Chemistry Class 9 Chapter 8 Important Questions Answers 2023
Chemistry Class 9
Chapter 8 Chemical Reactivity
Write a note on the physical and chemical characteristics of metals.
Except for hydrogen, metals are electropositive elements that lose electrons to produce cations. Metals can be grouped.
a. Potassium, sodium, calcium, magnesium, and aluminum are all highly reactive.
b. Lead, tin, zinc, and iron are moderately reactive metals.
c. Copper, mercury, silver, and gold are the least reactive or noble metals.
Physical Characteristics Of Metals
The following is a list of significant physical features of metals:
I. The majority of metals are solids (except mercury)
ii. Their melting and boiling points are high (except alkali metals)
iii. They can be polished and have a metallic gloss.
iv. They emit sound when struck, are ductile (can be pulled into wires), and are malleable (can be hammered into sheets).
v. They are effective heat and electricity conductors.
vi. They have high density
vii. They are very hard (except sodium and potassium
Chemical Characteristics of Metals
Metals have the following crucial chemical characteristics:
- They readily lose electrons and create positive ions.
ii. They easily transform into basic oxides when exposed to oxygen.
iii. They frequently combine with non-metals to generate ionic compounds.
iv. They possess metallic bonding.
What is the electropositive character of metals?
Metals frequently experience valence electron loss. Electro positivity or metallic character are terms used to describe this characteristic of metals. A metal is said to be electropositive if its electrons can be lost more readily. The quantity of electrons lost by a given atom a metal’s valency is referred to. A sodium atom, for instance, can lose 1 electron to create a positive ion.
Na → Na+ + 1e-
Therefore, sodium metal has a valency of 1.
The valence shell of zinc metal can also lose two electrons. Its valency is therefore 2.
Zn → Zn+2 + 2e–
Trends Of Electropositivity
As atom sizes grow down the group, electropositive character increases. Lithium metal, for instance, has a lower electropositive value than sodium, which in turn has a lower electropositive value than potassium.
Because atomic diameters or size drop as nuclear charge increases, electropositive character diminishes over the period from left to right in the periodic table. It denotes that elements are more metallic at the beginning of a period. As we go from left to right along the period, this character gets smaller
What is the relationship between ionization energy and electropositivity.
Ionization Energy And Electropositivity
The ionization energy, which in turn depends on the atom’s size and nuclear charge, determines how electropositive an object is. High nuclear charge in small atoms results in high ionization energy. In this manner, highly ionized atoms have less metallic or electropositive energy. Alkali metals have the highest size and lowest ionization energy in their respective periods because of this. They, therefore, possess the most metallic character
Magnesium has a high first ionization energy, but it also has a very high second ionization energy. As nuclear charge aggressively pulls the remaining electrons, it becomes highly challenging to extract the second electron from the Mg+ ion. In light of this Ion attraction shrinks in size.
Write a comparative analysis of the reactivities of group 1 and group 2 elements.
Groups 1 and 2 of the periodic table’s elements are referred to as “Alkali” and “Alkaline Earth” metals, respectively. Alkali metals’ ns1 valence shell electronic configuration makes them highly reactive substances. As it stands they have just one electron in their valence shell, making it easily attainable. They always appear in nature as cations in the +1 oxidation state because of this. As a result, they easily combine with non-metals to generate salts.
Smaller and more nuclear-charged than other metals, known as alkaline earth metals. They have valence shells with two electrons or ns2. Although less so than alkali metals, they are comparatively less reactive.
1. Given their ease of oxidation, the metals near the top of the reactivity range are effective reducing agents. These metals corrode and discolor quite quickly.
2. While moving down the series, the metals’ reducing power becomes weaker.
3. While descending the metal reactivity series, the electro-positive of the elements similarly decreases.
4. When interacting with diluted HCl or diluted H2SO4, all metals above hydrogen in the activity series release H2 gas.
5. Higher metals on the reactivity scale have the power to remove lesser metals from salt solutions and replace them with higher metals.
6. In order to separate higher-ranking metals from ores and other compounds, more energy is needed.
What is the ionization energy of alkali and alkaline earth metals?
The amount of energy required to remove the outermost electron from an atom to form a gaseous cation is known as ionization energy.
In the corresponding times, alkali metals have the lowest ionization enthalpies. Their huge atomic sizes are the source of this. Additionally, they easily lose their only valence electron because, after losing it, they transition into a stable noble gas form.
In comparison to alkali metals, alkaline earth metals have smaller atomic sizes and a larger effective nuclear charge. Their initial ionization enthalpies are higher as a result than those of alkali metals. However, compared to the comparable alkali metals, their second ionization enthalpy is lower. This is because alkali metals obtain a highly stable noble gas structure after losing one electron.
Write a note on the reactivity of alkali and alkaline earth metals.
Reactivity Of Alkali Metals
At higher temperatures, hydrogen reacts with alkali metals to produce metallic hydrides. Hydrides ions are created by metallic hydrides
2M + H2 → 2MH → M+ + H–
Alkali metals react with the oxygen in the air and lose their lustrous appearance. Oxygen and alkali’s combine to burn, forming oxides. However, the nature of the produced oxides differs.
They contain oxygen in a distinct oxidation state. Smaller Lithium atoms produce a typical oxide, whereas larger atoms of sodium produce peroxides and superoxides.
4 Li + O2 → 2Li2O (Oxidation Number of Oxygen= -2)
2 Na + O2 → Na2O (Oxidation Number of Oxygen= -1)
K /Rb /Ce + O2 → (K/ Rb / Ce) O2 (Oxidation Number of Oxygen= -1/2
Reactivity Of Alkaline Earth Metals
Hydrogen does not immediately react with beryllium. By reducing beryllium chloride with lithium aluminum hydride, one can create beryllium hydride
2BeCl2 + LiAlH4 → 2BeH2 + LiCl + AlCl3
Only over 600°C does beryllium react with oxygen. Barium produces peroxides whereas magnesium, strontium, and oxygen burn to produce oxides.
The other oxides are ionic, whereas BeO and MgO are more covalent. While most oxides are basic and magnesium oxide and calcium oxide are slightly basic, beryllium oxide is amphoteric.
Write down the uses of sodium, magnesium and calcium.
i. Nuclear reactors use a sodium-potassium alloy as a coolant.
ii. In sodium vapour lamps, it is utilized to provide yellow light.
iii. It serves as a reducing agent when metals like Ti are extracted.
i. Flashlights and fireworks both include magnesium.
ii. It is employed in the production of lightweight alloys.
iii. Thermite process is used to ignite aluminum using a magnesium ribbon.
iv. Magnesium is used as an anode to stop corrosion.
i. Sulphur is taken out of petroleum products using this method.
ii. Cr, U, and Zr are produced using it as a reducing agent.
Write a note on the inertness of noble metals.
Inertness of Noble Metals
Transition metals, often known as d-group elements, are a category of metals made up of elements whose d-orbitals are currently filling. They display several different oxidation states. The transitional elements are divided into three series, each of which has ten elements.
Silver is a shiny, white metal. It is a very good heat and electrical conductor.
Additionally, the metal is quite malleable and ductile. Its smooth surfaces serve as effective light reflectors. It becomes largely inert when a thin oxide or sulfide layer forms on its surface. Air has no impact on silver under typical atmospheric circumstances. In the presence of substances like H2S that contain sulphur, it tarnishes.
It is rarely used as such because it is a very soft metal. Coins, silverware, and ornaments are frequently made with alloys of silver and copper. Silver compounds are frequently utilized in dental pastes and photographic films. Important uses for silver can be found in the mirror business.
Gold is a yellow soft metal. It is the most malleable and ductile of all the metals. One gm of gold can be shaped into a wire of 1.5km. Gold is an extremely nonreactive or inert metal. It isn’t affected by atmosphere. It is not even affected by any mineral acid or base.
Because of its noble behavior in the atmosphere, it is an ornamental metal as well as used in making coins. Gold is too soft to be used as such. It is always alloyed with copper, silver or some other metal.
Due to its distinct qualities, including color, beauty, strength, flexibility, and resistance to tarnish, platinum is used to create jewelry. It gives diamonds and other gemstones a safe setting, boosting their brilliance.
In cars, a catalytic converter made of an alloy of platinum, palladium, and rhodium serves as the catalyst. Most of the poisonous gases (CO, NO) released by two vehicles are transformed into less dangerous carbon dioxide, nitrogen, and water vapor.
Hard disk drive coatings and fiber optic cables are both made using platinum. Fiberglass-reinforced plastic and glass for liquid crystal displays are made with platinum (LCD).
Write a note on the physical and chemical characteristics of non-metals.
By acquiring electrons, non-metals can produce negative ions called anions. Non-metals are electronegative by nature and produce acidic oxides in this fashion. Some non-metals valency is dependent on how many electrons they can accept. For instance, the chlorine atom has a valency of 1, as it can only receive one electron into its outermost shell.
Cl + 1e→Cl-1
The atom’s electron affinity and electronegativity determine how non-metallic it is. Electronegative elements are small in size and have a strong nuclear charge. They have a strong affinity for electrons. Consequently, they have a nonmetallic character. As a result, the non-metallic character grows from left to right up to halogens and declines in a group downward. The least metallic element is fluorine.
Therefore, the non-metals are elements :
(Carbon), (Nitrogen and Phosphorus), (Oxygen, Sulfur, and Selenium), and (Halogens, including Fluorine, Chlorine, Bromine, and Iodine).
A collection of non-metals physical characteristics gradually but distinctively change over time. All three of the physical states of matter typically contain nonmetals.
While other non-metals are either liquids or solids, the non-metals at the top of the group are typically gases.
(1) Solid nonmetals are brittle (break easily).
ii. Non-metals are poor heat- and electricity-conductors (except graphite).
iii. Except for iodine, they are drab and not glossy (it is lustrous like metals).
iv. They are typically supple (except diamond).
v. Their melting and boiling points are low (except silicon, graphite and diamond).
vi. They are not very dense.
i. Because they lack electrons in their valence shells, they are willing to take them in order to complete their valence shells and stabilize them.
ii. They react with other non-metals, such as CO, NO, etc., to produce covalent compounds and ionic compounds with metals.
iii. Non-metals and water often do not interact.
iv. Because non-metals are themselves electron acceptors, they do not react with diluted acids.
Write a note on the electronegativity of non-metals.
Electronegativity is the propensity of an atom in a molecule to pull the shared pair of electrons toward itself.
The value of electronegativity increases across a period in the contemporary periodic table as we move from left to right because atomic number increases and atomic size decreases.
As we travel down the group in the current periodic table, the atomic number rises.The nuclear charge consequently rises, and the effect of the rise is mitigated by the addition of one shell. As we descend the group, electronegativity’s value drops. For instance, in the halogen group, the electronegativity value falls as we proceed from fluorine to astatine.
A general observation is that metals exhibit lower electronegativity values than non-metals. As a result, the nature of metals and non-metals is electropositive and electronegative, respectively. Due to their extremely small size and relatively greater electronegativity values, the elements in period two have different properties from the elements in their respective groups.
Describe the reactivity of halogens.
Reactivity Of Halogens
Group 7 elements are less reactive as you move down the group. When non-metal atoms interact with metals, they gain electrons. One electron is added to the outer shell of a halogen atom during a reaction to create a single, negatively charged ion.
An extra electron shell is added as we move down the group, increasing the atom’s atomic radius. As we descend the group, the outer shell electrons become farther away from the nucleus and the nucleus-electron attraction force gets less and weaker. It is more difficult to obtain an electron because of the weaker pull in the larger atoms. As a result, the atom’s capacity to draw electrons into its outermost shell declines.
The only periodic table group with elements in all three of the recognized states of matter at standard pressure and temperature is the group of halogens.
- Fluorine (F) is a colorless gas.
- Chlorine (Cl) is a bluish-green gas.
- The liquid form of bromine (Br) is dark red.
- Iodine (I) is a black substance that transforms into a purple vapour when heated.
- A dark solid called astatine (At)
- The halogens all have a powerful and frequently unpleasant odor.
- Halogen substances are quite harmful.
- Ineffective heat and electricity conductors
- Decreased melting and boiling points
Reaction with Hydrogen
When halogens and hydrogen react, binary compounds like these are created. Usually, when fluorine, chlorine, and bromine are combined, the reaction takes the form shown below.
H2 + X2 → 2HX
When dissolved in water, hydrogen halides produce potent hydrohalic acids (commonly termed as Hydrogen Halides). These acids pose a risk.
The bond strength of hydrogen halides determines how acidic they are. The HF bond is stronger and the HI bond is weaker As a result, HF is the weakest acid and HI is the strongest acid
Reactivity Of Fluorine
Fluorine has a high electron affinity, which means that its ability to receive electrons depends on its electron gain enthalpy because if it reduces readily itself, it has a high electron affinity and is a powerful oxidizer.
F2 + 2KCl → 2KF+ Cl2
F2+ 2KBr → 2KF + Br2
F2 + 2NaI → 2NaF + I2
Iodine cannot oxidize any hydrogen atom.
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