Science 10th grade
LEARNING UNIT
How do components of the
world relate?
S/K
LEARNING OBJECT
What information can we obtain from the electronegativity
values of atoms?
ü Use the difference of electronegativity between
atoms to classify ionic, polar covalent and non-polar
covalent bonds.
ü Classify valence electrons into free and bonding
electrons.
Language
Socio cultural context of
the LO
Curricular axis
Standard competencies
Background Knowledge
English Review topic
Vocabulary box
ü Explain high melting points, dilation resistance, and
the hard and weak characteristics of ionic
compounds, based on the force of ionic interaction.
English
Colombia
Physical environment
Relate the structure of organic and inorganic molecules to
their physical and chemical properties, as well as, their
capability for chemical change.
Periodic Table, Chemical Groups, Chemical Periods, Lewis
Structure, Anion - Cation, Octet rule, Valence Electrons,
Oxidation States.
Possessives: When we want to show that something
belongs to somebody or something, we usually add an
apostrophe + s ('s) to a singular noun and an apostrophe
(') to a plural noun, for example:
- The boy’s ball (one boy).
- The boys’ ball (two or more boys).
- The Queen of England’s dogs (one subject ‘The Queen of
England’)
In proper nouns, such as names, we use apostrophes
regularly.
- Mary’s new car.
- That is Charles’s guitar (note that names ending in ‘S’
still have an extra ‘S’ after apostrophes).
- The university’s information center was very close (an
additional ‘S’ is also added for objects or things).
(Retrieved from:
https://www.englishclub.com/grammar/nounspossessive.htm)
ü Bond: something that binds, fastens, confines, or
holds together.
ü Melt: to become liquefied by warmth or heat, as ice,
snow, butter, or metal.
ü Boil: to change from a liquid to a gaseous state,
producing bubbles of gas that rise to the surface of
the liquid, agitating it as they rise.
ü Compound: something formed by compounding or
combining parts, elements, etc.
ü Achieve: to bring to a successful end; carry
through; accomplish.
ü Arouse: to stir to action or strong response; excite.
(Retrieved from: http://www.dictionary.com/)
NAME: _________________________________________________
GRADE: ________________________________________________
Lewis Structure helps represent the existing relation of chemical bonds in
molecules. This structure is used to know the number of valence electrons in an
element interacting with each other or with other elements. In this structure,
electrons are distributed around the element.
For instance: Carbon has 4 valence electrons in its last energy field, represented
like this:
On the other hand, the structure of electrons in a chemical compound such as
methane should be represented as follows:
Bonds between elements are represented by dashes, while free electrons are
represented as dots. For example, sodium chloride is represented as:
Electrons in a bond are called bonding pairs, whilst electrons out of a bond are
known as free electrons.
All Atoms tend to have eight electrons in their last energy field, which is known
as the Octet Rule. Atoms may lose, gain or share electrons in order to achieve a
stable setup so they take the electronic classification of a noble gas (Gonzáles,
2010).
In order to attain the Octet Rule, elements bond based on their electronegativity,
which is the capability of atoms to attract electrons from a another atom, when
they are bonded. This is a periodic property used to predict and explain the
characteristics of a bond (Chang, 2010).
The variation of electronegativity in the elements of the periodic table is shown
below.
Electronegativity is affected by two variables: atomic mass and average distance
of valence electrons from the atom nucleus. This data is measured using Pauling
Scale, starting at 0.7 (Francium) for the least electronegative element to 4.0
(Fluoride) for the most electronegative element, as noted in the periodic table.
The electronegativity of elements is used to determine the type of bond they can
perform (ionic, polar covalent and non-polar covalent). For this purpose, we
subtract the highest electronegativity value from the lowest electronegativity
value to determine the strength of a bond. The higher the result the stronger
the bond.
Types of bonds based on their electronegativity
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Non-polar covalent bond: The same amount of electrons is shared by each
bonding element. It is mostly found in two atoms of the same element,
with the same electronegativity value. The fluoride molecule is an
example of non-polar bond since the difference of electronegativity values
result is between 0.0 and 0.5.
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Polar covalent bond: Shared electrons show no symmetry because
electrons spend more time around one of the atoms than around the other
atom. They are more likely to be present in non-metallic elements such
as HF, which results in a difference between 0.5 and 1.9.
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Ionic bond: All electrons are transferred from the atom with the highest
electronegativity value to the lowest one. This generally occurs when
metallic and non-metallic elements bond, as their electronegativity values
are very different, resulting in a positive element (cation) and a negative
one (anion). The difference is higher than 2.0, for instance, LiF: (Chang,
2002).
Example:
Did you know that…?
The covalent bond of nitric oxide (NO), a molecule produced by the human body,
takes part in the cellular communication process for activities such as muscle
relaxation, control of bacteria, signals sent from the brain or even genitalia
enlargement during sexual arousal?
Activity 1
Resolve the following exercises:
1. These bonds are represented by the Lewis Structure. Using the periodic table,
find the electronegativity value of each element and obtain the difference to
determine the type of bond they produce:
2. What type of bond can you expect from the following cases? (Use the
electronegativity values from the periodic table):
a) Mg and O
b) O and O
c) Ca and Cl
Na
f) C and H
d) F and Cl
e) Br and
3. Organize the following elements from the highest to the lowest value of
electronegativity: Selenium, oxygen, chlorine, potassium, antimony, gallium and
magnesium.
4. Determine bonding pairs, free pairs and type of bond in the following
structures:
Activity 2:
Some properties of ionic compounds are:
Ionic compounds are solid at room temperature since their ions are so strongly
bonded. They create organized crystal structures based on their well-defined
anion and cation positions. Consequently, their melting and boiling points are
high because high temperature is necessary to break their bonds.
Ionic bonds stability is as strong as it may be weak. Any sort of impact can lead
to energy field overlapping, causing electrostatic repulsive forces between
evenly charged ions (both are positive or negative). These forces break the
crystal structures of ions.
In groups of three, explain to the class, why and how one of the following
phenomenon may occur:
1. Why does a pottery plate break when dropped or hit?
2. How is tempered glass fabricated and why does it fragment so easily?
3. Why are bones and teeth so strong and what does it take to break them?
4. What is the high melting point for NaCl? (Explain why).
5. Why do metallic structures in buildings such as bridges or train tracks have
holes?
ABSTRACT
Electronegativity is the capability of atoms to attract electrons from other atoms
towards their nucleus to create chemical bonds. Their electronegative
magnitudes are measured using the Pauling Scale, from lowest (Francium, 0.7)
to highest (Fluoride, 4.0) electronegativity. In the periodic table, magnitudes
increase from left to the right in periods and diminish to from top to bottom in
groups. This means that atomic numbers rise as electronegativity decreases.
The difference between electronegativity values helps categorize bonds. If the
result is over 2.0, the bond is ionic. Polar covalent bonds are between 0.5 and
1.9 and non-polar covalent bonds are in the 0.0 to 0.5 range.
In ionic bonds, all of the electrons are transferred from one atom to another,
generating a positive ion and a negative one. Polar covalent bonds happen when
shared electrons spend more time around an atom than around the other atom.
Ultimately, non-polar covalent bonds can be identified because each atom shares
the same amount of electrons.
Valence electrons in a bond are known as bonding pairs, while not-linked
electrons are called free pairs.
For instance, ionic compounds are solid at room temperature since their ions are
so strongly bonded. They create organized crystal structures based on their
anion and cation positions. These positions determine the high melting points of
elements. Their high melting points tend to be elevated as it takes higher
temperatures to break the bonds.
Ionic bonds stability is as strong as it may be weak. Any sort of impact might
lead to energy field overlapping, causing electrostatic repulsive forces between
evenly charged ions (both are positive or negative). These forces break the
crystal structures of ions.
HOMEWORK
1. Using any material, build an ionic covalent, a polar covalent and a non-polar
covalent bond, where electronegativity is used to explain such bonds.
2. Based on the model, explain the properties of the ionic bond to the class,
specifying details of high melting and boiling point, dilation resistance and
compound intermolecular strength and weakness.
EVALUATION
Based on this unit, answer the following questions to determine understanding
of the concepts.
1. Select the correct answer:
- Ionic compounds are generated by bonding:
a. Atoms of elements at the left side of the periodic table.
b. Atoms of elements at the right side of the periodic table.
c. Atoms of elements located anywhere in the periodic table.
d. Atoms with the same electronegativity values.
- Based on Lewis Structures of nitrogen (N) and hydrogen (H), how many
hydrogen atoms will pair to a nitrogen atom?
a. Left to right and bottom to top.
b. Left to right and top to bottom.
c. Right to left and top to bottom.
d. Right to left and bottom to top.
- How does electronegativity augment in the periodic table?
a. Left to right and bottom to top.
b. Left to right and top to bottom.
c. Right to left and top to bottom.
d. Right to left and bottom to top.
2. Complete the sentences:
- Atoms have ____________ in their last energy field. They are called
____________ and allow the atoms of elements to bond because they are
attracted by the ____________ of other atoms.
- Types of bonds produced are determined by ____________ obtained through
the difference in the __________ of each element.
.
3. Use the differences of electronegativity values to fill in the chart. Classify
the bonds as ionic, polar covalent or non-polar covalent bonds.
Elements
Electronegativity
H+N
Na + Cl
H-P
As -
H: 2.2
Na: 0.9
H:2.2
As:2.18
Differences of
electronegativity values
Type of
bond
N: 3.04
Cl:3.0
P: 2.19
O: 3.44
Carefully read and answer:
“Ceramic properties of compounds are the result of their chemical structure and
composition. Many of these are metallic oxides and are unlikely to have new
chemical reactions because they are already oxidized. Consequently, they
tolerate corrosive environments”.
Atoms in ceramic compounds are strongly bonded, creating gigantic 3D
formations that resist high temperatures without melting or breaking apart.
Throughout our history, ceramic structures have been used in metallic products.
They can be found in the form of building blocks for the internal walls of ovens
or boiler rooms, due to their resistance to high temperature. These are called
refractive materials”.
Retrieved from:
http://www.creces.cl/new/index.asp?imat=%20%20%3E%20%2067&tc=3&nc
=5&art=1129
4. Why are building blocks resistant?
a). Because of their covalent bonds.
b) Because of intermolecular forces.
c). Because of intramolecular strengths.
d). Because of their dilation resistance.
5. What bonds are responsible of intermolecular strength in ceramic compounds?
a). London forces.
b). Hydrogen bonds.
c). Non-polar covalent bonds.
d). Polar covalent bonds.
e). Ionic bonds.
BIBLIOGRAPHY
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Chang, R. (2002). Química, 6ª ed. México: McGraw-Hill 1999.
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Ciencias, F. d (2011). Facultad de Ciencias – Universidad Javeriana.
Retrieved from:
http://www.javeriana.edu.co/Facultades/Ciencias/neurobioquimica/libros
/celular/quimicacelular.htm
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DefiniciónABC (2010). Definición de electronegatividad. Retrieved from:
http://www.definicionabc.com/ciencia/electronegatividad.php
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Ebbing, D., & Gammon, S. (2010). Química General. México: Cengage
Learning Editores.
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EcuRed. (2016). Electronegatividad. Retrieved from:
http://www.ecured.cu/Electronegatividad
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ibio.ddns.net. (2011). Electronegatividad: clasificando el tipo de enlace..
Retrieved from: http://ibio.ddns.net/electronegatividad_web.pdf
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Gacía, A., García, M., Navarrete, A., Quijano, M., Azuara, P., Ballesteros,
J., Rodríguez, P. (2011). Iniciación a la Química. Preparación para el
acceso a la Universidad. Andaluz: Consejería de Innovación. Ciencia y
Empresa.
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Gonzáles, M. (2010). La Guía de Química. Retrieved from:
http://quimica.laguia2000.com/conceptos-basicos/propiedades-de-lassustancias-ionicas-y-moleculares
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González, M. (2011). La Guía de Química. Retrieved from:
http://quimica.laguia2000.com/conceptos-basicos/concepto-deelectronegatividad
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Gutiérrez, E. (2000). Química. México: Recerte SA.
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concurso.cnice.mec.es/. (2005). Enlace covalente. Retrieved from:
http://concurso.cnice.mec.es/cnice2005/93_iniciacion_interactiva_mater
ia/curso/materiales/enlaces/covalente.htm
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Mondragón, C., Peña, L., Sánchez, M., Arbelaez, F., & González, D.
(2010). Química. Colombia: Santillana.
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Mora, G., Sasal, J., Ceballada, J., & Laborda, J. (2010). Física y Química.
Educación secundaria para personas adultas. España: Dirección general
de formación profesional y educación permanente.
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QuimiTube.com. (2014). Propiedades de los compuestos iónicos.
Retrieved from: http://www.quimitube.com/videos/propiedades-de-loscompuestos-ionicos
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Sánchez, J., Gacía, M., & Balderas, Y. (2012). Química I. Retrieved from:
http://prepaunivas.edu.mx/v1/images/pdf/libros/quimica_I.pdf
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Sang, D. (2001). CRECES: Ciencia y Tecnología. Retrieved from:
http://www.creces.cl/new/index.asp?imat=%20%20%3E%20%2067&tc
=3&nc=5&art=1129
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Watkins, C. (2013). EHow en Español. Retrieved from:
http://www.ehowenespanol.com/definicion-electrones-libresinfo_255697/
GLOSSARY
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Anion: Ion that has gained electrons, so it becomes negatively charged.
Cation: Positively charged ion that has lost electrons.
Strength: Physical property materials consisting in a very strong
molecular bond that prevents them from breaking apart.
Boiling: Physical process of turning matter from liquid state to gas
state, using heat.
Electrostatic: Analyzes the mutual effects on compounds affected by
their electric charge.
Electrons: Elemental and stable particle of the atom. It is negatively
charged.
Valence Electrons: Electrons located in the last energy field of an
atom. They are responsible of the interaction between atoms of the
same or different elements, to produce compounds.
Lewis Structure: Graphic representation of electron bonding pairs and
electron free pairs that could exist in a molecule.
Weakness: Capability of materials to fracture or break with a low level
of impact over the object.
Melting: Physical process of turning matter from solid state to liquid
state, using high temperatures.
Groups: Organizational structure of elements based on the number of
electrons in the last energy fields of atoms. In the periodic table,
elements with the same amount of electrons are located in one single
column.
Molecule: Organized atoms representing the smallest portion of a
substance that keeps all of its properties.
Periods: Categorization of elements in the horizontal lines of the
periodic table (rows). Elements in periods match their last electron shell,
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for example, an element with five electron shells is located in the fifth
period.
Octet Rule: Tendency of atoms to achieve stability by completing their
energy fields with eight electrons, either losing or earing electrons to
become stable.