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# Periodic table. Electron configuration of carbon atoms and molecules. - PowerPoint PPT Presentation

Periodic table. Electron configuration of carbon atoms and molecules. . John Summerscales. Fundamental particles in atom. Atomic number = number of protons for balanced charge (in atom) = number of electrons value is characteristic of a specific element

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### Periodic table.Electron configuration of carbon atoms and molecules.

John Summerscales

• 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

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

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

Periodic table of the Elements

s-block

p-block

d-block

f-block

Fibres - glass: B, O, Al, Si

aramid: H, C, N, O

Resins - H, C, N, O

Periodic table of the Elements

This column has a full electron shell- the most stable configuration

Periodic table of the Elements

This column lose one electron to become X+

This column lose two electrons to become X2+

This column lose three electrons to become X3+

Periodic table of the Elements

This column gains one electron to become X-

This column gains two electrons to become X2-

This column gains three electrons to become X3-

Periodic table of the Elements

This column could become either X4+ or X4- ??

Carbon 4+ or 4- ??

• In practice,

• six protons holding three electrons> strong force/electron (difficult to remove 4th e-)

• six protons holding ten electrons> weak force/electron (difficult to retain 10th e-)

• so, carbon shares electrons

> covalent bonding

• one bond ... is ... two shared electrons

• carbon has 4 electrons in the outer shell

needs four electrons to fill shell

• can share with 2, 3 or 4 other atoms

• 4 other atoms = 4 x single (σ) bonds

• 3 other atoms = 3 x σ and 1 x double (π) bond

• 2 other atoms = two σ and two π bonds

- 1 x single and 1 x triple (2π) bonds

• but ....

• electron shells divide into electron orbitals

• each has up to two electrons of opposite spin

• electrons enter empty orbitals first

• at level 2 of Periodic Table, maximum of:

• 2 electrons in a spherical orbital

• 2 electrons in a dumbbell orbit on x-axis

• 2 electrons in a dumbbell orbit on y-axis

• 2 electrons in a dumbbell orbit on z-axis

1s 2s2px2py

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

x

z

Electron orbitals (px, py, pz)

Animation

Periodic table of the Elements

• 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

2p1 = px1

2p2 = px1 py1

2p3 = px1 py1 pz1

2p4 = px2 py1 pz1

2p5 = px2 py2 pz1

2p6 = px2 py2 pz2

• carbon bonded to four hydrogen atoms

• if each H bonds to a different electron orbitalthe resulting molecule is asymmetric

• symmetrical molecules have lowest energyand are thus the most stable form

• so (2s + 2px +2py + 2pz) reorganise tofour hybrid sp3 orbitals (think s1p3 !!)oriented along each line from theapex 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

• Methane CH4 generic CnH2n+2

• Ethane C2H6

• Propane C3H8

• Butane C4H10

• Pentane C5H12

• Hexane C6H14

• Heptane c7H16

• Octane C8H18

• ...paraffins ... polyethylene

• Methene n/ageneric CnH2n

• Ethene C2H4 a.k.a. ethylene

• Propene C3H6 a.k.a. propylene

• Butene C4H8 a.k.a. butylene

• Pentene C5H10

• Hexene C6H12

• Heptene c7H14

• Octene C8H16

• etcetera ....

• Methyne n/ageneric CnH2n-2

• Ethyne C2H2 a.k.a. acetylene

• Propyne C3H4

• Butyne C4H6

• Pentyne C5H8

• Hexyne C6H10

• Heptyne c7H12

• Octyne C8H14

• etcetera ....

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

π (1e-)

σ (2e-)

π (1e-)

half of double (π) bond electrons above atom centres

centres single (σ) bond on line of atom centres

half of double (π) bond electrons below atom centres

Triple bond (C=C) has π orbitalsabove, below, in front and behind the σ bond

Consider σ and πbonds as springs

compression

tension

torsion

• sp3 bonds to 4 other atoms4σ (single) bonds bond angle = 109° 28’ (tetrahedral molecule)

• sp2 bonds to 3 other atoms3σ and 1πbond bond angle = 120° (triangular molecule)1σand1πbond = the double bond (i.e. 1+1 = 2)

• sp bonds to 2 other atoms2σ and 2πbonds bond angle = 180° (linear molecule)1σand2πbonds = the triple bond (i.e. 1+2 = 3)

Benzene (C6H6 - cyclohextriene)

• ring of six carbon atomsignore 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

• 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

• 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

Chemical bond typeand chemical bond densityeach determine materialstiffness/strengthand chemical durability

Conclusion: