Water Chemistry

Water Chemistry

• http://bonfirehealth.com/wp-content/uploads/2011/09/blue_wave_of_water-wide.jpg

Quick Chemistry: Atoms

• All matter is made of atoms.
• Each atom is made of:
• Neutrons (0 charge)
• Protons (+ charge)
• Electrons (- charge)

Using a Periodic Table

• Each block in the periodic chart contains the following:
• Element symbol
• Atomic number
• Atomic mass

Using a Periodic Table

• Electrons (-) = the atomic number.
• Protons (+) = the atomic number also. (Atoms are neutral so protons and electrons cancel each other out.)
• Neutrons (0) = the atomic mass minus the atomic number.

Practice…

• How many electrons?
• How many protons?
• How many neutrons?
• **Refer back to your notes or the last few slides to help answer each practice problem**

Answer…

• How many electrons - 6
• How many protons - 6
• How many neutrons - 6

Practice…

• How many electrons?
• How many protons?
• How many neutrons?
• **Refer back to your notes or the last few slides to help answer each practice problem**

Answer…

• How many electrons - 8
• How many protons - 8
• How many neutrons - 8

Practice…

• How many electrons?
• How many protons?
• How many neutrons?
• **Refer back to your notes or the last few slides to help answer each practice problem**

Answer…

• How many electrons - 16
• How many protons - 16
• How many neutrons - 16

Practice…

• How many electrons?
• How many protons?
• How many neutrons?
• **Refer back to your notes or the last few slides to help answer each practice problem**

Answer…

• How many electrons - 15
• How many protons - 15
• How many neutrons - 16

Electrons and Bonding

• Electrons arranged in valance shells around the outside of the atoms.
• Each shell holds a specific number of electrons:
• 1st shell = 2 electrons
• 2nd shell = 8 electrons
• Atoms like to have the shells filled and they do this through bonding.

Electrons and Bonding

• Bonding is the linking of atoms to form molecules.
• The strongest bond is the covalent bond.
• Covalent bond - when atoms share two electrons.
• The more electrons that are shared, the stronger the covalent bonds.

• sharing electrons video

Electrons and Bonding

• Hydrogen bonds are the weakest bond.
• These bonds happen when the electrons in hydrogen are shared unevenly with nitrogen, oxygen, or fluorine.
• As a result, the hydrogen has slightly positive charge and the other atom has slightly negative charge – they attract like a magnet.

• If hydrogen is losing part of its atomic structure, how could it become more positive?

• BrainPOP

The Water Molecule

• The chemical formula for water is H2O.
• 2 hydrogen atoms
• 1 oxygen atom
• Use your periodic chart to complete the water molecule diagram:
• How many electrons for oxygen?
• How many electrons for hydrogen?
• Are the outside valences full?

The Water Molecule

• Water molecules are formed when each hydrogen atom forms a covalent bond with the oxygen molecule.
• Oxygen now has 8 electrons in its outside valence shell and each hydrogen has 2 electrons in the outside valence shell.

The Water Molecule

• Because oxygen is big, it pulls the extra electrons and has a slightly negative charge.
• The hydrogens have a slightly positive charge.
• This makes water a “polar” molecule (having opposite ends with different charges).

The Water Molecule

• Water Link

• Polar water molecules are attracted to each other.
• When they get close, they form weak hydrogen bonds between each water molecule.
• These bonds allow water to have important traits that support all life on Earth.

Properties of Water

• http://www.nsf.gov/news/special_reports/chemistrynow/chem_water.jsp

Trait	Description	Biological Importance
Water is a polar molecule.	Opposite ends with opposite charges	Polar molecules are attracted to other polar molecules. (“Like dissolves like”)
Frozen water is less dense than liquid water	Frozen water floats (think ice cubes!)	Frozen water floats to the tops of ponds and lakes, trapping warmer water underneath for aquatic organisms to survive
Cohesion	Molecules sticking to each other	Surface tension
Adhesion	Molecules sticking to other, different, molecules	Capillary action