2.chemical Bonds

INTERNATIONAL UNIVERSITY

SCHOOL OF BIOTECHNOLOGY

CHEMICAL BONDS Lecturer: Dr. Hoang Le Son Course title: Organic Chemistry Group: 2

GROUP 2 • • • • • •

Trần Triệu Quân – BTUN08027 Huỳnh Hải Vân – BTIU08080 Lê Thị Trúc My – BTWE08016 Phạm Thị Ngọc Thúy – BTIU08065 Nguyễn Bảo Ngọc – BTUN08052 Nguyễn Quang Huy – BTWE08012

OUTLINE I.

Introduction: - Chemical bonds – Classification. - Octet Rule – Valence electron – Electronegativity. - Bond length – Bond strength.

II. Important chemical bonds: - Ionic bond - Covalent bond. - Comparison between Ionic bond and Covalent bond. - Hydrogen bond. III. Summary: IV. Reference:

I. INTRODUCTION

I. INTRODUCTION • Definition: Chemical bond is link between atoms of two or more elements by mutual attraction.

• Purpose: Chemical bond influences to the nature of chemical compounds. - Physical properties: effects to the solubility, the melting and boiling point, etc … - Chemical properties: makes the bonds become long or short, weak or strong, etc ….

CLASSIFICATION

Important chemical bonds.

OCTET RULE The Octet rule: says that atoms tend to gain, lose or share electrons so as to have eight electrons in their outermost energy level and obtain stable configuration of noble gas.

Metals tend to lose electrons to obey the Octet rule and become Cations. A neutral sodium atom and a positively charged sodium ion after sodium loses the one electron in its outer orbital.

OCTET RULE

It is easy for nonmetal to gain electron to have full outermost energy level and become Anions.

A neutral chlorine atom becomes negatively charged chlorine ion after gaining the one electron in its outer orbital.

VALENCE ELECTRONS  Electrons in the outermost energy level Ex: Na is 1s2 2s2 2p6 3s1  Valence electrons

outer energy level is 1 Bond pairs Lone pairs

Ex:

Na

••

Cl •• ••

bond pair

lone pair

VALENCE ELECTRONS

The number of valence electron is the group number A

ELECTRONEGATIVITY • Definition: A measure of the force of an atom’s attraction for electrons which are bonded with the electrons of another atom.

• Classification in Electronegativity: The difference of electronegativity determine type of chemical bond. 0.0 → 0.3: Non-polar covalent 0.3 → 1.7: Polar covalent 1.7 → 4.0: Ionic bond

ELECTRONEGATIVITY

BOND STRENGTH – BOND LENGTH Bond strength •

The strength with which a chemical bond holds two atoms together.

•

The stronger bond need more dissociation energy to break it.

BOND STRENGTH – BOND LENGTH Bond length:

The distance between two bonded atoms at their minimum potential energy.

BOND STRENGTH – BOND LENGTH Bond length • Determine the overall size and shape of a molecule.

Longer bonds are weaker than shorter bonds. Multiple bonds are shorter and stronger than their single bond counterparts.

BOND STRENGTH – BOND LENGTH Example: Bond

Bond strength (Kcal/mol)

Bond length (pm)

Ethane (CH3CH3)

C—C

90

154

Ethylene (CH2= CH2)

C—C

174

134

II. IMPORTANT CHEMICAL BONDS

IONIC BOND

IONIC BOND Definition: An ionic bond is bond formed when one or more electrons are transferred from one atom to another.  Extremely strong bond. Ex: NaCl, AlCl3, MgO, CaCl2, K2O…

IONIC BOND Formation: Anions and Cations which have opposite charges will attract one each other by electrostatic forces. The forces of this attraction are called Ionic bonds Ionic bonds are between metals and nonmetals. In Ionic bond, the electrons are not shared, as the anion steals the electrons from the cation.

IONIC BOND

The summary of ionic bond formation contains 3 steps: • • •

The removal of an electron(s) by one element. The gain of an electron(s) by second element. The attaction between oppositely charged ions.

IONIC BOND Example: Consider the reaction of Sodium and Chlorine.

IONIC BOND Properties: • • • •

Metals and nonmetals. Transfer of electrons. Oppositely charged ions. Electrostatic attraction.

IONIC COMPOUNDS Definition: Ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. In any sample of ionic compound, the positive charges of the cations must equal to the negative charges of the anions.

Lattice structure of sodium chloride

Sodium Chloride

Iron oxide

IONIC COMPOUNDS Properties of ionic compounds:

State: solid Crystal pattern: every ion is attracted to all other ions with the opposite charge and repulsions are minimized, resulting a well-defined crystal.

IONIC COMPOUNDS Properties of ionic compounds: High melting point and boiling point Solubility: are soluble in water and many polar solvents.

Conductivity: ionic compound can conduct electricity when it dissolves in water or melts.

COVALENT BOND

COVALENT BOND Definition: Covalent bonds are generated between two or more atoms by sharing electrons.

Formation Each atom contributes one electron to a shared electron pair to attain stable configuration for each atom.

COVALENT BOND Example: Dihydrogen

Two hydrogen atoms are connected each other by sharing two valance electrons of each atom.

COVALENT BOND Another example: Water

An oxygen atom which has two unpaired electrons in its outer shell and two hydrogen atoms which also have two valence electrons attract each other to form two covalent bonds by sharing electrons.

COVALENT BOND Properties • Generated by sharing electrons, not transferring • Formed between nonmetals • Formed between atoms of the same elements or different elements.

POLAR VS. NONPOLAR BOND Nonpolar bond • The electron pair is equally shared. • The bond is usually formed by identical atoms. • The bond is not polarized. Example:

H2

O2

POLAR VS. NONPOLAR BOND Polar bond • The electron pair is not equally shared. • The bond is usually formed by different electronegative atoms. • The bond is polarized because it has one positive end and one negative end. •The share electron pair is shifted from the center and pulled away from one atom. Example: HCl, H2O

HCl

H2O

POLAR VS. NONPOLAR BOND NON POLAR BOND

• Equally shared • Same elements • Longer bond • Weaker bonds

POLAR BOND

• Not equally shared • Different elements • Shorter bonds • Stronger bonds

POLAR VS. NONPOLAR LIQUID NON POLAR LIQUID

POLAR LIQUID

Dissolve better in other non polar liquid

Dissolve better in other polar liquid and ionic salts

COVALENT BOND Single bond: - Have a one pair of shared electrons

Multiple bonds: - include double bond and triple bond. - more than one pair of shared electrons. Example: O2, N2

O2

N2

MOLECULAR GEOMETRY

VSEPR Valence

Shell Electron

Pair Repulsiontheory

SOME COMMON GEOMETRIES Linear 180o apart

H

Be

H

2 hydrogen atoms bonded to central atom

SOME COMMON GEOMETRIES Trigonal Planar

120o apart

SOME COMMON GEOMETRIES Tetrahedral 109.50 apart

IONIC BOND vs COVALENT BOND

IONIC BOND VS. COVALENT BOND IONIC BOND Totally transfer electrons from one atom to another Metals and nonmetals Single bond

COVALENT BOND Sharing electrons between the atoms Nonmetals Single & Multiple bond

IONIC BOND VS. COVALENT BOND IONIC BOND  Crystalline solids  High melting and boiling point  Good electrical conductor  Often soluble in water but not in carbon tetracloride

COVALENT BOND  Gases, liquids or solids  Low melting and boiling point  Poor conductor of electricity and heat  Often soluble in carbon tetracloride but not in water

HYDROGEN BOND

HYDROGEN BOND Definition: A hydrogen bond forms when a hydrogen atom covalently bonded to an electronegative atom.

Not be confused hydrogen bond with a covalent bond to hydrogen atom!!!

HYDROGEN BOND What do you need? o A hydrogen atom covalently bonded to a high electronegative atom … usually N, O or F. o A lone pair of electrons on the electronegative atom.

If only one of these conditions is satisfied, you don’t get hydrogen bond!!!

HYDROGEN BOND Give me an example! ammonia, NH3 …

This does have hydrogen bond. Nitrogen is very electronegative, and it has one lone pair of electrons in ammonia.

HYDROGEN BOND Example!

Water

Oxygen atom is very electronegative, and it has two lone pairs of electrons in water. Two hydrogen bonds are formed by the attraction between the oxygen atom carrying negative charge and hydrogen atoms covalently bonded with other oxygen atoms.

IMPORTANCE OF HYDROGEN BOND - Explain the properties of water. - Hydrogen bond plays a very important part in complementary base-paring which is essential for the proper functioning of DNA.

SUMMARY

SUMMARY IONIC BOND AND COVALENT BOND:

SUMMARY HYDROGEN BOND Importance: -The properties of water and ice - Protein and nucleic acid

WEBSITES: http://chemlab.truman.edu/CHEM121Labs/MM1Files/TrigonalPlanar.gif http://www.elmhurst.edu/~chm/vchembook/images/203bh3.gif http://www.ausetute.com.au/namiform.html http://www.docstoc.com/docs/10611490/Introduction-to-Ionic-Bonds http://www.chemguide.co.uk/atoms/bonding/ionic.html http://www.authorstream.com/presentation/ankush85-180239-ionic-bonding-ions-eleme http://iss.cet.edu/electricity/pages/b11.xml http://www.sb.fsu.edu/~fajer/Education/2010/Lectures/3_Chemical_Bonds.htm

HYDROGEN BOND

HYDROGEN BOND BOOKS: - Bruice PY, 2003, Organic Chemistry, 4th edition, Prentice Hall - Draganova K and Springer S, 2006, Fundamental Chemistry for the Life Sciences, 3rd edition, International University Bremen - Philip M, 2009, Essential Chemistry: Chemical bonds, Chelsea House