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Our PDF notes for Class 9 Punjab Textbook Board Chemistry, Chapter 8: Chemical Reactivity, are here.
These notes cover topic-wise all the Important long questions and short questions. Also, they contain topic-wise possible MCQs and easy-to-learn solved test yourself. Besides these, solved exercise and solved numerical problems of the chapter are also present in the notes.
Chemical Reactivity: The Dynamics of Molecular Interactions
Chemical reactivity refers to the ability of substances to undergo chemical reactions and form new compounds. It encompasses various factors such as bond strength, electron configuration, and environmental conditions.
Understanding chemical reactivity is crucial for predicting and controlling the outcome of chemical reactions in diverse contexts.
Non-Metals and Their Position in the Periodic Table
Non-metals occupy the upper right portion of the periodic table and exhibit diverse physical and chemical properties.
They typically have high electronegativity and tend to gain or share electrons in chemical reactions. Non-metals include elements such as hydrogen, carbon, nitrogen, oxygen, and the noble gases.
Metals
Metals are elements characterized by their lustrous appearance, malleability, ductility, and excellent conductivity of heat and electricity.
They are categorized based on their position in the periodic table, with alkali metals, alkaline earth metals, transition metals, and lanthanides and actinides being the major groups.
Metals exhibit a wide range of physical and chemical properties, including high melting and boiling points, ability to form alloys, and reactivity with acids and other substances.
Electropositive Character
Electropositive character refers to the tendency of an atom to donate or lose electrons in a chemical reaction, resulting in the formation of positively charged ions, known as cations.
This characteristic is crucial in understanding the behavior of elements in various chemical reactions, especially those involving the transfer of electrons.
Trends of Electropositivity in the Periodic Table
Across Periods (Left to Right):
As one moves from left to right across a period in the periodic table, the electropositive character of elements generally decreases.
This trend is primarily due to the increasing effective nuclear charge experienced by the outermost electrons as the number of protons in the nucleus increases.
With the increased nuclear charge, the attraction for the valence electrons becomes stronger, making it more difficult for the atoms to lose electrons and exhibit electropositive behavior.
Down the Groups (Top to Bottom):
In contrast to the trend across periods, the electropositive character of elements generally increases as one moves down a group in the periodic table.
This trend can be attributed to the increasing atomic size and decreasing effective nuclear charge experienced by the outermost electrons as one descends the group.
The outermost electrons are farther from the nucleus in larger atoms, leading to weaker attraction between the nucleus and the valence electrons. As a result, these electrons are more easily lost, promoting electropositive behavior.
Electropositivity and Ionization Energy
- Electropositivity has inverse relation to ionization energy. Ionization energy is the energy required to remove an electron from an atom or ion.
- Elements with low ionization energies tend to exhibit high electropositivity because their valence electrons are more easily removed, leading to the formation of cations.
Practical Implications
- Understanding the trend of electropositivity in the periodic table is essential in predicting the behavior of elements in chemical reactions, especially those involving the formation of ionic compounds.
- Metals, which are located on the left side of the periodic table, generally exhibit high electropositivity and tend to lose electrons to form cations.
- The trend of electropositivity also influences the reactivity of elements and their ability to participate in redox reaction
Electropositivity and Ionization Energy
Electropositivity is inversely related to ionization energy, which is the energy required to remove an electron from an atom or ion. Elements with low ionization energies tend to be more electropositive and readily form positive ions.
Comparison of Reactivities of Alkali and Alkaline Earth Metals
| Property | Alkali Metals | Alkaline Earth Metals |
|---|---|---|
| Electropositivity | Highly electropositive | Moderately electropositive |
| Reactivity with Water | React vigorously with water, forming alkaline solutions | React less vigorously with water, also forming alkaline solutions |
| Reaction with Oxygen | React with oxygen to form oxides | React with oxygen to form oxides and peroxides |
Electronegative Characteristics of Non-Metals
Non-metals exhibit high electronegativity, meaning they have a strong tendency to attract electrons in chemical bonds.
They often form covalent bonds by sharing electrons with other non-metal atoms. Examples of non-metals include fluorine, chlorine, oxygen, nitrogen, sulfur, and iodine.
Trend of Electronegativity in the Periodic Table
Electronegativity tends to increase from left to right across a period and decrease from top to bottom down a group in the periodic table.
Fluorine, the most electronegative element. It occupies the upper right corner of the periodic table. While, francium the least electronegative element, resides in the lower left corner.
Comparison of Reactivities of the Halogens
Halogens represent a group of non-metal elements in the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
Each halogen exhibits distinct chemical properties and reactivity levels, which can be attributed to their electronic configurations and atomic structures.
Fluorine (F)
Fluorine is the most reactive halogen and one of the most reactive elements overall.
It readily reacts with almost all other elements, including noble gases, forming a wide range of compounds.
Fluorine’s high reactivity is due to its small atomic size and strong electronegativity. It allows it to attract electrons from other elements with great force.
Chlorine (Cl):
Chlorine is the second most reactive halogen after fluorine.
We commonlu use it as a disinfectant and bleaching agent due to its ability to oxidize organic compounds.
Chlorine reacts vigorously with metals to form metal chlorides and can undergo substitution reactions with organic compounds.
Bromine (Br)
Bromine is less reactive than chlorine and fluorine but more reactive than iodine.
It is a volatile liquid at room temperature and readily forms bromides with metals.
Bromine’s reactivity increases with temperature and in the presence of a catalyst.
Iodine (I)
Iodine is the least reactive halogen under standard conditions.
It exists as a solid at room temperature and forms dark purple vapors when heated.
Iodine reacts slowly with metals to form metal iodides and undergoes substitution reactions with organic compounds.
Astatine (At)
Astatine is a radioactive element and the rarest naturally occurring halogen.
Its reactivity is similar to iodine, although its scarcity and radioactive nature limit experimental studies.
Factors Influencing Reactivity
- Atomic Size: Generally, as atomic size increases down the group, reactivity decreases.
- Electronegativity: Fluorine, being the most electronegative element, exhibits the highest reactivity among the halogens.
- Bond Strength: Halogens tend to become less reactive as the bond strength between halogen atoms increases down the group.
Applications
- Halogens find various applications in industry, medicine, and everyday life. We use Chlorine is in water purification, bromine in flame retardants, and iodine in antiseptics.
- We use Fluorine compounds in toothpaste, non-stick coatings, and refrigerants.
Conclusion
In conclusion, Chapter 8 – Chemical Reactivity offers a comprehensive exploration of the dynamic interactions between elements and compounds. By understanding the properties and behaviors of metals, non-metals, and halogens, as well as the trends of electropositivity and electronegativity in the periodic table, students gain valuable insights into the fundamental principles governing chemical reactivity.