GHW# 4: Louisiana Tech University, Chemistry 100 POGIL (Process Oriented Guided
Inquiry Learning) exercise on Chapter 2. Atoms and Elements: Atomic Structure
Why?
Why is our planet made up of some 92 stable elements? Why are only 25 or so out of those 92
are found in living things? How is the structure of atoms that make up these elements play a major role
in determining their chemistry? Why is it important to understand the structure of atoms to explain
chemistry? How did the efforts of many scientists over a period of time have contributed to unraveling
the structure of atoms? Is there any direct evidence for the existence of atoms? How does the
arrangement of sub atomic particles explain concepts relating to the nuclear atom, the atomic number,
the isotopes of an element that have different atomic masses, and average atomic weight? How does
the periodic table of elements summarize and provide comprehensive data on the chemical elements
including structure, chemical and physical properties, element names and symbols? Why is it important
to know how to extract the information from the periodic table in applying chemical knowledge and
solving problems?
Learning Objectives
Atomic Structure and Subatomic Particles
1. Describe radioactivity, electrons, nuclear atom, nucleus, protons, neutrons and the general structure of
the atom.
2. Describe how early experiments (Thomson's cathode ray tube experiments and Millikan's oil drop
experiments) lead to the discovery of the electron, its mass, and its charge
The Nuclear Atom
1. Describe how Rutherford’s experiment leads to the concept of a nuclear atom and atomic number.
Atomic Numbers and Mass Numbers
1. Explain isotopes and isotopic symbols with atomic number and mass number for an element.
2. Define isotopes and given the atomic numbers and number of neutrons for a specific element.
3. Compare mass and charges of an electron, proton, and neutron.
4. Count number of neutrons, protons given an isotopic name or symbol.
The periodic Table
1. Describe the use of periodic table: periods, groups, families, metals, non-metals, metalloids, main
group elements, transition metals, actinides, lanthanides
2. Compare the relative abundances of elements in the periodic table that are found in biological
systems.
Success Criteria
Understand how atomic structure was discovered, differences between subatomic particles
(electron, proton and neutron), the concept of nuclear atom, atomic number, mass number, and
the importance of periodic classification elements.
Resources
Chemistry: A Molecular Approach, 2nd Edition-Nivaldo J. Tro - Pearson Prentice Hall
Prerequisites
High school chemistry: Definition of matter, Scientific method, Dalton’s Atomic theory, and atomic
symbols. Components of atoms: nucleus (proton and neutrons) and electrons. Three states of matter,
hierarchy of matter, and separation of mixtures.
New Concepts
Atomic Structure and Subatomic Particles
Radioactivity: Henri Becquerel discovered the decay of unstable elements (E.g. uranium) to stable
elements emitting , , and  radiation.
Radiation
Mass
 radiation
-particles:
particles
Electrons
Charge
High energy electro magnetic radiation (EMR)
1.674928716 x 10-24 g
4.0087 amu
Positive
(2 x 1.602176462 x 10-19 C)
0.000549 amu
Negative
(1.602176462 x 10-19 C)
9.10938188 x 10-28 g
Half-life: Radioactive decay proceeds according to a principal called the half-life. The half-life (t½) is
the amount of time necessary for ½ of the radioactive material to decay. This is useful in measuring the
age of rocks and ancient artifacts.
J.J.Thomson's cathode ray tube experiments led to the discovery of electron.
Robert Millikan's oil drop experiments measured the charge of electrons.
Earnest Rutherford’s experiment leads to the concept of a nuclear atom, atomic number, and how
subatomic particles (nucleus, electrons, protons, neutrons) are arranged in the atom.
Subatomic Particle
Proton
Neutron
Electrons
Mass
1.67262158 x 10
-24
g
1.674928716 x 10-24 g
9.10938188 x 10-28 g
Charge
1.0073 amu
Positive
(1.602176462 x 10-19 C)
1.0087 amu
Neutral
0.000549 amu
Negative
(1.602176462 x 10-19 C)
Atomic number (Z): Number of protons in a nucleus of an atom is called atomic number (Z), Z is
characteristic to an element.
Mass Numbers (A): Number of neutrons and protons together in a nucleus of an atom is called mass
number (A).
Isotopes: Atoms of the same element with different masses or different number of neutrons in the
nucleus. E.g. 1H (hydrogen with one proton and one electron)and 2H (deuterium with one proton, one
neutron and one electron).
Isotopic Symbols
A
12
X
E.g carbon-12:
C
Z
6
The periodic Table
Dmitrii Mendeleev summarized all comprehensive data of chemical elements including mass,
structure, chemical and physical properties, element names and symbols in a table named periodic table
based on increasing atomic mass. Modern periodic table is based on atomic number and consists of,
groups, families, metals, non-metals, metalloids, main group elements, transition metals, actinides, and
lanthanides.
GHW#4 Name: ___________ Date submitted:________ Group Name:______
Key Questions (relatively simple to answer using the Focus Information)
Imaging and Moving Individual Atoms
1) What are following experimental techniques that are being used to image individual atoms?
a)
STM (SPM)
b) AFM (SPM)
c)
SEM (e-beam)
d)
TEM (e-beam)
Early Ideas about the Building Blocks of Matter
Modern Atomic Theory and the Laws That Led to It
Early scientist observed changes of matter. They called these changes chemical reactions when there are
changes in substances or the chemical properties of matter. They also observed a pattern or a repeatable
observation in chemical reactions. They observed repeatedly during chemical reactions that mass was
neither destroyed nor created (E.g. Hydrogen (4g) + oxygen (32g) gives water 36g after the reaction), and
elements combine in constant proportions (36g of water contains 4g of hydrogen and 32g of oxygen) and
in compounds multiple proportion (E.g. In CO, 1g C contains 1.33 g of O and In CO2 1g C contains 2.66 g
of O).
2) What are the patterns of observations in conducting chemical reactions by early chemists?
a)
b)
c)
3) What theory John Dalton came up with to explain the body of chemical observations and laws?
4) What are the postulates of Dalton’s atomic theory?
a)
b)
c)
d)
5) How was Dalton’s atomic theory modified based on new experimental observations leading to the
discovery of the electron, nucleus, protons and neutrons? Reword Dalton’s postulates to accommodate
new observations and particles.
a)
b)
c)
d)
6) What is radioactive decay?
7) What are following radiation?
a) 

b) 
c) 
8) Which of the following radiation, and  is most harmful?
The Discovery of the Electron, Nucleus
Subatomic Particles: Protons, Neutrons, and Electrons in Atoms
9) How did Thompson know that every element has electrons?
10) How did Thompson know that an electron has a negative charge?
11) In the Millikan’s oil drop experiment, how did he remove electrons from atoms?
12) In the Millikan’s oil drop experiment, where did some of the electrons removed from atoms ended up?
13) In the Millikan’s oil drop experiment, why was some oil drops had multiples (1,2,3 of −1.60 x 10-19 ) of
charges?
14) Thomson calculated the mass/charge (m/e) ratio for an e- to be = −5.60 x 10-9 g/C. and then Millikan
found the charge on an e- to be −1.60 x 10-19 C. What is the mass on an electron?
15) In the Rutherford’s experiment, what caused a few α’s were deflected through large angles and some
came almost straight back!