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ChemistryClass 9CBSE

What is the significance of the number of valence electrons in determining an element's chemical properties?

The number of valence electrons (electrons in the outermost shell) is crucial because these are the electrons involved in chemical bonding. Atoms tend to gain, lose, or share valence electrons to achieve a stable electron configuration, typically an octet. This behavior directly dictates an element's reactivity, the types of bonds it forms, and its chemical properties.

ChemistryClass 9CBSE

How did J.J. Thomson's 'plum pudding' model describe the atom? What was its major flaw?

Thomson's 'plum pudding' model proposed that the atom was a sphere of uniformly distributed positive charge, with negatively charged electrons (like 'plums') embedded within it. Its major flaw was its inability to explain the results of Rutherford's gold foil experiment, particularly the large deflections of alpha particles, which indicated a concentrated positive nucleus.

ChemistryClass 9CBSE

Differentiate between atomic mass and mass number. Why are they usually different?

Mass number (A) is the total count of protons and neutrons in a specific atom, always a whole number. Atomic mass (or atomic weight) is the weighted average of the masses of all naturally occurring isotopes of an element, often a decimal number. They differ because atomic mass accounts for the varying abundances of isotopes and the slight mass defect from nuclear binding energy, whereas mass number is just a count of nucleons for a single isotope.

ChemistryClass 9CBSE

Explain why atoms are generally electrically neutral. What happens if an atom gains or loses electrons?

Atoms are generally electrically neutral because they contain an equal number of positively charged protons in the nucleus and negatively charged electrons orbiting the nucleus, balancing out the overall charge. If an atom gains electrons, it becomes a negatively charged ion (anion). If an atom loses electrons, it becomes a positively charged ion (cation).

ChemistryClass 9CBSE

Consider an atom with 17 protons, 18 neutrons, and 17 electrons. Identify the element, determine its atomic number and mass number, and state whether it is a neutral atom or an ion.

The element is Chlorine (Cl) because it has 17 protons (atomic number = 17). Its atomic number is 17. Its mass number is 17 (protons) + 18 (neutrons) = 35. Since the number of protons (17) equals the number of electrons (17), it is a neutral atom.

ChemistryClass 9CBSE

Draw a simple diagram representing the atomic structure of an oxygen atom (atomic number 8, mass number 16). Label the nucleus, protons, neutrons, and electrons.

The diagram should show a central nucleus with 8 protons and 8 neutrons. The first electron shell should contain 2 electrons, and the second electron shell should contain 6 electrons. All components should be clearly labeled.

ChemistryClass 9CBSE

Define valency and explain how it is related to the electron configuration of an atom.

Valency is the combining capacity of an element, indicating the number of electrons an atom will gain, lose, or share to achieve a stable electron configuration (usually a full outermost shell). It is determined by the number of electrons in the outermost shell (valence electrons); atoms tend to react to achieve an octet (or duet for hydrogen/helium).

ChemistryClass 9CBSE

Discuss the limitations of Rutherford's nuclear model of the atom that led to the development of Bohr's model.

Rutherford's model could not explain why electrons orbiting the nucleus didn't continuously lose energy and spiral into the nucleus, causing the atom to collapse. It also failed to explain the discrete line spectra observed for elements, suggesting electrons could only exist in specific energy levels.

ChemistryClass 9CBSE

How does the atomic number differ from the mass number? What information does each provide about an atom?

The atomic number (Z) represents the number of protons in an atom's nucleus and uniquely identifies an element. The mass number (A) represents the total number of protons and neutrons in an atom's nucleus. The atomic number tells us the element and the number of electrons in a neutral atom, while the mass number indicates the atom's total nuclear mass.

ChemistryClass 9CBSE

Explain the concept of electron shells (or energy levels) and how electrons are distributed within them according to Bohr's model.

Bohr's model proposes that electrons orbit the nucleus in specific, fixed energy levels called electron shells. Each shell can hold a maximum number of electrons: 2 in the first shell, 8 in the second, and 18 in the third (for the first few elements). Electrons fill the lowest energy shells first.

ChemistryClass 9CBSE

What is an isotope? Provide an example to illustrate your explanation.

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers. For example, Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) are isotopes of carbon.

ChemistryClass 9CBSE

Describe Rutherford's Gold Foil Experiment and explain how its results led to the proposal of the nuclear model of the atom.

Rutherford's Gold Foil Experiment involved firing alpha particles at a thin sheet of gold foil. Most alpha particles passed straight through, suggesting atoms are mostly empty space. However, a small fraction were deflected at large angles, and some even bounced back, indicating the presence of a small, dense, positively charged nucleus at the center of the atom.

ChemistryClass 9CBSE

Explain the fundamental differences between protons, neutrons, and electrons in terms of their charge, mass, and location within an atom.

Protons have a positive charge (+1), a mass of approximately 1 atomic mass unit (amu), and are located in the nucleus. Neutrons have no charge (neutral), a mass of approximately 1 amu, and are also located in the nucleus. Electrons have a negative charge (-1), a very small mass (approximately 1/1836 amu), and orbit the nucleus in electron shells.

ChemistryClass 10ICSE

. A metal salt MX when exposed to light splits up to form metal M and a gas X2. Metal M is used in making ornaments whereas gas X2 is used in making bleaching powder. The salt MX is itself used in black and white photography. (a) What do you think metal M is? (b) What could be gas X2? (c) Name the metal salt MX. (d) Name any two salt solutions which on mixing together can produce a precipitate of salt MX. (e) What type of chemical reaction takes place when salt MX is exposed to light? Write the equation of the reaction.

Silver will be metal X Chlorine is the gas evolved when MX salt is exposed to light Silver chloride is the metal salt MX which is used in black and white Silver nitrate and Sodium chloride are the two salt solutions which on mixing together produce a precipitate of salt silver chloride Decomposition reaction is the reaction taking place here when compound decomposes to form simpler new products. Silver chloride decomposes to form silver and chlor

ChemistryClass 10ICSE

When a strip of red-brown metal X is placed in a colourless salt solution YNO3 then metal Y is set free and a blue coloured salt solution X(NO3)2 is formed. The liberated metal Y forms a shining white deposit on the strip of metal X. (a) What do you think metal X is? (b) Name the salt YNO3. (c) What could be metal Y? (d) Name the salt X(NO3)2 (e) What type of reaction takes place between metal X and salt solution YNO3?

Copper is the metal X which is a red brown strip Silver nitrate is the salt YNO3 which is a colourless salt Silver is the metal formed Y upon reaction of copper and silver nitrate solution thus it forms a shining white deposit on the strip metal X Copper nitrate is X(NO3)2 the salt formed which is blue coloured as copper is present in it Displacement reaction will be the type of reaction taking place here Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) +

ChemistryClass 10ICSE

A red-brown metal X forms a salt XSO4. When hydrogen sulphide gas is passed through an aqueous solution of XSO4, then a black precipitate of XS is formed along with sulphuric acid solution. (a) What could the salt XSO4 be? (b) What is the colour of salt XSO4? (c) Name the black precipitate XS. (a) By using the formula of the salt obtained in (a) above, write an equation of the reaction which takes place when hydrogen sulphide gas is passed through its aqueous solution. (e) What type of chemical reaction takes place in this case?

Copper sulphate will be the salt formed named as XSO4 Blue colour is the colour of the salt as it is copper sulphate Copper sulphide is responsible for the black precipitate XS CuSO4 (aq) + H2S (g) → CuS (s) + H2SO4 (aq) Double displacement reaction in which reactant ions exchange places to form new products which results in precipitation reaction.

ChemistryClass 10ICSE

Two metals X and Y form the salts XSO4 and Y2SO4, respectively. The solution of salt XSO4 is blue in colour whereas that of Y2SO4 is colourless. When barium chloride solution is added to XSO4 solution, then a white precipitate Z is formed along with a salt which turns the solution green. And when barium chloride solution is added to Y2SO4 solution, then the same white precipitate Z is formed along with colourless common salt solution. (a) What could the metals X and Y be? (b) Write the name and formula of salt XSO4. (c) Write the name and formula of salt Y2SO4. (d) What is the name and formula of white precipitate Z? Write the name and formula of the salt which turns the solution green in the first case.

Copper is Metal X and Metal Y is Both forms sulphate salts on reaction Copper sulphate, CuSO4is XSO4, the salt formed which is blue in colour Sodium sulphate, Na2SO4 is Y2SO4 which is a colourless salt Barium sulphate, BaSO4 is Z which is a white precipitate formed upon the reaction when barium chloride is added to copper sulphate and turns the solution green Copper chloride, CuCl2 is the salt having yellowish brown colour which turns the solutio

ChemistryClass 10ICSE

A metal X forms a water soluble salt XNO3. When an aqueous solution of XNO3 is added to common salt solution, then a white precipitate of compound Y is formed alongwith sodium nitrate solution. Metal X is said to be the best conductor of electricity and it does not evolve hydrogen when put in dilute hydrochloric acid. (a) What is metal X ? (b) What is salt XNO3? (c) Name the compound Y. (d) Write the chemical equation of the reaction which takes place on reacting XNO3 solution and common salt solution giving the physical states of all the reactants and products. What type of chemical reaction is illustrated by the above equation?

Silver (Ag) will be metal which conducts electricity and does not evolve hydrogen when put in dilute hydrochloric acid Silver nitrate (AgNO3) is XNO3 which is reacts with NaCl (common salt) to give white precipitate Silver chloride (AgCl) is the compound Y formed which is the white precipitate formed from the reaction of silver nitrate and sodium chloride. AgNO3(aq) + NaCl (aq)→ AgCl (s) + NaNO3 (aq) Double displacement reaction

ChemistryClass 10ICSE

When a black metal compound XO is heated with a colourless gas Y2, then metal X and another compound Y2O are formed. Metal X is red-brown in colour which does not react with dilute acids at all. Gas Y2 can be prepared by the action of a dilute acid on any active metal. The compound Y2O is a liquid at room temperature which can turn anhydrous copper sulphate blue. (a) What do you think is metal X? (b) What could be gas Y 2? (c) What is compound XO? (d) What is compound Y2O? (e) Write the chemical equation of the reaction which takes place on heating XO with Y2. What type of chemical reaction is illustrated in the above equation?

Copper (Cu) will be the metal X which is red brown in colour and does not react with dilute acids Hydrogen (H2) is the colourless gas Y2 Copper oxide (CuO) will be the compound XO a black metal compound Water (H2O) is the product formed Y2O CuO + H2 →Cu + H2O Displacement reaction (which is also a redox reaction).Which one active element displaces a less reactive element from its salt solution

ChemistryClass 10ICSE

A strip of metal X is dipped in a blue coloured salt solution YSO4. After some time, a layer of metal Y from the salt solution is formed on the surface of metal strip X. Metal X is used in galvanisation whereas metal Y is used in making electric wires. Metal X and metal Y together form an alloy Z. (a) What could metal X be? (b) What could metal Y be? (c) Name the metal salt YSO4 (d) What type of chemical reaction takes place when metal X reacts with salt solution YSO4? Write the equation of the chemical reaction involved. Name the alloy Z.

Metal X is Zinc (Zn) Metal Y is Copper (Cu) Copper sulphate (CuSO4) is named as YSO4 Displacement reaction;Displacement reaction is a reaction in which one active element displaces a less reactive element from its salt solution CuSO4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s) Brass

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