COVALENT BONDS: NONPOLAR AND POLAR

Covalent Bonds Definition 1) chemical bond in which two atoms share a pair of valence electrons 2) can be a single, double, or triple bond single, 2e-’s (-); double, 4e-’s (=); triple, 6e-’s( ) 3)2 types of bonds - polar - non polar

Electrons are shared between atoms. Both elements are nonmetals Electrons are shared between atoms. Both elements are nonmetals. Molecules are formed with covalent bonds. Two types: Polar and non-polar Covalent bonded molecules are not conductors at any state Ex: H2O, O2, CO2, C2H6, SiO2, C6H12O6 Covalent Bonds

Covalent Bonds

Bond and Lone Pairs Valence electrons are distributed as shared or BOND PAIRS and unshared or LONE PAIRS. • •• H Cl shared or bond pair lone pair (LP) This is called a LEWIS structure.

Electron distribution is depicted with Lewis electron dot structures This is how you decide how many atoms will bond covalently. (In ionic bonds, it was decided with oxidation numbers) G. N. Lewis 1875 - 1946

Nonpolar Covalent Molecules

Nonpolar Covalent Molecules Equal distribution of charge around a central atom. Molecule has a symmetrical shape Nonpolar Covalent Molecules

THEY BOTH GET FULL OUTER SHELLS (AN OCTET) In a chlorine molecule, each of the atoms shares a pair of electrons circled in GREEN, making the covalent bond. Since it’s just one pair being shared, this is a SINGLE COVALENT BOND. Each of the chlorine atoms also has three pairs each of UNSHARED ELECTRONS. THEY BOTH GET FULL OUTER SHELLS (AN OCTET) BY SHARING.

unshared electrons When electrons are written as a Lewis diagrams, they are usually paired. Electrons prefer being in pairs. When electrons are shared between atoms, one electron from each atom connects together, making a SINGLE BOND. Electrons not involved in bonding are mostly paired away from the bond. They are the “unshared” electrons. If they connect 2 or 3 pairs at a time, they make DOUBLE or TRIPLE BONDS.

When 2 oxygen atoms combine to form a molecule, each keeps two pairs of unshared electrons, but shares two pairs (in the middle) with each other. That is a DOUBLE COVALENT BOND

and each atom also has one pair of UNSHARED ELECTRONS. Diatomic Nitrogen makes a TRIPLE COVALENT BOND and each atom also has one pair of UNSHARED ELECTRONS.

Double and even triple bonds are commonly observed for C, N, P, O, and S H2CO SO3 C2F4

Chlorine forms a covalent bond with itself Cl2

How will two chlorine atoms react? Cl Cl

Cl Cl Each chlorine atom wants to gain one electron to achieve a full outer shell.

Cl Cl do to achieve an octet? Neither atom will give up an electron - chlorine is highly electronegative. What’s the solution – what can they do to achieve an octet?

Cl Cl

Cl Cl

Cl Cl

Cl Cl

Cl Cl Full (octet)

Cl Cl Full (octet) We circle the shared electrons

Cl Cl The octet is achieved by each atom sharing the electron pair in the middle We circle the shared electrons

Cl Cl Full shells are achieved by each atom sharing the electron pair in the middle

Cl Cl This is the bonding pair circle the electrons for each atom that completes their octets

Cl Cl It is a single bonding pair circle the electrons for each atom that completes their octets

Cl Cl It is called a SINGLE BOND circle the electrons for each atom that completes their octets

Single bonds are abbreviated Cl Cl Single bonds are abbreviated with a dash

This is the chlorine molecule, Cl Cl This is the chlorine molecule, Cl2

O2 Oxygen is also one of the diatomic molecules

O How will two oxygen atoms bond?

O Each atom has two unpaired electrons

O

O

O

O

O

O

O Oxygen atoms are highly electronegative, so both atoms want to gain two electrons.

O

O

O O

O O

O O

Both electron pairs are shared.

O O 6 valence electrons plus 2 shared electrons = full shell (octet)

O O 6 valence electrons plus 2 shared electrons = full shell (octet)

O O two bonding pairs, making a double bond

O O = For convenience, the double bond can be shown as two dashes.

O = this is so cool!! This is the oxygen molecule, O2

Polyatomic ions are composed of two or more atoms, held together by covalent bonds. Polyatomic ions act as a unit in bonding. Bicarbonate ion Phosphate ion Charge is -1. Charge is -1.

Covalent Bonds Can be polar or nonpolar Non Polar bonded atoms that share e-’s equally true when same atoms bonded ex. Cl – Cl: Cl2 Polar bonded atoms that do not share e-’s equally different atoms bonded, depends on shape, too H ex: NH3 H – N – H

Polar Bonds HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity) Cl has a greater share of the bonding electron’s time than does H Cl end has slight negative charge and H end has slight positive charge.

Polar Bonds This is why oil and water will not mix! Oil is nonpolar, and water is polar. The two will repel each other, and so you can not dissolve one in the other

Polar Bonds “Like Dissolves Like” Polar dissolves Polar Nonpolar dissolves Nonpolar

Polar Covalent Molecules

polar compounds Formed when 2 atoms with different electro-negativities form a covalent bond. The atoms DO NOT SHARE electrons equally. The electrons are more strongly attracted to the MOST electronegative atom. Molecules are asymmetrical.

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

MOLECULAR POLARITY A molecule can also be polar, if the electrons are moved about by polar bonds giving the WHOLE MOLECULE a positive and a negative side. The opposite sides of polarity are called dipoles, which means 2 poles, one positive and the other end negative. The oxygen side is negative since it takes the electrons, the hydrogen side is more positive because it lost the electrons.

Naming Covalent Compounds

Naming Covalent Compounds Cont. Rules for the prefix system 1. Less electronegative (leftmost) element is given first. It is given a prefix only if there’s more than one atom in the molecule. 2. The second element gets the ide ending and a prefix indicating the number of atoms contributed ex. Monoxide or pentoxide

Covalent Naming of 2 Nonmetals To name compounds of different elements: Name the first element Change the last element’s last syllable to –ide Add prefixes: mon/mono 1 hexa 6 di 2 hepta 7 tri 3 octa 8 tetra 4 nona 9 penta 5 deca 10 Covalent Naming of 2 Nonmetals

Fill in the blanks to complete the following names of covalent compounds. CO carbon ______oxide SiO2 silicon ______oxide PCl3 phosphorus _______chloride CCl4 carbon ________chloride N2O _____nitrogen ___oxide P2O5 ___phosphorus ____oxide Learning Check

Solution CO carbon monoxide CO2 carbon dioxide PCl3 phosphorus trichloride CCl4 carbon tetrachloride N2O dinitrogen monoxide P2O5 diphosphorus pentoxide Solution