Chapter 6: ChemicalBonding 1 Lewis structure Bond polarity and bond strength. students should be able to understand and explain: • • • • • Ionic bonding.Learning outcomes • At the end of the lesson. 2 . Octet rule. Covalent bonding. • This is known as the octet rule.Octet rule • Almost all elements in its natural state are not stable. • Only elements of group 8 are stable. • Elements that do not have fully filled valence shells will try to achieve octet stability by either: • Donating electron • Accepting electron • Sharing electron 3 . • The stability of group 8 elements are due to the fact that its valence shell are full. Ionic bond • Ionic bonds are usually formed between metals and non metals. • Metals: • Tend to donate its valence electrons • Forms positive ion or cation • Non-metals: • Tend to accept electrons • Forms negative ion or anion • Ionic bond is the strong electrostatic forces of attraction between two oppositely charged ions. 4 . non-metals tend to share its valence electrons. atom B will also share one electron) • An atom will share exactly the same amount of electrons it needs to achieve octet configuration (chlorine has 7 valence electrons. hence it will share only 1 e) 5 . • Rules of covalent bond: • The sharing of electron between atoms are mutual (if atom A shares one electron. it needs 1 e to achieve octet stability. • Covalent bond is formed when non-metals’ valence shell overlaps to allow sharing of electrons.Covalent bond • Covalent bonds are usually formed between non-metals • In order to achieve octet configuration. • Lewis structure is simplified as it removes the need to draw the other inner shells. • ‘Dots and crosses’ are still used to represent different electrons. 6 .Lewis structure • Lewis structure only shows the valence electrons of atoms that are involved in covalent bonding. Lewis structure 7 . the greater the ability to attract electrons • General pattern: • Non-metals have greater electronegativity compared to metals • Electronegativity increases across the period • Electronegativity decreases down the group 8 .Electronegativity • Electronegativity is the ability of an atom to attract electrons in a covalent bond • Different atoms have different value of electronegativity • The stronger the electronegativity. Bond polarity • When two of the same atoms forms a covalent bond. the electrons are not shared equally • The more electronegative atom will pull the electrons closer towards itself • The electrons are unsymmetrically distributed • The difference in electronegativity of atoms in a covalent bond results in polar bonds 9 . the electrons are shared equally resulting in a non-polar bond • When two different elements are bonded. Bond Polarity 10 . Bond Polarity • The unequal distribution of electrons results in polar bonds • The bond has a dipole indicated by • 𝛿 + (less electronegative atoms) • 𝛿 – (more electronegative atoms) 11 . • Bond energies varies from compound to compound. • One of the factors that affect bond energy is the length of the bond. • The shorter the bond. 12 . the higher the bond energy. • Bond energy can be defined as the energy needed to break one mole of a particular covalent bond.Bond strength • Bond strength refers to the strength of a particular covalent bond. • Bond strength can be measured based on bond energy. 110 941 H-Cl 0.074 435 Cl-Cl 0.Bond strength Bond Bond length (nm) Bond energy (kJ mol-1) H-H 0.198 243 O=O 0.121 495 N≡N 0.109 414 13 . THE END 14 .