Bonds

The eternal mystery of the world is its comprehensibility

- Albert Einstein

Chemical Bonds• Chemical compounds

are formed by the joining of two or more atoms.

• This point of union is called a bond.

• The bond means there is an attractive force between the atoms.

• Bonds are more like springs then sticks. Some atom movement is possible.

• There are 3 main types of bonds, Ionic, Metallic and Covalent.

Ionic Bonds• Ionic bonds are formed by a transfer of electrons.

• One of the atoms gains the electron(s) that the other lost.

• Both end up with full outer energy levels and opposite charges.

• The oppositely charged ions are attracted to each other.

• Many ions bond together forming networks.

• This is shown in the diagram of NaCl to the right.

• In the diagram, Na is red and Cl is green.

• In this situation there really is no single molecule but there is a simplest formula..

Ionic Bonds

• Ionic bonds are formed by a transfer of electrons.

• One of the atoms gains the electron(s) that the other lost.

• Both end up with full outer energy levels and opposite charges.

Ionic compounds and conduction• Electric current is

moving charges.• Solid ionic

compounds do not conduct electricity because the charged ions are locked in place.

• When dissolved, ionic compounds disassociate or separate into their ions.

• The solution can now conduct electricity because the ions are free to move.

• A solid block of salt and a beaker of distilled water will not conduct electricity, but a beaker of salty water will!

Metallic Bonds

• The attraction between a metal atom’s nucleus and a neighboring atoms electrons is strong and packs the atoms closely together.

• This causes the outermost energy levels of the atoms to overlap.

• These outermost electrons are free to move from atom to atom.

• This explains why metals are good conductors and why they are so flexible and malleable when compared to the non-metals.

Covalent Bonds• A covalent bond

forms when two or more atoms share valence electrons.

• This occurs most often between elements in groups IVA, VA, VIA and VIIA.

• The sharing of electrons allows each atom in the molecule to have a stable octet in its outermost energy level.

Methane (CH4) • The methane molecule illustrated has 4 covalent bonds.

• The bonds are between each hydrogen atom and the carbon atom.

• The sharing of electrons means sometimes they are going around the carbon and sometimes they are going around the hydrogens.

• In this way each element gets to have a full outer energy orbital.

Polar Covalent bonds

• The shared electrons in a covalent bond may not be shared equally.

• Electrons are strongly attracted to atoms located to the upper right of the periodic table.

• In the water molecule, the oxygen atom has a much stronger attraction for the electrons then either hydrogen.

• This means that the electrons from the two hydrogens spend most of their time orbiting the oxygen atom.

• Because of this unequal sharing a molecule of water has a negative and a positive end (poles).

Water is Special!

• Because of the polar nature of the water molecule it is attracted to itself!

• Water molecules are attracted to each other and this is the main reason that such a small molecule is a liquid at room temperature!

Many water molecules showing hydrogen bonding

Ice Structure - note similarities to snowflakes!

Glacial Blue ice - ice that is formed by the recrystallization of snow that is compacted in a glacier.

Huge tabular iceberg from Antarctica

Blue ice berg, Antarctica

Carbon dioxide, polar covalent but with a twist!

• In the CO2 molecule the oxygen atoms have the electrons more often than the carbon atoms.

• This makes the oxygen ends of the molecule negative and the area between the oxygen and the carbon positive.

• How does this explain the fact the CO2 is a gas at room temperature even though it is a much bigger molecule than water?

Dry Ice

• Dry ice is the solid form of the gas carbon dioxide. 

• A full block, measuring about 10 inches square, weighs 50 lbs. 

• The temperature of dry ice is 110° below zero. 

• When handling dry ice, wear work gloves as the extremely low temperature will cause frostbite. 

• Dry ice has many uses, chief among them as a refrigerant to prevent food form perishing and to ship blood products.