Q16 of 216 Page 469

Write the names and symbols of two most reactive metals belonging to group I of the periodic table. Explain by drawing electronic structure how either one of the two metals reacts with a halogen. With which name is the bond formed between these elements known and what is the class of the compound so formed known? State any four physical properties of such compounds.

Most reactive metals belonging to group I of the periodic table are Sodium and Potassium. Their symbols are “Na” and “K”.


Electron dot structure – valence electrons are represented by dots placed around the chemical symbol. Electrons are placed up to two on each side of the elemental symbol for a maximum of eight, which is the number of electrons in a filled s and p shell. We place a single electron on each side before pairing them up (this is related to Hund’s rule). Period one (hydrogen and helium) represents an exception where only a maximum of two electrons are placed on one side of the element.


Electron dot structure for sodium:


Reaction of Na with halogen (eg: Chlorine)


Formation of sodium chloride:


STEP 1: Formation of cation-


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STEP 2: Formation of anion-


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STEP 3: Formation of NaCl-


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Properties of NaCl:


• This compound is a solid and is somewhat hard because of strong force of attraction between the positive- positive ions. It is generally brittle and breaks into pieces when pressure is applied.


• NaCl has high melting and boiling point because a considerable amount of energy is required to break the strong inter-ionic attraction.


• It is generally soluble in water.


• It conducts electricity in molten state because the movement of ions is possible.


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14

Given that R1 = 10 Ω, R2 = 40Ω, R3 = 30Ω, R4 = 20Ω and RA is the parallel combination of R1 and R2 whereas RB is the parallel combination of R3 and R4. Combination RA is connected to the positive terminal of 12 V battery while combination RB is connected to the negative terminal. Ammeter A is connected between the resistors RA and RB.

(i) Find RA and RB Also calculate total resistance in the circuit.


(ii) Daw the circuit diagram showing above combinations connected to battery and ammeter.

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State the rule to determine the direction of a

(i) magnetic field produced around a straight conductor-carrying current


(ii) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it and


(iii) current induced in a coil due to its rotation in a magnetic field.


OR


What is the role of fuse used in series with any electrical appliance? Why should a fuse with defined rating not be replaced by one with a larger rating?

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Why certain compounds are called hydrocarbons? Write the general formula for homologous series of alkenes, alkenes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkenes and also write a chemical equation to show the necessary conditions for the reaction to occur.

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i. (a) which part of the nervous system controls reflex arcs?

(b) With the help of a diagram trace the sequence of events, which occur when we touch a hot object.


(c) Mention the part of the neuron that acquires information and the form in which information travels.


ii. Name the hormone synthesised at the shoot tips. How does it help the plant to response to light?


OR


i. What causes tendril to encircle or coil around the object in contact with it? Explain the process involved.


ii. What is chemotropism? Give one example.