GA 3. Louisiana Tech University, Chemistry 100. POGIL(Process
Oriented Guided Inquiry Learning) exercise on Chapter 2. Atoms and
Elements
Why?
Why our planet is made up of some 92 stable elements? Why only 25 or so out of
those 92 are found in living things? How the structure of atoms making up these elements
does plays 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. How does the
atomic structure explain the concepts relating to nuclear atom, atomic number which
defines each element, isotopes 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 (Sections 2.1 - 2.2).
1. 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 (Section 2.1, pages 43-44).
The Nuclear Atom
1. Describe how Rutherford’s experiment leads to the concept of a nuclear atom and
atomic number. (Section 2.2, pages 45-46).
Atomic Numbers and Mass Numbers
1. Explain isotopes and isotopic symbols with atomic number and mass number for an
element. (Section 2.5, page 54)
2. Define isotope and given the atomic number and number of neutrons for a specific
isotope (Section 2.5, page 55).
3. Compare mass and charges of electron, proton and neutron (Section 2.5, page 57)
4. Count number of neutrons, protons given an isotopic name or symbol (Section 2.5,
page 57).
The periodic Table
1. Describe the use of periodic table: periods, groups, families, metals, non-metals,
metalloids, main group elements, transition metals, actinides, lanthanides (section 2.9,
pages 64-69)
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), concept of nuclear atom, atomic number,
mass number, and the importance of periodic classification elements.
Resources
Chemistry: The Molecular Science 3rd Edition, John W. Moore, Conrad L. Stanitski and
Peter C. Jurs.
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
9.10938188 x 10-28 g
4.0087 amu
Positive
(2 x 1.602176462 x 10-19 C)
0.000549 amu
Negative
(1.602176462 x 10-19 C)
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
Charge
Positive
(1.602176462 x 10-19 C)
1.0073 amu
1.674928716 x 10-24 g 1.0087 amu
Neutral
9.10938188 x 10-28 g
Negative
(1.602176462 x 10-19 C)
0.000549 amu
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
Z
E.g carbon-12:
C
6
The periodic Table
Dmitrii Mendeleev summarized all comprehensive data on chemical elements
including mass, structure, chemical and physical properties, element names and symbols
in a table named periodic table baseh 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.
Key Questions (relatively simple to answer using the Focus Information)
1) What is radioactive decay?
2) What are following radiation?
a) 
b) 
c) 
3) Which of the following radiation, and  is most harmful?
4) How did Thompson know that every element has electrons?
5) How did Thompson know that an electron has a negative charge?
6) In the Millikan’s oil drop experiment, how did he remove electrons from atoms?
7) In the Millikan’s oil drop experiment, where did some of the electrons removed
from atoms ended up?
8) 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?
9) In the Rutherford’s experiment, what caused a few α’s were deflected through large
angles and some came almost straight back!
10) What subatomic particles take up the most space in the atom?
11) Which particle has lager mass? Proton or neutron. What maybe the reason?
12) How many times a proton weighs compared to an electron?
13) What are isotopes?
14) How many isotopes the elemental hydrogen, has? Give their symbols. Are they all
these isotopes stable?
15) Naturally occurring carbon had two stable isotopes (carbon-12 and carbon 13) and an
unstable isotope, carbon -14. Write isotopic symbols for
a) carbon-12
b) carbon-13
c) carbon-14:
b) How many protons, neutrons and electrons are in the carbon-12 isotope?
16) What group or family following elements belong to:
a) Na
b) Ca
c) Cl
d) He
17) List two elements in each of the following:
a) Main group elements b) Transition elements c) Lanthanides
d) Actinides
18) Identify following elements as either metals, non-metals, metalloids, noble gases,
transition metals, actinides or, and lanthanides.
a) Si
b) Ca c) Cl
d) Eu
e) Pu
f) Ni
g) Ar
19) Which of the following are main group elements?
a) Si
b) Ca
c) Cl
d) Eu
e) Pu
f) Ni
Exercises (Applying concepts)
g) Ar
20) How long will take for carbon -14 to decay from 16 g to 2 g if the half life of carbon 14 is 5730 years.
21) 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?
22) How many electrons, protons and neutrons a
24
Mg2+ isotope have?
23) Order of elements in the modern periodic table is arranged according to atomic
number. In his periodic table, Mendeleev used atomic weights not atomic number.
a) In the periodic table what elements should have been swapped if Mendeleev was
to following order of increasing atomic masses strictly?
b) In the periodic table, Why is atomic masses approximately correlated with atomic
number?
c) What is most directly involved in chemical reactivity: nucleus or the outermost
electrons?
d) Why do the elements in a group of the periodic table have similar chemical
properties