CHEMICAL BONDING

CHEMICAL BONDING Molecular Orbital and Lewis Structure

Review • Chemical Bonding occurs when there are electrons transferred ( Ionic Bonds ) or shared ( Covalent Bonds ). • Example: ● ● ● ● + - ● ● Na x ● x Cl H x H x Br ● ● ● ● ● ● ● The transfer of electrons = ionic bond Opposite charges attract. The sharing of electrons = covalent bond

Not Actually • What determines weather a bond is ionic or covalent is the electronegativity difference between the two elements. • Electronegativity: the attraction for electrons. • The element with the highest EN will become negative. • It is the EN difference that determines weather a bond is classified ionic or covalent.

Example • What is the EN difference between the elements in Lithium chloride. LiCl • Li = 1.0 v • Cl = 3.0 v 3.0v-1.0v = 2.0v Ionic The Following is a chart of chemical bond classification EN Diff % ionic character Bond Type 0.0 – 0.4 <10% Non-Polar covalent (NPC) 0.41 – 1.7 <50% Polar covalent (PC) >1.7 >50% Ionic (I)

Practice • More Examples: • Polar means a separation of charge. Some covalent molecules are polar and some are not. • H2S • SO3 • NCl5 2.5v – 2.1v = 0.4v NPC 3.5v – 2.5v = 1.0v PC 3.0v – 3.0v = 0.0v NPC

Bonding Orbitals • When elements form compounds the electron involved in the bonding are from the s and p Orbitals. • However, equal energy distribution sometimes alters the structure of the electrons from the free element state to better satisfy a lower energy state when bonding to another element.

Group s p hybrid name shape • I 0 000 none s1 spherical • II 0 000 00 sp1 linear • III 0 000 000 sp2 Triangular • IV 0 000 0000 sp3 Tetrahedral • V 0 000 none p3 Pyramidal • VI 0 000 none p4 bent • VII 0 000 none p5 linear * * * * * *

Molecular Orbital and Lewis Structure • CaF2Ca is in Group II +2 • F is in Group VII -1 • The ratio is 2 to 1 therefore calcium is in the middle. • Lewis Structure • :F—Ca—F: sp1 p5 p5 .. .. .. ..

More Examples • Let’s Try H2O H = +1 And O = -2 • Group 1 Group 6 p4 . . H O : S1P4 s1 * H * s1 Lewis Structure Molecular Orbital Bond Type

Polarity • A polar molecule occurs when the structure allows a separation of charge. There are two things that determine weather a molecule is polar or non-polar. 1. bond polarity 2. shape. Shapes that do not allow polarity because any polarity in the bonds is canceled by equal forces Linear TetrahedralTriangular

There’s Only Two • What determines polarity? • Polar Molecules • Polar bonds ( PC or I ) • AND • 2.Irregular Shape ( Bent, diatomic linear ) • Non-Polar Molecules • Non-polar bonds ( NPC ) • OR • 2.Regular Shape ( Linear, Triangular, or Tetrahedral )

Review • Polar Bonds: Ionic, and Polar Covalent • Non-Polar Bonds: Non-Polar Covalent • There are Two Kinds of Molecules Polar Molecules Non-Polar Molecules No Separation of charge -2 Separation of charge +1 -2 +1 +1 +1

Lewis Structure for Compounds with PAI • Compounds with polyatomic Ions are both covalent and ionic by definition. • Polyatomic Ion: a group of covalently bonded atoms that carry a charge. • In order to draw a Lewis structure for a compound with a PAI remember the trends of the groups when the elements are central atoms. • Group 2 – linear • Group 3 – triangular • Group 4 - tetrahedral Group 5 - pyramidal Group 6 - bent

Tinker Toys • Draw the Lewis Structure for H2SO4 • Start with the charges H2+1SO4-2 What about sulfur “S” Rule 3: the sum of the oxidation #’s in the formula =0 H2+1 = +2S=xO4-2=-8 = 0 What must S be to get 0? H2+1S+6O4-2 The charge tell the # bonds

Let’s Build Start with charge The charge tell the # bonds H2+1S+6O4-2 Sulfur is the Central atom with 4 Oxygen’s : : H O .. : .. O S O .. : H .. O Sulfur is +6 and has 6 bonds and Oxygen 2 bonds

Legands • Sometimes compounds form within the same group. Chlorine Fluoride Cl is +7 and Fluorine is -1 ClF5 .. .. .. .. .F: :F. .. .. :Cl: .. . .F: .. :F. . .. Octahedral :F: ..

CHEMICAL BONDING