
dx2 y2
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Electron Orbitals
1s
2s
3s
4s
5s
6s
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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7s
The Principal Quantum Number
1s
2s
3s
4s
The increase in size of atomic orbitals
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Position of Orbitals Around Nucleus
4πr2R(r)2
30
1s
25
Probability
Energy increase
20
15
2s
10
3s
5
0
Nucleus
0
5
10
15
Distance from atomic nucleus (r, atomic units)
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20
Energy, E
Relationship Between Principal
Quantum Number and Energy
0
n=∞
n=6
n=5
n=4
n=3
Energy levels
become closer
together
n=2
n=1
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Comparing the Energy for n=3
4πr2R(r)2
25
3d
Probability
20
Energy increase
3p
3s
15
10
5
0
0
5
10
15
20
25
Distance from the nucleus (r,atomic units)
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Energy
The Energy of Orbitals
3d
3p
N=3
3s
2p
N=2
N=1
2s
1s
Link to “Energy level
diagrams” video
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
2p
3p
4p
5p
6p
3d
4d
5d
4f
5f
7s
1s < 2s < 2p< 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p<
6s < 4f  5d < 6p < 7s < 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 >1 there is both an s- and a porbital. 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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H
Li
He
Be
Na Mg
K
Ca
Sc
Ti
V
Cr
Mn Fe
Rb
Sr
Y
Zr
Nb Mo Tc
Cs
Ba
La
Hf
Ta
W
Fr
Ra
Ac
Ce
Th
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Re
Os
Ir
Pt
Au
Hg Tl
Pb
Bi
Po
At
Rn
Pr
Nd Pm
Sm
Eu
Gd Tb
Dy
Ho
Er
Tm Yb
Lu
Pa
U
Np Pu
Am
Cm
Cf
Es
Fm
Md No
Lr
Bk
Noble gases:
All orbitals are filled
Noble gases: Group 18
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Energy Level Diagrams Arrangement of Electrons in Orbitals
2p
2s
1s
He
Energy
C
Energy
Energy
Work out the number of electrons that are present, and then
start filling the lowest energy orbitals first
1s
Li
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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