Maharashtra State Board Science-1-Chapter-2-Periodic Classification of Elements-Can You Tell? : In the realm of chemistry, the Periodic Table stands as a foundational pillar, organizing elements into a systematic framework that reveals their unique properties and behaviors. Studied by students worldwide, this arrangement of elements sheds light on the building blocks of matter and their intricate relationships.
Class 10 textbooks delve into the Periodic Table’s structure, its historical development, and the fundamental principles guiding its organization. Let’s explore this essential topic and unravel the mysteries of elements and their periodic patterns.
Identify Dobereiner’s triads from the following groups of elements having similar chemical properties.
1. Mg (24.3), Ca (40.1), Sr (87.6)
Dobereiner’s triads were a set of groups of three elements that exhibited similar chemical properties. Each triad had one element with properties that were roughly the average of the other two. The elements Mg (Magnesium), Ca (Calcium), and Sr (Strontium) form one of Dobereiner’s triads.
Here’s how they fit into a triad:
- Magnesium (Mg) – Atomic mass: 24.3
- Calcium (Ca) – Atomic mass: 40.1
- Strontium (Sr) – Atomic mass: 87.6
In this triad:
- Magnesium (Mg) has an atomic mass close to the average of Calcium (Ca) and Strontium (Sr).
- Calcium (Ca) and Strontium (Sr) exhibit similar chemical properties, with Strontium (Sr) being slightly heavier and having properties closer to the average of the three.
Dobereiner’s triads were an early attempt to classify elements based on their chemical properties and atomic masses. While this classification method has been superseded by the modern periodic table, the idea of grouping elements with similar properties based on their atomic masses was an important step in the development of the periodic law.
2. S (32.1), Se (79.0), Te (127.6)
The elements Sulfur (S), Selenium (Se), and Tellurium (Te) form another example of Dobereiner’s triads. Here’s how they fit into a triad:
- Sulfur (S) – Atomic mass: 32.1
- Selenium (Se) – Atomic mass: 79.0
- Tellurium (Te) – Atomic mass: 127.6
In this triad:
- Sulfur (S) has properties that are roughly the average of Selenium (Se) and Tellurium (Te).
- Selenium (Se) and Tellurium (Te) exhibit similar chemical properties, with Tellurium (Te) being heavier and having properties closer to the average of the three.
Dobereiner’s triads were based on the concept that elements with similar chemical properties could be grouped together, and one element in each triad would have properties that were approximately the average of the other two. While not all elements fit neatly into triads, the concept contributed to the development of the periodic table and our understanding of periodic trends in elemental properties.
3. Be (9.0), Mg (24.3), Ca (40.1)
Beryllium (Be), Magnesium (Mg), and Calcium (Ca) form another example of Dobereiner’s triads. Here’s how they fit into a triad:
- Beryllium (Be) – Atomic mass: 9.0
- Magnesium (Mg) – Atomic mass: 24.3
- Calcium (Ca) – Atomic mass: 40.1
In this triad:
- Beryllium (Be) has properties that are roughly the average of Magnesium (Mg) and Calcium (Ca).
- Magnesium (Mg) and Calcium (Ca) exhibit similar chemical properties, with Calcium (Ca) being heavier and having properties closer to the average of the three.
Dobereiner’s triads were based on the observation that certain groups of three elements had similar chemical properties, with one element in each triad having properties that were approximately the average of the other two. This concept was a precursor to the modern periodic table, which organizes elements based on atomic number and periodic trends rather than just atomic mass and chemical properties.
Go through the modern periodic table (table no. 2.7) and write the names one below the other of the elements of group 1.
In the modern periodic table, elements of Group 1 are known as the alkali metals. Here are the names of the elements of Group 1, listed one below the other:
- Hydrogen (H)
- Lithium (Li)
- Sodium (Na)
- Potassium (K)
- Rubidium (Rb)
- Cesium (Cs)
- Francium (Fr)
These elements are placed in Group 1 because they all have one valence electron in their outermost shell, which gives them similar chemical properties. They are highly reactive metals and are typically found in nature combined with other elements rather than in their pure metallic form.
Write the electronic configuration of the first four elements in this group.
Certainly! Here are the electronic configurations of the first four elements in Group 1 (alkali metals) in the format of electron distribution across shells:
- Hydrogen (H) – Atomic number 1
- Electronic configuration: 1
- Lithium (Li) – Atomic number 3
- Electronic configuration: 2,1
- Sodium (Na) – Atomic number 11
- Electronic configuration: 2,8,1
- Potassium (K) – Atomic number 19
- Electronic configuration: 2,8,8,1
In this format:
- The numbers indicate the distribution of electrons in each shell.
- For example, “2,8,8,1” for Potassium (K) means:
- 2 electrons in the first shell (K shell),
- 8 electrons in the second shell (L shell),
- 8 electrons in the third shell (M shell),
- 1 electron in the fourth shell (N shell).
This format helps in visualizing how electrons fill the shells as we move down the Group 1 elements, showing the gradual filling of outer electron shells which determines their chemical properties.
Which similarity do you find in their configuration?
One key similarity found in the electronic configurations of Group 1 elements (alkali metals) is the presence of a single electron in their outermost shell (valence shell). Specifically:
- Hydrogen (H): 1 electron in its 1st shell (valence shell).
- Lithium (Li): 1 electron in its 2nd shell (valence shell).
- Sodium (Na): 1 electron in its 3rd shell (valence shell).
- Potassium (K): 1 electron in its 4th shell (valence shell).
This single electron in the outermost shell is responsible for the similar chemical properties observed among the alkali metals. It makes them highly reactive and eager to lose that single electron to achieve a stable electron configuration (usually achieving a noble gas configuration similar to the nearest noble gas element in the periodic table).
Due to this similarity in their valence electron configuration (having 1 valence electron), Group 1 elements exhibit similar trends in reactivity, metallic properties, and the formation of compounds, making them a distinct and cohesive group in the periodic table.
How many valence electrons are there in each of these elements?
In Group 1 (alkali metals), each element has 1 valence electron. Here’s how many valence electrons each of these elements has:
- Hydrogen (H) – 1 valence electron
- Electronic configuration: 1
- Lithium (Li) – 1 valence electron
- Electronic configuration: 2,1
- Sodium (Na) – 1 valence electron
- Electronic configuration: 2,8,1
- Potassium (K) – 1 valence electron
- Electronic configuration: 2,8,8,1
Valence electrons are the electrons in the outermost shell (valence shell) of an atom. In the case of alkali metals (Group 1), they have 1 electron in their outermost shell, which determines their similar chemical properties, such as high reactivity and tendency to lose that single valence electron to achieve a stable configuration.
On going through the modern periodic table it is seen that the elements Li, Be, B, C, N, O, F and Ne belong to the period-2. Write down electronic configuration of all of them.
- Electronic configuration of elements in period 2 (Li to Ne), in the format 2,8,8…:
- Lithium (Li) – Atomic number 3
- Electronic configuration: 2,1
- Beryllium (Be) – Atomic number 4
- Electronic configuration: 2,2
- Boron (B) – Atomic number 5
- Electronic configuration: 2,3
- Carbon (C) – Atomic number 6
- Electronic configuration: 2,4
- Nitrogen (N) – Atomic number 7
- Electronic configuration: 2,5
- Oxygen (O) – Atomic number 8
- Electronic configuration: 2,6
- Fluorine (F) – Atomic number 9
- Electronic configuration: 2,7
- Neon (Ne) – Atomic number 10
- Electronic configuration: 2,8
Is the number of valence electrons same for all these elements?
- Number of valence electrons:
- Lithium (Li): 1 valence electron
- Beryllium (Be): 2 valence electrons
- Boron (B): 3 valence electrons
- Carbon (C): 4 valence electrons
- Nitrogen (N): 5 valence electrons
- Oxygen (O): 6 valence electrons
- Fluorine (F): 7 valence electrons
- Neon (Ne): 8 valence electrons The number of valence electrons corresponds to the number of electrons in the outermost shell (L shell) for each element.
Is the number of shells the same in these ?
- Number of shells:
- For all these elements (Li to Ne) in period 2, the number of shells is the same, which is 2.
- The first shell (K shell) is always fully filled with 2 electrons (2, as per the format), and the second shell (L shell) contains the remaining electrons according to each element’s atomic number.
These elements exhibit a gradual filling of electrons in their shells as we move across period 2 of the periodic table, showcasing the periodicity of electron configuration and chemical properties.