Group Properties and Elements

Ans. As we go down Group 1 of the periodic table, alkali metals become easier to cut because their atomic size increases. This means the outermost electron is farther away from the nucleus and experiences less attraction. Additionally, the inner electrons shield the outer electron, making it easier to remove. These factors weaken the metallic bonds, allowing the metals to be cut more easily.

Ans. Potassium reacts vigorously with halogens to form potassium halides.

Reaction with Chlorine (Cl₂):
When potassium reacts with chlorine gas, the reaction is highly exothermic and produces potassium chloride (KCl).

2 K_(s) + Cl₂_(g) ⟶ 2 KCl_(s)

Reaction with Bromine (Br₂):
Similarly, when potassium reacts with bromine, it forms potassium bromide (KBr).

2 K_(s) + Br₂_(ℓ) ⟶ 2 KBr_(s)

In both reactions, potassium donates its outer electron to the halogen, resulting in the formation of ionic compounds.

Ans. Cl₂_(aq) + 2NaBr_(aq) ⟶ 2NaCl_(aq) + Br₂_(g)

According to this equation chlorine does not act as reducing agent;

Cl₂_(aq) + 2NaBr_(aq) ⟶ 2NaCl_(aq) + Br₂_(g)

Chlorine (Cl₂) is act as a oxidizing agent because it is being reduced to chloride ions(Cl⁻) while causing bromide ions (Br⁻) to be oxidized to bromine (Br₂).

To identify the oxidizing agent, we look for the species that is being reduced. In this case, the bromide ions (Br⁻) are oxidized to bromine (Br₂). Therefore, the reducing agent in this reaction is the bromide ion (Br⁻), as it is losing electrons.

Ans. Iodine exists in the solid state at room temperature due to its molecular structure and the type of intermolecular forces present.

Iodine (I₂) consists of diatomic molecules held together by intermolecular forces. These forces are relatively weak, but as the size of the iodine molecules increases, the strength of these forces also increases.

At room temperature, the energy is not sufficient to overcome these intermolecular forces, which keeps iodine in the solid state. Additionally, iodine has a relatively high molecular mass as compared to other halogens, which contributes to its solid state at room temperature.

Ans. Nickel (Ni) catalyzes the hydrogenation of oils by providing a surface for the reaction. It helps to absorb both the unsaturated oil and hydrogen gas.

Vegetable Oil + H₂ ⟶ Margarine

The nickel breaks the H-H bond in hydrogen, creating reactive hydrogen atoms. These atoms then add to the double bonds in the oil, converting them to single bonds. Finally, the saturated fats are released, allowing nickel to be reused.

Ans. Reaction of alkali metals with oxygen becomes more vigorous as we go down the group.

4Li + O₂ —Heat→ 2Li₂O

4Na + O₂ —Vigorous reaction→ 2Na₂O

4K + O₂ —Vigorous reaction→ 2K₂O

Ans. Halogens, which include fluorine, chlorine, bromine, and iodine, react with water in different ways depending on their position in the periodic table.

Fluorine (F₂):
Fluorine is highly reactive and can react explosively with water. The reaction produces hydrofluoric acid and oxygen.

2 F₂ + 2 H₂O —Dark and cold→ 4 HF + O₂

Chlorine (Cl₂):
Chlorine reacts with water to form hydrochloric acid and hypochlorous acid. This reaction is less violent than that of fluorine.

Cl₂ + H₂O —Sunlight→ HCl + HOCl

Bromine (Br₂):
Bromine also reacts with water, but the reaction is less vigorous than that of chlorine. It produces hydrobromic acid and hypobromous acid.

Br₂ + H₂O —Heat→ HBr + HOBr

Iodine (I₂):
Iodine does not react with water under the conditions of temperature and catalyst.

I₂ + H₂O —Heat→ No Reaction

Ans. Tensile strength refers to the maximum amount of tensile (pulling) stress that a material can withstand before breaking or deforming. When we say that transition metals have high tensile strength, it means that these metals can endure a significant amount of stretching or pulling forces without breaking.

This property is primarily due to the strong metallic bonds present in transition metals. Transition metals are not only strong but also ductile, meaning they can be stretched into wires without breaking.

Ans. All the elements present in group 1 have ns¹ configuration in their outer shells. They are also called alkali metals. This single electron can be removed easily which makes these metals very reactive except the first element hydrogen which is a gas and a non-metal.

Ans. Li, Na and K are lighter than water but rubidium sinks in water. Cesium explodes on contact with water, possibly shattering the container.

Ans. When we move from top to bottom in group, the atomic size increases and nuclear charge decreases. Owing to this, it becomes easier for elements to lose electron down the group which is reflected in the increased reactivities of the lower members of the group.

Ans. Lithium reacts with water steadily giving hydrogen and lithium hydroxide. Sodium reacts vigorously while potassium reacts violently with water giving their respective water soluble hydroxides.

Li_(s) + H₂O_(ℓ) ⟶ LiOH_(aq) + H₂_(g)
Na_(s) + H₂O_(ℓ) ⟶ NaOH_(aq) + H₂_(g)
2K_(s) + H₂O_(ℓ) ⟶ KOH_(aq) + H₂_(g)

Ans. Reaction of alkali metals with chlorine becomes more vigorous as we go down the group.

2Li_(s) + Cl₂_(g) —Heat→ 2LiCl_(s)
2Na_(s) + Cl₂_(g) —Heat, Vigorous reaction→ 2NaCl_(s)
2K_(s) + Cl₂_(g) —Heat, Violent reaction→ 2KCl_(s)

Ans. Increase in the atomic size down the group also weakens the interatomic attraction of the atomic metals. This fact makes alkali metals softer down the group and their melting points decrease.

Ans. As we go down the first group, both the size and volume of the atoms increase as the number of electrons and protons increases. But the increase in mass of the elements is greater than the increase in volume; so the density which is defined as the mass per unit volume increases gradually down the group.

e.g:

Ans. It is the addition of chlorine solution in water. Chlorine kills bacteria and other microorganisms. Chlorine itself does not kill microorganisms. Chlorine itself does not kill rather it dissociate in water to from hypochlorous acid (HOCl) and hydrochloric acid (HCl).

Cl₂_(g) + H₂O_(ℓ) ⟶ HOCl_(aq) + Cl⁻ + H⁺_(aq)

HOCl further ionizes to produces hypochlorite and proton.

HOCl_(aq) ⟶ OCl⁻_(aq) + H⁺_(aq)

So, swimming people are cleaned by chlorination. Both the products: HOCl and OCl⁻ kill bacteria and microorganisms.

Ans. All the elements in the group 17 have seven electrons in their outermost shells (ns²np⁵). They are electronegative non-metals because they have strong tendency to accept one electron to become an anion. They exist as diatomic molecules and behave as very reactive non-metals. They are also called halogens (salt forming elements)

Ans. Melting and boiling points of halogens increase when you go down the group. This is because the atoms get larger as they have more electrons. Because of their larger size they experience stronger intermolecular forces between molecules. Because of this, they require more heat energy to overcome their intermolecular forces and so their melting and boiling points are increased.

Ans. Unlike metals, the reactivity of halogens decreases from top to bottom in the group. This is due to the fact that atomic size increases down the group and tendency to accept electron from other atoms decreases making them less reactive.

Ans. The attractive forces present between the halogen molecules increase down the group so as we go down the group the halogens become more dense.

Ans. Metal halides are formed when halogens react directly with alkali and alkaline earth metals. Metal halides behave usually as ionic compounds. e.g.

2Na + Cl₂ ⟶ 2NaCl_(s)

Ans. Oxidation is a process in which an electron is lost. The substance which loses an electron is called a reducing agent.

Na_(s) ⟶ Na⁺ + e⁻

Ans. Reduction is a process in which an electron is gained and the substance which accepts the electron is called oxidizing agent.

Cl₂ + 2e ⟶ 2Cl⁻

Ans. Bond length between hydrogen and halogen increases down the group because as the halogen atom gets bigger the bonding pairs of electron get further away from the halogen nucleus. The bond between hydrogen and halogen therefore gets weaker. The weaker the bond, the less heat energy it will need to break it. Hence the thermal stability of hydrogen halides decreases down the group.

HF > HCl > HBr > HI

Ans. Elements present at the center of the modern periodic table from group 3 to group 12 are called d block elements or transition elements.

Ans. It means that transition metals can with stand high levels of stress before breaking.

Ans. All transition elements are metals having the similar properties:

i. Transition elements are often hard with higher densities.
ii. Their melting and boiling points are also high.
iii. These metals show variable oxidation states.
iv. The compounds they form are often coloured.
v. They are malleable and ductile.

Ans. A transition metal nickel is used as a catalyst for the hydrogenation of oils to give solid margarine. Margarine is less likely to spoil than butter. e.g:

Vegetable oil + H₂ —Ni, 250-300°C→ Margarine

Ans. Elements present in group 18 of the modern periodic table are called Noble elements. All noble elements are monoatomic gases having very low boiling points, Helium (He), Neon (Ne), Krypton (Kr), Xenone (Xe) and Radon (Ra). All these gases have eight electrons (s²p⁶) in their outermost shells except He which has s² electronic configuration. Since their outer shells are complete, they show very little chemical reactivity.

Ans. Malleable means a material that can be hammered into sheets and ductile means a material that can be drawn into wires.

Ans. Physical Properties of Metals:

i. Almost all metals are solid except mercury.
ii. They have high melting and boiling points. (except alkali metals)
iii. They possess metallic luster and can be polished.
iv. They are malleable (can be hammered into sheets), ductile (can be drawn into wires) and give off a tone when hit. (Sonorous)
v. They are good conductor of heat and electricity.
vi. They have high densities.
vii. They are hard (except sodium and potassium).

Ans. Non-metals are the elements which form negative ions (anions) by gaining electrons. They are electronegative in nature and form acidic oxides.

Ans. Non-metals cannot conduct heat and electricity. Graphite is the only exception. It conducts electricity because of its special crystalline arrangements. The electrons which are present between the layers of graphite crystal are loosely held and hence they can become mobile. The conduction of electricity of graphite is due to the mobility of these electrons.

Ans. Non-metals cannot be polished because they either exist in powder or gaseous form. Most of the powders are dull in texture.

Ans. Due to non-ductile and non-malleable properties, non-metals are not strong at all. Their bonds being weak break easily. All non-metals have low melting and boiling points. The melting point of sulphur is 115°C. Graphite and diamond have high melting points and these are exceptions. Non-metals have low densities as compared to metals. This means that in non-metals atoms are not strongly bound with each other.

Ans. According to one report nine elements are facing serious threat of extinction. Some of those elements are arsenic, gallium, gold, helium and zinc.

Ans. The noble gas with the lowest boiling point is helium (He).

Helium has the smallest atomic size and the lowest molar mass among all the noble gases. Since helium atoms are very light and have fewer electrons, they exhibit very weak intermolecular forces as compared to heavier noble gases like neon (Ne) or argon (Ar). These weak forces mean that less energy is required to separate helium atoms from each other, resulting in a lower boiling point.

Ans. Reaction of alkali metals with chlorine becomes more vigorous as we go down the group.

2Li_(s) + Cl₂_(g) —Heat→ 2LiCl_(s)
2Na_(s) + Cl₂_(g) —Heat, Vigorous reaction→ 2NaCl_(s)
2K_(s) + Cl₂_(g) —Heat, Violent reaction→ 2KCl_(s)

Ans. Metals have a crystalline structure where atoms are closely packed together in a lattice arrangement. This strong metallic bonding, which involves the sharing of free electrons among a lattice of positively charged ions gives metals their solidity, high melting points and malleability.

Non-metals can exist as gases, liquids or solids at room temperature because of their different bonding and molecular structures. Non-metals tend to form covalent bonds which can lead to the formation of molecules that are not as tightly packed as in metals.

For example gases like oxygen (O₂) and nitrogen (N₂) consist of small, individual molecules that are far apart, allowing them to exist in a gaseous state.

Some non-metals, like sulphur and phosphorus can form solid structures but they do not have the same degree of metallic bonding that gives metals their solid state.

Ans. Three elements in the periodic table that exist as liquids at room temperature are:

Mercury (Hg): It is the only metal that is liquid at room temperature.

Bromine (Br): This is a non-metal that is a reddish-brown liquid at room temperature.

Francium (Fr): While it is highly radioactive and rare, francium is predicted to be a liquid at room temperature.

Ans.

Ans. To illustrate the differences in reactivity between chlorine and bromine as reducing agents following example is given.

Chlorine (Cl₂) can react with sodium bromide (NaBr) to oxidize bromide ions (Br⁻) to bromine (Br₂).

Cl₂ + 2NaBr ⟶ 2NaCl + Br₂

In this reaction, chlorine is acting as an oxidizing agent because it gains electrons from bromide ions, which are oxidized to bromine go in this reaction and more reducing than chlorine. Bromine acts as a reducing Agent.

Ans. Among the halogens, fluorine is the most reactive element, while iodine is the least reactive.

Fluorine's Reactivity:

i. Fluorine has the highest electronegativity of all elements, which means it has a strong tendency to attract electrons. This property makes it very reactive as it readily forms bonds with other elements by accepting electrons.
ii. Fluorine has a small atomic radius, which allows its outer electrons to be held tightly by the nucleus. This tight hold makes it easier for fluorine to react with other elements to achieve a stable electronic configuration.

Iodine's Reactivity:

i. Iodine has a lower electronegativity as compared to fluorine, making it less effective at attracting electrons. As a result, it does not react as readily with other elements.
ii. Iodine has a larger atomic radius, which means its outer electrons are further from the nucleus and are held less tightly.