Elements, Compounds, Mixtures,
Law of Definite Proportions, and an
Introduction to the Periodic Table
Elements and Compounds
Element: A pure substance that CANNOT be separated into a
simpler substance by physical or chemical means.
GOLD
COPPER
There are 91 naturally occurring elements on earth
Approximately 24 synthetic elements have been identified
Symbols of Elements
The symbols of elements are regulated by the International
Union of Pure and Applied Chemistry (IUPAC), and they are
derived in several ways. Many elemental symbols are simply
the capitalized letter of the first letter of the English name of
the element:
C is for Carbon
N is for Nitrogen
If two elements start with the same first letter, then a second
lowercase letter will be added to differentiate them:
Ca is for Calcium
Ni is for Nickel
Derivation of Element Names
Many elements are named after their Latin derivation:
Lead which is “plumbus” in Latin is Pb
Gold which is “aurum” in Latin is Au
Potassium which is “kalium” in Latin is K
Other elements are named to honor a famous scientist:
Es for Einsteinium
Cm for Curium
Rf for Ruthifordium
Still other elements are named for the country in which
they were discovered:
Fr for Francium
Am for Americium
Compounds
Combinations of two or more elements that are
combined chemically:
H20
NaCl
C6H12O6
Al2O3
Fe2O3
Matter
Mixture
Homogeneous
Substance
Heterogeneous
Solution
Colloid
Suspension
Element
Compound
Elements and Compounds
Similarities
1. Both are substances
Differences
1. Compounds are
substances that can be
broken down into
elements
2. Both have physical and 2. Elements are
chemical properties
substances that cannot
be broken down
Mixtures of Matter
Characteristics of a mixture:
a.) A combination of two or more
pure substances in which each
individual substance that makes
up the mixture retains its
individual properties
b.) Properties are largely those of its
component parts; conversely when the
individual substances combine new
properties are NOT created
c.) It is a blend of two or more substances
d.) It does not have a constant composition
e.) A mixture is a blend of substances; not a chemical bonding
of substances
f.) They can be separated by physical means
Types of Mixtures
Heterogeneous: Individual substances still remain distinct
A mixture that may have many phases
Homogenous: A mixture is the same throughout
A mixture that contains a single phase
ALSO CALLED A SOLUTION!
Same or Different?
a.) substance and a pure substance
b.) heterogeneous mixture and solution
c.) substance and mixture
d.) homogenous mixture and solution
Law of Definite Proportions
A compound is always composed of the same elements in the
same proportions by mass, regardless of the amount.
% by mass =
mass of element x 100
mass of compound
OR (in other words)
% by mass =
part
whole
x 100
Mass of H20:
H: 2(1) = 2 amu
O: 1(16) = 16 amu
2 amu from H + 16 amu from O = 18 amu for H20
% of H in H2O: (2 amu/18 amu) x 100 = 11.1% Hydrogen
% of O in H2O: (16 amu/18 amu) x 100 = 88.9% Oxygen
Sample Problem 1:
Suppose you break a compound down into its elements and find that 25.00 g of
the compound is composed of 6.77 g of tin and 18.23 g of bromine. The
percent by mass of tin in the compound can be determined as follows:
Percent by mass of tin =
mass of tin
mass of compound
x 100
Percent by mass of tin =
6.77 g x 100 = 27.1% tin
25.00 g
Follow the procedure described above to determine the percent by mass of
bromine in the compound discussed above. What is the sum of the percents of
the two elements?
Sample Problem 2:
A 134.50 g sample of aspirin is made up of 6.03 g of hydrogen,
80.70 g of carbon, and 47.77 g of oxygen. What is the percent
by mass of each element in aspirin?
Sample Problem 3:
A 2.89 g sample of sulfur reacts with 5.72 g of copper to form a
black compound. What is the percentage composition of the
compound?
Practice I
1. If hydrogen composes 11% of a 100
gram sample of water, what is the
mass of the hydrogen in the sample?
2. If one gram of hydrogen reacts
completely with 19.9 g of fluorine, what
is the % by mass of hydrogen in the
compound that is formed?
Practice Continued
3. If 3% of a 100 g HCl solution is hydrogen,
what is the mass of the chlorine in the
sample?
4. A 78.0 g sample of an unknown
compound contains 12.4 g of hydrogen.
What is the percent by mass of hydrogen
in the compound?
Practice Continued
5. If 40% of a 300 g NaCl solution is
sodium, what is the mass of the sodium
present in the sample?
The Periodic Table
The Periodic Table – A chart that organizes the
elements based on their similarities and proton
number.
The
original
Periodic
Table was
developed
by a
Russian
named
Dmetri
Mendeleev
in 1869
Subatomic Particles:
Protons, Neutrons, Electrons
Upon looking at the periodic table, we find
many clues as to how to find information
about each individual element.
Finding Protons,
Neutrons, Electrons
The Number of Protons (p+) is... the number of p+ in an atom of an
element. In this example, krypton's atomic number
is 36. This tells us that an atom of krypton has
36 protons in its nucleus.
The Number of Electrons (e-) is... by definition, atoms have no overall electrical
charge. That means that there must be a balance between the positively charged
protons and the negatively charged electrons. Atoms must have equal numbers of
protons and electrons. In our example, an atom of krypton must contain 36
electrons since it contains 36 protons.
The Number of Neutrons (no) is... # of Neutrons = Mass Number - Atomic Number
– to find the mass number, all you need to do is round the atomic weight to the
nearest whole number. In our example, krypton's mass number is 84 amu
since its atomic weight, 83.80, rounds up to 84 amu.
– The mass number is a count of the number of particles in an atom's nucleus.
Remember that the nucleus is made up of protons and neutrons. So, we can
write:
Mass Number = (Number of Protons) + (Number of Neutrons)
For Krypton, this equation becomes:
84 = (Number of Protons) + (Number of Neutrons)
States of Matter and the Periodic Table
Organization of the Periodic Table
Properties of the Periodic Table