SCIENCE 8 WEEK 7

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Let’s Try
SCIENCE 8
Third Quarter
Week 7 and 8
Periodic Table of Elements
MELC: Use the periodic table to predict the chemical behavior of an element.
Objectives:
• trace the development of the periodic table;
• identify the different basis of arranging the elements in the periodic table
• identify parts of the periodic table
• explain trends in reactivity, metallic and atomic radius
• arrange elements based on the reactivity, metallic and atomic radius trend
Multiple Choices. Identify the choice that best completes the statement or answers the
question.
Write your answer on a separate sheet of paper.
1. Which law or basis did Johann Wolfgang Dobereiner used in his arrangement of Periodic
Table?
A. Triads
B. Periodic Law
C. Law of Octaves
D. None of the above
2. According to periodic law the properties of element vary periodically with what number?
A. Atomic number
B. Number of nuclei
C. Number of neutrons
D. Atomic mass number
3. Which of the following does NOT belong to group IIA?
A. Ba B. Mg C. Na D. Sr

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4. Which of the following groups of elements have stable configuration?
A. Alkali metals
B. Alkaline earth metals
C. Halogens
D. Noble gases
5. Which of the following elements is NOT included in the actinide series?
A. Am B. Cm C. Er D. Np
6. In what period of elements does silver belong?
A. 4 B. 5 C. 6 D. 7
7. Which of the following is a lanthanide?
A. Es B. Eu C. Pu D. Pr
8. Which of the following is the most metallic element?
A. Al B. Ga C. Ge D. Si
9. Which element belongs to group 15 and in the sixth period?
A. At B. Bi C. Po D. Sb
10. All of the following elements are metals EXCEPT?
A. Br B. Co C. Cu D. Zn

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Elements are essential on our daily survival. We use some of them as food,
medicine, hygiene and many more. Some are naturally found in our environment and
some are synthetically made from the laboratory. But, all of them are found and
presented in the periodic table of elements.
This periodic table was developed as a result of years of painstaking work by
different scientists. Its present form was a result of meticulous and thorough study by
scientists. The information and data of every element was arranged and organized in
ways that will make it more understandable, meaningful, and useful.
Historical Development of Periodic Table
The development of the Periodic table could be traced back in 1817 to the work of
Johann Dobereiner, a German chemist who formed the triads of elements with similar
properties like the triad of calcium, barium and strontium. In 1863, John Newlands, an
English chemist proposed the Law of Octaves. He based his classification of elements on
the fact that similar properties could be noted for every eight elements when they are
arranged in order of increasing atomic masses. Around 1869 two scientists determined a
way to put the elements in order. Lothar Meyer and Dmitri Mendeleev both came up with
periodic tables that showed how elements should be grouped. It is interesting to note that
these two scientists did not personally know each other, yet they came up with the same
conclusions. Both scientists were teachers living and working in different places. Meyer
lived and worked in Germany while Mendeleev in Russia. Both arranged the elements in
order of increasing atomic mass while putting in groups those with similar properties. Both
of them also left blank spaces in their tables, believing that these spaces would be filled
later with elements yet to be discovered.
Later, in 1914, Henry Moseley, an English physicist observed that the order of the X-
ray frequencies emitted by elements follows the ordering of the elements by atomic number.
This observation led to the development of the modern periodic law which “states that the
properties of elements vary periodically with atomic number”.
The modern periodic table
The modern periodic table organizes
elements in such a way that information
about the elements and their compounds
are easily revealed.
• The vertical columns of the periodic
table, called groups, identify the
principal families of elements.
• Some families have their special
names. Refer to the figure on the right,
Let’s Explore and Discover
Source: Illustrated in the Grade 8 – Science Learning Module
published on 2013.

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✓ Group 1 is named as the alkali
metals,
✓ Group 2 as the alkaline earth
metals,
✓ Group 17 as the halogens and
✓ Group 18 as the noble gases.
✓ Groups 13 to 16 are named based on the first element found in their families.
• The horizontal rows are called periods are numbered from the top to bottom. There
are 7 horizontal rows or periods in the periodic table.
• Group 3 to Group 12 constitutes one block wherein elements in this block are referred
as the
transition elements.
• The lanthanides and actinides are special series of elements but are also part of
the transition block; they are also called the inner transition elements.
• Elements from the taller columns (groups 1, 2, and 13, through 18) are called the
representative elements or main groups of the periodic table.
• A stair step line separates metals and
nonmetals. Elements along the stair step line
are the semimetals.
• The seven elements commonly regarded
as
semimetals are boron, silicon, germanium,
arsenic, antimony, tellurium, and polonium.
• The majority of the elements on the left
side of the table are metals. The physical
properties of metals include luster,
malleability, ductility, and conductivity. Metals
vary in reactivity.
• The nonmetals are confined to the right
side of the table.
In the Bohr’s model of an atom, an atom has an energy
shell occupied by a specific number of electrons. Each electron
shell can hold only a certain number of electrons. The way the
electrons of an atom are distributed in the various energy levels
or electron shells is called electronic configuration.
The lowest energy level is the one nearest to the
nucleus. This is the energy level that electrons occupy first. It
can accommodate a maximum of 2 electrons. If there are more
than 2 electrons, they occupy the succeeding higher energy
levels. The
highest energy level that an electron occupies is referred to as the outermost shell or
valence shell. The electrons in the valence shells are called valence electrons. These
electrons are the ones involved in chemical reactions. The chemical properties of an
element depend on the number of valence electrons.
Source: https://sites.google.com/site/
comerschemistryclassroom/useful-
links/bohr-s-model-2
Source: Illustrated in the Grade 8 – Science Learning
Module published on 2013.

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Looking at the table below, Representative elements has their respective valence
electron number. You can see that the number of their old grouping is also the number of
their valence electron. As stated in the Octet Rule elements gain or lose electrons to
attain an electron configuration of the nearest noble gas, to become stable. When an
atom/element gains an electron it becomes negatively charged ion and it is called
ANION, while if an atom/element loses an electron it becomes positively charged ion and
it is CATION.
Activity 2. Sorting: How do they do it?
Directions. Fill in the missing data that is needed to complete the identification card of
scientist who contributed in the development of periodic table. Write your answer on a
separate sheet

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What I Have Learned
I. Directions: Answer the questions with the proper information using your notes, book, and
the periodic table. Write your answer on a clean sheet of paper.
1. Define a family.
2. What is a period?
3. In what period do the following elements belong?
a. He b. Ge
c. Rb d. I
4. In what group do the following elements belong?
a. Sulfur b. Ca
c. Iodine d. Fe
5. The periodic law states that “ ”
Short Response
What is the importance of a periodic table?
.
RUBRICS:

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Activity 5. Atomic Radius Trends
Objectives:
✓ compare atomic radius of elements
✓ explain the trends in atomic
radius Materials Needed:
✓ Periodic Table of Elements
✓ Paper
✓ pen
Procedure:
1. Study the figure presented.
2. Determine the trend in terms of atomic radius.
3. Choose among the pair of elements bigger
atomic radius.
a. Be and Ca
b. Cl and F
c. Rb and Li
4. Arrange the following sets of element into
increasing size in atomic radius.
a. Si, Mg, S, Na, Cl
b. Te, O, Po, S, Se
Comprehension Check
Directions: Read and analyze the following questions. Write your answer on your Science
study notebook.
1. What happens to the atomic radius across a period?
2. What happens to the atomic radius down a group?
RUBRICS:
Source: https://saylordotorg.github.io/text_introductory-
chemistry/s12-05-periodic-trends.html

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What I Have Learned
I. Directions: Answer the questions with the proper information using your notes, book, and
the periodic table. Write your answer on a clean sheet of paper.
1. Define a family.
2. What is a period?
3. In what period do the following elements belong?
a. He b. Ge
c. Rb d. I
4. In what group do the following elements belong?
a. Sulfur b. Ca
c. Iodine d. Fe
5. The periodic law states that “ ”
Short Response
What is the importance of a periodic table?
.
RUBRICS:

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LET’S ASSESS
Multiple Choices. Identify the choice that best completes the statement or answers the
question.
Write your answer on a separate sheet of paper.
1. What was the contribution of Mendeleev in developing the periodic table?
a. discovering protons
b. discovering Mendelevium
c. creating today’s atomic model
d. publishing the first periodic table
2. What do you call each column of the periodic table?
a. a group c. an isotope.
b. a period. d. an element.
3. What do you call each row of the periodic table?
a. a group c. an isotope.
b. a period. d. an element.
4. According to the periodic law, how do elements that have similar properties appear?
a. to the left of each other
b. to the right of each other
c. at every tenth element
d. at regular intervals periodically
5. Why do elements within the same group in the periodic table have similar properties?
a. They have the same number ions.
b. They have the same number neutrons.
c. They have the same number protons.
d. They have the same number valence electrons.
_____6. What have you observed in the elements as you move down the same column of the
periodic table?
a. Elements have fewer protons
b. Elements have a lower atomic number
c. Elements have more energy levels
d. Elements have a different group number
7. What is the tendency of an element having one valence electron?
a. be highly reactive
b. forms ions
c. becomes charged
d. all of the above
8. Which is not a family of the periodic table?
a. alkaline-earth metals
b. anions
c. halogens
d. noble gases
9. What do you call atoms that gain or lose electrons?
a. metals. c. ions.
b. nonmetals. d. isotopes.
______10. Who proposed the law of octaves which classifies elements based on the fact that
similar properties could be noted for every eight elements when they are arranged in order of
increasing atomic masses?
a. Dmitri Mendeleev
b. Henry Moseley
c. Johann Doberiener
d. John Newlands

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References
Annenberg Foundation (2012). Workshop session 2: The particle nature of matter: Solids,
liquids, and gases. In Essential Science for Teachers: Physical Science. Retrieved
fromhttp://www.learner.org/courses/essential/physicalsci/support/ps_session2.p df
Atkins, Peter, and Jones, Loretta (2002). Chemical Principles: The Quest for Insight,
second edition. New York: W. H. Freeman.
Brady, J.E.,& Senese, F. (2004). Chemistry: Matter and its changes (4th ed.). River
Street Hoboken, NJ: John Wiley & Sons, Inc.
Bucat, R.B. (Ed.). (1984). Elements of chemistry: Earth, air, fire and water, Vol. 2.
Canberra City, A.C.T., Australia.
Chang, Raymond (2002). Chemistry, seventh edition. Boston: McGraw-Hill.
Elvins, C., Jones, D., Lukins, N., Miskin, J., Ross, B., & Sanders, R. (1991).Chemistry
one: Materials, chemistry in everyday life. Port Melbourne, Australia: Heinemann
Educational Australia.
Fricke, M. (1976). "Quantum Mechanics." In Method and Appraisal in the Physical
Sciences: The Critical Background to Modern Science, 1800–1905, ed. C. Howson.
New York: Cambridge University Press.
Fong, P. (1962). Elementary Quantum Mechanics. Reading, MA: Addison-Wesley.
Philippines. Department of Education. 2013. Grade 8 Science Learner’s Module. First
Edition.
Meralco Avenue, Pasig City
Philippines. Department of Education. 2013. Grade 8 Teacher’s Guide. First Edition.
Meralco Avenue, Pasig City
Mendoza, E.E. &Religioso, T.F. (1997).Chemistry.Phoenix Publishing House, Inc.
Quezon City. The American Chemical Society (1988).Chemistry in the
community.Kendall/Hunt Publishing
Company. Dubuque, Iowa.
Tsaparlis, Georgios. "Atomic Structure." Chemistry: Foundations and Applications.
2004.Encyclopedia.com. 18 May. 2016 <http://www.encyclopedia.com>.

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Answer Key
Let’s Try
1. A 6. B
2. A 7. B
3. C 8. D
4. D 9. C
5. D 10. A
Let’s Assess
1. D
2. A
3. B
4. D
5. D
6. C
7. A
8. B
9. C
10.D
Let’s Practice
Activity 1 and Activity 2. Answers may vary
Activity 3
Q1. The reactivity increases as it goes from top to bottom of
the periodic table.
Q2. Yes, Group 2 metals followed the same trend for Group 1
metals in terms of reactivity.
Q3. The reactivity decreases as it goes from left to right of the
periodic table.
Q6.
a. Na is more reactive than Mg with HCl
b. Al is more reactive than Ag
c. Zn is more reactive than Fe
Activity 4
2. a – Ca 3. a – Cl, S, Si, Mg, Na
b – Cl b – O, S, Se, Te,
Po c – Rb
Activity 5
3. a – Ca 4. a – Cl, S, Si, Mg, Na
b – Cl b – O, S, Se, Te,
Po c – Rb
Comprehension Check
1. Atomic radius decreases across the period from left to
right.
2. Atomic radius increases down a group from top to bottom.
What I Have Learned
1. Answers may vary
2. Answers may vary
3. a – 1 c – 5
b – 4 d – 5
4. a – 16/ VI A / oxygen group
b – 2 / II A / alkaline earth
metal c – 17 / VII A /
Chalcogen
d – 8
5. “the properties of elements vary periodically with atomic number”
Short Response (Answers may vary)

19. Periodic Table of Elements
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