Chemistry - Unit 6 - Covalent Bonding

What elements (IE and IE) are likley to form a covalent bond?

Elements with high EN and high IE are likely to gain electrons and not likley to lose electrons. When they combine, EN is not strong nough to pull electrons off (other has high IN) so they SHARE electrons (covalent bonds)

What are the steps to drawing a covalent compound?

1)Determine the total number of valence electrons (add/remove correct number if it is an ion)

2)Put the least electronegative element that isn't H in the center (central atom)

3)Place other atoms (terminal atoms) symmetrically around the central atom

4)Connect all terminal atoms to the central atom with a single bond (2 v.e. each)

5)Add remaining v.e. to terminal atoms until they have 8 (full octet)

6)Place any remaining v.e. on the central atom and (if necessary) use lone pair v.e. To create double or triple bonds so all atoms have an octet

What are single, double, and triple covalent bonds? How many electrons do each share and what is the strength of each?

Single (one bonding pair)- 2 electrons shared, weakest

Double (two bonding pairs) - 4 electrons shared, middle strength

Triple (three bonding pairs)- 6 electrons shared, strongest

Polarity

How charge is distributed

Even in a covalent bond the electrons can be pulled more towards one atom than the other because of differences in electronegativity.

Polar

charge is distributed unequally/asymmetrically

Nonpolar

charge is distributed equally/symmetrically

Nonpolar Covalent Bond

when e- are shared equally

<0.4 E.N. difference

C-H bonds are nonpolar

Polar Covalent Bond

when e- are NOT shared equally

0.4 - 1.8 E.N. difference

Ionic Bond v. Polar Bond

Ionic: when one atom (high EN) takes e- from another atom (low IE), Greater than 1.8 E.N. difference, between a metal and a non metal

Covalent: when two atoms have high EN and high IE that there is not a large enough difference so electrons want to stay on both atoms so electrons are SHARED to complete both atom's octet. Between nonmetals.

Ionic Bond

Ionic: when one atom (high EN) takes e- from another atom (low IE), Greater than 1.8 E.N. difference, between a metal and a non metal

Ionic v Covalent v Metal

Ionic: metal and nonmetal

Covalent: 2 nonmetals

Metal: 2 metals

Drawing Arrows (rules)

In polar covalent bond you can either draw a polarity arrow

Or draw a partial negative and partial positive chargeto show where the electrons are

Molecular Polarity

-Molecules are polar if charge (EN difference) is distributed unequally around the central atom (H2O)

-Molecules are nonpolar if charge (EN difference) is distributed equally around the central atom (CO2)

Remember SNAP

Symmetric (around the central atom)

Nonpolar

Asymmetric (around the central atom)

Polar

What is SNAP

Symmetric (around the central atom)

Nonpolar

Asymmetric (around the central atom)

Polar

Do polar and nonpolar molecules mix? What type of molecules mix?

Polar and nonpolar molecules do not mix

Like mixes with like (polar with polar, nonpolar with nonpolar)

Metals: solid vs liquid state

Metals atoms in the solid and liquid state are held together by the attraction between the "sea of valence electrons" and the positive metal cations.

The mobile electrons (mobile charge) allows electrical current to pass through metal.

Ionic Compounds: Solid vs Aqueous

Cations and anions in solid Ionic compounds are held together and in place by the attraction between opposite charges.

When dissolved in water, polar water molecules are able to separate the ions because of the attraction between opposite charges.

partial positive charge on H attracted to Cl anion

partial negative charge on O attracted to Na cation

What is needed in order for something to conduct electricity?

Must have mobile charge, ions or electrons

Ionic conductivity, solubility, and melting point

Not conductive in solid form, soluble in water, high melting and boiling point

Metallic conductivity, solublity, and melting point

Conductive, insoluble in water, high melting points

Covalent conductivity, solubility, and melting point

Not conductive, insoluble in water, low melting points

In terms of EN what's the difference between polar and non polar BONDS?

Non polar- equal EN less then .5 EN difference

Polar - different EN more then .5 EN difference

hydrogen and oxygen are ____

Non polar

Requirements for polar

Any lone pairs in the central atom.

-UNEQUAL distribution of charge

What atom goes in the middle of Lewis structures?

Least electronegative (Central atom)

What can obscure the symmetry of a molecule?

Valance electrons on the central atom

Arrows point to ————

More electronegativity

For conductivity of electricity you need —- so ionic is only conductive in water

Moving electrobs

Is water polar or non polar and why?

Central atom has a lone pair so the two hydrogens are offset and the molecule is POLAR

Partial charges

-elements with stronger EN have negative partial charge becuase they are pull electrons closer to them (More electrons = negative charge)

-elements with lower EN have positive partial charge becuase they have a weaker pull to electrons (Less electrons = positive charge)

-This seperation in charges is call a DIPOLE moment

Covalent V Ionic Bonding

Ionic = difference in electronegativity is over 1.7 so electrons are FULLY exchanged, only one element has one full shell, they are held together by electostatic forces, conductive. Requires one metal and one nonmetal.

Covalent = differrence in electronegativity is less than 1.7 so electrons are SHARED (becuase its so close they must satsify both shells), both elements have full shells, not conductive, happens between nonmetals