95
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
How Do Students Draw A Lewis Structure Of Nitric Acid Molecule?
Şenol Alpat Dokuz Eylül University senol.alpat@deu.edu.tr
Sibel Kılınç Alpat Dokuz Eylül University sibel.kilinc@deu.edu.tr
Özge Ozbayrak Dokuz Eylül University ozge.ozbayrak@deu.edu.tr
Melis Arzu Uyulgan Dokuz Eylül University melis.cekci@deu.edu.tr
Abstract
In this study writing a Lewis structure of nitric acid molecule was required from the
students at mid-term examination. Many of the students had a mistake to draw Lewis
structure of the molecule in the examination. According to the examination results, a
working group comprising of twelve students was randomly selected. Sixteen major
mistaken structures were chosen, and discussion was requested from the students on
these molecules. Some questions related to whether there were mistakes or not in
these molecules were asked to the students. Choosing a central atom, total valance
electrons, the octet rule, placing electrons, formal charge and drawing a molecule
were discussed and their opinions were evaluated in video records. Obtained results
were evaluated.
Keywords: Lewis structure, nitric acid, octet rule, mistake.
INTRODUCTION
Students use their own understanding styles while they are giving meaning to new concepts in
their minds. In literature, students’ giving meaning to concepts is often touched on with the terms like
advance information, availability, advance acquisition and intuitive concepts. The concepts envisaged
and grasped in students’ minds mostly include some scientific mistakes (Furio and Calatayud, 1996).
Many concepts in theory of chemistry have an abstract structure. The most basic concepts of
these are the concepts of atom and molecule. The concept of atom, as is known, is the smallest
building structure of a substance which is too small to see, fixed and have obtained variety in term of
mass, magnitude and shape. And the concept of molecule is stated as a structure which gets different
shapes as a result of combination of atoms. The chemistry science based on these concepts is
classified in different forms by many researchers. Tsarpalis (2001) classified chemistry as molecular,
atomic and electronic, and in his study he stated that Johnstone (1982; 1991; 2000) made this
classification as macro (experimental and observational concrete chemistry), symbolic (chemistry
related with symbol, calculation and equalities) and micro (chemistry related with atom, molecule,
bounding the shapes of molecule).
Lewis structure of molecule is a sub-topic of the chemical bounding in General Chemistry, and
it has importance for chemistry students in the view of understanding of organic and inorganic
molecules. Because the general chemistry lesson is basis of other chemistry lessons such as organic,
inorganic and physical chemistry, understanding of general chemistry subjects have major significance
for chemistry students.
Lewis structures, also named electron-dot structures or electron-dot diagrams, are diagrams
showing the bonding between atoms of a molecule, and the ion pairs of electrons that may exist in
the molecule. As well as covalently-bonded molecule, Lewis structure can be drawn for the
coordination compounds. The Lewis structure is explained with choosing a central atom, total valence
electrons, the octet rule, placing electrons, formal charge and drawing a molecule.
In recent years, great efforts have been made for solution of students’ difficulties on
understanding logical problems by using various teaching methods. There are some researches based
on founding an easy method for writing of Lewis structure and consistent understanding of the Lewis
structure (Clark, 1984; Gallup, 1988; Reed, 1994). Furthermore it is found the studies based on
deficiencies and mistakes of students in the subject.
96
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
Furio and Calatayud (1996) firstly researched what students in high school twelfth grade and
in university know and what they need to know in the subjects of molecule geometry and polarity. At
the same time, they revealed some misconceptions related to the subject. In their studies they used a
questionnaire including 16 questions. This questionnaire involves questions about Lewis structures,
molecule geometries and polarity of molecules. According to results of the research it is stated that
students have difficulty in both drawing and showing Lewis structure. These difficulties are particularly
related to determining the central atom in the molecule, valence electrons and drawing Lewis
structure.
Yılmaz and Morgil (2001) used a two-tier diagnostic test including 25 questions with the aim
of assessing students’ standards of knowledge. Under the subjects of bond polarity, molecule polarity,
VSEPR theory, Lewis structure, molecule shape on the subject of chemical bonds. They aimed to state
misconceptions of students related to the subject they learned by using the misconception in relation
with the subject in literature. This study has been applied on second and fourth year students from
the department of chemistry education. Furthermore, they have stated some misconceptions related
to Lewis structure, such as “Lewis structures can be written into all molecules and polyatomic ions
with covalent bond” and “Lewis structure is completely enough for explaining ionic and covalent
bounding molecules and geometric structures and shapes of polyatomic ions”.
When we look into applied researches, we understand that the subject is rather complicated
and students have a lot of mistakes on this subject. Especially, determination of misconceptions which
constitutes a great obstacle in the understanding of this subject is significant. Because of this, in this
research Lewis structure of HNO3 molecule was used as a sample in order to signify the mistakes
students make.
METHOD
In this study; of the qualitative research methods the interviews and document analysis
methods were used. Qualitative document analysis is a technique used in historical and qualitative
researches. As can be seen in written documents, the documents in this technique can also be such
visual documents as video, film, etc. (Altheide, 2000). In document analysis, it can be taken into
consideration the person’s behaviors such as actions like mime, body actions and the ones which are
not be expressed orally by utilizing film, video or such documents. At the same time, these records
can be watched by other researchers and in this way the validity of results can be tested. In this study
possibility of observation is also provided with utilizing video records to obtain qualitative data. Like
this validity of research has been increased (Karasar, 2006).
This research is carried out with first year students in Dokuz Eylul University, Buca Education
Faculty, Chemistry Teaching Department. Lewis structure on chemical bonds was taught to students
in general chemistry class. Afterwards, midterm exams were done to determine their success on this
subject. Depending on the results of mid-term exams, students were separated in achievement
groups as high, mid and low and from these students, 3 groups consisting of 4 people were created
by randomization. These groups later gathered in the assistance of a lecturer and they discussed for
the purpose of determining potential mistakes on this subject and the reasons behind them.
In the study, the students’ views on the mistaken Lewis structures were recorded. These
records were watched, and the views of students were deciphered into a written form and examined
by the researchers.
Students’ statements which are used during their defining defects of erroneous structures and
basic theme including these statements can be seen in Table 2. These themes about the subject are
determined by being referred to the literature with the expert views. As seen in Table 2, seven
categories were determined.
Four stages were used in the investigation of the documents (Forster, 1995). In the first
stage, working group was determined. This was done by randomization. In the second stage,
categories were determined with the investigation of data. In the third stage; content analysis was
97
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
made. The basic topic was obtained depending on the number of repetition of qualitative data in the
content analysis and the students’ statements related to these topics were determined. Finally, the
educators who are experts in their own fields are consulted and their views are taken into
consideration about how much the interpretation of data obtained in investigation is correct. This way,
validity and reliability of the research was increased.
RESULTS AND DISCUSSION
Students gave 42 different answers for the question “Draw the Lewis structure of HNO3” midterm exam. In Table 1, 16 answers of which errors are rather distinctive has been selected and
showed.
Table 1: HNO3 mistaken molecules made by students.
1.Molecule
2.Molecule
3.Molecule
4.Molecule
5.Molecule
6.Molecule
7.Molecule
8.Molecule
9.Molecule
10.Molecule
11.Molecule
12.Molecule
13.Molecule
14.Molecule
15.Molecule
16.Molecule
In Table 2, some statements of students about the mistakes on molecules are stated. Also
these statements in the Table 2 are showed in their categories. Frequency (f) and percentage (%) are
determined depending on the total expression number related to each category and can be seen in
the Table 2.
98
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
MN
*
1
Table 2: Statements of the students about mistakes on molecules
f
%
f %
Formal charge 33
32
“Formal charges were not
written” “Oxygen was written
+(plus) while it should have
been -(minus)”
2
3
4
5
Bond number
42 40
“Oxygen in the below should
have been bound to
nitrogen”
“Oxygen is charged +”
“There are 6 bonds.”
“Normally molecule must be
neutral’.
6
7
“If he/she wrote formal charges
it would be better”
10 “Formal charges can not be -2”
12
“The person who makes this
molecule does not need to
read. It is wrong in every
respect”
13
“Negative charges cannot be
side by side.”
15
“Nitrogen cannot make 5
bonds when the number of
bond is wrong, Formal charge
is also wrong”
“Oxygen made 3 bonds in
there”
8
16
* MN: Molecule Number
“Nitrogen made 4 bonds it
makes 4 bonds but 5 bonds
are needed for molecule”
“There are 6 bonds”
f
%
Bonding
7 6.7
“Central atom will be nitrogen,
all oxygen will be bonded to
nitrogen in this way hydrogen
will have been bound to
oxygen”
99
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
Continuing Table 2.
f %
F %
f
%
MN
12 11.5 Central
2 2 Hybridi 2
2
* Non-bonding
electrons
atom
zation
1 “There is something wrong in
there because there should
have been 14 pairs of
electrons”
2
“Isn't nitrogen
required to make a
bond with both
hydrogen and
oxygen? Because
atom is the
center.”
3
“Normally nitrogen
makes 3 bonds, at
most 4 bonds. Due
to the fact that it is
the group of 5A , it
makes 3 bonds. In
order to make 4
bonds it needs to
be changed into
hybrid”
14
f
%
Octet and
6 5.8
Dublet rules
“The fact that nitrogen
made 4 bonds is
resulted from not
suiting the Octet rule”
“There are 12 pairs of
electrons but two
electrons are missing.
Octets don’t suit”
* MN: Molecule Number
In the tables above, the answers of students are in reference to most important feature that
they paid attention. Generally the questions of students have intensified on formal charges of
molecule and atoms in molecule, bond number made by atom and also total electron number in
molecule which is not being common. Students could be able to determine the mistakes in molecule,
however owing to the fact that some concepts they had while determining mistakes are defective,
they went wrong. Some of them are showed in below;
Lecturer: Is nitric acid neutral, charged, or not charged?
Student: It has got 14 electrons which are not being shared, so it must be charged .We are
placing 14 pairs of electrons, there is a mistake.
This statement belongs to a student from low group. According to the students’ statements,
nitric acid should be charged whereas collection of formal charges is equal to zero and so, molecule is
not charged. Student could not pay attention to collection of formal charges and made a mistake.
Moreover, when analysis results are taken into consideration, it is resulted that students in
low group didn’t consider octet and dublet rules. They grasped well that nitrogen is the central atom;
but they could not reach the result that if nitrogen makes 5 bonds there will be a mistake.
The fact that student from mid-group doesn’t know the answer for the question “Which
elements do covalent bond compounds occur between?” can be seen below;
Lecturer: In what kind of compound do we see Lewis structures?
Student: In covalent compounds. They occur between two non-metals.
Lecturer: Is there a covalent bond between metal and metal?
Student: It can be. It can be but we say ionic because there are more ionic bonds.
100
International Conference on New Trends in Education and Their Implications
11-13 November, 2010 Antalya-Turkey
ISBN: 978 605 364 104 9
Student: No. They are covalent because difference of electronegativity among them is too
little. In ionic bond, there is covalent character. It is like that being ionic is repressing being covalent
because of its quantitative.
Consequently, obtained results were evaluated. Following the study of document analysis, it
was concluded that the students knew non-paired electron pairs, central atom and formal charge. The
reason why students make mistakes is not to know how they can decide to the molecule shape. It
was observed that the all working group students wrote a correct Lewis structure of sulphuric acid
after the discussions. So we can say that using answer/question and discussion technique affect the
students’ interviews on drawing Lewis structure of molecules towards positively.
REFERENCES
Altheide, D.L. (2000). “Tracking discourse and qualitative document analysis”, Poetics, 27, 287-299.
Clark, T.J.(1984). “Another Procedure for Writing Lewis Structure”, Journal of Chemical Education, 61,
(2), 100-104.
Forster, N. (1995). “The analysis of company documentation”. C. Cassell and G. Symon (Eds.),
Qualitative Methods in Organizational Research: A practical guide. London: Sage.
Furio, C. and Calatayud L. (1996). “Difficulties with The Geometry and Polarity of Molecules: Beyond
Misconceptions”. Journal of Chemical Education. 73, (1), 36-41.
Gallup, A. G. (1988). “The Lewis Electron- Pair Model, Spectroscopy, and the Role of Orbital Picture in
Describing the Electronic Structure of Molecules”, Journal of Chemical Education, 65 (8), 671-674.
Johnstone, A.H. (1982). “Macro and microchemistry”. School Science Review, 64, 377-379.
Johnstone, A.H. (1991). “Thinking about thinking”. International Newsletter on Chemical Education, 6,
7-11.
Johnstone, A.H. (2000). “The presentation of chemistry - logical or psychological?” Chemistry
1,
9-15.
Education:
Research
and
Practice
in
Europe
(CERAPIE),
[http://www.uoi.gr/conf_sem/cerapie].
Karasar, N. (2006). “Sosyal Bilimlerde Nitel Araştırma Yöntemleri“. Seçkin Yayıncılık, Ankara.
Reed, J.L. (1994). “The Lewis Structure: An Expanded Perspective”, Journal of Chemical Education, 71
(2), 98-100.
Tsaparlis, G. (2001). “Preface, Molecules and Atoms at the Centre Stage”. Chemistry Education:
Research and Practice in Europe. 2(2), 57-65.
Yılmaz, A. and Morgil, İ. (2001). “Üniversite Öğrencilerinin Kimyasal Bağlar Konusundaki Kavram
Yanılgılarının Belirlenmesi”. Hacettepe Üniversitesi Eğitim Fakültesi Dergisi, 20, 172 - 178.