Periodic Classification of Element Textbook Solution 10 Standard SSC Maharashtra State Board
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Rearrange the columns 2 and 3 so as to match with the column 1.
| Column 1 | Column 2 | Column 3 |
|---|---|---|
| i. Triad | a. Lightest and negatively charged particle in all the atoms | 1. Mendeleev |
| ii. Octave | b. Concentrated mass and positive charge | 2. Thomson |
| iii. Atomic number | c. Average of the first and the third atomic mass | 3. Newlands |
| iv. Period | d. Properties of the eighth element similar to the first | 4. Rutherford |
| v. Nucleus | e. Positive charge on the nucleus | 5. Dobereiner |
| vi. Electron | f. Sequential change in molecular formulae | 6. Moseley |
Scientific and Written Exam Answer:
| Column 1 | Column 2 | Column 3 |
|---|---|---|
| Triad | Average of the first and the third atomic mass | Dobereiner |
| Octave | Properties of the eighth element similar to the first | Newlands |
| Atomic number | Sequential change in molecular formulae | Moseley |
| Period | Sequential change in molecular formulae | Mendeleev |
| Nucleus | Concentrated mass and positive charge | Rutherford |
| Electron | Lightest and negatively charged particle in all the atoms | Thomson |
Choose the correct option and rewrite the statement.
The number of electrons in the outermost shell of alkali metals is _______.
- 1
- 2
- 3
- 7
Scientific and Written Exam Answer:
Alkali metals belong to Group 1 of the periodic table. They have only one electron in their outermost shell, which makes them highly reactive.
Correct Answer: The number of electrons in the outermost shell of alkali metals is 1.
Simple and Understandable Answer:
Alkali metals like sodium (Na) and potassium (K) have only one electron in their last shell. This single electron makes them very reactive.
Answer: The number of electrons in the outermost shell of alkali metals is 1.
Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in ___________.
- Group 2
- Group 16
- Period 2
- d-block
Scientific and Written Exam Answer:
Alkaline earth metals belong to Group 2 of the modern periodic table. They have two valence electrons in their outermost shell, allowing them to form divalent cations (M²⁺).
Correct Answer: The position of alkaline earth metals in the modern periodic table is in Group 2.
Simple and Understandable Answer:
Alkaline earth metals like magnesium (Mg) and calcium (Ca) always lose two electrons to form bonds. Because of this, they are placed in Group 2 of the periodic table.
Answer: The position of alkaline earth metals in the modern periodic table is in Group 2.
The molecular formula of the chloride of element X is XCl. This compound is a solid having a high melting point. Which of the following elements will be present in the same group as X?
- Na
- Mg
- Al
- Si
Scientific and Written Exam Answer:
The given compound has the molecular formula XCl, which indicates that element X has a valency of +1. Elements forming such compounds typically belong to Group 1 of the modern periodic table.
Since sodium (Na) belongs to Group 1 and forms NaCl, which is a solid with a high melting point, element X should be sodium (Na).
Correct Answer: The element present in the same group as X is Na (Sodium).
Simple and Understandable Answer:
The formula XCl tells us that X combines with chlorine in a 1:1 ratio. This happens with alkali metals like sodium (Na), which belong to Group 1.
Also, table salt (NaCl) is a solid with a high melting point, just like the given compound. So, X must be in the same group as sodium.
Answer: The element present in the same group as X is Na (Sodium).
In which block of the modern periodic table are the nonmetals found?
- s-block
- p-block
- d-block
- f-block
Scientific and Written Exam Answer:
Nonmetals are primarily found in the p-block of the modern periodic table. This block contains elements such as carbon (C), nitrogen (N), oxygen (O), fluorine (F), and noble gases, which are all nonmetals.
Nonmetals have properties such as high electronegativity, poor electrical conductivity, and low melting and boiling points. The p-block elements also include metalloids and some metals, but nonmetals are mainly concentrated in this block.
Correct Answer: The nonmetals are found in the p-block of the modern periodic table.
Simple and Understandable Answer:
Nonmetals like oxygen, nitrogen, and fluorine are present in the p-block of the periodic table. This block also contains noble gases like helium and neon. Nonmetals are usually poor conductors of electricity and have low melting points.
Answer: Nonmetals are found in the p-block of the modern periodic table.
An element has its electron configuration as 2, 8, 2. Now answer the following question.
What is the atomic number of this element?
Scientific and Written Exam Answer:
The atomic number of an element is the total number of protons (or electrons) in a neutral atom.
Given electronic configuration: 2, 8, 2
The sum of electrons = 2 + 8 + 2 = 12
Answer: The atomic number of this element is 12.
Simple and Understandable Answer:
The atomic number tells us how many protons an element has.
The electron configuration 2, 8, 2 means:
- 2 electrons in the first shell
- 8 electrons in the second shell
- 2 electrons in the third shell
Adding them gives 12.
Answer: The atomic number is 12.
An element has its electron configuration as 2, 8, 2. Now answer the following question.
What is the group of this element?
Scientific and Written Exam Answer:
The group number of an element in the modern periodic table is determined by the number of valence electrons.
The given electronic configuration 2, 8, 2 shows that the outermost shell contains 2 electrons.
Elements with 2 valence electrons belong to Group 2 (Alkaline Earth Metals).
Answer: This element belongs to Group 2.
Simple and Understandable Answer:
The last shell has 2 electrons. In the periodic table, elements with 2 outer electrons are in Group 2.
Answer: The element is in Group 2.
An element has its electron configuration as 2, 8, 2. Now answer the following question.
To which period does this element belong?
Scientific and Written Exam Answer:
The period number of an element is determined by the number of electron shells.
The given electronic configuration 2, 8, 2 has electrons distributed in three shells.
Elements with three shells belong to Period 3.
Answer: This element belongs to Period 3.
Simple and Understandable Answer:
The number of shells in an atom decides the period number.
This element has 3 shells (2, 8, 2), so it is in Period 3.
Answer: The element belongs to Period 3.
An element has its electron configuration as 2, 8, 2. Now answer the following question.
With which of the following elements would this element resemble?
(Atomic numbers are given in the brackets) N(7), Be(4), Ar(18), Cl(17)
Scientific and Written Exam Answer:
Elements in the same group have similar chemical properties.
The given element has an electron configuration of 2, 8, 2, meaning it belongs to Group 2.
Now, we compare with the given elements:
- Nitrogen (N) - Atomic number 7: 2, 5 (Group 15) ❌
- Beryllium (Be) - Atomic number 4: 2, 2 (Group 2) ✅
- Argon (Ar) - Atomic number 18: 2, 8, 8 (Group 18) ❌
- Chlorine (Cl) - Atomic number 17: 2, 8, 7 (Group 17) ❌
Answer: The element resembles Beryllium (Be), as they are in the same group.
Simple and Understandable Answer:
Elements in the same group behave in the same way.
This element has 2 valence electrons, so it belongs to Group 2.
Among the given options, Beryllium (Be) is also in Group 2.
Answer: The element resembles Beryllium (Be).
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
(3Li, 14Si, 2He, 11Na, 15P)
Which of these elements belong to period 3?
Scientific and Written Exam Answer:
The period number of an element is determined by the number of electron shells.
Electronic configurations of the given elements:
- Li (Lithium) - Atomic number 3: 2, 1 (Period 2)
- Si (Silicon) - Atomic number 14: 2, 8, 4 (✔️ Period 3)
- He (Helium) - Atomic number 2: 2 (Period 1)
- Na (Sodium) - Atomic number 11: 2, 8, 1 (✔️ Period 3)
- P (Phosphorus) - Atomic number 15: 2, 8, 5 (✔️ Period 3)
Elements in Period 3 have electrons in three shells.
Answer: The elements belonging to Period 3 are Silicon (14Si), Sodium (11Na), and Phosphorus (15P) ✔️.
Simple and Understandable Answer:
The number of shells in an atom decides its period.
If an element has electrons in three shells, it is in Period 3.
From the given elements:
- Silicon (14Si) - 2, 8, 4 → Period 3 ✔️
- Sodium (11Na) - 2, 8, 1 → Period 3 ✔️
- Phosphorus (15P) - 2, 8, 5 → Period 3 ✔️
Answer: The elements in Period 3 are Silicon (14Si), Sodium (11Na), and Phosphorus (15P) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
(1H, 7N, 20Ca, 16S, 4Be, 18Ar)
Which of these elements belong to the second group?
Scientific and Written Exam Answer:
The group number of an element is determined by the number of valence electrons.
Electronic configurations of the given elements:
- H (Hydrogen) - Atomic number 1: 1 (Group 1)
- N (Nitrogen) - Atomic number 7: 2, 5 (Group 15)
- Ca (Calcium) - Atomic number 20: 2, 8, 8, 2 (✔️ Group 2)
- S (Sulfur) - Atomic number 16: 2, 8, 6 (Group 16)
- Be (Beryllium) - Atomic number 4: 2, 2 (✔️ Group 2)
- Ar (Argon) - Atomic number 18: 2, 8, 8 (Group 18 - Noble Gas)
Elements in Group 2 have two electrons in their outermost shell.
Answer: The elements belonging to Group 2 are Calcium (20Ca) and Beryllium (4Be) ✔️.
Simple and Understandable Answer:
The group number of an element depends on its outermost electrons.
Elements in Group 2 have two valence electrons.
From the given elements:
- Calcium (20Ca) - 2, 8, 8, 2 → Group 2 ✔️
- Beryllium (4Be) - 2, 2 → Group 2 ✔️
Answer: The elements in Group 2 are Calcium (20Ca) and Beryllium (4Be) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
(7N, 6C, 8O, 5B, 13Al)
Which is the most electronegative element among these?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- N (Nitrogen) - Atomic number 7: 2, 5
- C (Carbon) - Atomic number 6: 2, 4
- O (Oxygen) - Atomic number 8: 2, 6 (✔️ Most electronegative)
- B (Boron) - Atomic number 5: 2, 3
- Al (Aluminum) - Atomic number 13: 2, 8, 3
Electronegativity is the tendency of an atom to attract electrons towards itself. In the periodic table:
- Electronegativity increases from left to right in a period.
- Oxygen is in Group 16 and is highly electronegative.
Answer: The most electronegative element among these is Oxygen (8O) ✔️.
Simple and Understandable Answer:
The element with the strongest ability to attract electrons is called the most electronegative element.
Among the given elements, Oxygen (8O) has the highest electronegativity because:
- It has 6 valence electrons and needs only 2 more to complete its octet.
- It belongs to Group 16, where elements have high electronegativity.
Answer: The most electronegative element is Oxygen (8O) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
(4Be, 6C, 8O, 5B, 13Al)
Which is the most electropositive element among these?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- Be (Beryllium) - Atomic number 4: 2, 2
- C (Carbon) - Atomic number 6: 2, 4
- O (Oxygen) - Atomic number 8: 2, 6
- B (Boron) - Atomic number 5: 2, 3
- Al (Aluminum) - Atomic number 13: 2, 8, 3 (✔️ Most electropositive)
Electropositivity is the tendency of an atom to lose electrons and form positive ions. It:
- Increases down a group.
- Decreases from left to right in a period.
Answer: The most electropositive element among these is Aluminum (13Al) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
(11Na, 15P, 17Cl, 14Si, 12Mg)
Which of these has the largest atoms?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- Na (Sodium) - Atomic number 11: 2, 8, 1 (✔️ Largest atom)
- P (Phosphorus) - Atomic number 15: 2, 8, 5
- Cl (Chlorine) - Atomic number 17: 2, 8, 7
- Si (Silicon) - Atomic number 14: 2, 8, 4
- Mg (Magnesium) - Atomic number 12: 2, 8, 2
Atomic size depends on the number of electron shells and effective nuclear charge. It:
- Increases down a group.
- Decreases from left to right in a period.
Answer: The element with the largest atomic size is Sodium (11Na) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with an explanation.
(19K, 3Li, 11Na, 4Be)
Which of these atoms has the smallest atomic radius?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- K (Potassium) - Atomic number 19: 2, 8, 8, 1
- Li (Lithium) - Atomic number 3: 2, 1
- Na (Sodium) - Atomic number 11: 2, 8, 1
- Be (Beryllium) - Atomic number 4: 2, 2 (✔️ Smallest radius)
Atomic radius is influenced by:
- Decreasing size across a period (left to right).
- Increasing size down a group (top to bottom).
Answer: The element with the smallest atomic radius is Beryllium (4Be) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with an explanation.
(13Al, 14Si, 11Na, 12Mg, 16S)
Which of the above elements has the highest metallic character?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- Al (Aluminum) - Atomic number 13: 2, 8, 3
- Si (Silicon) - Atomic number 14: 2, 8, 4
- Na (Sodium) - Atomic number 11: 2, 8, 1 (✔️ Highest metallic character)
- Mg (Magnesium) - Atomic number 12: 2, 8, 2
- S (Sulfur) - Atomic number 16: 2, 8, 6
Metallic character is determined by:
- Increasing from right to left across a period.
- Increasing from top to bottom in a group.
Answer: The element with the highest metallic character is Sodium (11Na) ✔️.
Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with an explanation.
(6C, 3Li, 9F, 7N, 8O)
Which of the above elements has the highest nonmetallic character?
Scientific and Written Exam Answer:
Electronic configurations of the given elements:
- C (Carbon) - Atomic number 6: 2, 4
- Li (Lithium) - Atomic number 3: 2, 1
- F (Fluorine) - Atomic number 9: 2, 7 (✔️ Highest nonmetallic character)
- N (Nitrogen) - Atomic number 7: 2, 5
- O (Oxygen) - Atomic number 8: 2, 6
Nonmetallic character is determined by:
- Increasing from left to right across a period.
- Decreasing from top to bottom in a group.
Answer: The element with the highest nonmetallic character is Fluorine (9F) ✔️.
Write the name and symbol of the element from the description.
The atom having the smallest size.
Answer:
The element with the smallest atomic size is Helium (2He) ✔️.
Write the name and symbol of the element from the description.
The atom having the smallest atomic mass.
Answer:
The element with the smallest atomic mass is Hydrogen (1H) ✔️.
Write the name and symbol of the element from the description.
The most electronegative atom.
Answer:
The most electronegative element is Fluorine (9F) ✔️.
Write the name and symbol of the element from the description.
The noble gas with the smallest atomic radius.
Answer:
The noble gas with the smallest atomic radius is Helium (2He) ✔️.
Write the name and symbol of the element from the description.
The most reactive nonmetal.
Answer:
The most reactive nonmetal is Fluorine (9F) ✔️.
Write a short note.
Mendeleev’s Periodic Law
Scientific and Written Exam Answer:
Mendeleev’s Periodic Law states that "The physical and chemical properties of elements are a periodic function of their atomic masses." In 1869, Dmitri Mendeleev arranged the known elements in order of increasing atomic mass and observed that elements with similar properties appeared at regular intervals. This led to the formation of Mendeleev’s Periodic Table.
Key Features of Mendeleev’s Periodic Table:
- Elements were arranged in increasing order of atomic masses.
- Similar properties were grouped into vertical columns called "groups."
- He left gaps for undiscovered elements and predicted their properties.
- Some elements were placed out of order to maintain similar properties.
Limitations:
- Elements with similar properties were sometimes placed in different groups.
- The increasing atomic mass order was not strictly followed in some cases.
- It could not explain the position of isotopes.
Despite its limitations, Mendeleev’s Periodic Law was a major step toward the modern Periodic Table, which is now based on atomic number rather than atomic mass.
Simple and Understandable Answer:
Mendeleev’s Periodic Law states that the properties of elements repeat periodically when arranged in order of increasing atomic mass. This means that elements with similar properties appear at regular intervals.
Example: Lithium (Li), Sodium (Na), and Potassium (K) have similar properties and appear in the same group in Mendeleev’s table.
Why is it important?
- Mendeleev organized elements in a table, making it easier to study them.
- He predicted the properties of elements that were not yet discovered.
- His work helped in the development of the modern Periodic Table.
Although some elements did not fit perfectly, Mendeleev’s Periodic Table was an important foundation for understanding elements and their properties.
Structure of the Modern Periodic Table
Scientific and Written Exam Answer:
The modern periodic table is based on the Modern Periodic Law, which states that "The physical and chemical properties of elements are a periodic function of their atomic number (Z)." It was developed by Henry Moseley in 1913 and is an improved version of Mendeleev’s table.
Structure of the Modern Periodic Table:
- It consists of 18 vertical columns called groups and 7 horizontal rows called periods.
- Elements are arranged in increasing order of atomic number (Z).
- Elements in the same group have similar chemical properties.
- The periodic table is divided into four blocks: s-block, p-block, d-block, and f-block.
- The lanthanides and actinides are placed separately at the bottom.
Significance:
- It explains the periodic trends in atomic size, ionization energy, electronegativity, etc.
- It helps predict the chemical behavior of elements.
- It provides a systematic classification of all known elements.
Simple and Understandable Answer:
The modern periodic table is arranged according to the atomic number of elements. It is divided into groups (columns) and periods (rows). Elements in the same group have similar properties.
Key Features:
- There are 18 groups and 7 periods.
- Elements are arranged in increasing atomic number.
- Metals are on the left, nonmetals on the right, and metalloids in between.
- Special rows at the bottom contain lanthanides and actinides.
Example: Hydrogen (H) is in group 1, while Oxygen (O) is in group 16.
The modern periodic table helps us understand elements better and predict their behavior in chemical reactions.
Write a short note on the Structure of the Modern Periodic Table.
Scientific and Written Exam Answer:
The modern periodic table is based on Moseley’s Periodic Law, which states that "The properties of elements are the periodic function of their atomic numbers." This table arranges elements in increasing order of atomic number rather than atomic mass, as in Mendeleev’s table.
Structure of the Modern Periodic Table:
- It consists of 7 periods (horizontal rows) and 18 groups (vertical columns).
- Elements in the same group have similar chemical properties due to the same valence electron configuration.
- The table is divided into s-block, p-block, d-block, and f-block based on the electron configuration.
- Metals are placed on the left, non-metals on the right, and metalloids are found in between.
- Noble gases (Group 18) have complete outer electron shells and are highly stable.
Advantages of the Modern Periodic Table:
- Elements are arranged in proper order based on atomic number.
- It explains periodicity in properties more accurately.
- It resolves the placement issues of isotopes and anomalous element positions.
The modern periodic table is widely accepted and serves as the foundation for studying the chemical behavior of elements.
Simple and Understandable Answer:
The modern periodic table is an improved version of Mendeleev’s table. Instead of atomic mass, it arranges elements in order of increasing atomic number.
Key Features:
- It has 7 periods (rows) and 18 groups (columns).
- Elements in the same group have similar chemical properties.
- The table is divided into metals, non-metals, and metalloids.
- Noble gases (like helium, neon) are placed in the last group.
Why is it important?
- The table makes it easier to study elements.
- It correctly arranges elements without confusion.
- Scientists use it to predict element properties.
The modern periodic table is the best way to organize elements and is used in all scientific studies.
Write a short note on the Position of Isotopes in the Mendeleev’s and the Modern Periodic Table.
Scientific and Written Exam Answer:
Isotopes are atoms of the same element with the same atomic number but different atomic masses. For example, hydrogen has three isotopes: protium (\(^1H\)), deuterium (\(^2H\)), and tritium (\(^3H\)).
Position of Isotopes in Mendeleev’s Periodic Table:
- Mendeleev’s periodic table was based on atomic mass, so isotopes should have been placed separately.
- However, all isotopes of an element had similar chemical properties, making their placement difficult.
- Mendeleev could not provide a proper position for isotopes, creating a limitation in his table.
Position of Isotopes in the Modern Periodic Table:
- The modern periodic table is based on atomic number, not atomic mass.
- Since all isotopes have the same atomic number, they occupy the same position in the table.
- This resolved the issue that Mendeleev faced and provided a logical classification of elements.
Thus, the modern periodic table correctly accommodates isotopes, making it more accurate and widely accepted.
Simple and Understandable Answer:
What are isotopes? Isotopes are different forms of the same element with the same atomic number but different atomic masses. For example, carbon has two isotopes: \(^12C\) and \(^14C\).
Position of Isotopes:
- In Mendeleev’s Table: Isotopes could not be placed properly because the table was arranged by atomic mass.
- In the Modern Table: Isotopes are placed in the same position because the table is arranged by atomic number.
The modern periodic table solved the problem of isotope placement, making it more useful for scientists.
Give scientific reasons: Atomic radius goes on decreasing while going from left to right in a period.
Scientific and Written Exam Answer:
The atomic radius decreases across a period due to the following reasons:
- As we move from left to right in a period, the atomic number increases, meaning the number of protons in the nucleus increases.
- The increased nuclear charge pulls electrons closer to the nucleus, reducing the atomic size.
- Electrons are added to the same energy level, so there is no significant increase in electron shielding.
- Due to the strong nuclear attraction, the atomic radius decreases from left to right.
Example: In period 2, the atomic radius decreases from lithium (Li) to fluorine (F).
Simple and Understandable Answer:
- More protons in the nucleus pull electrons closer.
- Electrons are added in the same shell, so atomic size shrinks.
- As a result, atomic radius decreases from left to right.
Example: Lithium (Li) is bigger than Fluorine (F) due to increasing nuclear charge.
Write scientific reason: Metallic character goes on decreasing while going from left to right in a period.
Scientific and Written Exam Answer:
The metallic character of elements decreases from left to right in a period due to the following reasons:
- Metals have a tendency to lose electrons and form positive ions.
- As we move across a period, nuclear charge increases, making it harder for atoms to lose electrons.
- Elements on the left (like Na, Mg) lose electrons easily, whereas elements on the right (like Cl, F) tend to gain electrons.
- This leads to a decrease in metallic character across a period.
Example: Sodium (Na) is highly metallic, but chlorine (Cl) is non-metallic.
Simple and Understandable Answer:
- Metals give away electrons easily, but non-metals do not.
- As nuclear charge increases, losing electrons becomes harder.
- So, metallic nature decreases from left to right in a period.
Example: Sodium (Na) is a metal, but chlorine (Cl) is a non-metal because it does not lose electrons easily.
Write scientific reason: Atomic radius goes on increasing down a group.
Scientific and Written Exam Answer:
The atomic radius increases as we move down a group due to the following reasons:
- As we move down a group, a new electron shell is added, increasing the size of the atom.
- The nuclear charge increases, but the effect of electron shielding reduces the attraction between the nucleus and outer electrons.
- Since the outer electrons experience less pull from the nucleus, the atomic size increases.
Example: Lithium (Li) has a smaller atomic radius than Cesium (Cs) in Group 1.
Simple and Understandable Answer:
- Every time we move down a group, a new electron shell is added.
- The inner electrons shield the outer electrons from the nucleus.
- This makes the atom bigger, so the atomic radius increases.
Example: Lithium (Li) is smaller than Potassium (K) in Group 1.
Write scientific reason: Elements belonging to the same group have the same valency.
Scientific and Written Exam Answer:
Elements in the same group have the same valency due to the following reasons:
- Valency depends on the number of valence electrons present in the outermost shell of an atom.
- All elements in a group have the same number of valence electrons, leading to the same combining capacity (valency).
- For example, all Group 1 elements (Li, Na, K) have 1 valence electron, so their valency is 1.
Simple and Understandable Answer:
- Elements in the same group have the same number of electrons in their last shell.
- Since valency depends on these electrons, all elements in a group have the same valency.
Example: Sodium (Na) and Potassium (K) both belong to Group 1 and have valency = 1.
Write scientific reason: The third period contains only eight elements even though the electron capacity of the third shell is 18.
Scientific and Written Exam Answer:
The third period contains only 8 elements due to the following reasons:
- According to the Aufbau principle, electrons are filled in increasing order of energy levels.
- The third shell (M-shell) can hold 18 electrons, but the 4s orbital has lower energy than the 3d orbital.
- After filling the 3s and 3p orbitals (total 8 electrons), electrons go into the 4s orbital instead of 3d.
- Hence, the third period has only 8 elements before the fourth period starts.
Simple and Understandable Answer:
- The third shell can hold up to 18 electrons, but electrons do not follow a simple rule.
- Instead of filling all 18 spaces, electrons move to the next energy level earlier.
- Because of this, the third period contains only 8 elements.
Example: The third period starts with Sodium (Na) and ends with Argon (Ar), containing 8 elements.
Write the name from the description: The period with electrons in the shells K, L, and M.
Answer:
The third period has electrons in the shells K, L, and M.
Write the name from the description: The group with valency zero.
Answer:
The Noble Gases (Group 18) have a valency of zero.
Write the name from the description: The family of nonmetals having valency one.
Answer:
The Halogens (Group 17) are nonmetals with a valency of one.
Write the name from the description: The family of metals having valency one.
Answer:
The Alkali Metals (Group 1) have a valency of one.
Write the name from the description: The family of metals having valency two.
Answer:
The Alkaline Earth Metals (Group 2) have a valency of two.
Write the name from the description: The metalloids in the second and third periods.
Answer:
The metalloids in the second and third periods are Boron (B) and Silicon (Si).
Write the name from the description: Nonmetals in the third period.
Answer:
The nonmetals in the third period are Phosphorus (P), Sulfur (S), and Chlorine (Cl).
Write the name from the description: Two elements having valency 4.
Answer:
The elements with a valency of 4 are Carbon (C) and Silicon (Si).