THE BUILDING BLOCKS OF MATTER
Democritus – First person known to suggest that matter
can be broken down into small particles that he named:
In the 1790s, chemists are using better instruments and are
able to make better measurements.
Using these instruments, theories about matter are
developed. Some of which are still valid today.
In the late 19th century and early 20th century, some
fundamental discoveries were made about the atom due to
the further development of instruments.
What did Einstein propose?
WHAT DOES THE LAW STATE?
Mass is neither destroyed nor created
during ordinary chemical reactions or
If you have 50 grams of matter before a chemical
reaction or physical change, the total mass will
be 50 grams after the chemical reaction or
What is the formula for water?
A chemical compound contains the same elements in
exactly the same proportions by mass even if the size of
the samples change. It is the law of Definite Proportions
Carbon dioxide is always 1 Carbon and 2 Oxygen atoms
Carbon Monoxide is always 1 Carbon and 1 Oxygen atoms
Hydrogen Peroxide is always 2 Hydrogen and 2 Oxygen atoms
What is the ratio of elements in Hydrogen Peroxide and how
is that different from Water?
What is different between the two examples?
What is the same?
What is the ratio between the mass of Oxygen in the first
example and that in the second example?
If we have two different substances that have the
same two elements, if we combine the second
element with the same amount of the first, the
ratio of the elements are always small whole
2:1, 3:1, 3:2, etc….
In the examples below, find the whole number
C2H2 and C2H6
H2O2 and H2O
Dalton’s Atomic Theory
year 1808 Today - 2010
1. Matter made of extremely Statement 1, 4 and 5 are still
small particles called atoms accepted today
2. Atoms of an element are Statement 2 has been modified
identical in: mass, size and because we now know that
other properties atoms of an element can differ. A
3. Atoms cannot be subdivided, given element can have atoms of
created or destroyed different masses
4. Atoms combine in simple Statement 3 is incorrect. Atoms
whole number ratios to for can be subdivided and have
chemical compounds been
5. In chemical reactions, atoms
combine, separate or are
Discovery of the Discovery of the Nucleus & Discovery of the
Electron Proton Neutron
Discover/Experimenter: Discover/Experimenters: Ernest Discover/Experimenter:
Joseph John Thomson Rutherford, Hans Geiger and Chadwick
Experiment/year: Experiment/year: commonly Experiment/year:
Cathode Tube; 1897 known as “Rutherford’s Complete for
experiment”; 1911 homework
What was his greatest discovery and
what was the controversy this created
Showed: existence of a Showed: existence of a nucleus with Complete for homework
negatively cathode ray; the positive particles. A thin piece of gold
ray had mass and force; ray foil was bombarded with a narrow
deflected by magnetic field beam of alpha (+) particles. Some of the
and negatively charged particles were redirected by the gold foil
objects; all cathode rays back toward the source. Rutherford’s
composed of negatively hypothesis: negatively charged
charged particles that were electrons surround positively charged
later named electrons nucleus
What is the difference between the charge of a proton and an
Which particle has the least mass? By how much less?
Which of them is neutral and where is it located?
Protons are closely Similar attraction
packed at the center of the between neutrons in the
When protons are
extremely close, there is a
between them. More than
100 protons can exist close
together in the nucleus
The forces that hold the protons and neutrons together are referred to
as NUCLEAR FORCES
Why is matter mostly empty space? Hint: look at the radius
difference between the atomic radius and nucleus radius)
Homework: Are there other sub particles in the atom? If there
are, give some examples.
Protons Neutrons Electrons
The atomic number The number of neutrons The number of
of an element can differ in atoms of the electrons is equal to
represents the number same element. For the atomic number
of protons . The example: Hydrogen-2 when the atom is
atomic number (Z) is (Deuterium) has 1 neutrons neutral
the same for all atoms while Hydrogen-3 has 2
of a specific element. neutrons.
For example, all Helium-3 has 1 neutron and
Hydrogen atoms have 1 Helium-4 has 2 neutrons.
proton, all helium These examples above are
atoms have 2 protons. called ISOTOPES or atoms
Elements are listed in of the same element with
the periodic table different masses.
according the atomic # of neutrons = mass
number number – atomic number
Mass number is equal to the total number of
protons and neutrons or the atomic number + the
number of neutrons
1. Two ways of writing isotopes: Formula
1. Hyphen notation: example:
1. Chlorine-37; uranium-235; carbon-14
2. Nuclear Symbol: example: the bottom
1. 235 U the top number is the atomic mass
92 and the bottom number is the
atomic number atomic
Example Find the number of protons, neutrons
and electrons of: Chlorine-37:
Find the atomic number from the Periodic Table. The
atomic number = Number of protons = number of
Mass number = number of neutrons –atomic number
Atomic number from the Periodic Table = 17
The number of electrons is = 17
The number of neutrons is:
37 – 17 protons = 20 neutrons.
How many protons, neutrons and electrons are there is
atom of bromine-80?
The standard used by scientists to apply to atomic
mass is based on an atom: carbon-12 nuclide.
The mass assigned to this nuclide is 12 atomic mass
One atomic mass unit or 1 amu is 1/12 the mass of a
Average Atomic Mass Example
Weighted Copper has two naturally
average of the occurring isotopes:
atomic masses 69.17% of Copper-63 with a mass
of the naturally of 62.929599 amu and 30.83% of
occurring Copper-65 with atomic mass
isotopes of an 64.927793 amu.
.6917 X 62929599 amu + .3083 X
64.927793 amu = 63.55 amu
The Mole Avogadro’s Number Molar Mass
Like a dozen, the mole The number of particles The mass of one mole of a
represents a certain in a mole or pure substance in grams.
amount of a substance. 6.022 X 1023 particles in It is equal to the atomic
one mole of a pure mass that we find in the
substance periodic table for each
Example: for example, Example: one mole of Examples: one molar
number of carbon has 12 copper has 6.022 X 1023 mass of Lithium is 6.94
grams of carbon atoms grams/mole
One molar mass of
mercury (Hg) is 200.59
What is the mass in grams of 3.50 mol of
the element copper, Cu?
Given: 3.50 mol Cu
Unknown: mass of Cu in grams
Solution: the mass of an element in grams
can be calculated by multiplying the
amount of the element in moles by the
element’s molar mass.
The molar mass of copper from the
periodic table is rounded to 63.55 g/mol.
A chemist produced 11.9 g of aluminum, Al.
How many moles of aluminum were
Given: 11.9 g Al
Unknown: amount of Al in moles
The molar mass of aluminum from the
periodic table is rounded to 26.98
How many moles of silver, Ag, are in 3.01
1023 atoms of silver?
Given: 3.01 × 1023 atoms of Ag
Unknown: amount of Ag in moles
What is the mass in grams of 1.20 108
atoms of copper, Cu?
Given: 1.20 × 108 atoms of Cu
Unknown: mass of Cu in grams
The molar mass of copper from the
periodic table is rounded to 63.55