✅Notes on s-Block Elements:

Physical Properties of Alkali Metals:

➖These are soft in nature and can be cut with the help of knife except the lithium.
➖The atoms of alkali metals have the largest size in their respective periods.
➖The first ionization energy of the alkali metals are the lowest as compared to the elements in the other group.
➖The alkali metals show +1 oxidation state.
➖The alkali metals have low values of reduction potential (as shown in table-I) and therefore have a strong tendency to lose electrons and act as good reducing agents.
➖The melting and boiling points of alkali metals are very low because the intermetallic bonds in them are quite weak.

Hydroxides of Alkali Metals:

a)All the alkali metals, their oxides, peroxides and superoxides readily dissolve in water to produce corresponding hydroxides which are strong alkalies.

➖2Na + 2H2O → 2NaOH + H2

➖Na2O + 2H2O 2NaOH

➖Na2O2 + 2H2O → 2NaOH + H2O2

➖2KO2 + 2H2O → 2KOH + H2O2 + O2

b) The basic strength of these hydroxides increases as we move down the group Li to Cs.
c) All these hydroxides are highly soluble in water and thermally stable except lithium hydroxide.
d) Alkali metals hydroxides being strongly basic react with all acids forming salts.

➖NaOH + HCI → NacI + H2O
➖2NaOH + H2 SO4 → Na2SO4 + 2H2O

Halides of Alkali metals:
➖M2O + 2HX → 2MX + H2O
➖MOH + HX → MX + H2O
➖M2CO3 + 2HX → 2MX + CO2 + H2O (M = Li, Na, K, Rb or Cs)

(X = F, Cl, Br or I)
➖ll the alkali metals form ionic (electrovalent) compounds.
➖The alkali metals are good conductors of heat and electricity.
➖Alkali metals (except Li) exhibit photoelectric effect
➖The alkali metals and their salts impart a characteristic colour to flame.

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🔰Carbon and its Compounds🔰

✍️ Introduction
➖Carbon plays very important roles for all living beings.
➖The amount of carbon in the earth’s crust is merely 0.02%, which is available in the form of minerals such as carbonates, hydrogen-carbonates, coal, and petroleum.
➖The presence of carbon in the atmosphere of the earth is 0.03%, in the form of carbon dioxide.

✍️ Compounds of Carbon
➖Almost all carbon compounds (except a few) are poor conductors of the electricity.
➖The diamond and graphite both are formed by carbon atoms; however, the difference lies between them in the manner in which the carbon atoms are bonded to one another.
➖In diamond, each atom of the carbon, is bonded to four other carbon atoms and form a rigid three-dimensional structure.
➖In graphite, each atom of the carbon, is bonded to three other carbon atoms in the same plane, which gives a hexagonal array.
➖There is also difference in some physical structure of diamond and graphite.
➖Diamond is the hardest substance known whereas graphite is smooth and slippery substance.
➖Graphite is good conductor of electricity whereas diamond is not.
➖The compounds, which has identical molecular formula, but different structures, are known as structural isomers.
➖The saturated hydrocarbons are known as alkanes.
➖The unsaturated hydrocarbons, which comprise of one or more double bonds, are known as alkenes.
➖The unsaturated hydrocarbons, which comprise of one or more triple bonds, are known as alkynes.

✍️ Use of Alcohol as Fuel
➖Sugarcane plants very efficient convert sunlight into chemical energy and its juice can be used to prepare molasses.
➖When molasses is fermented, it produces alcohol (ethanol).
➖Some of the countries now using alcohol as an additive in petrol, as it is a cleaner fuel.
➖These alcohol, on burning in sufficient air (oxygen), gives rise to only carbon dioxide and water.


✍️ Esters
➖Esters are sweet-smelling substances, which are most commonly formed by reaction of an acid and an alcohol.
➖When esters react in the presence of an acid or a base, it gives back the alcohol and carboxylic acid.
➖The reaction of esters with an acid or a base, is known as saponification because it is used in the preparation of soap.
➖The molecules of soap normally are sodium or potassium salts of long-chain carboxylic acids.
➖Interestingly, the ionic-end of soap dissolves in water whereas the carbon chain dissolves in oil. This typical features of the soap molecules forms structures known as micelles.
➖In micelles, one end of the molecules is towards the oil droplet whereas the ionic-end remains outside.
➖The soap micelle helps in dissolving the dirt in water; likewise, the clothes get cleaned.
➖On the other hand, detergents are usually ammonium or sulphonate salts of long chain carboxylic acids, which remain effective even in hard water.
➖Detergents are customarily used to make shampoos and some other products for cleaning clothes.

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💠Terminologies in Progressive Wave Motion💠

➖Amplitude
➖Period
➖Wavelength
➖Frequency
➖Wave velocity
➖Phase or phase angle (O)
➖Phase difference
➖Path difference
➖Time difference


🔹Amplitude (A): The amplitude of a wave is the maximum displacement of any particle of the medium from its equilibrium position.

🔹Period (T): Period (T) of a wave is the time taken by any particle of the medium to complete one vibration during a period (T).

🔹Wavelength (λ): Wavelength (λ) is equal to the distance between two consecutive particles of the medium which are in the same state of vibration it is equal to the distance travelled by the wave by its time period (T).

🔹Frequency (f): It is the number of vibrations made per second by any particles of the medium (f = 1/T). Since the frequency of a wave is a characteristic property of the source which is producing the wave motion, hence, the frequency of a wave does not change when a wave travels from one medium to another medium.

🔹Phase or Phase Angle (Φ): It represents the state of vibration of the particle of a medium with respect to its mean position.

🔹Phase Difference Δ(Φ): It represents the different state of vibration of a particle at two different instants (or) any pair of particles at the same instant. ΔΦ = Φ2 – Φ1.

Wave Velocity (v): It is the distance travelled by the wave in one second (v = λ/T). It is determined by the mechanical properties of the medium through which the wave propagates. The velocity of wave motion is measured with respect to the medium, the wave velocity changes when the medium is in motion i.e. speed of sound through air changes when the wind is blowing.

⇒ Check: Sound Waves

There are two velocities associated with a wave. One is the wave velocity and the other one is particle velocity (which is the speed with which the particle of the medium vibrate when the wave passes through the medium).

🔹Path Difference (Δx) or (x): It indicates the distance between two points measured along the direction of propagation of the wave through the medium.

🔹Time Difference (ΔT): It indicates the time taken by the wave to travel from one point to another through the medium.

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🔷Matter In Our Surroundings🔷

Everything found in this universe is made up of some materials, scientists have named them as “matter.” For example, the food we eat, the air we breathe, stones, clouds, stars, plants, animals, water, dust, everything is categorized as matter.

♦️Characteristics of Particles of Matter
➖Particles of matter are very small, normally, not visible from naked eye.
➖Particles of matter keep moving continuously, which is known as the “kinetic energy.”
➖Kinetic energy of particles directly depends on the temperature, as temperature increases, the speed of the movement also increases.
➖The particles of matter have attracting force; therefore, they attract each other.
➖The attracting force of the particles keeps the particles together; however, the strength of the attracting force varies from one kind of matter to another.

States of Matter
Matter has three following states −
➖Solid State
➖Liquid State
➖Gaseous State

🧿Solid State
➖All the solid materials have a definite shape, distinct boundaries, and fixed volumes.
➖Most of the solid materials have negligible compressibility.
➖All the solid materials have a natural tendency to maintain their shape when subjected to outside force.
➖The solid materials can be broken under applied force, but it is very difficult to change their shape, as they are rigid.

🧿Liquid State
➖Unlike solids, liquids have no fixed shape; however, they have a fixed volume
➖Liquids take up the shape of the container in which they are kept.
➖Liquids have the property to flow and change shape.

🧿Gaseous State
➖Matter in the form of air, which is neither solid nor liquid, is known as gas. For example, oxygen, nitrogen, hydrogen, etc.
➖Unlike solid, gas has not definite size and shape.
➖The gases, such as liquefied petroleum gas (LPG – used in cooking); compressed natural gas (CNG – used as fuel in vehicles), etc. have high compressibility; therefore, large volume of a gas can be compressed into a small cylinder and can be transported easily.
➖Gases, normally, show the property of diffusing very fast into other gases. This is the reason that we can smell (either good or bad) from the distance.

🔷Matter Can Change its State
➖Water can exist in all three states, e.g. Ice as solid; water (H2O) as liquid; and water vapor as gas.
➖The temperature, at which solid melt and transform into the liquid (at the given atmospheric pressure), is known as “melting point.”
➖The melting point of a solid is an indication of the strength of the force of attraction between its particles.
➖The melting point of ice is 273.16 K, i.e. 00 C.
➖The process of melting (i.e. change of solid state into liquid state) is known as fusion.
➖The amount of heat energy, which is required to change 1 kg of a solid materials into liquid materials at a given atmospheric pressure, is known as the latent heat of fusion.
➖The temperature at which a liquid starts boiling at the given atmospheric pressure is known as “boiling point.”
➖The boiling point of water is 373 K i.e. 1000C.
➖A change of state of a matter directly from solid to gas without changing into liquid state (or vice versa) is known as “sublimation.”
➖The phenomenon i.e. change of a liquid into vapors at any temperature below its boiling point is known as “evaporation.”
➖Solid carbon dioxide (CO2) is stored under high pressure.
➖Solid CO2 gets converted directly into gaseous state once the pressure decreases to 1 atmosphere.
➖Atmosphere (atm) is a unit of measuring pressure exerted by the gas and the unit of pressure is Pascal (Pa); 1 atmosphere = 1.01 × 105 Pa.


🔷The Fourth State of Matter
➖Plasma is the state that consists of super energetic and super excited particles.
➖The super excited particles are found in the form of ionized gases. E.g. the fluorescent tube (which contains helium gas) and neon sign bulbs (which contain neon gas) consist of plasma.