Chemical bonding

A. Introduction

Four types of bonds

Metallic bond

Ionic bond

Covalent bond

Intermediate type of bond between ionic and covalent

B. Defination

l a chemical bond refers to the strong electrostatic force binding atoms/ions together.

l Ionic bond is the strong non-directional electronic force of attraction between oppositely charged ions.

l Covalent bond is the strong directional electrostatic attraction between shared electrons (negatively charged) and two nuclei (positively charged) of the bonded atoms.

C. Electrical conductivity of compounds

Solid NaCl

Solid KI

Wax

Sugar

Pure water

Conclusion: 1._________________________________________________________

2._________________________________________________________

however,NaCl (aq) and KI(aq) conduct with chemical reaction called electrolysis.

3._________________________________________________________

4._________________________________________________________

e.g. PbBr2

e.g.CuCl2

D. Naming of ions

They are many simple ions :

If they make up of one atoms only ,they are called simple ions.

l For anions,add ‘ide’ at the end.

l E.g.

l For cations, just call its name and add ‘ion’ after it.

l E.g.

For the first 20 atoms, no need to add (II), (III) after its name, but starting from 21,it is required.

But when there is only one kind of compound, no need to add (II), (III).

e.g.

E. polyatomic ions

form from more than one atoms/ions

F. the colour of ions

*all group 1 and 2 elements’ ions are colourless.

So,NaCl and NaSO4 are colourless

CuCl2 ,CuSO4 are blue

G. migration of ions

H. formation of ions

1.to become stable as noble gas. There are 8 outermost shell electrons.

2.Octet rule:_____________________________________________ .

3.Others elements can obtain octet structure by gaining or giving elections(to obtain noble gas structure)

4.Unlike charges attract and form new substance.(i.e. )

5.Because they contain ions, they are called ionic compound .

e.g.

6.Electrostatic force joins two electrons together.

e.g.1 Na

e.g.2 Cl

e.g.3 NaCl

conclusion:

e.g.4 Mg

remark:anion should be drawn larger than cations .

I. Ionic giant structure

1.ionic compound has giant structures.

2.In a crystalline form (ionic crystals)

This arrangement is called lattice.

e.g.NaCl

Na ion is smaller in size.(3-D structure)

e.g.NaOH

Note:

1.potassium should be stored under oil.(Why?)

2.phosphorous should be stored under water.(Why?)

3.which of them contains free element in the world?

a.Li and Na

b.B and Si

c.oxygen and nitrogen

d.C and S

4.fluorine and potassium are the most reactive elements.their reaction is

very vigorous.

Because F is most electronegative.

K is most electropositive.

5.HCl is covalent compounds, not ionic compound.

It is formed by sharing of elections.

6.For halogens

F-

Cl-

Br-

I-

…..

As-

J.formula and names of ionic compounds

Empirical formula

Shows the simplest ratio of different element in a compounds

E.g.NaCl but not Na2Cl2

KI
Na2CO3 but not Na4CO6

Can be ionic or covalent compound.

Ionic formula

Shows the simplest ratio of different ions and the charge .

Must be ionic compounds.

E.g.1

E.g. 2

Remark:

l Ionic formula:simplest ratio

l Molecular formula:actual no. of atoms.

l Structural formula:the true structure.

e.g.ethene

l empirical formula: the simplest ratio of the element.

K.prediction of formula

Overall charge of formula must be zero.

i.e.electrically neutral (simplest integer ratio)

e.g.

L.Name of ionic compounds

We write cation before anion

e.g.NaCl sodium chloride

KI
PbBr2

CuO

Cu2O

Al2O3

NaCO3

NaOH

Naming of hydrates:

Solid :

Na2CO3-10 H2O----------

CuSO4-5 H2O-------------

M.periodic table

Conclusion:

1.metal forms cations

2.non-metal forms anions.

O.isoelectronic

Isoelectronic –have the same elecronic arrangement.

e.g.F,Ar,Cl,Cl,K,K,Br

isoelectronic=

cations=

anions=

P.isotope

Isotope-have the same no of proton but different no. of neutrons.

e.g.C-12 and C-14

Q.covalent Bonds

Q:How can a substance form electrolysis?

A:a.have free electrons(liquid state)

b.have ions

if it hasn’t , not ionic c’pds.

Not ionic bond

Not metallic bonds

IT MUST BE COVALENT BOND

Covalent bond is formed by sharing of elections.

e.g.1 chlorine gas 2,8,7

Pure covalent bond is formed by the equal sharing of electrons between two atoms.

i.e.electrons at the middle of 2 atoms.

Molecule is a small basic unit of covalent substance formed by a group of atoms which are joined together with covalent bonds.

In a molecule,no ions,no ionic bond.

In an ion ,no molecule,no covalent bond.

e.g.Cl2

l chlorine molecules or chlorine gas.

l There is one covalent bond .Cl—Cl

l No ionic bond .

l Do not conduct electricity.

Coclusion:

1.A molecule must be electrically neutral.

2.So it doesn’t conduct electricity, not an electrolyte.

3.The electrons are localized between the atoms at the covalent bond.(i.e. directional). No mobile ions.

R.molecule example

e.g.1 O(2,6)

e.g.2 N(2,5)

e.g.3 C(2,4)

S.covalent compound example

e.g.1 HCl

e.g.2 H2O

T.covalent bond pairs

Cl—Cl (single bond)

O O (double bond)

N N (triple bond)

e.g.1 Cl,Cl

e.g.2 C,H

e.g.3 N,H

N.B.:NH3=NH4(ions)

Ammonia= ammonium(ions)

e.g.4 O,H

e.g.5 Cl,H

Remark:the name of covalent bond compound is always one word.

e.g.ethene,ammonia

The name of ionic bond compound is always two words.

e.g.sodium chloride.

U.shape of molecules

e.g.1 Cl—Cl(linear)

e.g.2 H2O(V-shape)

e.g.3 NH3(trigonal pymidal)

e.g.4 CH4(tetrahedral)

V.formula for molecules

Molecular formula

Formula for molecules--

(covalent bond) Structural formula

a.molecular formula

the actual no. of each kind of atom in a molecule of the substance.

e.g.ethene

but empirical formula=

(note the difference)

b.structural formula

show how the atoms joined together in a molecule.

e.g.ethene

W.intermolecular force

A weak force

Easily broken

X.steps to write chemical formula for ionic bonds(for reference)

Y.steps to write chemical formula for covalent compounds.(for reference)

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