MZGIN M. AYOOB Types of chemical bond

› Force that holds groups of two or more atoms together and makes the atoms function as a unit.

› Atoms or ions are held together in molecules or compounds by chemical bonds.

› The type and number of electrons in the outer electronic shells of atoms or ions are instrumental in how atoms react with each other to form stable chemical bonds.

› Over the last 150 years scientists developed several theories to explain why and how elements combine with each other.

Whats the chemical bond

› named after Gilbert N. Lewis, who introduced › it in his 1916 

› also known as Lewis dot diagrams, electron dot diagrams, "Lewis Dot formula" Lewis dot structures, and electron dot structures) 

› are diagrams that show the bonding  between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.

LEWIS DOT STRUCTURE

LEWIS STRUCTURES

C H PCARBON HYDROGEN PHOSPHOROUS

Ca ArCALCIUM

ARGON

Symbols of atoms with dots to represent the valence-shell electrons

1 2 13 14 15 16 17 18

H He: Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl

:Ar :

LEWIS STRUCTURES

› Strong, STABLE bonds require lots of energy to be formed or broken

› weak bonds require little E

BOND STRENGTH

›IONIC BONDING – FORMS IONIC COMPOUNDS– TRANSFER OF E-

›COVALENT BONDING– FORMS MOLECULES– SHARING E-

›METALLIC BONDING– Occurs between like atoms of a metal in the

free state

TYPES OF BONDING

› electrons are transferred between valence shells of atoms

› ionic compounds are

made of ions

• ionic compounds are called Salts or Crystals

NOT MOLECULES

ELECTROVALENT OR IONIC BOND

› Always formed between metals and non-metals

[METALS ]+ [NON-METALS ]-

Lost e- Gained e-

ELECTROVALENT OR IONIC BOND

Ionic Bonds› Metal to nonmetal.› Metal loses electrons to form cation.› Nonmetal gains electrons to form

anion.› The electronegativity between the

metal and the nonmetal must be > than 2.

› Ionic bond results from + to − attraction.› Larger charge = stronger attraction.› Smaller ion = stronger attraction.

› Lewis theory allows us to predict the correct formulas of ionic compounds.

IONIC BOND: FACTORS GOVERNING ITS FORMATION

The formations of ionic bond governed by the following factors:

1. Ionization energy: • Formation of ionic bond metal atom loses electron to form

cation• Energy required for this equal to ionization energy• Alkali metals have lowest ionization energy, thus have more

tendency to form cation2. Electron gain enthalpy:

• Electron released in the formation of cation are to be accepted by the other atom taking part in the ionic bond formation

• Electron accepting tendencies depend on upon the electron gain enthalpy

• Defined as energy released when isolated gaseous atom takes up an electron to form anion.

• Greater the negative enthalpy, easier the formation of anion

IONIC BOND: FACTORS GOVERNING ITS FORMATION

3. Lattice energy: • Combination of oppositely charged ions to form ionic crystal, with

release of energy is referred as lattice energy• Higher value of lattice energy, greater will be the stability of

compound• Magnitude of lattice energy gives idea about the strength of interionic

forces• Size of ions:

• In case of similar ions inter-nuclear distance is lesser due to which inter-ionic attraction is greater and hence the magnitude of lattice energy will be larger

• Charge on the ions: • Ions have higher charge exerts stronger forces of attraction and hence

larger amount of energy is released. Thus value of lattice energy is higher

IONIC BOND PROPERTIES

• Ionic compound exist in solid state• The network of ions have a definite geometric pattern which depends on the size and charge of ions• Posses high melting and boiling points due to strong electrostatic force of attraction between the ions• Good conductor of electricity in molten or dissolved state• Does not conduct electricity in solid state as ions are not free to move• Are soluble in polar solvent like water as solvent interacts with the ions of ionic solid•The chemical reactions between ionic compounds in aqueous solution involves the combination between their ions, such reactions are called ionic reactions.

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electron pairs

• Stable non-ionizing particles, they are not conductors at any state

• Examples; O2, CO2, C2H6, H2O, SiC

COVALENT BOND

The Convalent Bond

• Shared electrons are attracted to the nuclei of both atoms.

• They move back and forth between the outer energy levels of each atom in the covalent bond.

• So, each atom has a stable outer energy level some of the time.

Chemical Bonds

Covalent bonds form when atoms share 2 or more valence electrons.

Covalent bond strength depends on the number of electron pairs shared by the atoms.

single bond

doublebond

triplebond

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Chemical bond

Sigma bonds

Sigma bonds are covalent bonds formed by direct overlapping between two

adjacent atom's outer most orbitals. The single electrons from each atom's orbital

combine to form an electron pair creating the sigma bond

π bonds

pi bonds  are covalent chemical bonds where two lobes of one involved atomic

orbital overlap two lobes of the other involved atomic orbital

The hydrogen bond 

A hydrogen bond is formed between H atom attached to an

electronegative atom, and an electronegative atom that possesses a

lone pair of electrons

when electrons are shared equally

H2 or Cl2

NON POLAR COVALENT BOND

Oxygen Atom Oxygen Atom

Oxygen Molecule (O2)

when electrons are shared but shared unequally

H2O

POLAR COVALENT BOND

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

PROPERTIES OF COVALENT BOND

• Compounds formed exist as discrete molecules •Weak intermolecular force due to small molecular size

•Mainly exist in liquid or gaseous state

•Sugar, urea, starch etc. exist in solid state

•Low melting and Boiling points due to weak attractive forces

•Poor conductor of electricity in fused or dissolved state

•Less soluble in water

•Gives molecular reaction

›A covalent bond is formed by two atoms sharing a pair of electrons. The atoms are held together because the electron pair is

attracted by both of the nuclei.›In a simple covalent bond, each atom

supplies one electron to the bond - but that doesn't have to be the case .

›A co-ordinate bond is a covalent bond (a shared pair of electrons) in which both

electrons come from the same atom.

COORDINATE BOND

Example: NH4+

 

COORDINATE BOND

COORDINATE BOND

Properties of Coordinate bond :

1. Are generally soluble in water and organic solvents

2. Boiling and melting points of these compounds are less than electrovalent compounds but are higher than covalent compounds

3. Compounds ionize in aqueous solution giving simple and complex ions

4. These bonds are also directional and stereoisomerism is also found

5. Molecules possess definite shape and definite bond angles, thus have definite geometry

 

Metallic bonding is the electrostatic attraction between the positively charged atomic nuclei of metal atoms and the delocalised electrons in the metal. In the solid state, both metallic and ionic compounds possess ordered arrays of atoms or ions and form crystalline materials with lattice structures.

Metallic bond

Metallic Bonding

› The model of metallic bonding can be used to explain the properties of metals.

› The luster, malleability, ductility, and electrical and thermal conductivity are all related to the mobility of the electrons in the solid.

› The strength of the metallic bond varies, depending on the charge and size of the cations, so the melting points of metals vary as well.

Sea of Electrons• Electrons are free to move

through the solid.• Metals conduct electricity.