Periodic table.
Electron configuration of carbon
atoms and molecules.
John Summerscales
Fundamental particles in atom
Charge
Mass
Position
Proton
+1
1673 x 10-27g
in nucleus
Neutron
Electron
zero
-1
1675 x 10-27 g
0.91 x 10-27 g
in nucleus
in orbit
Atomic number = number of protons
• for balanced charge (in atom) = number of electrons
• value is characteristic of a specific element
Atomic weight = number of (protons + neutrons)
• can have partial values as isotopes have
different numbers of neutrons and different proportions
The atom (simple model)
If K=1, L=2, M=3, N=4,
then at each level there are 2n2 electrons:
n=1 gives 2 electrons
n=2 gives 8 electrons
n=3 gives 18 electrons
n=4 gives 32 electrons
K L M N
The atom (simple model)
If n = shell number - 1,
then each shell has 2(2n+1) additional electrons:
n=0 gives 2 electrons (s-block)
n=1 gives 6 electrons (p-block)
n=2 gives 10 electrons (d-block)
n=3 gives 14 electrons (f-block)
nucleus (protons and neutrons)
level 1 = 2
level 2 = 2+6 = 8
level 3 = 2+6+10 = 18
level 4 = 2+6+10+14 =32
The Periodic Table
s-block
H He
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
p-block
d-block
Periodic table of the Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac
f-block
B
Al
Ga
In
Tl
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
He
Ne
Ar
Kr
Xe
Rn
Inert gases
Fibres - glass: B, O, Al, Si
aramid: H, C, N, O
Resins - H, C, N, O
This column has a full electron shell
- the most stable configuration
H He
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Periodic table of the Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac
B
Al
Ga
In
Tl
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
He
Ne
Ar
Kr
Xe
Rn
Ionic bonding
This column lose one electron to become X+
This column lose two electrons to become X2+
This column lose three electrons to become X3+
H He
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Periodic table of the Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac
B
Al
Ga
In
Tl
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
He
Ne
Ar
Kr
Xe
Rn
Ionic bonding
This column gains one electron to become XThis column gains two electrons to become X2This column gains three electrons to become X3H He
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Periodic table of the Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac
B
Al
Ga
In
Tl
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
He
Ne
Ar
Kr
Xe
Rn
Carbon (and Si, Ge, Sn, Pb)
This column could become
either X4+ or X4- ??
H He
Li Be
Na Mg
K Ca
Rb Sr
Cs Ba
Fr Ra
Periodic table of the Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os Ir Pt Au Hg
Ac
B
Al
Ga
In
Tl
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
He
Ne
Ar
Kr
Xe
Rn
Carbon 4+ or 4- ??
• In practice,
six protons holding three electrons
> strong force/electron (difficult to remove 4th e-)
o six protons holding ten electrons
> weak force/electron (difficult to retain 10th e-)
o
• so, carbon shares electrons
> covalent bonding
• one bond ... is ... two shared electrons
Carbon - covalent bonding
• carbon has 4 electrons in the outer shell
needs four electrons to fill shell
• can share with 2, 3 or 4 other atoms
o
4 other atoms = 4 x single (σ) bonds
o
3 other atoms = 3 x σ and 1 x double (π) bond
o
2 other atoms = two σ and two π bonds
- 1 x single and 1 x triple (2π) bonds
• but ....
Carbon - electron orbitals
• electron shells divide into electron orbitals
each has up to two electrons of opposite spin
o electrons enter empty orbitals first
o at level 2 of Periodic Table, maximum of:
o
2
2
2
2

electrons
electrons
electrons
electrons
in
in
in
in
a
a
a
a
spherical orbital
dumbbell orbit on x-axis
dumbbell orbit on y-axis
dumbbell orbit on z-axis
Electron orbitals
1s
2s
2px
2py
Note: the orbitals are not drawn to scale.
They are probabilities of finding an electron.
The pz orbital is normal to the plane of this image.
Electron orbitals (2s 2px 2py 2pz)
y
z
x
Electron orbitals (px, py, pz)
Animation
Electron configurations
•
•
•
•
•
•
•
•
•
•
H 1s1
He 1s2
Li 1s2 2s1
Be 1s2 2s2
B 1s2 2s2 2p1
C 1s2 2s2 2p2
N 1s2 2s2 2p3
O 1s2 2s2 2p4
F 1s2 2s2 2p5
Ne 1s2 2s2 2p6
H
Li
Na
K
Rb
Cs
Fr
He
Be
Mg
Ca
Sr
Ba
Ra
B
Al
Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In
La Hf Ta W Re Os Ir Pt Au Hg Tl
Ac
Periodic table of the Elements
C
Si
Ge
Sn
Pb
N
P
As
Sb
Bi
O
S
Se
Te
Po
F
Cl
Br
I
At
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lw
2p1 = px1
2p2 = px1 py1
2p3 = px1 py1 pz1
2p4 = px2 py1 pz1
2p5 = px2 py2 pz1
2p6 = px2 py2 pz2
He
Ne
Ar
Kr
Xe
Rn
Methane (CH4)
• carbon bonded to four hydrogen atoms
• if each H bonds to a different electron orbital
the resulting molecule is asymmetric
• symmetrical molecules have lowest energy
and are thus the most stable form
• so (2s + 2px +2py + 2pz) reorganise to
four hybrid sp3 orbitals (think s1p3 !!)
oriented along each line from the
apex to the centre of a tetrahedron
CH4 tetrahedron
• Pyramid with a triangular base
• carbon nucleus at centre
• hydrogen at each apex
• sp3 orbital on each line
from apex to base centre
Electron orbitals
(sp3 hybrid molecular orbital)
y
x
forward
behind plane
forward
Electron orbitals
(sp3 hybrid molecular orbital)
Animation
add a methylene group -CH2•
•
•
•
•
•
•
•
•
Methane
CH4
generic CnH2n+2
Ethane
C2H6
Propane
C3H8
Butane
C4H10
Pentane
C5H12
Hexane
C6H14
Heptane
c7H16
Octane
C8H18
...paraffins ... polyethylene
... with one double bond:
•
•
•
•
•
•
•
•
•
Methene
Ethene
Propene
Butene
Pentene
Hexene
Heptene
Octene
etcetera ....
n/a
C2H4
C3H6
C4H8
C5H10
C6H12
c7H14
C8H16
generic CnH2n
a.k.a. ethylene
a.k.a. propylene
a.k.a. butylene
... with one triple bond:
•
•
•
•
•
•
•
•
•
Methyne
Ethyne
Propyne
Butyne
Pentyne
Hexyne
Heptyne
Octyne
etcetera ....
n/a
C2H2
C3H4
C4H6
C5H8
C6H10
c7H12
C8H14
generic CnH2n-2
a.k.a. acetylene
sp2 hybrid orbital
• 2s + 2px + 2py hybridise to 3 x sp2 orbitals
• 2pz orbital remains and forms double bond
< plan view
(excl. pz)
side view >
pz
Double bond (C=C)
half of double (π) bond
electrons above atom centres
π (1e-)
centres single (σ) bond on
line of atom centres
σ (2e-)
half of double (π) bond
electrons below atom centres
π (1e-)
Triple bond (C=C) has π orbitals
above, below, in front and behind the σ bond
Consider σ and π
bonds as springs
compression
tension
torsion
Hybrid orbitals - summary
• sp3 bonds to 4 other atoms
4 σ (single) bonds
bond angle = 109° 28’ (tetrahedral molecule)
• sp2 bonds to 3 other atoms
3 σ and 1 π bond
bond angle = 120° (triangular molecule)
1σ and 1π bond = the double bond (i.e. 1+1 = 2)
• sp bonds to 2 other atoms
2 σ and 2 π bonds
bond angle = 180° (linear molecule)
1σ and 2π bonds = the triple bond (i.e. 1+2 = 3)
Benzene (C6H6 - cyclohextriene)
• ring of six carbon atoms
ignore H atoms to give C at each corner
tri-ene is three double bonds
symmetry results in hexagonal molecule
symmetry gives lowest energy so stable molecule
Benzene (Kekulé resonance)
• left molecule is same as right molecule
but upside down
• double bonds constantly switch positions
• change is so fast that
upper 3 electrons appear as a single ring
lower 3 electrons appear as a single ring
Benzene ring
• delocalised (conjugated) electrons
C-C bond length 1.54 Å
C:C bond in benzene 1.39 Å
C=C bond length 1.33 Å
Graphite (E in-plane ~ 1000 GPa)
Conclusion:
Chemical bond type
and chemical bond density
each determine material
stiffness/strength
and chemical durability