Unit 1 Notes: Part 3 – Chemical Bonding, Properties of Water, pH, Buffers
Atomic Facts
•An atom is still the same element if it gains or loses an electron.
•An atom is still the same element if it gains or loses a neutron.
•However, if the number of protons does not change; if it were to change, the
atom would be a different element.
Isotopes
•Let's say an atom is missing a neutron or has an extra neutron.
•That type of atom is called an isotope.
•For example, there are a lot of carbon (C) atoms in the Universe. The normal
ones have a mass number of 12. Those atoms have 6 protons and 6 neutrons.
There are a few straggler atoms that have more than 6 neutrons . They may
have 7 or even 8 neutrons. Carbon-14 has 8 neutrons (2 extra). C-14 is
considered an isotope of the element carbon.
What changes in an isotope due to the change in neutrons?
Ions
•A normal atom has a neutral charge.
•Meaning # protons = # electrons
•Remember atoms want to fill their outermost shell of electrons. Sometimes this
requires gaining or losing electrons.
•When you are missing one or two electrons, you have a positive charge. This
is called a positive ion.
•When you have an extra electron or two, you have a negative charge. This is
called a negative ion.
•An ion is an atom or molecule with a charge.
Ionic Bond
•An ionic bond is the attraction between two oppositely charged ions.
•For example: Sodium Chloride (NaCl)
•Draw the Bohr Model and/or the Lewis Dot Diagram of an atom of each element.
•Try this one on your own… Magnesium Oxide (MgO)
•Draw the Bohr Model and/or the Lewis Dot Diagram of an atom of each element.
Covalent Bond
•A covalent bond forms when two atoms share one or more pairs of electrons.
•For example: Hydrogen (H2)
•Draw the Bohr Model and/or the Lewis Dot Diagram of an atom of each element.
•Try this one on your own... Oxygen (O2)
•Draw the Bohr Model and/or the Lewis Dot Diagram of an atom of each element.
Physical/Chemical Properties and Changes
•Physical Properties – Can be observed without changing the identity of the
substance.
•Chemical Properties – Describe how the substance changes into a completely
different substance.
•Physical Change – Altering a substance without changing its composition.
•Cutting, tearing, crushing, bending, dissolving, phase changes.
•Chemical Change – A new substance is formed; a reaction occurs.
•Reacts, decomposes, corrodes, burns, combusts, tarnish, oxidizes.
Structure of Water (H2O)
Draw the Bohr Model and Lewis Dot Structure of a molecule of water (H2O).
•All living things are dependent on water
•Cells are surrounded by fluid that is mostly water
•Cells are 70-95% water
•The formula for water is H2O
•H atoms are joined to O atoms by a single covalent bond
Key to water’s unique properties:
1.Electrons of each covalent bond are not shared equally between the H & O
atoms.
2.Oxygen has a stronger pull on the electrons.
3.The unequal sharing causes the Oxygen to have a slightly negative (-) charge,
while the hydrogen ends have a slightly positive (+) charge.
Polarity
•A molecule in which opposite ends have opposite electrical charges is called a
polar molecule.
•Water is a polar molecule.
How are water molecules attracted to each other?
•Slightly negative oxygen attracts the slightly positive hydrogen of adjacent
molecules, causing molecules to become arranged using hydrogen bonds.
•A hydrogen bond is a unique chemical bond between the hydrogen atom in
one molecule and the negatively charged region of another.
Water’s Unique Properties
1.Cohesion and Adhesion
2.Temperature Moderation
3.Low Density of Ice
4.Ability to Dissolve Other Substances
1. Cohesion and Adhesion
•Cohesion - Tendency of molecules of the same kind to stick to one another.
•Adhesion - Attraction between unlike molecules
*Adhesion and cohesion together to give water the property known
as capillarity.
•Capillarity allows water to move up the stem of a plant.
2. Temperature Moderation
•Water must gain or lose a relatively large amount of energy for its temperature
to change.
•When you heat water, a lot of energy is absorbed to break the hydrogen bonds
between molecules.
•Only after these bonds are broken can water molecules increase motion and
raise the temperature.
•Water’s ability to absorb large amounts of energy help keep cells at an even
temperature despite changes in the surrounding environment.
3. Low Density of Ice
•What is the formula for ice?
•Water is more dense than ice (solid water).
•This is because of hydrogen bonds
4. Ability to Dissolve Other Substances
•Solution - Uniform mixture of 2 or more substances
•Solute - Substance that is dissolved and present in a lesser amount
•Solvent - Substance that dissolves the other substance and is present in a
greater amount.
•Aqueous solution - Solution in water.
•Water is the main solvent in all cells.
•Charged molecules are easily broken down by water because of its polarity.
pH Scale (copy from the Do Now)
Dissociation of Water
•Water dissociates (or breaks apart) into a hydroxide ion and a hydronium ion.
•Hydroxide ion is the OH- product of this reaction.
•Hydronium ion is the H3O+ product of this reaction.
Acids and Bases
•Acids have a greater number of hydronium ions than the number of hydroxide
ions.
•Bases have a greater number of hydroxide ions than the number of hydronium
ions.
pH Scale
•The pH scale compares the relative concentrations of hydronium ions and
hydroxide ions in a solution.
•It ranges from 0 – 14
•0 is very acidic
•7 is neutral
•14 is very basic
Buffers
•A buffer is a chemical substance that neutralizes small amounts of either acids
or bases to a solution.
•Some of your body fluids, such as stomach acid and urine, are acids.
•Others, such as intestinal fluid and blood, are basic.
•Complex buffering systems maintain the pH values of your body's many fluids
to stay at normal, safe levels.