Chemical Chemical BondingBonding

Chemical Chemical BondingBonding

Learning Outcomes

• Explaining tend of elements to obtain their stability

• Drawing valence electrons of noble gases atom (duplet and octet) and valence electrons of non noble gases (Lewis's structure)

• Explaining formation process of ionic bonding

• Explaining formation process of covalent single, double and triple covalent bonding

• Explaining formation process of coordinate covalent bonding of some compounds

Why do atoms bond together?

• Some atoms are very reluctant to combine with other atoms and exist in the air around us as single atoms. These are the Noble Gases and have very stable because their outer shells are full.

Why do atoms bond together?

• All other atoms therefore, bond together to become electronically more stable, that is to become like Noble Gases in electron arrangement.

• Bonding produces new substances and usually involves only the 'outer shell' or 'valency' electrons and atoms can bond in two ways.

Ionic Bonding

• Ionic bonds are formed by one atom transferring electrons to another atom (take and give electron)

• Metal and non metal• The atom losing electrons forms a

positive ion and is usually a metal. • The atom gaining electrons forms a

negative ion and is usually a non-metallic element.

• Example 1: A Group 1 metal + a Group 7 non-metal e.g. sodium + chlorine ==> sodium chloride NaCl or ionic formula Na+ Cl- 

In terms of electron arrangement, the sodium donates its outer electron to a chlorine atom forming a single positive sodium ion and a single negative chloride ion. The atoms have become stable ions, because electronically, sodium becomes like neon and chlorine like argon.

Na (2.8.1) + Cl (2.8.7) ==> Na+ (2.8) Cl- (2.8.8)

• Example 2: • A Group 2 metal + a Group 7 non-metal

e.g. magnesium + chlorine ==> magnesium chloride MgCl2 or ionic formula Mg2+ (Cl-)2 

• In terms of electron arrangement, the magnesium donates its two outer electrons to two chlorine atoms forming a double positive magnesium ion and two single negative chloride ions. The atoms have become stable ions, because electronically, magnesium becomes like neon and chlorine like argon.

• Mg (2.8.2) + 2Cl (2.8.7) ==> Mg2+ (2.8) 2Cl- (2.8.8)

Covalent Bonding • Covalent bonds are formed by atoms

sharing electrons to form molecules. • This type of bond usually formed

between two non-metallic elements. The molecules might be that of an element

• The covalent bonding is caused by the mutual electrical attraction between the two positive nuclei of the two atoms of the bond, and the negative electrons between them.

Single Covalent Bond•One single covalent bond is a sharing of 1 pair of electrons

•Example : H2, Cl2

Double Covalent Bond•two pairs of shared electrons between the same two atoms gives a double bond

•Example : O2 , CO2

Triple Covalent Bond•for two atoms to share 3 pairs of electrons and give a triple bond

•Example : N2.

Learning Outcomes

• Investigating polarity of some compounds and their relation with electronegativity through experiment

• Describing formation process of metallic bonding and its relation with physical properties of metals

• Relating physical properties of matter to their type of bonding

Polarity

• Polar covalentThe difference of electronegativity is highExample : HCl

• Non polar covalentThe difference of electronegativity is not highExample : H2

Polarity

• Polar moleculeElectron distribution is not well distributed

• Nonpolar moleculeElectron distribution is well distributed

Properties of ionic compound

• They are crystalline solids at room temperature

• They have high melting and boiling points

• They are often soluble in water• They arenot soluble in trikloroethene• They conduct electricity when molten or

dissolved in water

Properties of covalent compound

• They are often liquids or gases at room temperature

• They have low melting and boiling points

• They arenot soluble in water• They are soluble in trikloroethene• They do not conduct electricity

Metallic bonding

• Metals atom have relatively few electrons in their outer shells

• When they are packed together, each metal loses its outer electrons into a ‘sea’ of free electron

• Those free electrons are delocalised and form a kind of electrostatic glue holding the structure together.