CHAPTER 1: ATOMS & ELEMENTS (NOTES)
(1) WHAT IS AN ATOM?
-Aristotle believed matter was infinitely divisible.
-Democritus believed that matter was made up of minuscule particles (which he called atomos)
that couldn’t be divided and he was right.
- Both were philosophical theories that weren’t backed up by experiments
Definition of the atom:
•Tiny particles that make up matter
•They are the building block of matter;
•They cannot be chemically divided;
•They are extremely small e.g. 1 cm = approximately 50 million atoms lined up!
Evolution of the atomic theory through the ages:
Democritus
Approximately 400 B.C. (Greece)
1. Matter is discontinuous
2. Particles are separated
3. Particles are infinitely
small
4. Particles cannot be
divided (Atomos)
Aristotle
approximately 300 B.C.
1. Matter is continuous
2. Substance completely fills
up the space it occupies
DO NOT MEMORIZE
Roger Bacon:
Joseph Proust:
Experimentation is
necessary to an
understanding of
the structure of
matter.
Chemical
reactions
happen with
definite
proportions.
1214-1294
1627-1691
1783
Robert Boyle:
Compression and
expansion of gases.
Antoine Laurent
Lavoisier:
Conservation of
matter during a
chemical reaction.
1799
DO NOT MEMORIZE
Antoine-Laurent de Lavoisier (August 26, 1743
– May 8, 1794), the father of modern chemistry
[1], was a French nobleman prominent in the
histories of chemistry, finance, biology, and
economics. He stated the first version of the
law of conservation of mass, recognized and
named oxygen (1778) and hydrogen (1783),
disproved the phlogiston theory, introduced
the metric system, wrote the first extensive list
of elements, and helped to reform chemical
nomenclature. He was also an investor and
administrator of the "Ferme Générale" a
private tax collection company; chairman of
the board of the Discount Bank (later the
Banque de France); and a powerful member of
a number of other aristocratic administrative
councils. All of these political and economic
activities enabled him to fund his scientific
research. But because of his prominence in the
pre-revolutionary government in France, he
was beheaded at the height of the French
Revolution.
John Dalton
1.1 DALTON’S ATOMIC MODEL
From grade eight, recall Lavoisier’s law of conservation of mass: the mass of matter present at
the beginning of a chemical reaction is equal to the mass of matter present at the end of a
chemical reaction, hence:
greactants = gproducts
-Dalton’s model is based on scientific experimentation.
-It contains the following points:
(1) Matter is formed of atoms which are extremely small and indivisible
(2) Each element is made of atoms which are all the same
(3) Atoms of one element are different from atoms of another element
(4) Atoms of different elements can combine in fixed ratios
(5) No atom is created, divided, or destroyed during a chemical reaction, they are only
rearranged to form new compounds.
- These wooden spheres (right) were used by Dalton (circa 1810) to demonstrate his theory
J.J. Thomson
English Physicist
(1856-1940)
1.2 THOMSON’S ATOMIC MODEL
-By experimenting with cathode rays, Thomson theorized that the atom contained indivisible,
negatively charged particles (electrons) and that these particles could separate from the atom
fairly easily.
-Thomson used gas discharge tubes to conduct his experiments where he studied the flow of
electricity through gases at extremely low pressure in a cylindrical glass tube.
- The gas discharge tube consists of a high-voltage source, a vacuum pump, a glass tube, 2
terminals: a positive one (cathode) and a negative one (anode) and it works in the following
manner:
(1) The tube is filled with a certain gas.
(2) The gas is then taken out of the tube
with the help of a vacuum pump thus
greatly reducing the pressure in the
tube
(3) A high voltage current is sent through
the terminals
(4) The gas particles remaining begin to
glow (color of the light emitted depends
on the gas used, e.g. Ne gas gives off a
red light)
(5) It was discovered that the glow was
produced by a stream of electrons
(called cathode ray) that originated
from the cathode and travelled to the
positive anode
Gas discharge tube conclusions:
-At very low temperatures gases conduct electricity.
-Because the glow produced migrated towards the positive anode, it was deduced that this glow
was made up of a stream of negative particles, namely electrons .
-- Cathode ray tubes were extensively used for TV’s and computer screens before the arrival of
liquid crystal and plasma technology.
The electron
-J.J. Thomson called the negatively charged particles emitted by the cathode electrons
- He believed the atom to be a positively charged ball covered with electrons, particles that
could easily detach themselves from the rest of the atom. He named his model the plum
pudding model.
Characteristics of a cathode ray tube:
1. Cathode ray tube have a negative charge.
Power source goes on.
The screen is made of a
phosphorous derivative
that shines lights when
hit by the ray.
What if you have oppositely charged plates around the tube?
Power source goes on.
2. Cathode ray tube proves the “particle” aspect of the electron (kinetics).
So Thomson’s model of the atom is called the plum-pudding model where
negative charges called electrons float in a positive sphere.
3. The charge in the cathode ray
tube has a rectilinear trajectory
and produces light.
And now for
something
completely
different.
Discovery of radioactivity (436)
DO NOT MEMORIZE
In 1896, a man by the name of Antoine
Henry Becquerel discovered radioactivity
when he left radioactive salts over a
photographic plate. He noticed that the
salts left an imprint on the plates. In
1903, he shared the Nobel Prize in
Physics with Pierre and Marie Curie "in
recognition of the extraordinary services
he has rendered by his discovery of
spontaneous radioactivity". In 1908, the
year of his death, Becquerel was elected
permanent secretary of the Académie
des Sciences. He died at the age of 55 in
Le Croisic.
The SI unit for radioactivity, the
becquerel (Bq), is named after him, and
there are Becquerel craters on the moon
and Becquerel craters on Mars.
DO NOT MEMORIZE
Image of Becquerel's photographic plate which has been fogged by exposure to radiation
from uranium salts. The shadow of a metal Maltese Cross placed between the plate and
the uranium salts is clearly visible.
DO NOT MEMORIZE
DO NOT MEMORIZE
In 1903, the Royal Swedish Academy of Sciences awarded
Pierre Curie, Marie Curie, and Henri Becquerel the Nobel
Prize in Physics, "in recognition of the extraordinary
services they have rendered by their joint researches on
the radiation phenomena discovered by Professor Henri
Becquerel."
Curie was the first woman to be awarded a Nobel Prize.
Eight years later, she received the 1911 Nobel Prize in
Chemistry, "in recognition of her services to the
advancement of chemistry by the discovery of the
elements radium and polonium, by the isolation of radium
and the study of the nature and compounds of this
remarkable element". Her death near Sallanches, Savoy, in
1934 was from aplastic anemia, almost certainly due to
exposure to radiation, as the damaging effects of hard
radiation were not yet known, and much of her work had
been carried out in a shed with no safety measures. She
had carried test tubes containing radioactive isotopes in
her pocket and stored them in her desk drawer, remarking
on the pretty blue-green light the substances gave off in
the dark.
DO NOT MEMORIZE
DO NOT MEMORIZE
DO NOT MEMORIZE
Radiation under the influence of electric fields:
Ernest Rutherford, 1st Baron Rutherford of Nelson
(30 August 1871 - 19 October 1937), widely
referred to as Lord Rutherford, was a nuclear
physicist who became known as the "father" of
nuclear physics with the help of his assistant and
godfather Spencer Isitt of Condradale. He
pioneered the orbital theory of the atom through
his discovery of Rutherford scattering off the
nucleus with his gold foil experiment.1903: Ernest
Rutherford
Using Henri Becquerel’s discovery, Ernest
Rutherford observed the effects of electric
fields on a radioactive substance.
In science there is only physics; all the rest is stamp collecting
1.3 RUTHERFORD’S ATOMIC MODEL
- Subsequent to the discovery of cathode rays, was the discovery of X-rays and radioactivity
The Atomic Nucleus & the Proton
-At the time Rutherford (1871-1937) conducted his radioactivity experiments ,it was known that
radioactive substances could emit 3 types of radioactive particles:
Alpha (+)
Beta (-)
Gamma (neutral)
-Rutherford attempted to learn more about the location of electrons in atoms by bombarding a
very thin gold sheet with a stream of positively charged alpha particles.
-He expected most of the alpha particles would pass right through the very thin (160 atoms
thick) gold foil.
-He also expected a few alpha particles would be mildly deflected as they would come in contact
with an electron; instead a few alpha particles bounced back with considerable force of
unexpected strength while the others passed through the gold sheet.
-Because of these findings Rutherford concluded:
(1) Atoms are mostly empty space since the majority of alpha particles passed right through the
gold foil and thus through the gold atoms
(2) Atoms contain a very dense and small, solid-like positively charged nucleus since positive
alpha particles bounce back with great strength when they come in contact with the nuclear
core (thus 2 positives repulse each other)
- Rutherford called the positive particle in the nucleus the proton and he deduced that
in an atom the no. protons = the no. electrons since the atom as a whole is neutral .
+
Power
source
-
Lead block
+
β
γ
Power
source
Lead block
β: Beta (-), (electron, e-)
γ: Gamma (Neutral), energy ray
α: Alpha (+), Ionized helium, He+
α
To give you an idea of the radiation effect on us:
Rutherford’s experiment on alpha particle dispersion (Scattering) (pp 67)
In 1907, E. Rutherford performed a famous experiment at McGill University.
β
+
γ
Power
source
Lead block
-
α
So the alpha radiation which has a positive charge floats into a chamber surrounded by
fluorescent material. The alpha radiation encounters a gold sheet.
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1.4 THE RUTHERFORD-BOHR ATOMIC MODEL
-Rutherford’s model was problematic. Scientists wondered why protons and electrons did not
collide with one another. Two years later, Bohr expanded on Rutherford’s model and provided
some explanation.
- Bohr’s experiments consisted of shining a glowing hydrogen-filled discharge tube through a
plate containing a slit. This slit would break the incoming glow into 4 bands of differing color
(just like a prism would separate white light into the colorful electromagnetic spectrum)
-To explain the 4 differently colored bands Bohr concluded:
(1) That electrons were found in specific areas he called orbitals as opposed to being randomly
found. Bohr speculated that electrons could jump from one orbit to the next.
(2) An orbit correspond to a level of energy.
(3) An electron can “jump” to another orbital (farther from the nucleus) when it receives extra
energy and gets “excited”.
(4) If a previously excited electron returns to its original orbital, it emits light thus releasing
energy.
1.5 THE SIMPLIFIED ATOMIC MODEL
-Bohr’s improvement still did not explain all questions, e.g. why being all positive, the nucleus
does not cause an explosion (excessive repulsion bet. + charges)
The Neutron
- Chadwick (1891-1974) discovered the neutron, a neutral nuclear particle; he speculated that
the neutron acted as the ‘glue’ that holds protons in place in the nucleus
- The simplified atomic model is a representation of the atom containing the no. of protons and
neutrons in the nucleus and the no. of electrons in their respective shells
The simplified atomic model:
DO NOT MEMORIZE
At
legendary First
First Solvay
Solvay Conference
Conference (1911),
(1911), Skłodowska-Curie
from right),
the only
only woman
At the
the legendary
Skłodowska-Curie (seated,
(seated, 2nd
2nd from
right), the
woman
present,
confers
with
Henri
Poincaré.
Standing,
4th
from
right,
is
Ernest
Rutherford;
2nd
from
right,
Albert
present, confers with Henri Poincaré. Standing, 4th from right, is Ernest Rutherford; 2nd from right, Albert
Einstein;
at far
Einstein; at
far right,
right, Paul
Paul Langevin.
Langevin.
(2) THE PERIODIC CLASSIFICATION OF THE ELEMENTS
Definition: periodic classification: a method whereby objects are classify according to their
characteristics in order to make things more comprehensible.
-Today’s periodic table is based on a version developed by Dmitri Mendeleev (1834-1907) who
offered the best classification solution for elements.
-Definition: periodic table of elements: a visual model whereby the elements are classified
according to their physical and chemical properties; makes the relationships between elements
more understandable.
DO NOT MEMORIZE
Dimitri Mendeleev (Russian: Дми́ трий Ива́нович
Менделе́ев, Dimitriy Ivanovich Mendeleyev (8 February
[O.S. 27 January] 1834 in Tobolsk – 2 February [O.S. 20
January] 1907 in Saint Petersburg), was a Russian chemist.
He is credited as being the primary creator of the first
version of the periodic table of elements. Unlike other
contributors to the table, Mendeleev predicted the
properties of elements yet to be discovered.
DO NOT MEMORIZE
General info: As a better understanding of atomic weights was developed and better data
became available, Mendeleev made for himself the following table:
Cl 35.5 K 39
Ca 40
Br 80
Rb 85
Sr 88
I 127
Cs 133 Ba 137
DO NOT MEMORIZE
By adding additional elements following this pattern, he developed his version of the periodic table.
On March 6, 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The
Dependence between the Properties of the Atomic Weights of the Elements, which described elements
according to both weight and valence. This presentation stated that
1.
The elements, if arranged according to their atomic mass, exhibit an apparent
periodicity of properties.
2.
Elements which are similar as regards to their chemical properties have atomic
weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase
regularly (e.g., K, Rb, Cs).
3.
The arrangement of the elements in groups of elements in the order of their atomic
weights corresponds to their so-called valencies, as well as, to some extent, to their
distinctive chemical properties; as is apparent among other series in that of Li, Be,
C, N, O, and F.
4.
The elements which are the most widely diffused have small atomic weights.
5.
The magnitude of the atomic weight determines the character of the element, just as
the magnitude of the molecule determines the character of a compound body.
6.
We must expect the discovery of many yet unknown elements–for example, two
elements, analogous to aluminium and silicon, whose atomic weights would be
between 65 and 75.
7.
The atomic weight of an element may sometimes be amended by a knowledge of
those of its contiguous elements. Thus the atomic weight of tellurium must lie
between 123 and 126, and cannot be 128. Here Mendeleev was wrong as the
atomic mass of tellurium (127.6) remains higher than that of iodine (126.9).
8.
Certain characteristic properties of elements can be foretold from their atomic
weights.
B,
One form of Mendeleev's
periodic table, from the 1st
English edition of his textbook
(1891, based on the Russian
5th edition)
Sculpture in honor of Mendeleev and the
periodic table, located in Bratislava, Slovakia
2.1 METALS, NONMETALS, & METALLOIDS
-The staircase divides the periodic table into metals to the left and nonmetals to the right;
except for Al and Po (metals), metalloids are found immediately to the right and left of the
staircase.
-Metals: are usually good conductors of heat and electricity. They are often ductile and
malleable. Usually shiny. Solid at room Temperature except for Hg which is liquid. Many react
with acids.
- Nonmetals: usually weak heat and electricity conductors. Many are gases at room
Temperature. Solid nonmetals are brittle and can easily be reduced to powder.
- Metalloids or Semimetals: 7 elements (B, Si, As, Sb, Te, I, Po, At) have properties from each ,
category; maybe be good electrical conductors in some conditions and weak conductors under
other conditions, because their conductance can vary with current and voltage, metalloids are
used extensively for the control of electrical current in devices that use radio waves; called
semiconductors.
2.2 THE GROUPS OF THE PERIODIC TABLE
-The columns of the periodic table form groups; vertical groupings
-Elements of a group have similar chemical properties and have the same number of valence
electrons (electrons on the last shell)
-Note: hydrogen doesn’t belong to a group
-Groups are identified with the letter A or B and a Roman numeral that indicates the number of
electrons in the outermost shell; e.g. elements of group IIA ,all have 2 valence electrons and
elements of group VIIB have 7 valence electrons
Li
Be
Na
Mg
K
Ca
Rb
Sr
Alkaline family
Cs
Alkaline-Earth family
Ba
He
Fr
Ra
F
Halogen family
Cl
Br
I
At
Noble or inert
gases family
Ne
Ar
Kr
Xe
Rn
(1) Alkali Metals (group IA; 1st column): e.g. Na, Li, K…; are soft and reactive; must be stored in
oil since they will react with humidity in the air; so reactive that they are never found in their
elemental form in nature, found only in compound form.
(2) Alkaline Earth Metals (group IIA; 2nd column): e.g. Be, Mg, Ca…; highly malleable & reactive;
burn easily in the presence of heat; although can be exposed to air, are not found in their
elemental state in nature (too reactive); form many compounds formed in rocks
(3) Halogens (group VIIA; before last column): e.g. F, Cl, Br…; react easily to form compounds,
including salts (compounds formed when an acid reacts with a base or with a metal);
nonmetals; several are powerful cleaners;
(4) Noble Gases or Rare Gases or Inert Gases (group VIIIA; last column): ex. He, Ne, Ar…; very
stable; rarely react, therefore are found in their elemental form in nature; image shows the
color emitted by noble gases as an electric current is passed through them, explaining why
they are used in glowing signs
2.3 THE PERIODS OF THE PERIODIC TABLE
- The rows of the periodic table; horizontal groupings
-Elements of a same period will all have the same number of shells around their nucleus
The Periodicity of Properties
- Refers to how properties vary within a period.
-E.g. the size of an atom will decrease from left to right within a period; as there are more
protons and electrons in each element as you go to the right of a period, the attraction between
the + and - forces increase causing the compacting of the atom
- Properties include: melting point, boiling point, density, atomic radius, first ionization energy
(energy needed to move the outmost electron away from an atom), electronegativity (the
degree of ability an atom has to attract electrons from other atoms in order to form bonds – the
higher the electronegativity, the more readily an atom will react – F has the highest
electronegativity value at 4.0)
Li
Radius gets bigger
is you go down a
family.
e- e-
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Na
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2.4 ATOMIC NUMBER
- Whole number in the squares of the periodic table; ex. phosphorous: 15
- Equal to the number of protons in the nucleus of an atom (and electrons in a neutral atom)
- Symbol e.g. P
Symbol
Name
Atomic mass
2.5 RELATIVE ATOMIC MASS
- The mass of one atom of a particular element derived by using carbon-12 atom as a
reference; ex. phosphorous: 30.97 u
-Expressed in amu or u, atomic mass units
-1 u = approx. 1.66 x 10-24g
- Because atomic masses are very small, they are difficult to measure directly. As a solution to
this problem, a reference atom was used to establish the meaning of the atomic mass unit and
to determine the mass of all other atoms; scientists agreed to give 1 carbon-12 atom (a carbon
atom which has 6 protons and 6 electrons) a mass of 12u; by extension it was calculated that
the mass of 1 proton or 1 neutron was about 1u (electrons being extremely light have an almost
negligible mass)
Mass number
-Whole number that represents the mass of protons + the mass of neutrons
-Determined by rounding off the relative atomic mass, ex. P = 30.97 = 31
-Atoms are often represented with a notation; where A is mass no; Z is atomic no and E is
element symbol; ex. for phosphorus:
-To calculate no. of neutrons, you must subsrtracted the atomic number from the atomic mass:
No. of neutrons = mass number – atomic number
2.6 ISOTOPES
-An atom may exist in different versions where the number of neutrons will vary from one atom
to the next
-Ex. hydrogen has 3 isotopes:
• most common form, atomic mass = 1, also called: hydrogen-1
• (deuterium): heavy hydrogen, atomic mass = 2, also called: hydrogen-2
• (tritium): super-heavy hydrogen, atomic mass = 3, also called: hydrogen-3
- All isotopes of an element have the same number of protons and the same chemical
properties but they have different physical properties.
Isotopes (436)
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Hydrogen
Deuterium
Tritium
1 Proton (+)
1 Proton (+)
1 Proton (+)
1 Electron (-)
1 Electron (-)
1 Electron (-)
Zero Neutron (Ø)
1 Neutron (Ø)
2 Neutrons (Ø)
(3) REPRESENTING ATOMS
-Usually electrons fill the shell closest to the positively charged nucleus before filling a shell that
is farther away from the nucleus
-The 1st electron shell can contain a maximum of 2 electrons and the 2nd shell a maximum of 8
electrons
-The 3rd shell also can carry 8 electrons.
-Once 8 electrons are filled in the 3rd shell, the 9th electron jumps over to the 4th shell followed
by other electrons.
3.1 LEWIS NOTATION
- Atoms are represented by their symbol and paired dots. The dots represent the valence
electrons. The dots will make up a cross shape before starting to double up
3.1 LEWIS NOTATION
Lewis notation can also be used for compounds.
This is the Lewis structure for water.
3.2 REPRESENTING AN ATOM ACCORDING TO
THE RUTHERFORD-BOHR MODEL
-Must know the period (its no. indicates the no.
of shells), the group (indicates the no. of valence
electrons), and the atomic no. (indicates the no.
of protons and electrons)
-The small sphere is drawn and the no. of
protons is written in it; each electron shell is
represented by a circle around the nucleus;
electrons are drawn on the electron shell circles
to indicate their location
- This type of model is sometimes called the
planetary model (right); what is inaccurate
about this representation?
3.3 REPRESENTING AN ATOM ACCORDING TO THE SIMPLIFIED ATOMIC MODEL
-In this model, protons, neutrons and electrons are represented; ex. oxygen below which has 8
protons, electrons and(in this case also) 8 neutrons
- The no. of neutrons is calculated by rounding the atomic mass up/down and subtracting the
atomic number; ex. Be, beryllium (the 4th element) has an atomic mass of 9.01; this would be
rounded down to 9; the no. of neutrons would be calculated by subtracting 4 from the nine,
giving 5; therefore a Be atom would have 4 protons , 4 electrons and 5 neutrons
Reminder: Chemical group and electron configuration: Simplified atomic model
ee-
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Nucleus:
Composed of the
proton and the
neutron.
e-
e-
e-Valence electron:
e-
An electron located on
the outermost electron
shell..
e-
Electron shells:
The most probable positions
occupied by electrons in an atom.
Li
e- e-
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Na
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1
18
IA
VIA
2
13
14
15
16
17
IIA
IIIA
IVA
VA
VIA
VIA
Li
Lithium:
Group number one, hence one valence electron
Period two, hence two electron shells or levels
e-
e- e-
1
18
IA
VIA
2
13
14
15
16
17
IIA
IIIA
IVA
VA
VIA
VIA
Na
Sodium:
Group number one, hence one valence electron
Period three, hence three electron shells or levels
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Shorthand technique:
Lithium
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1 e-
2 e-
8 e-
Phosphorous
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e5 e-
3.4 THE ‘BALL-AND-STICK’ MODEL
- In this model the whole atom is represented by a ball & bonds are represented by a line (stick);
ex. image; different colors indicate different atoms; plastic ball & stick of methane (CH4)
(4) THE CONCEPT OF MOLE
-A mole is a quantity used to express the amount of atoms & molecules present in a sample
-It is a concept similar to a pair, a dozen, or a hundred, where each notion equates a specific
amount, except that it refers to a much greater quantity
-Once again the carbon-12 atom is used as a reference; to be exact:
1 mole is equal to number of atoms in exactly 12g of carbon-12
- The symbol for the mole is mol
4.1 MOLAR MASS
-Molar mass is the mass of one mole of a substance
-From above we know that 1 mole carbon-12 = 12g (from 12u which is the
relative atomic mass for carbon-12); because of this knowledge we can to say
that the mass of a mole of a substance = to its atomic mass
-Molar mass is expressed in g/mol
-Therefore molar mass is determined by using the relative atomic mass;
because one atom of N has a relative atomic mass of 14.01u then the mass for
one mole of N is 14.01g/mol
-If we wanted the molecular molar mass for N, meaning the molar mass for N2,
then we would multiply 14.01 x 2 to obtain 28.02g/mol
-Can you figure out H2O & CO2’s molar mass?
- There is a formula associated with molar mass, it is:
4.2 AVOGADRO’S NUMBER
-The Avogadro constant was named in honor of Amedeo Avagadro’s (physicist, 1776-1856)
contribution to the field; image
-Through experimentation it was determined 6.02 x 1023 atoms are contained in 12g of carbon12; this number is the Avogadro constant or Avogadro number
-This means that 1 mole of anything will contain 6.02 x 1023 entities; ex. 1 mole of apples
represents 6.02 x 1023 apples
- By extension the molar mass (derived by the relative atomic mass) of any element will equal to
6.02 x 1023 atoms; 24.31g of Mg & 6.94g of Li will respectively equal 6.02 x 1023 atoms of Mg & Li
respectively
DO NOT MEMORIZE
DO NOT MEMORIZE
Using Avogadro's result that
any gas under the same
conditions has the same
number of molecules per
Mole
(unit),
Loschmidt
determined that number,
now
called
Avogadro's
number as being 6.023 ×
1023 molecules. This is why
on rare occasions this
"Avogadro number" is called
the "Loschmidt number" in
English (in German, though,
"Loschmidt'sche Zahl" is the
commonly used name).
DO NOT MEMORIZE
-Can you figure out H2O & CO2’s molar mass?
-There is a formula associated with molar mass, it is:
M=m/n, where M=molar mass in g/mol; m=mass in g; n=number of moles in mol
- Ex. How many moles are there in 84 g of CO2?
n = m/M
= 84g/44.01g/mol
= 1.9mol of CO2
MMM:
2 (H)
+
1 (S)
+
4(O)
2 (1)
+
1 (32)
+
4(16)
2
+
32
+
64
98 g/mol
MMM:
2 (1 (N) +
4 (H))
+
1(C)
+
3(O)
2 (1 (14) +
4 (1))
+
1(12)
+
3(16)
2 (14
+
4)
+
12
+
48
2 (18 )
+
12
+
48
36
+
12
+
48
96 g/mol
n: number of moles (mol)
M: Molecular molar mass (g/mol)
m: mass (g)
m ___
M
n