CHEMICAL BONDING

A force that holds two atoms together is known as a Chemical Bond.

The bond occurs when two nuclei attract the same electrons.

Bonding is when a chemical bond is formed.

When chemical bonds are broken and new bonds formed, this is a Chemical Reaction.

Valence: Outer

The valence energy level (shell) is the highest energy level in an atom where there is at least one electron.

The electrons in the highest energy level of an atom are known as Valence Electrons.

Chemical bonding involves a transfer of valence electrons.

Noble Gases

Helium Neon Argon Krypton Xenon Radon

These six elements form only very few bonds.

What similarities do they have?

Consider their valence energy levels.

Noble Gases

He – 1s2

Ne – 2s2 2p6

Ar – 3s2 3p6

Kr – 4s2 4p6

Xe – 5s2 5p6

Rn – 6s2 6p6

Helium has only the 1st energy level and room for electrons.

All the others have two sublevels (s and p) in their valence energy levels.

This means that eight electrons will fill the valence energy level.

Octet

There is something special about having eight electrons in the valence energy level. It is called an OCTET.

All of the Noble gases are chemically inactive (inert) because the valence energy level is stable.

Chemical Reactions!!!

All of the other elements have between one and seven valence electrons. All of the other elements will react in order to get an octet.

This can occur by either by the transfer of electron or by the sharing of electrons.

IONIC BONDING

Ionic bonding is a transfer of electrons from one atom to another.

Most elements that lose electrons are metals.

Most elements that gain electrons are nonmetals.

IONIC BONDING

Ionic bonds are formed between a metal and a nonmetal.

The metal loses electrons and becomes positive. The nonmetal gains electrons and becomes negative.

The positive ion attracts the negative ion… and they BOND. An IONIC BOND!!

Let’s look at a typical metal

POTASSIUM K 1s22s22p63s23p64s1

Potassium’s valence shell is the fourth energy level. If potassium lost an electron, then the third energy level

would be the valence or outermost level.

K 1s22s22p63s23p6

Now the valence shell only has 8 electrons in it. By losing an electron, the K atom has become a positive

ion, a cation.

K+ 1s22s22p63s23p6

Now let’s look at a typical nonmetal

Chlorine Cl 1s22s22p63s23p5

Chlorines valence shell is the third.

If Cl is to have a stable octet, it must gain one more electron.

By gaining another electron, the Cl atom has become a negative ion, an anion.

Cl- 1s22s22p63s23p6

The Plot Begins To Unfold

K needs to get rid of one electron:

K 1s22s22p63s23p64s1

Cl needs to accept one electron:

Cl 1s22s22p63s23p5

The results are a positive K ion, a CATION, and a negative Cl ion, and ANION.

K has… Cl has…19 protons 17 protons19 electrons 17 electrons

The potassium gives the chlorine an electron and…

K has… Cl has…19 protons 17 protons18 electrons 18 electrons

The Potassium is now a CATION.

The Chlorine is now an ANION.

The cation attracts the anion and….

K+ Cl-….an ionic bond is formed.

The compound Potassium chloride.

KCl

In some cases more than one electron must be transferred in order to give all the atoms a complete valence energy level. For instance, when magnesium bonds to fluorine.

Magnesium 1s2 2s2 2p63s2

Fluorine 1s2 2s2 2p5

Magnesium can give fluorine one electron to give it a complete octet, but then magnesium is

1s2 2s2 2p6 1s2 2s2 2p63s1

So, Magnesium can give an electron to another fluorine. Now it has a complete octet in the second energy level.

1s2 2s2 2p6

Mg+2 + F-1 + F-1

MgF2

Covalent Bonding Bonds are formed by sharing

electrons. Electrons are held in

overlapping orbitals. Typically this occurs when a

nonmetal bonds to another nonmetal.

Electron Dot Structures

This type of bonding can be easily demonstrated with electron dot structures.

Diatomic Elements7 elements naturally bond in pairs. These can be easily shown with electron dot structures.

Hydrogen is first, it shares its one electron with another hydrogen atom to form the diatomic H2. Any hydrogen gas found in nature is H2.

Column VII

Notice how the elements of column VII share electrons to get an octet.

OxygenOxygen has a double bond, the oxygen you breath is O2.

NitrogenNitrogen in the air has a triple bond, sharing 6 electrons.

DIATOMICSThere are 2 ways to remember the diatomic elements:

ClIF H. BrON is the name of the person who discovered the diatomics. Not really, but the letters in his name are the symbols of the diatomic elements.Cl - chlorineI - iodineF - fluorineH - hydrogenBr - bromineO - oxygenN - nitrogen

7 Diatomic ElementsThe other way to remember the diatomic elements is the number 7. There are 7 diatomic elements and they kind of form a 7 on the periodic table.

H N O F

Cl

Br I

Coordinate Covalent Bond

Typically when two atoms share electrons, one electron comes from one atom and one electron comes from the other atom.

But in a coordinate covalent bond, both electrons in the bond come from one atom.