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ONLINE ISSN 1821-7249
2012: Volume 3, Issue 2, 544-551
Research Article
Evaluation of Atomic Structure in Chemistry Textbooks Used in Secondary
Schools in Tanzania
Tumikia R. Sanga and Stelyus L. Mkoma*
Department of Physical Sciences, Faculty of Science, Sokoine University of Agriculture,
P.O. Box 3038, Chuo Kikuu, Morogoro, Tanzania
Received: 17 March 2012,
Accepted: 04 December 2012
Published: 21 December 2012
ABSTRACT
Teaching atomic structure within a history and philosophy of chemistry perspective has
been recognized by researchers in science education. The present study aimed at evaluation
of the presentation of chemistry textbooks used in secondary schools in Tanzania. The
criteria used for evaluation were the atomic models of Thomson, Rutherford and Bohr and
twenty seven chemistry textbooks were analyzed. Results obtained showed that none of the
studied textbooks explained satisfactorily that Bohr’s model was based on an inconsistent
foundation in which he ‘grafted’ Planck’s ‘quantum of action’ on to Maxwell’s
electrodynamics. On the other hand few textbooks described satisfactory that Bohr had not
even heard of the Balmer and Paschen formulae for hydrogen line spectrum, when he wrote
the first version of his article; Similarly, The rivalry between Rutherford’s hypothesis of
single scattering based on a single encounter and Thomson’s hypothesis of compound
scattering led to a bitter dispute and the Thomson’s experiments on cathode rays were
conducted to clarify the controversy with respect to the nature of cathode rays, that is
charged particles or waves in the ether. Some textbooks explained satisfactorily that
Rutherford’s model of the atom had to compete with that of Thomson; and that Bohr’s
main objective was to explain the paradoxical stability of the Rutherford model. It is
concluded that the inclusion of historical reconstructions of atomic structure in chemistry
textbooks used in Tanzania can provide students with a better appreciation of the dynamics
of scientific progress.
KEYWORDS:
Secondary schools, Chemistry textbooks, Atomic structure, Tanzania.
INTRODUCTION
Science education persists with presenting an
idealized view of science as objective, detached and
value free. Science curriculum must emphasize the
study of the history of ideas and the evidence on
which they are founded must lie at the core, which
would provide students an opportunity to consider
data which has no clear interpretation and to consider
plural alternatives (Osborne, 2007). Also, science
(e.g. atomic structure) cannot be taught as an
unmitigated rhetoric of conclusions in which the
current and temporary constructions of scientific
knowledge are conveyed as empirical, literal, and
irrevocable truths (Schwab, 1962).
Atomic structure is a content of most chemistry
courses in the world. Research in science education
* Corresponding author
Email: [email protected]
has recognized the importance of teaching atomic
structure within a history and philosophy of
chemistry perspective (Atkins and Jones, 1997; Niaz,
1998; Justi and Gilbert, 2000; Taber, 2003; Rodríguez
and Niaz, 2002). The inclusion of history and
philosophy of science in the chemistry course
contents facilitates both conceptual understanding
and the various aspects of the nature of science
(Taber, 2008). Historical reconstruction of atomic
models can provide secondary students an
opportunity to appreciate how scientists work and
science progress. The history of atomic structure can
provide a deeper level of understanding chemistry;
also chemistry can be enhanced when shared in
informative and interesting way. The history and
philosophy of the structure of the atom shows that
© 2012, St. John’s University of Tanzania
http://www.sjut.org/journals/ojs/index.php/tajonas
SANGA et al.
data from Thomson’s cathode ray experiments,
Rutherford’s alpha particle experiments and Bohr’s
‘quantum of action’ were difficult to understand and
scientists presented alternative interpretations, which
led to conflicts and controversies. These aspects have
been analysed in chemistry textbooks by various
studies around the word, however, no such similar
study have been done in Tanzania. This paper
therefore aimed for the first time to evaluate the
presentation of atomic structure in chemistry
textbooks used in Tanzania secondary schools based
on the criteria developed by Niaz (1998).
MATERIALS AND METHODS
Criteria for textbooks evaluation
The criteria used by Niaz (1998) were adopted in this
study for the evaluation of atomic structure in
chemistry textbooks used in Tanzania secondary
schools. The symbols TS = Thomson; RF =
Rutherford; and BH = Bohr were used to refer the
criteria based on Thomson, Rutherford and Bohr
principles, respectively.
TS1- Cathode rays as charged particles or waves in
the ether (Thomson, 1897; Achinstein, 1991).
TS2- Determination of mass-to-charge ratio to decide
whether cathode rays were ions or a universal
charged particle (Thomson, 1897; Achinstein,
1991).
RF1-Rutherford’s nuclear atom verses Thomson’s
model of the atom (Rutherford, 1911; Niaz,
1994).
RF2- Probability of large angle deflection verses
deflection of 1 in 20,000 particles, as the
atom is the seat of an intense electric field
(Rutherford, 1911; Herron, 1977).
RF3- Single/compound scattering of alpha particles
(Rutherford, 1911; Wilson, 1983).
BH1- Paradoxical stability of the Rutherford model
of the atom (Bohr, 1913; Niaz, 1994).
BH2- Bohr’s explanation of the hydrogen line
spectrum (Bohr, 1913; Petrucci et al., 2002).
BH3– Incorporation of Planck’s ideas – a deep
philosophical chasm (Bohr, 1913; Holton,
1986).
Besides these criteria, textbooks were also evaluated
on the space utilized, mathematical details,
illustrations of experimental apparatus and models.
These criteria are considered to be related to the
history and philosophy of science framework.
545
a) Space utilized (SU) by the textbooks; that is,
number of pages used for presenting the
work of Thomson, Rutherford, and Bohr.
b) Mathematical
(MAT)
details
that
complement to understand the atomic model.
c) Illustrations of experimental apparatus (EXP)
used by Thomson and Rutherford.
d) Illustrations of the atomic models (MOD) of
Thomson, Rutherford, and Bohr.
Classification and selection criteria for textbooks
The following classifications were used as procedure
for implementing the criteria to evaluate the
chemistry textbooks. Based on the selected
classification each textbook was awarded points.
a) Satisfactory (SA = 2 points)– Treatment of
the subject in the textbook is considered to
be reasonable if the role of conflicting
frameworks based on competing models of
the atom is briefly described.
b) Mention (ME = 1 point) – A simple statement
of the conflicting frameworks or controversy
without details.
c) No mention (NO = 0 point) – No discussion
about the conflicting frameworks.
The following criteria were used to select the
chemistry textbooks.
a) Availability of chemistry textbooks in
schools, public and private libraries.
b) Inclusion of older and recent textbooks
published below and above 2000 respectively
c) Textbooks widely used by chemistry
teachers and students in secondary schools in
Tanzania.
RESULTS AND DISCUSSION
Thomson criteria (TS1 and TS2)
The results for the evaluation of chemistry textbooks
based on the history and philosophy of science
framework are shown in Table 1. It can be observed
that only four of the textbooks described
satisfactorily (SA) and one mentioned (ME) the
conflicting framework; namely cathode rays could
have been charged particles or waves in the ether
(criterion TS1). As for TS2, only one textbook
described satisfactorily (SA) that Thomson
determined mass-to-charge ratio to decide if cathode
rays were ions or a universal charge particle, whereas
five textbooks mentioned (ME) it. An example that
© 2012, St. John’s University of Tanzania
SANGA et al.
was considered as a satisfactory (SA) description of
criterion TS2 was:
Thomson proposed that cathode rays were universal
charged particles and not ions (Raffan et al., 1975).
In this case; First, Thomson computed cathode rays’
(electrons) charge-to-mass (e/m) ratio by measuring
deflections in both electrical and magnetic field.
Second, it was also known earlier that charge-tomass ratio for electrolysis is less than the carriers of
the electricity in the cathode rays and takes different
values for different gaseous ions.
Rutherford (Criteria RF1, RF2, and RF3)
Thirteen textbooks described satisfactorily (SA) that
Rutherford’s model of the nuclear atom had to
compete with the framework of Thomson’s model of
the atom (criterion RF1), whereas fourteen textbooks
only mentioned (ME) the conflict. An example that
was considered as a satisfactory (SA) description of
criterion RF1 was:
In an alpha particle experiment of the Thomson
model of atom also known as ‘plum-pudding’, it was
546
observed that most of the particles pass through with
no deflection and a few particles pass through with
little deflection or reflected backwards. Ernest
Rutherford (1871-1937) performed an alpha particle
scattering experiment to verify the Thomson model.
Rutherford concluded that rare scattering of
particles at big angles may be explained by the
presence in matter of a massive nucleus, the size of
which is much smaller when compared to the atom
(Raffan et al., 1975; Hunt, 1979; Sinclair and
Afolayan, 1985). Rutherford proposed that the
positive electricity and mass in an atom are
concentrated in very small regions (Holderness and
Lambert, 1987; Ryan, 2000; Mjema et al., 1990).
Ten of the textbooks described satisfactorily (SA)
and none mentioned it (ME) the rivalry that
Rutherford’s model was not the large angle
deflections of alpha particles but rather the
knowledge that 1 in 20,000 particles deflected
through large angles (criterion RF2). An example that
TABLE 1: Evaluation of chemistry textbooks based on history and philosophy of science framework
S/N
Textbook
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Ann and Fullick, 2001
Atkinson and Hibbert, 2000
Cane and Sellwood, 1971
Cane and Sellwood, 1973
Chadwick, 1972
Clynes et al., 1981
Holderness and Lambert, 1987
Hunt, 1979
Hunt, 2000
King, 2005
Lambert and Mohamed, 1993
Lees and Payne, 2001
Lewis and Waller, 1980
Long and White, 1977
Mahumbwe et al., 2007
Maro-Gu´termann et al., 1989
Mason, 2008
McDuel, 1976
Mjema et al., 1990
Ndar’lu et al., 1993
Stephenson and Otter, 2008
Palmer and Shaw, 1980
Raffan et al., 1975
Ryan, 2000
Sinclair and Afolayan, 1985
Tanzania Institute of Education, 1995
Wilson and Newall, 1966
Criteria
TS1
NO
NO
NO
NO
NO
NO
ME
SA
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
SA
NO
SA
NO
NO
SA
TS2
NO
NO
NO
NO
NO
ME
ME
ME
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
SA
NO
ME
NO
NO
ME
RFI
ME
ME
SA
SA
ME
SA
SA
ME
ME
ME
SA
ME
SA
ME
ME
ME
ME
ME
SA
ME
SA
SA
SA
SA
SA
ME
SA
RF2
NO
NO
NO
SA
NO
NO
SA
SA
NO
NO
NO
NO
SA
NO
NO
NO
NO
NO
NO
SA
SA
SA
SA
SA
NO
NO
SA
RF3
NO
NO
NO
ME
NO
ME
SA
SA
NO
NO
ME
NO
SA
NO
NO
NO
NO
NO
NO
NO
NO
SA
ME
NO
NO
NO
SA
BHI
NO
NO
ME
ME
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
ME
NO
NO
SA
SA
NO
NO
NO
SA
BH2
NO
NO
SA
ME
NO
NO
ME
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
SA
NO
SA
BH3
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
POINTS
1
1
5
7
1
4
9
8
1
1
3
1
4
1
1
1
1
1
3
1
4
12
7
7
4
1
13
Criteria: refer to materials and methods section
© 2012, St. John’s University of Tanzania
SANGA et al.
was considered as a satisfactory (SA) description of
criterion RF2 was:
From the alpha particle experiments, it was observed
that most of the particles pass through with no
deflection; however, one alpha particle in 20,000 was
deflected through an angle greater than 90°. If
Thomson’s model in which the positive charge and
the mass are distributed evenly throughout the atom
was valid, alpha particles must pass through with
little deflection and not scattered backwards.
Rutherford therefore concluded the following from
this observation: (a) Since most of the alpha
particles pass through with no deflection, an atom
must consist largely of empty space. (b) Since few
alpha particles, atoms of helium with charge +2,
were deflected through an angle greater than 90°, an
atom must consist of a positively charged nucleus the
size of which is much smaller when compared to the
atom (Wilson and Newall, 1966; Sinclair and
Afolayan, 1985; Holderness and Lambert, 1987;
Ndar’lu et al., 1993).
Five textbooks described satisfactorily (SA) that the
crucial argument in favour of the rivalry between two
conflicting frameworks, namely Rutherford’s
hypothesis of single scattering and Thomson’s
hypothesis of compound scattering (criterion RF3),
put forward to explain Rutherford’s alpha particle
experiments. None of the textbooks mentioned (ME)
it, however, most of the textbooks presented
Rutherford’s experiments as a ‘rhetoric of
conclusions’ (Schwab, 1962) and the following is an
example.
Rutherford performed an experiment known as alpha
particles scattering by sending alpha particles
radiated from a radioactive source to a layer of goldfoil about 0.5 micron thick. Most of the alpha
particles (99%) pass through with no deflection,
whereas a very few alpha particles (1%) passed
through with large deflection or scatter backwards.
Rutherford concluded that the deflection of the very
few alpha particles (1%) through an angle greater
than 90° proved the presence of a massive nucleus
while most of the particles (99%) passing through
with no deflection proved the presence of a largely
empty space in an atom (Wilson and Newall, 1966;
Raffan et al., 1975; Holderness and Lambert, 1987).
It is surprising to note that this presentation contrasts
with the actual statement written by Rutherford
(1911).
547
“The observations, however, of Geiger and Marsden
on the scattering of alpha particles indicate that
some of the alpha particles must suffer a deflexion of
more than a right angle at a single encounter. They
found, for example, that a small fraction of the
incident alpha particles, about 1 in 20,000 were
turned through an average angle of 90o in passing
through a layer of gold-foil about .00004 cm. thick”.
Bohr (Criteria BH1, BH2, and BH3)
Three textbooks described satisfactorily (SA) or
mentioned (ME) that Bohr’s main objective was to
explain the paradoxical stability of the Rutherford
model of the atom, which constituted a rival
framework (criterion BH1). An example that was
considered as a satisfactory (SA) description of
criterion BH1 was:
Describing atomic spectra based on Rutherford’s
atom model is entirely invalid, since, in that model,
the negatively charged electrons revolve around the
positively charged atomic nucleus. However, Bohr’s
model of spectral emission or absorption lines
showed that atoms will only absorb or emit
electromagnetic radiation at discrete frequencies
(Wilson and Newall, 1966; Raffan et al., 1975).
Three of the textbooks described satisfactorily (SA)
and two mentioned (ME) the quantization of the
Rutherford model of the atom within a historical
perspective (criterion BH2). However, none of the
textbooks described satisfactorily (SA) or mentioned
(ME) how Bohr when faced with difficulties, often
resort to contradictory ‘grafts’ that represent a deep
philosophical chasm (criterion BH3). In contrast to
both Thomson’s and Rutherford’s experiments, few
textbooks (Wilson and Newall, 1966; Cane and
Sellwood, 1971; Raffan et al., 1975; Stephenson and
Otter, 2008) presented Bohr’s work as a ‘rhetoric of
conclusions’ (Schwab, 1962). The following is an
example of a textbook that was classified as no
mention (NO) on criterion BH1.
Because atoms consisted of a small dense positively
charged nucleus surrounded by orbiting negatively
charged electrons, there must be an attractive
electrostatic force between two opposite charged
particles, according to Coulomb's law. If there was
no different force to compensate for the attractive
electrostatic force, the electron would spiral into the
nucleus. However, this does not occur. Thus, Niels
Bohr proposed that there should be a centrifugal
© 2012, St. John’s University of Tanzania
SANGA et al.
force originating from orbiting electrons (Atkison
and Hibbert, 2000).
It is interesting to compare the presentation of this
textbook (Atkison and Hibbert, 2000) which was
classified as no mention (NO) on Criterion BH1,
with that of Wilson and Newall (1966) presented
above, that was classified as Satisfactory (SA). The
presentation by Atkison and Hibbert, (2000) has the
following major problems: 1) It does not refer to the
problematic nature (paradoxical stability) of
Rutherford’s model of the atom; 2) It refers to Bohr
having suggested, ‘a centrifugal force originating
from orbiting electrons’. There is no evidence that
Bohr may have suggested this. On the contrary, Bohr
hypothesized that atoms will only absorb or emit
electromagnetic radiation at discrete frequencies.
This shows that this textbook makes a factual error
and thus departs from the historical record.
548
Evaluation based on additional criteria
Table 2 presents the results of evaluation of the
chemistry textbooks used in secondary schools in
Tanzania based on additional criteria, such as space
utilized (SU) by the textbook, mathematical details
(MAT), illustrations of experimental apparatus (EXP),
and illustrations of the atomic models (MOD).
It can be observed that, on average, textbooks that
covered the subject devoted about 1 page to the work
of Thomson, 2 pages to the work of Rutherford, and
3 pages to the work of Bohr. In the case of Thomson,
six textbooks presented experimental details
accompanied by illustrations, whereas six textbooks
presented mathematical details of the determination
of the mass-to-charge ratio by Thomson, and four
textbooks presented illustrations of Thomson’s
model of the atom. It is important to note that the
rationale behind the determination of the mass-tocharge ratio by Thomson (criterion TS2) constitutes
precisely the ‘heuristic principle’ (Schwab, 1974) of
Thomson’s experimental work.
TABLE 2: Evaluation of chemistry textbooks based on space utilized, mathematical details, illustration of
experimental apparatus, and atomic models
S/N
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
SU
0.25
0.25
0.25
0.25
0.5
0.25
0.25
0.25
0.5
0.75
1.25
0.75
Thomson
MAT
EXP
N
N
N
N
Y
N
Y
N
Y
Y
N
N
Y
Y
Y
Y
N
Y
Y
Y
N
Y
MOD
Y
N
N
N
N
Y
N
Y
Y
N
N
SU
0.25
0.25
1
0.5
1
2
1.25
2.5
0.5
1.5
1
1
1
0.5
0.25
1.25
Rutherford
MAT
EXP
N
N
Y
N
Y
Y
Y
N
Y
Y
Y
Y
Y
Y
Y
Y
N
N
Y
Y
Y
Y
Y
Y
Y
Y
N
Y
Y
N
Y
Y
Bohr
MOD
Y
N
N
N
N
Y
Y
Y
Y
N
N
Y
Y
N
N
N
SU
3
0.5
1
1
0.25
0.5
O.75
0.5
1.5
1.25
MAT
Y
N
N
Y
N
N
N
N
Y
Y
EXP
N
N
N
N
N
N
N
N
N
N
MOD
N
Y
Y
Y
Y
Y
Y
Y
Y
N
The criteria are identified by Y = YES; N = NO; hyphen (–) = the text does not deal with the subject.
© 2012, St. John’s University of Tanzania
SANGA et al.
In the case of Rutherford, ten textbooks presented
experimental details accompanied by illustrations,
whereas thirteen textbooks presented mathematical
details and seven textbooks presented illustrations of
Rutherford’s model of the atom. And, in the case of
Bohr, four textbooks presented mathematical details
to derive Bohr’s equation for calculating the allowed
energies in a hydrogen atom, and eight textbooks
presented illustrations of Bohr’s model of the atom.
These results show that textbooks tend to emphasize
experimental details, perhaps at the expense of
mathematical and theoretical interpretations and
illustrations of the atomic models. In the case of
Bohr, textbooks emphasize the experimental details
of the hydrogen line spectrum and ignore Bohr’s
major contribution, that is, quantization of the
Rutherford model of the atom (criterion BF2). Such
graphic descriptions by textbooks demonstrate how
experimental findings are important, whereas the
theoretical details (heuristic principles) are important
only if they can furnish observable (tangible)
evidence. This illustrates the distinction between the
methodological (experimental, emphasized by
textbooks) and interpretative (heuristic principles)
components, as conceptualized by Schwab (1974).
Presentations of textbooks that emphasize only the
empirical findings, inevitably leads to a rhetoric of
conclusions (Schwab, 1962). The experimental
details mean nothing in the absence of a theoretical
framework relating to the instrumentation. This leads
to a dilemma: are the textbook authors deliberately
ignoring theoretical and historical details, or just
assuming they have provided enough background for
the student to interpret the results? A definitive
answer would require further study. Nevertheless,
given the widespread use of such presentations, it is
plausible to suggest that it represents the empiricist
epistemology of the textbook authors.
Table 3 shows that none of the textbooks had
satisfactory classification on criteria BH3 and few
textbooks were classified satisfactory on criteria
BH1, BH2, RF3, TS2 and TS1. Criterion BH3 could
provide the opportunity to make students aware as to
how Bohr’s theory was ‘grafted’ on to Maxwell’s
electrodynamics. Criterion BH2 is good indicator of
the ‘Baconian’ orientation of the textbooks and also
the lack of a historical perspective. There is enough
historical evidence to show that Bohr’s main concern
was the paradoxical stability of the Rutherford atom,
* Corresponding author
Email: [email protected]
549
and that at first he was not even aware of the
problems associated with atomic spectra. Criterion
RF3 is a good example of how two famous scientists
(Thomson and Rutherford) could not agree on the
interpretation of their experimental data. Despite the
close relationship between the two, the controversy
was bitter and lasted for many years (Wilson, 1983).
Criterion TS1 dealt with the context in which
Thomson conducted his experiments, namely to
clarify a controversy over the nature of cathode rays:
charged particles or waves in the ether. Inclusion of
this aspect in the textbooks would help students to
understand that experiments are generally designed
to solve and throw light on an existing problem in the
scientific community. Although a detailed
comparison with other studies is not direct, the
presentation of atomic structure in chemistry
textbooks used in Tanzania secondary schools is in
line to that of chemistry textbooks used in other
countries around the word (Chiappetta et al., 1991;
Harrison and Treagust, 1996; Niaz, 1998; Abd-ElKhalick et al., 2008).
TABLE 3: Distribution of chemistry textbooks used in
Tanzania according to criteria and classification
Atomic
model
SA
TS1
TS2
RF1
RF2
RF3
BH1
BH2
BH3
4
2
13
10
5
3
3
-
ME
1
4
14
-
4
3
2
-
NO
22
21
-
17
18
21
22
27
CONCLUSION
This study shows that the chemistry textbooks used
in curriculum for secondary schools in Tanzania
generally lack a history and philosophy of science
perspective. None of the studied textbooks explained
satisfactorily that Bohr’s model was based on an
inconsistent foundation in which he ‘grafted’
Planck’s ‘quantum of action’ on to Maxwell’s
electrodynamics (criterion BH3). On the other hand
few textbooks described satisfactory that Bohr had
not even heard of the Balmer and Paschen formulae
for hydrogen line spectrum, when he wrote the first
version of his article (criterion BH2); Similarly, The
rivalry between Rutherford’s hypothesis of single
scattering based on a single encounter and
Thomson’s hypothesis of compound scattering led to
a bitter dispute (criterion RF3) and the Thomson’s
experiments on cathode rays were conducted to
© 2012, St. John’s University of Tanzania
http://www.sjut.org/journals/ojs/index.php/tajonas
SANGA et al.
clarify the controversy with respect to the nature of
cathode rays, that is charged particles or waves in the
ether (criterion TS1). In recent years universities
authorities (including Sokoine University of
Agriculture) have encouraged its faculty academic
members of staff to engage in science education
research specifically publishing textbooks that could
be used by secondary school students. It is plausible
to suggest that this may encourage faculty members
to use in the classroom research articles alongside the
textbooks. Furthermore, it may stimulate some
textbook authors interested in research to incorporate
the criteria presented in this study. Finally, science
education in the 21st century cannot continue to
repeat the rhetoric of conclusions, but rather break
the mould and provide students an insight into the
dynamics of scientific progress. Textbooks, instead
of forcing students to memorize facts, can provide
historical reconstructions based on the development
of scientific theories that frequently involve
controversies, conflicts and rivalries among
scientists. Such presentations can stimulate students
to think that all the work has not yet been done and
scientific progress needs their contribution.
ACKNOWLEDGMENT
The authors acknowledge the consulted head of
various secondary schools and librarians in
Morogoro Municipality for cooperation and help in
logistics access chemistry textbooks in their libraries.
We express our sincere thanks to chemistry teachers
and students who willingly gave valuable
information to accomplish this study.
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