Introduction to chemical bondLewis StructureIonic bondCovalent bond Metallic bond Intermolecular attractive force

H2 chemical bond formation

O-H bond formation

MXn M diletakkan di tengah sehingga terdapat n M-X ikatan

H dan Halogen hanya memiliki 1 ikatan, group 16 2 ikatan, group 15 3 ikatan group 14 4 ikatan

Group2 dan group 13 electron deficient Element di bawah Mg hipervalence C,N,O,P,S effective -type overlap

Counting electrons The total number of electrons represented in a Lewis structure is equal to the

sum of the numbers of valence electrons on each individual atom. Non-valence electrons are not represented in Lewis structures.

The octet rule states atoms with eight electrons in their valence shell will be stable, regardless of whether these electrons are bonding or nonbonding. The rule applies well to acidic compounds. The 18-Electron rule is operative on atoms from period 4, which have to achieve 18 electrons to their orbitals and achieve a stable configuration which has the same electron configuration as a Noble gas. Similarly from period 6, the atoms have to achieve 32 electrons to fill their orbitals.

Placing electrons Lewis structures for oxygen, fluorine, the hydrogen sulfate anion, and

formamide Once the total number of available electrons has been determined, electrons

must be placed into the structure. They should be placed initially as lone pairs: one pair of dots for each pair of electrons available. Lone pairs should initially be placed on outer atoms (other than hydrogen) until each outer atom has eight electrons in bonding pairs and lone pairs; extra lone pairs may then be placed on the central atom. When in doubt, lone pairs should be placed on more electronegative atoms first.

Once all lone pairs are placed, atoms, especially the central atoms, may not have an octet of electrons. In this case, the atoms must form a double bond; a lone pair of electrons is

Examples

Tentukan struktur lewis dari :

O3, NO3- , NCO ?

PO43-, BrO3F, IO2F2 ?

ClO4-, SO4

2- , PF5 , SF4 ?

Hypervalence : P, S, Br

Calculate number of bond

Jika aturan oktet dipenuhi :

number of bond = (total e- needed) –(valence e- available)

2e- needed = 5x8 = 40 e- available = 6 + 4(7) =34Number of bonding = (40-34)/2 =3 ?

H-C≡Ne- needed = 1(2) +2(8) = 18 e- available = 1 + 4 + 5 = 10Number of bonding = (18-10)/2 =4 ?

'Formal Charge’ is defined as the number of valence electrons minus the number of lone pair electrons minus one half of the bonding electrons.

6-2-3 = +15-4-2=-1

6-6-1=-1

6-2-3=+1

The simplest Lewis theory cannot predict this without a 'fix' called

resonance.

6-6-1 =-1

S-O bond are chemically and symetrically equivalent, average f.c = -1/2

Secondary resonance structure

5-4-2= -1

4-3 = +1

Muatan formal + EN rendahMuatan formal - EN tinggi

Li-F Both atoms have 0 formal charges

Ionic resonanceH-F

Mengapa sebuah struktur memiliki muatan parsial?Apa perbedaan antara muatan formal dan muatan parsial?

Struktur molekul memiliki muatan parsial jika terbentuk dari element element yang memiliki perbedaan elektronegativitas

Intermolecular attractive force

Hydrogen bond vs covalence bond

CHCl3 61.2°C

CCl4 76.8°C

The boiling points are:

            

Hydrogen bond effect

ethanol (with hydrogen bonding)

78.5°C

methoxymethane (without hydrogen bonding)

-24.8°C

The boiling points of ethanol and methoxymethane show the dramatic effect that the hydrogen bonding has on the stickiness of the ethanol molecules:

The hydrogen bonding in the ethanol has lifted its boiling point about 100°C.It is important to realise that hydrogen bonding exists in addition to van der Waals attractions. For example, all the following molecules contain the same number of electrons, and the first two are much the same length. The higher boiling point of the butan-1-ol is due to the additional hydrogen bonding.