Class-7 Dalal Simplified Atomic Structure ICSE Chemistry Solutions
Class-7 Dalal Simplified Atomic Structure ICSE Chemistry Solutions Chapter-4. Step by step solutions of New Simplified Dr Viraf J Dalal Middle School Chemistry Allied Publishers for ICSE Class-7 with MCQ , Practice Problems, Exercise, Objective Type Questions and Fill in the Blanks.. Visit official Website CISCE for detail information about ICSE Board Class-7.
Class-7 Dalal Simplified Atomic Structure ICSE Chemistry Solutions Chapter-4
State the meaning of the term – (a) atom (b) molecule (c) radical – with a suitable example.
- Atom – The basic/smallest unit of matter which cannot be broken into more simpler particles.
- Molecule – The smallest particle of a substance which can exist independently and retain properties of the substance.
- Radical – An atom/ group of atoms which has charge
Draw the basic structure of an atom representing its –
(a) Subatomic particles
(c) Orbits or shells.
Diagram showing basic structure of atom
In the Modern Periodic Table – atoms of all elements are arranged according to the their increasing order of – atomic numbers. An atom of nitrogen has seven protons and seven electrons. State what would be its atomic number.
Atomic number [Z]
Z = No. of protons [p]
Z = No. of electrons [e]
Z = 7 = 7 (No of Proton=7 given)
Hence Atomic number = 7
State the main points of contradiction of Dalton’s atomic theory by the Modern Atomic Theory.
The main postulates of Dalton’s atomic theory are:
- The matter is made up of indivisible particles known as atoms.
- The properties of all the atoms of a given element are the same including mass. This can also be stated as all the atoms of an element have identical mass while the atoms of different elements have different masses.( 11H, 21 H,31H ) Isotopes
- Atoms of different elements combine in fixed ratios to form compounds.
- Atoms are neither created nor destroyed. This implies that during chemical reactions, no atoms are created nor destroyed.
- The formation of new products (compounds) results from the rearrangement of existing atoms (reactants).
- Atoms of an element are identical in mass, size and many other chemical or physical properties, but atoms of two-different elements differ in mass, size, and many other chemical or physical properties.
The modern atomic theory contradicts dalton’s atomic theory :
- Atoms are divisible into protons, neutrons, electrons.
- Atoms of the same element have different properties, such atoms are isotopes.
- Atoms of different elements have the same properties, such atoms are isobars.
- Atoms can combine in any ratio and not just whole numbers.
‘Atoms of the same element or different of Dalton’s atomic theory by the Modern Atomic Theory. Give two examples each of –
(a) Atoms of the same element
(b) Atoms of different elements combining to form a molecule.
Atoms of the same element or different elements combine to form a molecule.
Explain the term – ‘atomicity’. Give a reason why –
(a) Helium is considered monoatomic, but hydrogen a diatomic molecule.
(b) Ozone is considered triatomic, but phosphorus a tetratomic molecule.
Atomicity —Atomicity is the number of atoms that make a molecule of an element.
- Helium is considered mono-atomic because it has 1 atom in its molecule,
- hydrogen is considered diatomic because it has 2 atoms of hydrogen in its molecule.
- Ozone is considered triatomic because it has 3 atoms of oxygen,
- phosphorus is considered tetratomic because it has 4 atoms in its molecule.
State the atomicity of the following:
A.radical takes part – unsplit in a chemical reaction and retains its identity in reactions. With reference to the radical – (a) ammonium (b) bisulphate (c) carbonate – state the group of atoms present in each radical.
Differentiate between the following with suitable examples- A basic radical and a acid radical
The positive part of a radical is called basic radical and the negative part of a radical is called acid radical. Basic radical can be a metal while acid radical can be Non- Metal
In Sodium Chloride Compound
Basic radical – Sodium
Acid radical – Chloride
In Ammonium Hydroxide – Compound
Basic radical – Ammonium
Acid radical – Hydroxide
Name the cation and the anion in the salt – calcium sulphate.
In a salt of calcium sulphate the positive and negative parts exist as ions.
- The positively charged ions are called – cations. Ca1+
- The negative charged ions are called – anions. S041-
Explain the term – ‘valency’. State giving reasons the valency of –
(a) Chlorine in hydrogen chloride
(b) Sulphate in sulphuric acid
(c) Nitrogen in ammonia
(d) Magnesium in magnesium oxide
Valency is the number of hydrogen atoms that combine or displace with another atom to form a compound.
- One atom of hydrogen combines with one atom of chlorine to form HCl, Hence the valency of chlorine in this case is 1.
- Two atoms of hydrogen combine with one radical of sulphate to form H2SO4, the valency of sulphate is 2.
- Three atoms of hydrogen combine with one atom of nitrogen to form NH3, the valency of nitrogen in this case is 3.
- Valency of magnesium in MgO is 2, as it needs 2 oxygen atoms to form magnesium oxide.
Give the symbol and valency of the following elements and radicals.
Give an example of three elements exhibiting variable valency.
Few examples of elements exhibiting variable valency:
- Tin (Sn) has valency 2 or 4
- Iron (Fe) can show a valency of 2 and 3.
- Copper (Cu) can show a valency of 1 and 2.
- Phosphorus (P) can show a valency of 3 and 5.
State what is meant by the term – ‘chemical formula. Give the chemical formula of –
(a) sodium hydroxide
(b) sodium nitrate
(c) sodium bicarbonate
(d) sodium sulphite
(e) magnesium nitrate
(f) ammonium sulphate
(g) carbonic acid
(h) calcium phosphate
The Symbolic representation of a substance by means of symbols is called Chemical formula
(writing Radicle with charge and inter change the value by cris cross)
‘Dilute hydrochloric acid is added to sodium hydroxide’. Give a word equation and a molecular equation of the same. Is the equation written, a balanced equation. Give reasons.
Word equation of statement : – ‘Dilute hydrochloric acid is added to sodium hydroxide’
Sodium hydroxide + hydrochloric acid -> sodium chloride + water
Molecular equation of statement : – ‘Dilute hydrochloric acid is added to sodium hydroxide’
NaOH + HCl —–> NaCl + H20
No. of atoms of each element of reactant/s = No. of atoms of each element of product/s.
Therefore, the above equation is said to be balanced equation.
Group number signifies the number of electrons in the outermost shell of an atom of the element.
The number of electrons in the outer shell of all elements in one group is same, which implies that
They have the same valency and same chemical properties.
Group number signifies the number of electrons in the outer shell of an atom of the element.
- Number of electrons in the outer shell of all elements in a group is the same.
- Hence all elements in the same group of the periodic table have same ‘Valency’ and similar ‘Chemical properties’.
Objective Type Questions
Atomic Structure Class-7 Dalal ICSE New Simplified Dr Viraf J Dalal Middle School Allied Publishers Solutions. Chapter-4
Fill in the blanks with the correct words from the brackets.
- A molecule of an element is _____
- A radical with one atom of sulphur and three atoms of oxygen is ______
- An element with variable valency is _______
- The formula for aluminium sulphide is __________
- the element lithium in the modern periodic table with valency 1+ belongs to the group _____
- A molecule of an element is chorine
- A radical with one atom of sulphur and three atoms of oxygen is sulphite.
- An element with variable valency is copper
- The formula of aluminium sulphate is Al2(S04)3
- the element lithium in the modern periodic table with valency 1+ belongs to the group ___1 A_(Alkali Metals)_
Select the correct answer from A, B, C, D and E for each statement given below:
A: Molecule B: Orbits C: Atom D: Valency E: Radical
- The basic unit of matter not capable of independent existence.
- The smallest particle of a substance – capable of independent existence and which retains the characteristics of the substance
- An elementary particle of matter – of a group of atoms of different elements behaving as a single unit with charge on the group.
- Imaginary path around the nucleus of an atom in which electrons revolve.
- The term for the combining capacity of an element or the number of hydrogen atoms with which it combines or replaces.
- C: Atom
- A: Molecule
- E: Radical
- B: Orbit
- D: Valency
Match the radicals in List I with their correct names from List II.
- G: Nitrate
- J: Bisulphate
- F: Sulphate
- B: Phosphate
- E: Bicarbonate
State the correct formula of the following from the list given:
Name the following:
- A molecule of a compound containing two oxygen atoms and one nitrogen atom.
- The radical containing one nitrogen and four hydrogen atoms.
- The compound formed when iron [Fe2+] combines with oxygen [O2-].
- The group of the Modern Periodic Table to which calcium [Ca2+] belongs.
- A non-metal which forms a polyatomic molecule with more than three atoms.
- Nitrogen dioxide
- Iron (III) oxide.
- Group 2 or II A (Alkali earth Metals)
- Phosphorus (P4).
.– : End of Atomic Structure Changes Class-7 Dalal Simplified Solutions :–
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