Elements, Compounds, and
Chemical Changes
Separation
• How can you separate these solutions??
– Milk (proteins are suspended in solution)
– Blood (cells and proteins are suspended in solution)
– ___________________
» Yields two layers (solution on top, suspensions on
bottom)
Density
• Review:
– Mass- How much matter is contained in an object
– Volume- How much space an object takes up
– Density- ??
Density Derivation
• If density is the amount of matter per unit of
volume, then what is the equation to calculate
density?
• Equation  __________________________
• How much space will a 54.8 g sample of Fe
occupy if the density is 7.86 g/mL
– Note: g/mL = g/cm3 = g*mL-1 = g*cm3-1
Graphical Analysis
• Volume on the x-axis, Mass on the y-axis
• As the volume increases for a given substance, so
does the mass, at a constant rate.
• The slope of this line is the DENSITY!!
• We can determine the identity of an unknown
substance using its density.
Atoms are the Fundamental
Components of Elements
– The Periodic Table contains a relatively small
number of atoms that form an unlimited number
of different materials.
• This is based on how they combine or bond together
Atoms are the Fundamental
Components of Elements
– The Periodic Table contains a relatively small number
of atoms that form an unlimited number of different
materials.
• This is based on how they combine or bond together
– Element – Any material consisting of only one type of
atom.
– Atom – Submicroscopic particles in a sample. Each
element is designated by a symbol (Atomic Symbol)
• Co =/= CO, only the first letter is capital
Atoms are the Fundamental
Components of Elements
– Elemental Formula – How many atoms are
bonded together in an element
• Au = Gold
ii. N2 = Nitrogen
iii. Ni = Nickel
– Seven Diatomic Elements:
–Oxygen, Hydrogen, Nitrogen, Bromine,
Chlorine, Iodine, Fluorine
– How about diatomic oxygen vs. ozone, O3?
–Are they the same?
–No, BUT both are elemental forms of oxygen
Combining Elements to Form
Compounds
– Molecule- Consists of two or more atoms
combined in a definite ratio
– Compound– Atoms of different elements bound
to one another
– We had an Elemental Formula for elements, how
will we represent chemicals bound together to
form chemical compounds?
Combining Elements to Form
Compounds
– We had an Elemental Formula for elements, how
will we represent chemicals bound together to
form chemical compounds?
– Chemical Formula – How much of what is in the
compound (symbols and subscripts)
• NaCl: One sodium per chlorine atom
• MgCl2: One magnesium per two chlorine atoms
Combining Elements to Form
Compounds
– Hydrogen Sulfide is one of the smelliest
compounds. Rotten eggs get their characteristic
bad smell from the hydrogen sulfide that they
release. Can you infer from this information that
elemental sulfur is just as smelly?
– *Compounds have Physical and Chemical
properties that are different from the properties
of their elemental compounds
Chemical Changes (rxn)
• Remember, a change is chemical ONLY when
the BONDS are BROKEN and reformed.
• This process creates entirely new substances
called ________________.
• This change is NOT physical because you
CANNOT GO BACK!! 
Chemical Changes
• Compounds (several DIFFERENT elements
together) can be broken down CHEMICALLY to
their ELEMENTAL forms
• Elemental forms are those consisting of ONLY
one type of element
• Ex: H2O  O2 + H2 (new elemental
PRODUCTS were created)
Homework
• Page 47-48, #32, 33, 34, 35, 37, 44, 45, 46
• Please do on a separate sheet and be ready to
turn in for a grade (must have the assignment
written on the top line and be neat!!)