ch08 part5 complex lewis structures

8/11/2019 Ch08 Part5 Complex Lewis Structures

1/31


2/31

2

There are some molecules andpolyatomic ions for which no singleLewis structure consistent with allcharacteristics and bonding informationcan be written.


3/31

3

Step 1. The total number of valence electrons

is 24, 5 from the nitrogen atom and 6 fromeach O atom, and 1 from the 1 charge.

Write a Lewis structure for NO2.-

3 NO .


4/31

4

Since the extra electron present results innitrate having a 1 charge, the ion is enclosedin brackets with a charge.

Step 2. The three O atoms are bonded to a

central N atom. Write the skeletal structureand place two electrons between each pair ofatoms.


3 NO .

O N O: :O : -


5/31


6/31

6

O N OO

Step 4. Distribute the 18 electrons around the

N and O atoms.


3 NO .

: : : ::: : : :: : :electron deficient


7/31

7


3 NO .

Step 5. One pair of electrons is still needed to

give all the N and O atoms a noble gasstructure. Move the unbonded pair ofelectrons from the N atom and place it

between the N and the electron-deficient Oatom, making a double bond.

: : : ::: : : :O N OO: : :

-


8/31

8


3 NO .

Step 5. One pair of electrons is still needed to

give all the N and O atoms a noble gasstructure. Move the unbonded pair ofelectrons from the N atom and place it

between the N and the electron-deficient Oatom, making a double bond.

NO

::

O :: : O :: : :

-


9/31

9

A molecule or ion that shows multiplecorrect Lewis structures exhibits resonance.


3 NO .

Step 5. There are three possible Lewis

structures.

NO

::

O :: : O ::

: :

- :NO

::

O : : O :: : :

-Each Lewis structure is called a resonancestructure.

NO

::

O :: : O :: : :

-


10/31


11/31

11

Compounds ContainingPolyatomic Ions


12/31

12

A polyatomic ion is a stable group of atoms

that has either a positive or negative chargeand behaves as a single unit in many chemicalreactions.


13/31


14/31

14

The nitrate ion is a polyatomic ioncomposed of one nitrogen atom and three

oxygen atoms.

N

O :

:O :: : O :: : :

-

Na+

It has a charge of 1 One nitrogen and three oxygen atoms

have a total of 23 valence electrons.


15/31

15

The 1 charge on nitrate adds an additionalvalence electron for a total of 24.

N

O :

:O :: : O :: : :

-

Na+

The additional valence electron comesfrom a sodium atom which becomes asodium ion.


16/31

16

Sodium nitrate has both ionic and covalentbonds.

N

O :

:O :: : O :: : :

-

Na+

Ionic bonds exist between the sodiumions and the carbonate ions.

covalentbond

covalent

bond

covalent

bond

ionic bond

Covalent bonds are present betweenthe carbon and oxygen atoms withinthe carbonate ion.


17/31

17

When sodium nitrate is dissolved in water,the ionic bond breaks.

N

O :

:O :: : O :: : :

-

Na+

The sodium ions and nitrate ions separatefrom each other forming separate sodiumand nitrate ions.

N

O :

:O :: : O :: : :

-

Na+

The nitrate ion, which is held together bycovalent bonds, remains as a unit.


18/31

18

Molecular Shape


19/31

19

The 3-dimensional arrangement of the atomswithin a molecule is a significant determinantof molecular interactions.


20/31

2011.12


21/31

21

The Valence ShellElectron Pair (VSEPR)

Model


22/31

22

The VSEPR model is based on the idea

that electron pairs will repel each otherelectrically and will seek to minimize thisrepulsion.

To accomplish this minimization, theelectron pairs will be arranged as farapart as possible around a central atom.


23/31

23

BeCl2 is a molecule with only two pairs ofelectrons around beryllium, its centralatom.Its electrons are arranged 180 o apart formaximum separation.


24/31

24

BF3 is a molecule with three pairs of electronsaround boron, its central atom.

Its electrons are arranged 120 o apart formaximum separation.

This arrangement of atoms is called trigonalplanar.


25/31


26/31

26

Ball and stick models of methane, CH 4, and carbontetrachloride, CCl 4.

11.13


27/31

27

Ammonia, NH 3, has four electron pairsaround nitrogen.

The arrangementof electron pairsaround nitrogen istetrahedral.


28/31

28

The NH3

moleculeis pyramidal.

NH3 has oneunbonded pairof electrons.


29/31

29

Water has four electron pairs aroundoxygen.

The arrangementof electron pairsaround oxygen istetrahedral.


30/31

30

The H 2O moleculeis bent.

H2O has twounbonded pairsof electrons.


31/31

31

ch08 part5 complex lewis structures

Documents