Atoms And Molecules Class-7th Goyal Brothers ICSE Chemistry Solutions Chapter-4 (Atomic Structure) Unit-1(Atoms And Molecules). We Provide Step by Step Answers of Objectives, Fill in the blanks, Match the following, True/False, Incorrect and Correct, Question Type answers of Chapter-4 (Atomic Structure) Unit-1(Atoms And Molecules). Visit official Website CISCE for detail information about ICSE Board Class-7.
Atoms And Molecules ICSE Class-7th Goyal Brothers Chemistry Solutions Chapter-4 Unit-1
| Board | ICSE |
| Class | 7th |
| Subject |
Chemistry |
| Book Name | Goyal Brothers |
| Chapter-4 | Atomic Structure |
| Unit-1 |
Atoms And Molecules |
| Topic | Solution of exercise questions |
| Session | 2023-24 |
OBJECTIVE QUESTIONS
Atoms And Molecules ICSE Class-7th Goyal Brothers Chemistry Solutions Chapter-4 Unit-1
Que: A. Fill in the blanks spaces by choosing the correct words from the given list.
List : Eight, positive, nucleons, negative, variable
1. The particles present within the nucleus of an atom are called nucleons.
2. The outermost orbit of an atom cannot have more than eight electrons.
3. The element which exhibits more than one valency is said to exhibit variable valency.
4. Metals have electro positive valency.
5. Non-metals have electro negative valency.
Que: B. Statements given below are incorrect. Write the correct statements :
Question: 1. When an element accepts 2 electrons its valence shell, its valency is 2+.
Answer: When an element accepts 2 electrons its valence shell, its valency is 2-.
Question: 2. The shell closest to the nucleus of an atom is called valence shell.
Answer: The outermost shell to the nucleus of an atom is called valence shell.
Question: 3. The formula of an oxide of aluminum is Al3O2.
Answer: The formula of an oxide of aluminum is Al2O3.
Question: 4. The collective name of all particles found within the nucleus is nuclear particles.
Answer: The collective name of all particles found within the nucleus is nucleon.
Question: 5. The symbol of the chlorine gas is Cl2.
Answer: The symbol of the chlorine gas is Cl.
Que: C. Match the statements in Column A, with those in Column B :
| Column A | Column B |
| 1. A subatomic particle within the nucleus of an atom having no electric charge. | (a)Atom |
| 2. A negatively charged particle in an atom with a negligible mass. |
(b)Neutron |
| 3. The central core of an atom. | (c)Formula |
| 4. The smallest particle of an element, which may or may not have independent existence, but always takes part in a chemical reaction. | (d)Nucleus |
| 5. The symbolic representation of one molecule of a compound. |
(e)Electron |
Answer:
| Column A | Column B |
| 1. A subatomic particle within the nucleus of an atom having no electric charge. | (a)Electron |
| 2. A negatively charged particle in an atom with a negligible mass. |
(b)Neutron |
| 3. The central core of an atom. | (c)Nucleus |
| 4. The smallest particle of an element, which may or may not have independent existence, but always takes part in a chemical reaction. | (d)Atom |
| 5. The symbolic representation of one molecule of a compound. |
(e)Formula |
Que: D. Write ‘True’ or ‘False’ for the following statements :
| Statements | True/False |
| 1. An ion formed by the acceptance of one electron in the outermost shell is monovalent electronegative. | T |
| 2. The symbol of sulphate radical is SO3²-. |
F |
| 3. The smallest unit of a pure substance which always exists independently and can retain all the physical and chemical properties of that substance is called a molecule. | T |
| 4. The positively charged particle within the nucleus of an atom is called neutron. | F |
| 5. A group of two or more non-metals which have negative charge is called a radical. |
F |
Que: E. Tick (√) the most appropriate answer :
1. Sodium ion is formed :
(a) by the donation of one electron from its outermost shell
(b) by the acceptance of one electron in its outermost shell
(c) by the acceptance of one proton in its nucleus
(d) by the donation of one proton from its nucleus
Answer: option (a) by the donation of one electron from its outermost shell is correct.
2. Protons and neutrons in the nucleus of an atom are called :
(a) nucleons
(b) nuclear particles
(c) charged particles
(d) mass particles
Answer: option (a) nucleons is correct.
3. Ferrous and Ferric ions have valency :
(a) +1 and +2 respectively
(b) +2 and +3 respectively
(c) -2 and -3 respectively
(d)+1 and +3 respectively
Answer: option (b) +2 and +3 respectively is correct.
4. A group of two or more non-metals which has a negative charge on it is called :
(a) ion
(b) complex ion
(c) radical
(d) none of these
Answer: option (b) complex ion is correct.
5. Which noble gas has only two electrons in its valence shell?
(a) Radon
(b) Krypton
(c) Neon
(d) Helium
Answer: option (d) Helium is correct.
STUDY QUESTIONS
Atoms And Molecules ICSE Class-7th Goyal Brothers Chemistry Solutions Chapter-4 Unit-1
Question: 1. Name two particles found inside the nucleus of an atom and state their mass and charge. What is the collective name of these particles?
Answer: Nucleus: The small region situated in the center of an atom is called the nucleus. The two particles found inside the nucleus of an atom are the following:
Protons: Proton is a positively charged particle present inside the nucleus of an atom. Its charge is taken as a unit positive charge and its mass is 1.67262192 × 10¯²7 kilograms.
Neutrons: A neutron is a neutral particle present inside the nucleus of an atom. It has no electrical charge and its mass is almost equal to the mass of the proton. 1.67493 × 10¯²7 kilograms.
Protons and neutrons are the two particles found inside the nucleus. They are collectively called nucleons.
Question: 2. (a) Name the particles which revolves around the nucleus of an atom and state its mass and charge.
Answer: The electrons revolve around the nucleus of an atom in fixed paths which are called orbits. The mass of an electron is 1/1837 times the mass of one proton. Therefore, the mass of an electron is considered negligible. The charge on an electron is taken as a unit negative charge. Mass of electron is 9.1093837015×10-31kg
Hence, the particle which revolves around the nucleus of an atom is called an electron.
(b) Why is an atom of an element electrically neutral?
Answer: The number of protons (positively charged) and electrons (negatively charged) are equal in an atom. Therefore the opposite charges are balanced and thus there is no net charge on the atom. Moreover, neutrons present in the atom have no charge. Hence an atom is electrically neutral.
Question: 3. (a) What do you understand by the term valency?
Answer: The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
(b) What kind of valency do the metals generally have?
Answer: Metals have one to three electrons in their outermost shell, and they donate these electrons to other elements to attain a stable noble gas configuration. So, metals donate their electrons and form electropositive ions. Hence, metals generally have electropositive valency.
(c) Name two elements each, whose ions have valency +1, +2 and +3 respectively.
Answer: +1 = Hydrogen, Sodium, Potassium.
Question: 4. (a) What kind of valency do non-metals generally have?
Answer: The combining capacity of an atom is known as its valency. By gaining, sharing, and losing the electrons the atoms complete their outermost shell and make an octet. non-metals generally have electronegative valency.
(b) Name three non-metals/group of non-metals which have valency -1, -2, and -3 respectively.
Answer: -1 =Chlorine, Bromine, Iodine.
Question: 5. (a) What is variable valency?
Answer: Normally, the metals donate electrons from their valence shell, so as to form positively charged ions. However, some metals lose electrons from the shell next to the valence shell. In such a situation the element exhibits more than one electropositive valency Such elements are said to have variable valency.
(b) Give three examples of elements having variable valency.
Answer: Valency: The combining capacity of an atom is known as its valency. The number of bonds that an atom can form as part of a compound is expressed by the valency of the element.
Variable valency:
- Some metals can lose different numbers of electrons to form ions with different charges, this is called variable valency.
- In some cases, the metals can lose electrons from the inner shell of the atom.
- If an element exhibit two different electropositive valences, then for lower valency, the suffix -onus is used.
- For higher valency, the suffix – ic is used at the end of the metal name.
- Copper can show two valency Cu+2andCu+1.
- Cu+2 is called Cupric ion and Cu+1 is called Cuprous ion.
- Iron(Fe) can also show +2and+3 oxidation states.
- Mercury (Hg) can show +1and+2 oxidation states.
Hence the transition elements have variable valences. For example, Copper, Iron, and Mercury.
Question: 6. Write the formulae of following salts by criss-cross method.
(a) Sodium hydrogen carbonate
Answer: Symbol Na HCO3
Charge +1 -1
Formula = NaHCO3
(b) Ferrous sulphate
Answer: Symbol Fe SO4
Charge +2 -2
Formula = FeSO4
(c) Aluminum nitride
Answer: Symbol Al N
Charge +3 -3
Formula = AlN
(d) Potassium sulphate
Answer: Symbol K SO4
Charge +1 -2
Formula = K2SO4
(e) Ammonium chloride
Answer: Symbol NH4 Cl
Charge +1 -1
Formula = NH4Cl
(f) Lead nitrate
Answer: Symbol Pb NO3
Charge +2 -1
Formula = Pb(NO3)2
(g) Ammonium phosphate
Answer: Symbol NH4 PO4
Charge +1 -3
Formula = (NH4)3PO4
(h) Cupric oxide
Answer: Symbol Cu O
Charge +2 -2
Formula = Cu2O2 = CuO
(i) Calcium hydrogen sulphate
Answer: Symbol Ca HSO4
Charge +2 -1
Formula = Ca(HSO4)2
(j) Zinc hydroxide
Answer: Symbol Zn OH
Charge +2 -1
Formula = Zn(OH)2
Question: 7. Write the chemical names of following compounds :
(a) – Ammonium Sulphate
(b) – Calcium Nitrate
(c) FeS – Iron Sulphide
(d) – Sodium Phosphate
(e) – Ammonium Hydroxide
(f) – Copper Carbonate
(g) HgO – Mercuric Oxide
(h) – Zinc Chloride
(i) ZnS – Zinc Sulphide
(j) – Hydrogen Sulphide
Question: 8. Define the following :
(a) Atom
Answer: An atom is the basic building block of chemistry. It is the smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element.
(b) Molecule
Answer: The molecule is defined as the smallest unit of matter, which has an independent existence and can retain the complete physical and chemical properties of the matter. Even when two or more atoms of the same kind combine they can form a molecule.
(c) Atomicity
Answer: Atomicity refers to the number of atoms present in a single molecule of an element, substance or compound. It can also be considered as the nature of molecules.
(d) Periodic table
Answer: The periodic table is a tabular array of the chemical elements organized by atomic number, from the element with the lowest atomic number, hydrogen, to the element with the highest atomic number, oganesson. The atomic number of an element is the number of protons in the nucleus of an atom of that element.
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