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Chem. Educator 2011, 16, 190–194
Students’ Alternative Conceptions about Atomic Properties and the
Periodic Table
Issa I. Salame*,†, Samema Sarowar†, Sazea Begum† and David Krauss‡
† Chemistry Department, City College of New York, CUNY, 160 Convent Avenue, New York, NY, 10031,
salame@sci.ccny.cuny.edu; ‡ Department of Science, Borough of Manhattan Community College, CUNY, 200
Chambers Street, New York, NY, 10007
Received February 17, 2011. Accepted July 12, 2011.
Abstract: Students possess countless alternative conceptions about chemistry which are related to the fact that
students bring to chemistry views, theories and explanations that are different than those held by scientists.
Students resist changing their views and explanations in conventional teaching or lecturing classrooms because
the teacher-centered courses do not always cause conceptual change as they do not address the basic principle
that knowledge is constructed in the mind of the learner. Participants of this study are CCNY students who are
enrolled in the second-semester of general chemistry during the spring of 2009. The course contains about 240
students who have completed General Chemistry I. The methodology included a two part question on an exam
followed by interviewing students for further clarification and understanding of their reasoning. The data show
that the majority of students, 80%, do not understand atomic radius trends, they held onto their alternative
conceptions and could not answer a simple question related to those trends. Of those who answered correctly,
62% chose the answer based on rote memorization and could not provide an acceptable scientific explanation.
Introduction
Students possess countless alternative conceptions about
science in general and chemistry in particular. These
alternative conceptions are related to the fact that students
bring to science views, theories and explanations that are
different than those held by scientists. These alternative
conceptions are developed at the early stages of education and
an individual keeps building on their alternative conceptions.
Concepts that the students build about the atomic properties
could be aligned with what is scientifically agreed upon or can
differ from it. In this paper, we will refer to those that differ as
alternative conceptions [1]. In spite of those alternative
conceptions, students rely on algorithms to solve problems.
Misconception or alternative conceptions is defined as [2]
any concept that differs from the commonly accepted scientific
understanding of the term. Nakhleh also states that, “Once
these misconceptions have been integrated into a student’s
cognitive structure, these misconceptions interfere with
subsequent leaning. The student is then left to connect new
information into a cognitive structure that already holds
inappropriate knowledge.” The alternative conceptions that
students develop can hinder their conceptual understanding.
Conceptual understanding ensures that a student will not forget
the material that they have learned. Whereas memorization of a
method to solve a chemistry problem will be forgotten as soon
as the course is complete. Once students have these alternative
conceptions it is difficult to change it. Science education
research [3] has found that young children develop intuitive
ideas and beliefs about natural phenomena. As they learn more
about the natural world they develop new or revised concepts
*
Address correspondence to this author.
Chemistry Department, City College of New York.
‡
Department of Science, Borough of Manhattan Community College.
†
based on their interpretation of this new information from the
viewpoint of their existing ideas and belief. If students
encounter new information that contradicts their alternate
conceptions it may be difficult for them to accept the new
information because it seems wrong. For this reason instructors
should try to address briefly the concepts behind the
algorithmic problems which could improve students’
conceptual understanding of the topics.
Some students resist changing their views and explanations
in conventional teaching or lecturing classrooms. Researchers
[4] also found that students in science and math have been
consistently trained algorithmically, rather than conceptually.
Therefore, when exposed to a different type of instructional
and assessment method, students tend to be resistant. The
reason teacher-centered, lecture-based courses, do not cause
conceptual change is because they do not address the basic
principle that knowledge is constructed in the mind of the
learner [5]. One of the earlier papers in chemistry education
research [6] speaks about how most educators see solving
chemical problems to be the major behavioral objective of
freshmen chemistry. It also showed that textbooks were written
from this point of view, and this may be what establishes the
supreme importance of numerical problems in student minds.
Science educators [7, 8] have found that students were able
to do algorithmic problems but struggled with answering
conceptual problems. Their studies found that many students
could not use chemical concepts to solve conceptual problems.
Also the results of Nakhleh’s studies found that conceptual
problem-solving ability lagged far behind algorithmic problem
solving ability. Once again memorization is the skill that
students utilize to solve problems because that is the way they
have been instructed. Work by Nakhleh and Mitchell [8] states,
“It does not seem that presenting an algorithm and
demonstrating the myriad of problems that can be solved using
that algorithm facilitate understanding of the underlying
© 2011 The Chemical Educator, S1430-4171(11)12375-0, Published 07/19/2011, 10.1333/s00897112375a, 16110190.pdf
Students’ Alternative Conceptions about Atomic Properties and the Periodic Table
concept.” Other researchers offer an explanation for why some
students choose to memorize rather than develop a conceptual
understanding. For example, work done by Bunce illustrated
that students enter chemistry classes with many insecurities
and fears about their ability to be successful in chemistry [9].
And these fears often result in students choosing memorization
rather than understanding as a way to succeed and earn an
acceptable grade.
The lack of conceptual understanding inhibits students from
performing to the best of their abilities. In one study [10], the
results showed: “… success on algorithmic questions was
always higher than on conceptual questions, verifying the
results of previous studies. Additionally, the students with
better reasoning ability outperformed students with poorer
reasoning ability on all question types, and the scores of the
better reasoners were significantly higher than those of the
poorer reasoners on three of the four conceptual questions
administered.” If students possessed better reasoning skills,
which are based on a thorough conceptual understanding, then
students would perform better on not only algorithmic
problems but also conceptual problems.
Cognitive research shows that when students construct their
own knowledge they achieve a better conceptual understanding
of chemistry [11]. Bodner states that “Knowledge is
constructed in the mind of the learner” [5]. During the learning
process, students use their experiences and knowledge to
construct an understanding and achieve sense making. This
process is facilitated by the interactions they have with their
instructors and peers, which present conflicts of thoughts and
ideas that help students modify their thought processes [12].
Concepts that the students build about the atomic theory could
be aligned with what is scientifically agreed upon or can differ
from it.
The following research questions will be addressed as part
of this study:
1.
2.
What types of alternative conceptions do students possess
about atomic properties and periodic trends?
What is the role of mnemonic use, regurgitation, and
memorization in answering questions about periodic
trends?
A paper and pencil questionnaire, which is included in as
part of the in-class assessment, will be used to collect initial
data. These data will then be used to guide the question in a
semi-structured interview. In this interview, a student is asked
to elaborate on their answer, provide an explanation, and
discuss their thought process as they arrive at the answer. The
interviewer does not lead the student just elicits information.
This information can be used to determine the source of the
alternative conceptions, their type, how deeply embedded in
the cognition process, and how these misconceptions hinder
further learning.
Context of the Study
The research goals of this study are to identify alternative
conceptions that students hold about various topics in general
chemistry. Participants in this study were students enrolled in
second-semester general chemistry at an urban four-year
college. All students participating in the study had completed
the first semester of general chemistry. The data collected to
support our hypothesis that the majority students do not
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possess an in depth conceptual understanding of atomic
properties and periodic trends and this issue should me
addressed by chemistry educators at the high school level, as
well, as the college level. The research question is: “Which
element has the smallest atomic radius? Provide an explanation
for your answer.” We inserted the question that our research is
concentrated upon, in a routine exam taken by general
chemistry students.
Rubric Development and Results
The data were collected to examine the type of responses
that we would get and to help in the creation of a rubric. A
rubric would help us sort the data in manageable groups. We
attempted to look for patterns in the explanations that were
provided. The preliminary data that were collected, during the
month of October of 2009, helped in providing the needed
information for a rubric and to guide the design of the
interviews that were held during the month of December of
2009.
Majority of the students’ answers, 80%, provided an
unacceptable scientific explanation. Students indicated that
helium had the smallest atomic radius and then proceeded to
draw a rough periodic table which showed atomic radius
decreasing from left to right and from bottom to top. Based on
answers provided by the students, we then came up with a
rubric ranging from a score of 1 to 5. A score of 1 indicates
inadequate conceptual understating and a score of 5 indicates
complete conceptual understanding.
This rubric sorts the answers into a number scale based not
on the right or wrong answer but the understandings behind the
concepts. A complete conceptual understanding would not
only provide the correct answer but also an explanation that
shows a full understanding of effective nuclear charges. Smith
and Metz point out how students often learn how to solve
mathematical problems without understanding the chemistry
[13]. They memorize chemical definitions and use chemical
terms without true comprehension.
Researchers in Turkey argue that, “The analysis of written
responses showed that many students tend to leave the
explanation section of the questions blank or repeat some sort
of statements from the questions rather than giving any
detailed reason [14]. The written responses showed that at all
levels, many students were unable to use particular ideas.”
Even though many students knew that helium had the smallest
radius they were unable to demonstrate why. They mostly
resorted to rote memorization of periodic trends as an
explanation for their answers. We also wanted to observe the
knowledge that students possessed of effective nuclear
charges, for this is an important factor that aids in determining
which elements has the smallest radius and plays a role in
understanding atomic sizes, periodic trends, and
electronegativity.
The data that we collect helped us to create several guided
questions for the interviews. These interviews were openended and impromptu. We attempted to ask questions that
would help students elaborate on their answers. We did not
want to provide the students with the correct answer, we only
wanted to collect data on what the students’ perception and
understating is of their answers. Open-ended interviews
allowed us to follow the students’ train of thoughts giving us
insight
into
their
thought
processes.
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Table 1. Rubric Developed for the data analysis
Score
1
Inadequate Conceptual
Understanding
Response Characteristics
Example
Provides an incorrect answer. Explanation offers no
conceptual understanding of effective nuclear charge or
no explanation is provided at all.
Hydrogen. Hydrogen is a gas so it is smaller than all metals,
it only has one orbital 1s and it has the smallest molar mass.
Provides a correct answer based on memorization of
periodic trends. Or provides an incorrect answer with an
explanation that has little understanding of effective
nuclear charge.
Helium. One of the trends of the periodic table is that the
atomic radius of an element increases as you go down the
periodic table and to the left. Therefore the smallest element
would have to be the one that is the most to the right and top
of the table.
3
Approaching Conceptual
Understanding
Provides a correct answer. Explanation shows some
understanding of effective nuclear charge.
Helium. Since it has 2 protons compared to 1 proton in H it
has more + charge that pulls electrons thus has the smallest
size.
4
Acceptable Conceptual
Understanding
Provides a correct answer. Explanation shows good
understanding of effective nuclear charge.
I would say smallest element in radius is Helium. We know
that atomic radius decreases as we move along the periodic
table since the positive attraction effectuated by the nucleus
increases, pulling the electrons closer. This reduces the
radius. The smallest radius atom must have the least number
of electron shells, but the greatest protonic positive charge.
Our only two contestants are H and He. Since helium has
one more proton than hydrogen but also has its electrons in
1s it must be the smallest element.
Provides a correct answer. Explanation shows complete
understanding of effective nuclear charge. Diagrams are
provided to supplement their explanation.
There were no students who received a score of 5.
2
Minimal Conceptual
Understanding
5
Complete Conceptual
Understanding
90
Percentage of Respondents
80
70
60
50
40
30
20
10
0
1
2
3
4
5
Score
Figure 1. The percentages of responses of each answer based on the
rubric evaluation.
Results
We were able to analyze the data that were collected and
gained insight on the type of answers that students provided.
The graph shown in Figure 1 is based on the rubric.
There seems to be some confusion between the atomic mass
and atomic radius as illustrated by the following response:
“Hydrogen. Because hydrogen has the smallest atomic mass of
any other element in the periodic table.”
Some of the students related the number of electrons to the
atomic radius: “It has the smallest radius and the least amount
of electrons and therefore takes up the least amount of
volume.” It is noteworthy that hydrogen was the most common
incorrect answer with 78% of incorrect responses. Other
students who relied on regurgitation, recall, and mnemonic use
still ended up with incorrect answers, and some made them up
as they went along: “As you go from right to left the atomic
radius decreases. As you go from bottom to top the atomic
radius also decreases and H has the smallest molar mass
weight.” Francium was the second most common incorrect
choice, with 14% of incorrect responses, which we found to be
surprising. It is easy to see why students will choose hydrogen
and try to reason it, but it was peculiar that they choose
francium. Here is an example: “Francium. Metals are smaller
in size than non-metals are Fr has the most metallic
characteristics according to the periodic table of elements.
A majority of the students who picked helium as the
smallest element in the periodic table provided an explanation
that is not consistent with what is scientifically accepted or was
based on regurgitation, mnemonic use, coincidence, or
guessing. Here is an example of guess work and incorrect
explanations: “Helium. The column it is in, it is a gas.” Many
students relied on regurgitation and mnemonic use to arrive at
the correct answer and provided the mnemonic use as a
scientific explanation. For example: “Helium is the element
farthest from the bottom left (in which direction of atomic size
increases.” Figure 2 clearly shows that when students try to
answer questions about the periodic table and its properties,
they resort to regurgitation and mnemonic use such as the
diagram in Figure 2. This diagram was not uncommon and
many students drew this diagram as a scientific explanation for
the atomic size question.
The following student used regurgitation to figure out the
atomic radius question and then disregarded the answer,
helium, and went with hydrogen because it made more sense.
“It is Helium, because as you move to the right and towards
© 2011 The Chemical Educator, S1430-4171(11)12375-0, Published 07/19/2011, 10.1333/s00897112375a, 16110190.pdf
Students’ Alternative Conceptions about Atomic Properties and the Periodic Table
Figure 2. An example of a scientific reason about the atomic sizes.
the bottom of the periodic table, the number of electrons
increase which means that the radius also increases. So the
smallest element with the smallest radius would be the one to
the far right and all the way at the top of the periodic table,
which is helium, however because hydrogen has one less
electron than helium, hydrogen is the one with the smallest
radius”.
Discussion
Identifying misconceptions that students have and
addressing with in our instruction can help students to develop
a better conceptual understanding. Chemistry education
researchers bring up a possible explanation for why some
students have certain alternative conceptions [15]. Tyson’s
studies found that language emerged as a key factor in the
development of students understanding of chemical
equilibrium; we need to be alert to terms that are subject to
misinterpretation by our students.
Chemistry education research has helped identify many
alternative conceptions that students have. According to one of
the leading figures in chemistry education [16]: “Although
chemistry education researchers have identified common
misconceptions for almost every topic taught in introductory
since courses, probably nine out of ten instructors are not
aware of these misconceptions or do not utilize ways to
counteract them in instruction.” Identifying students'
alternative conceptions will provide instructors with an
opportunity to cause conceptual change and to help students
construct a clearer understanding of important concepts.
Memorization is not a growth in knowledge; it is at times just
short-term retention.
Our preliminary analysis of the data collected for the
purpose of creating the rubric suggested that students do not
posses conceptual understanding of atomic trends such as
atomic radius. One student answered the study question by
drawing the periodic table and indicating, with arrows, how
atomic radius decreases. Some students use memorization of
the periodic trend to justify their answer, but because they lack
the conceptual understanding they were unable to reason why
helium has the smallest radius instead of hydrogen. If they
were able to visualize electrons orbiting around the nucleus
and understood effective nuclear charge and electrostatic force
it may have been possible for them to reason out why helium
has the smallest atomic radius and not hydrogen. They were
only able to spit out memorized information, which shows no
conceptual understanding.
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Some of the answers that lacked any sort of understanding,
relied only on memorization, or were based on intuition or
pure guessing. Answers such as, “Hydrogen weighs the least
and it has only one valence shell”, indicate that this student
was tossing around terms. There were also many answers that
said, “Hydrogen has the smallest atomic radius because it has
the smallest atomic mass”. This was the most frequent answer
provided. Students were using intuition to answer, because
they reasoned out that something that has the smallest atomic
mass must also have the smallest atomic radius.
Another student drew out two images, one of a hydrogen
atom and another of a helium atom. They drew out the
electrons circling the nucleus, indicating that electrons were
repelling each other, while being attracted to the proton.
Some students’ responses show confusion about periodic
trends for atomic radius. Instead of thinking that atomic radius
decreases left to right and bottom to top, they thought that
atomic radius decreases right to left and top to bottom. These
students answered francium to be the element with the smallest
atomic radius. Rote memorization of periodic trends resulted in
such answers. They memorized the periodic trend but were
unable to recall it properly. One student that indicated
francium as the answer wrote, “As the amount of electrons
increase the force of attraction is greater between the proton
and electrons. So the radius gets smaller”. Answers based of
rote memorization show lack of conceptual understanding. We
should note that our interview results only confirmed our
findings.
Recent work done says that the teachers need to be trained
to diagnose students’ alternative conceptions, design
interventions using particle-level animation, access the
animation through textbook publishing companies, free digital
libraries, or commercial software suppliers, and make them
accessible to their students [17]. If teachers are not able to
catch these misconceptions then they will not be able to
address them.
Conclusion
The alternative conceptions about the atomic properties and
periodic trends were reflected in the written answers that the
students provided on the exam. Our preliminary results show
that the students who have completed “General Chemistry I”
and studied atomic properties and periodic trends show lack of
understanding of the topics. Students used memorization and
pointed arrows to answer questions about periodic trends. This
lack of understanding and reliance on memorization to learn
science could continue with them throughout their college
education. Chemistry topics especially the atomic properties
and periodic trends should be presented in a scientific context
and students should be part of the learning process. Teaching
for an in depth understanding in “General Chemistry I” classes
would provide a pipeline of future successful scientists and
researchers. It is our hope that understanding this phenomenon
will help instructors improve their teaching methods and thus
improve student understanding.
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© 2011 The Chemical Educator, S1430-4171(11)12375-0, Published 07/19/2011, 10.1333/s00897112375a, 16110190.pdf