Course Code: Chem 1
Course Title: General Chemistry 1
(Organic)
Unit: 2 (lecture)
Republic of the Philippines
INITAO COLLEGE
Jampason, Initao, Misamis Oriental
1st Semester, AY 2022 - 2023
COURSE
INSTRUCTORS
Instructor FB Name: ENGR. ALEX P. ECHAVEZ
Mobile Number:09153876637
e-mail: echavezalex082963@gmail.com
Class:Chem 1 Organic Chemistry
Module 2
Topic:
 Development of the
Atomic Model
 Atomic Structure
 Periodic Table
Duration: 3 hours
Desired Learning Outcomes:
 Trace the development of the atomic model through an
illustrated timeline
 Design a model of a 1s to 2p element atom Classify
elements according to blocks and families
INTRODUCTION
That question could perhaps be the same question too with the ancient people before. But record only starts way back
400 BC. We have all heard of atoms in connection with atomic bombs, “splitting the atom,” and atomic power.
Consider a boar of iron. Iron is an element. It has certain properties. Cutting the bar in half produces two pieces of iron.
Both pieces have the same properties as the original bar. Continued cutting procedures smaller and smaller pieces, all
with identical properties. In time, we would theoretically arrive at the smallest piece of iron attainable. This smallest
piece of iron is an atom – an atom of iron. If this atom of iron were cut in two, particles with different properties would
be produced. It would no longer be iron. Thus, an atom can be defined as the smallest portion of an element that retains
all the properties of the element.
A piece of iron is made up of many atoms of iron; a piece of copper, of many atoms of copper; and a piece of silver, of
many atoms of silver. The atoms of one element differ from those of another and so give characteristic properties of each
element. Atoms are called the building block of the universe. A chemist uses different kinds of atoms to build chemical
compounds, just as we all use the different letters of the alphabet to form words. Since there are more than 100 elements,
there are more than 100 different kinds of atoms.
DISCUSSION
Development of the Atomic Model
Democritus
The things we know about atoms today were discovered by many scientists over a long period of time. In fact, the first
person to hypothesize that atom exist was Democritus. Democritus was a Greek philosopher who lived in fourth century
BCE. He suggested that everything in the universe was made of tiny, indivisible units. He called these units atoms.
The word atom comes from the Greek work atomos. Atomos means “unable to be cut or divided.”
Democritus made many observations of how matter changes. He thought that the movements of atoms cause the changes
he observed. However, Democritus did not have any evidence to show that his theory was correct. Although
some people agreed with Democritus’s theory, others thought that different theories were correct.
As the science of chemistry was developing in the 1700s, scientists began to focus on making
careful measurements in experiments. Therefore, scientists began to collect more accurate and
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precise data about matter. Just as scientists do today, scientists in the past used data to decide which theories were most
correct.
John Dalton
In 1808, an English schoolteacher names John Dalton proposed a different atomic theory. Like Democritus, Dalton
proposed that atoms could not be divided in to smaller parts. However, unlike Democritus, Dalton performed scientific
experiments to find data to support his theory.
Dalton’s experiments showed that atoms of different elements could combine in certain ways to
form compounds. This is known as the “law of definite proportions.” The law of definite proportions states
that a chemical compound always contains the same proportion of a particular element. For example, in any sample of
water, hydrogen will make up 11% of the mass of the sample.
In other words, in 100g of water, there will be 11g of
hydrogen and 89g of oxygen.
Some parts of Dalton’s atomic theory are still
accepted by scientists today. In fact, Dalton’s
explanation of how atoms combine to form substances is
considered the foundation of modern atomic theory.
However, as scientists continued to carry our experiments,
they made new observations that did not fit
Dalton’s theory. New theories were developed that
better explained the new observations.
John Joseph Thomson
In 1897, a British scientist named J.J. Thomson was
working with cathode rays, mysterious rays in vacuum
tubes. His experiments helped scientists better understand
the structure of atoms.
In his experiments, Thomson used a vacuum tube that
contained two electrodes. One electrode, called the
cathode, was negatively charged. The other, called the
anode, was positively charged. When electricity was
sent through the tube, a glowing beam appeared inside the
tube. Other scientists had shown that
this beam came from the cathode. However, they had not been able to determine what the beam was made of.
When Thomson placed a magnet near the tube, the beam was deflected, or bent, as shown in
the figure below/ Only, streams of charged particles can be bent by a magnet. Light rays cannot. Therefore,
Thomson’s experiment suggested that cathode rays were actually streams of tiny, charged particles. Based on the
direction the beam bent, Thomson determined that the particles in the beam were negatively charged. His experiments
also showed that, no matter what substance the cathode was made of, the beam was always the same.
Based on his results, Thomson concluded that the particles in the beam came from atoms. He also concluded that the
particles were the same in atoms of different elements. This is how Thomson discovered electrons, the negatively
charged particles inside an atom.
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Ernest Rutherford
According to Thomson’s atomic theory, the
mass of an atom was spread evenly throughout its
volume. Ernest Rutherford, a former student of
Thomson’s, developed experiments to test this
idea.
In one experiment, Rutherford’s students
aimed a beam of positively charged particles at a very
thin sheet of gold foil. Rutherford predicted that the
positive charge in the gold atoms would be too weak
to affect the positively charged particles. Therefore, the particles would either pass straight through the foil or be
deflected slightly. However, this is not what the experiment showed.
Most of the particles passed straight through the
foil. Some were deflected slightly. However, some
of the particles bounced back at sharp angles.
These results are shown in the figure below.
The results of Rutherford’s experiment
were very surprising. In his notebook,
Rutherford wrote, “It was almost as
incredible as if you fired a 15-inch shell at a piece
of tissue paper and it came back
and hit you.” However, further experiments produced the same results. Therefore, Rutherford’s
results were confirmed.
Rutherford concluded that the sharply reflected particles collided with dense parts of the atoms in the gold foil. The
particles bounced back because they had the same charge as the dense parts of the atom. Because so few particles
bounced back at sharp angles, Rutherford concluded that these dense parts must be very tiny. Based on his
results, Rutherford concluded that an atom’s positive charge is concentrated at the center of atom. This
positively charge is concentrated If an atom were the size of a football stadium, its nucleus would be only as big as a
marble.
Rutherford’s results let to a new model of the atom. In the Rutherford model, negatively charged
electrons orbit the positively charged nucleus, as shown below. This is similar to the wat that the planets orbit the sun.
Atomic Structure
Atom - The smallest particle of an element that can exist and still have the properties of the
element. It is the limit of chemical subdivision. Atoms are extremely small particles. Atoms possess internal
structure; that is, they are made up of even smaller particles, which are called subatomic particles.
Subatomic Particle - a very small particle that is a building block for atoms. Three Types
of Subatomic Particles
• Electrons – found outside the nucleus; possesses a negative electrical charge;
smallest mass.
• Protons – found in the nucleus; positive charge equal in magnitude to the electron’s
negative charge.
• Neutrons – found in the nucleus; no charge; virtually same mass as a proton.
Charge and Mass Characteristics of Electrons, Protons, and Neutrons
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All protons a
very tiny v
Nucleus is:
-Small com pared with the overall size of the atom.
-Extremely dense; accounts for almost all of the atom’s mass.
-Positively c harged center of an atom.
An atom a
there are e
s a whole is electrically neutral (no net electrical charge), i.e, qual
numbers of protons and electrons present in an atom.
Molecule the atoms a
3.2.1 Electro
The space i n which electrons move rapidly about a nucleus is divided ces called
into subspa shells, subshells, and orbitals.
– is a region of space about a nucleus that contains electrons that have approximatel the same energy
and that spend most of their time approximately the same distanc
from the nucleus.
-these are numbered 1,2,3, and so on, outward from the nucleus. Electron energ
increases as the distance of the electron shell from the nucleus increases. An electro in shell 1 has the
minimum amount of energy that an electron can have.
Electron Subshell – is a region of space within an electron shell that contains electrons that have the same energy.
Analogy: The shells are analogous to the floors of the apartment complex, and the subshells are the counterparts
of the various apartments on each floor.
Subshells within a shell differ in size (that is, the maximum number of electrons they can accommodate) and energy.
The higher the energy of the contained electrons, the larger the subshell. Subshell size (type) is designated using the
letters s,p,d, and f. Listed in this order, these letters denoted subshells of increasing energy and size.
Electron
Shell
Both a number and a letter are used in identifying subshells. The number gives
the shell within which the subshell is located, and the letter gives the types of
subshell. Shell 1 has only one subshell
– the 1s. Shell 2 has two subshells – the 2s and 2p. Shell 3 has three subshells -- the 3s, 3p, and 3d, and so on.
Electron subshells have within them a certain, definite number of locations
(regions of space), called electron orbitals, where electrons may be found.
Electron Orbitals – is a region of space within an electron subshell where an
electron with a specific energy is most likely to be found. Independent of all
other consideration, electron orbitals can accommodate a maximum of 2
electros. Thus an s subshell (2 electrons) contains one orbital, a p subshell (6
electrons) contains three orbitals, a d subshell (10 electrons) contains five
orbitals, and an f subshell (14 electrons) contains seven orbitals.
Orbitals have distinct shapes that are related to the type of subshell in which they are found. Note
that it is not the shape of an electron, but rather the shape of the region in which the electron is found that is being
considered. An orbital orbital in an s subshell, which is called an s orbital, has a
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spherical shape. Orbitals found in p subshells – p orbitals – have shapes similar to the “figure 8” of an ice
skater. More complex shapes involving four and eight lobes, respectively, are associated with d and f orbitals.
Orbitals within the same subshell, which have the same shape, differ mainly in orientation. For example, the three 2p
orbitals extend out from the nucleus at 90° angles to one another (along the x, y, and z axes in a Cartesian coordinate
system), as is show in the figure below.
Electron Spin
Experimental studies indicate that as an electron “moves about” within an orbital, it spins on its
own axis in either a clockwise or a counterclockwise direction. Furthermore, when two electrons are present in an
orbital, they always have opposite spins; that is, one is spinning clockwise and the other counterclockwise. This
situation of opposite spins is energetically the most favorable state for two electrons in the same orbital.
3 Rules for Assigning Electrons to Shells, Subshells, and Orbitals
There are many orbitals about the nucleus of an atom. Electrons do not occupy these orbitals in a random, haphazard
fashion; a very predictable pattern exists for electron orbital occupancy. There are three rules, all quite simple, for
assigning electrons to various shells, subshells, and orbitals.
1. Electron subshells are filled in order of increasing energy.
2. Electrons occupy the orbitals of a subshell such that each orbital acquires one electron before
any orbital acquires a second electron. All electrons in such singly occupied orbitals must have
the same spin.
3. No more than two electrons may exist in a given orbital — and then only if they have opposite
spins.
Periodic Table
During the mid-nineteenth century, scientists began to look for order in the increasing amount of chemic information
that had become available. They knew that certain elements had properties that were very similar to those of other
elements, and they sought reasons for these similarities in the hope that these similarities would suggest a method for
arranging or classifying the elements. In 1869, these efforts culminated in the discovery of what is now called the
periodic law, proposed independently by the Russian chemist Dmitri Mendeleev and the German chemist Julius
Lothar Meyer. Given in its modern form, the periodic law states that when elements are arranged in
order of increasing atomic number, elements with similar chemical properties occur at periodic
(regularly recurring) intervals.
• Periodic Law – When elements are arranged in order of increasing atomic number, elements with
similar chemical properties occur at periodic (regularly recurring) intervals.
• Periodic Table – Tabular arrangement of the elements in order of increasing atomic
number such that elements having similar chemical properties are positioned in vertical columns.
Periods – horizontal rows of elements
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Groups – elements in the same vertical columns; have similar chemical properties
Fun Fact: There are 118 known elements: 88 of the elements occur naturally , 30 of the elements have been
synthesized
Names and Chemical Symbols of the Elements
Chemical Symbol - One- or two-letter designation for an element derived from the element’s
name. Two letter symbols are often, but not always, the first two letters of the element’s name.
First letter of a chemical symbol is always capitalized and the second is not:
H – hydrogen
Ba – barium
Co – cobalt
Pb – lead
Ag – silver
For some elements, the symbol is derived from the Latin name of the element:
Ag – silver
Au – gold
Fe – iron
Pb – lead
Cu – copper
Four group dos elements also have common (non-numerical) name:
Alkali metals- general name for any element in Group IA of the periodic table, excluding hydrogen (Li, Na, K, Rb)
Alkaline earth metal – general name for any elements in the group IIA, (Be, Mg, Car, Sr, Ba, Ra);
these metals are soft and shiny, but they are only moderately reactive toward water.
Halogens – general name for any element Group VIIA of the periodic table; these halogens are reactive elements that
are gases at room temperature or become such at temperatures slightly
above room temperature
Noble gas – general name for any elements in Group VIIIA of the periodic table; these gases are unreactive gases that
undergo few, if any, chemical reactions
The location of any element in the periodic table is specified by giving its group number and its period number. The
element gold, with an atomic number of 79, belongs to Group IB (or 11) and is in Period 6. The element nitrogen, with
an atomic number of 7, belongs to Group VA (or 15) and is in Period 2.
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Metals and Nonmetals
On the basis of selected physical properties, elements are classified into the categories metal and nonmetal.
Metal – is an element that has the characteristic properties of luster, thermal conductivity, electrical conductivity, and
malleability. With the exception of mercury, all metals are solid at room temperature. Metals are good conductors of
heat and electricity. Most metals are ductile (can be drawn into wires) and malleable (can be rolled into sheets). Most
metals have high luster (shine), high density, and high melting points.
Nonmetal- is an element characterized by the absence of the properties of luster, thermal conductivity, electrical
conductivity, and malleability. Many of the nonmetals such as hydrogen, oxygen, nitrogen, and the noble gases, are
gases. The only nonmetal that is liquid at room temperature is bromine. Solid nonmetals include carbon, iodine, sulfur,
and phosphorus. In general, the nonmetals have lower densities and lower melting points than metals.
Selected Physical Properties of
Metals and Nonmetals
Dividing Line Between Metals and Non-metals
Discovery and Abundance of Elements
Abundance of Elements (in Atom
Percent) in the Universe
Abundance of Elements (in
Atom %) in the Earth’s Crust
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Elemental Composition of the
Human Body (in Atom Percent)
APPLICATION
The electron microscope uses the wavelike properties of electrons to see extremely
small images. Because electrons are charged particles, they can be easily focused by an
electrical field. Recent advances in the electron microscope have allowed scientist to see
atoms for the first time. The electron microscope has become one of the most powerful
tools in chemical, biologic, and material science research.
A scanning electron microscope in use. By its use of a highly focused electron beam in
place of light, the electron microscope allows researchers to view objects at
magnifications that far exceed those of light microscopes. This photo is an example of
how a scanning electron microscope view the cells inside our bodies.
ASSESSMENT
Instructions:
ONLINE: Submit a clear picture of your hand written answer and illustration through Facebook
messenger. Start with the date of submission, name, year, group then your 2 pictures (answers) for A and B,
and type C as text (answer directly).
OFFLINE: Use a separate clean sheet of short or long bond paper. In case you consume more than 1 page,
staple your work and do not forget to write your details on each of the pages.
A. Using a clean sheet of paper, create a timeline with concise description of events in the development of
the atomic Model. (10 points)
B. Using a separate part of the clean paper, select only one of the following elements and draw
a Rutherford’s model out of your selected element. (10 points)
H, He, Li, Be, B, C, N, O, F or Ne
C. Classify the following element as METAL, NON-METAL or METALLOID
1. Lanthanum
2. Boron
3. Chlorine
4. Antimony
5. Potassium
6. Xenon
7. Silicon
8. Gold
9. Mercury
10. Polonium
REFERENCES
McMurry, J., (2011). Fundamentals of Organic Chemistry Seventh Edition. Brooks/Cole Cengage Learning
Sackheim, G. I., & Lehman, D. D. (2002). Chemistry for the Health Sciences (8th Edition). New Jersey, Upper
Saddle River: Prentice-Hall, Inc.
Stoker, S. H. (2013). General, Organic, and Biological Chemistry (6th Edition). Belmont, CA: Brooks/Cole Cengage
Learning.
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