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

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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.

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## 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

• 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

Periodic table of the Elements

s-block

p-block

d-block

f-block

### Inert gases

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

### Ionic bonding

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+

### Ionic bonding

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-

### Carbon (and Si, Ge, Sn, Pb)

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 - 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

• 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 ....

### Carbon - electron orbitals

• 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

### Electron orbitals

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.

y

x

z

Animation

### Electron configurations

Periodic table of the Elements

• H1s1

• He1s2

• Li1s2 2s1

• Be1s2 2s2

• B1s2 2s2 2p1

• C1s2 2s2 2p2

• N1s2 2s2 2p3

• O1s2 2s2 2p4

• F1s2 2s2 2p5

• Ne1s2 2s2 2p6

2p1 = px1

2p2 = px1 py1

2p3 = px1 py1 pz1

2p4 = px2 py1 pz1

2p5 = px2 py2 pz1

2p6 = px2 py2 pz2

### Methane (CH4)

• 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

Animation

### add a methylene group -CH2-

• MethaneCH4generic CnH2n+2

• Ethane C2H6

• PropaneC3H8

• ButaneC4H10

• PentaneC5H12

• HexaneC6H14

• Heptanec7H16

• OctaneC8H18

• ...paraffins ... polyethylene

### ... with one double bond:

• Methenen/ageneric CnH2n

• Ethene C2H4a.k.a. ethylene

• PropeneC3H6a.k.a. propylene

• ButeneC4H8a.k.a. butylene

• PenteneC5H10

• HexeneC6H12

• Heptenec7H14

• OcteneC8H16

• etcetera ....

### ... with one triple bond:

• Methynen/ageneric CnH2n-2

• Ethyne C2H2a.k.a. acetylene

• PropyneC3H4

• ButyneC4H6

• PentyneC5H8

• HexyneC6H10

• Heptynec7H12

• OctyneC8H14

• 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

### Double bond (C=C)

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

compression

tension

torsion

### Hybrid orbitals - summary

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

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

• sp bonds to 2 other atoms2σ and 2πbondsbond 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 cornertri-ene is three double bondssymmetry results in hexagonal moleculesymmetry 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 thatupper 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

Conclusion: