Chemistry
Notes
• A molecule consists of two or more atoms of
the same element, or different elements, that are
chemically bonded together.
• The smallest part of a pure substance (element or
compound)
• Ex. One molecule H20 vs. a glass of water.
• Diatomic molecule - composed of two of the
same atom
• Examples: H2, N2, O2, Cl2, Br2
•In the animation above, two nitrogen atoms
(N + N = N2) make one Nitrogen molecule .
• Two or more different types of atoms chemically
bonded to each other
Table Salt & Ammonia
are examples of compounds
•Compounds have different properties than the elements
it is made of.
•All compounds are molecules, but not all molecules are
compounds (diatomic molecules are NOT compounds)
• Organic Compounds- compounds containing
covalently bonded carbon.
• Example: C6H12O6 (Glucose)
• The rule of 8.
• Valence electrons are the electrons in the
outermost energy level.
• You must know the number of valence electrons
an atom has.
• When atoms chemically combine they try to end up
with a full outermost energy level or 8 valence
electrons by either gaining or losing electrons.
• To meet this need:
▫ Metals tend to lose (give away) electrons.
▫ Nonmetals tend to gain electrons.
• Nature seeks balance! Having a full outermost energy
level is stable.
• That’s why the Noble Gases do not react. They
already have a full outer level.
• The group (column) represents the number of valence
electrons in the outer shell.
• The period (row) represents the number of energy
levels in the atom.
•A Lewis dot diagram is a system to represent atoms
and their valence electrons.
•Drawing Lewis Dot Structures:
• An ionic bond is a bond that forms when valence
electrons are lost or gained (transferred). It is the
bond formed between oppositely charged ions.
Example:
•A lithium atom gives up an electron to a fluorine atom.
•The result is a positively charged lithium ion and a
negatively charged fluoride ion.
• Other ionic bond examples…….
• A metal bonded to a nonmetal
(Groups 1 & 2 with Groups 6 & 7)
• Conducts electricity when dissolved in water or
melted.
• High melting points.
• Solids at room temperature.
A metallic bond is the attraction of free
floating valence electrons.
• Metal atoms can bond
to atoms of the same
element, or to other
metals.
• Electrons divide evenly
among atoms- “electron sea”
A metallic compound is a metal bonded to
another metal.
• Metallic compounds have:
• High melting points
• Good conductors of heat
and electricity
• Malleable and ductile
• Strong bonds
• Atoms arranged in a
pattern
• A covalent bond is a chemical bond
formed when atoms share valence
electrons. Usually nonmetals with
nonmetals.
• Elements that are close together on the
periodic table are more likely to share
electrons in a covalent bond than to transfer
electrons.
• Hydrogen, Carbon, Nitrogen, and Oxygen
usually form covalent bonds.
• Drawing covalent bonds…..
•Hydrogen has one unpaired electron.
•Two hydrogen atoms share their single
electrons to form a pair.
•The shared pair of electrons
is a single covalent bond,
which holds the hydrogen
molecule H2 together.
Drawing single covalent bonds….
• Some atoms may form stronger bonds by
sharing more than one pair of electrons.
• A double bond has two pairs of shared
electrons and is stronger than a single
bond.
• A triple bond has three pairs of shared
electrons and is stronger than a double
bond.
Drawing double & triple bonds….
• Drawing covalent bonds…..
Hydrogen, Oxygen, Nitrogen, and
Carbon make up 98% of all living things
• Every Hydrogen atom has 1 line
connecting it to other atoms.
• Every Oxygen atom has 2 lines
connecting it to other atoms.
• Every Nitrogen atom has 3 lines
connecting it to other atoms.
• Every Carbon atom has 4 lines
connecting it to other atoms.
• Do not conduct electricity in water.
• More flammable than ionic compounds.
• Softer than ionic compounds.
• Low melting and boiling points.
• Usually do not dissolve in water (not soluble)
•Information about the atoms that make up a
molecule/compound
•Atoms will combine in specific rations due to
the number of electrons shared or transferred.
Example:
•The chemical formula for
sucrose, C12H22O11,
includes all the atoms in one
molecule.
•Step 1: Determine the elements to be used in the
formula and their oxidation numbers
Mg +2 F -1
•Step 2 Solve by making the charge of one
atom the subscript for the other.
**If the subscript is 1, you do not need to write it.
Mg +2 F -1 =
Mg F2
•Try it:
•Sodium Chloride
•Calcium Fluoride
•Carbon Tetrachloride
•Aluminum Oxide
•Magnesium Oxide
•Carbon Dioxide
**If the subscript is 1, you do not need to write it.
•A polymer is a covalent compound made up of
many repeating units linked together in a chain.
Analogy = Beaded Necklace
•A monomer is a single molecule that forms a
link (beads) in a polymer chain (necklace).
•Examples of Polymers:
•
•
•
•
•
Carbohydrates
Plastics
Proteins
DNA
Rubber
•Acids are substances that release a positively
charged hydrogen ion, H+, in water. The strength of
the acid depends on the concentration of H+ ions.
•Acids are also used in making many products, such as
fertilizers, detergent, and cleaners.
•Acids are important in several body processes,
including breaking down food in the stomach.
Acid Properties
•Can neutralize a base
•Sour
•Turn blue litmus paper red
•Feel like water
•Conduct electricity •pH between 1-6
•React with metals
•Bases are substances that produce negatively
charged hydroxide ions (OH-) when dissolved in
water.
•Common bases include baking soda and cleaning
agents.
Base Properties
•Feel slippery
•Dissolve fats, oils, and grease
•Bitter taste
•Neutralize acids to produce salt and water
•Turn red litmus paper blue •Conduct electricity
•Have a pH between 8-14
Acids and
Bases
•pH is a numerical scale used to determine the
strength or weakness of an acid or base.
• The pH scale runs from 0 to 14
– Acids are below 7; strong acids are near 0.
– Bases are above 7; strong bases near 14.
- Neutral solutions have a pH of 7.
•pH can be measured using different indicators:
•
•
•
•
Litmus paper (red or blue)
pH paper (pool test strips)
Universal indicator (cabbage juice)
pH meter
• A mixture is a combination of two or more substances that
can be separated by physical means (i.e. filtering,
evaporation, magnet, etc.)
•NO CHEMICAL BOND
• Solutions are also mixtures.
• Solutions are groups of molecules that are
mixed up in a completely even distribution.
• Also called solution
• Uniform appearance
• Evenly mixed at the
atomic level
• Ex: blood, milk, metal
alloy, air
• Also called solution
• Uniform appearance
• Evenly mixed at the
atomic level
• Ex: blood, milk, metal
alloy, air
• Not evenly mixed
• Distinct substances
• Ex: granite, mixed
nuts, salad, salad
dressing
Physical properties can be observed without
changing the substance.
Ex: phase of matter, color, taste, odor, shape,
texture, density, melting point, boiling point,
hardness, conductivity, malleability
A chemical property is the ability or inability
of a substance to combine with or change into
one or more new substances (how a
substance reacts with other substances).
•Examples of chemical properties include
burning or rusting.
•Some
substances
do not react.
•Physical change: What the substance is
made of does not change. Physical changes
are reversible.
•Ex) Changing from one state to another
Other Examples:
Cutting a lawn, breaking glass,
Melting ice
Chemical change: Change one substance
into a new substance.
•Chemical bonds are formed/rearranged
•New substances have different properties
and compositions than the original
substances.
•Usually chemical changes cannot be easily
reversed.
Property Changes
• If a substance reacts with another substance, it means
there is an attraction between atoms. A Chemical Bond
formed! Not easily separated.
Evidence that a chemical change (reaction) has occurred
• Heat produced/absorbed
• Gas produced (bubbles/fizzing)
• Odor produced
• Electricity produced
• Light produced
• Precipitate produced (solid/solute coming out of
solution)
• Color change (weakest evidence!)
•Chemical equations show that in chemical
reactions, atoms rearrange, but no atoms are
gained or lost.
•Reactants are the original substances in a chemical reaction
and are placed on the left side.
• Products are the new substances in a chemical reaction and
are placed on the right side.
reactant + reactant
original substances
2H2
3H2
+
+
product
new substance/s
O2
N2
2H2O
2NH3
•A subscript tells how many atoms
of an element are in
one molecule.
• A coefficient tells how many
atoms, molecules, or formula units
are in a reaction.
NaHCO3 + CH3COOH
CO2 + H2O + NaC2H3O2
Balanced
All chemical reactions must obey the
Law of Conservation of Matter
# of atoms on the left = # of atoms on the right
Step 1 Determine the correct symbols and formulas for
reactants and products.
Step 2 Write reactant symbols and formulas to the left of an
arrow and product symbols and formulas to the right.
Step 3 Count the number of each kind of atom on both sides.
Step 4 Use coefficients to make the number of each kind of
atom the same on both sides of the arrow.
Step 5 Check to see that each kind of atom balances.
Reaction of methane:
CH4 + O2
→
CO2 + H2O