Opposites Attract
Using Chemistry to Explain Biology
Atoms
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a - not
tom - to cut
a + tom = not cuttable
Basic units of all matter
Made up:
o Neutron = neutral
o Proton = positive
o Electron = negative
● Electrons and protons are attracted to
each other...
● But electrons move too much to join the
protons in the nucleus
Atoms
● When...
o there are equal numbers of protons and electrons = no charge
o there are more protons than electrons = positive charge
o there are less protons than electrons = negative charge
● If an atom has a charge, called ion
Compounds
● When two or more atoms (elements) bond to each other
● Compounds properties are very
different from individual atoms
● Ex) Na + Cl = Salt
https://www.youtube.com/watch?v=ODf_sPexS2Q
https://www.youtube.com/watch?v=aK85PZX2xNE
Compounds
● Created using bonds
● Three types of bonds...
Ionic Bonds (The Taker and the Giver)
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Electron is transferred from one atom to the other atom
One atom adds an electron and gains a negative charge
One atom loses an electron and gains a positive charge
Since the atoms are charged, they are ions
Ex) Salt = NaCl
o Na loses electron
o Cl gains electron
Covalent Bonds (The sharers)
● Neither atom has enough electrons
● Atoms share electrons
● Ex) Carbon dioxide
Van der Waals Forces
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(The Stickers)
Weakest of three bonds
Covalent bonds don’t always share equally
Some atoms attract electrons more than others
When molecules close together, creates attraction
“Sticky”
Ex) Water, H2O
o Electrons more attracted to oxygen (O) and stay near it more
o Oxygen slightly more negative than hydrogen (H)
Bonding Activity
● Form groups of four (student choice)
● Pretend you are all atoms trying to become compounds
● Create a simulation for all three types of bonds
o Ionic
o Covalent
o Van der Waals
● When you are ready, come to Ms. Crocker. She will pick
a bond for your group to act out
Water - The Most Important
Compound
Most abundant Compound in all life
● Many unique properties make it
suited to support life
o Polarity
o Hydrogen Bonds
o Solubility
o High specific heat capacity
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Polarity
● Caused by Van der waals forces
● Creates hydrogen bonds in
H2O
o Slightly negative O is
attracted to slightly positive
H
● Hydrogen bonds create
cohesion and adhesion
Hydrogen Bonds - Cohesion
● Slight charge of water molecules attract other water
molecules
http://www.youtube.com/watch?v=45yabrnryXk&t=0m46s
Hydrogen Bonds - Adhesion
● Slight charge in water molecules makes it stick to other
types of molecules
Solubility
● Polarity means it can break apart ionic and polar
molecules
● Ex) Salt Water
o Negative Cl surrounded by positive H
o Positive Na surrounded by negative O
● Nonpolar molecules stay separate
o Ex) Oil (nonpolar) and Water (polar) do not
mix
● Important for many characteristics of life
o Ex) Dissolves solids in our body to be carried
in our blood
High Specific Heat Capacity
● Water needs a lot of energy to raise by 1 degree
o Water is “sticky” due to cohesion, so needs
more energy
● Helps to maintain an important characteristic of
life - homeostasis
● Homeostasis maintains internal conditions like
temperature, nutrient levels, and water content
● High water content means our temperatures
don’t change easily
Properties of Water Worksheet
● Working individually or in pairs with the person sitting
next to you, fill out the worksheet
● We will discuss this in class
● Be prepared to share your answers
Acids and Bases
● Water is constantly reacting (breaking apart) to form
ions (charged molecules)
o H2O → H+ & OH- (Ions - Broken apart)
o H+ & OH- → H2O (Neutral - Reformed)
● In pure water - 1 in 550 million water molecules are ions
pH Scale
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Measures H+ ions in a solution
On a scale from 0 to 14
More H+ is lower on the scale
7 is neutral
Logarithmic scale (something with a ph of 1 has 10x more H+ atoms than
something with a pH of 2)
pH Indicators
● Tests the amount of free H+ ions in a solution
● Will change different colors depending on the pH level
of a solution
● Ex) Bromothymol Blue
o http://www.youtube.com/watch?v=opsNV4VqAbk
Acids
● Chemicals that contain more H+
than pure water
● More H+ than OH● pH is below seven
● Strong acids have a pH of 0-2
Bases
● Chemicals that contain less H+
than pure water
● Less H+ than OH● pH greater than 7
● Strong bases have a pH of 11-14
Turn and Talk
● Why do you think strong acids and strong
bases are so corrosive (damaging, can
cause burns)?
Turn and Talk
● What do you think happens when you mix a
strong acid and a strong base?
Buffers
● To maintain homeostasis, the body needs to maintain fluids between pH of
6.5 and 7.5
● Uses buffers
o can either be a weak acid or base (close in pH to the neutral of 7)
o in presence of strong acid, acts as weak base to accept extra H+
o in presence of strong base, acts as weak acid to accept OHo reduces rapid pH changes
● Ex) Bicarbonate molecules in blood (HCO3-)
pH Practice
● In your notes, identify the following as acid or base
o Human Blood - 7.4
o Rain - 5.6
o Bleach - 12.6
o Stomach Acid - 1.5
o Battery Acid - 0
o Urine - 6
o Seawater - 8
● Identify the strongest acid and strongest base
● Identify the weakest acid and weakest base