GSEB Solutions for Class 8 Science and Technology – Molecular Structure (English Medium)
GSEB SolutionsMathsScience
Exercise 15:
Solution 1(a):
In the solar system, the Sun is present at the centre, likewise, in the atomic structure, the nucleus is present at the centre. All planets are revolving around the sun in a definite path; in the same way, electrons are revolving around the nucleus in various orbits.
Solution 1(b):
Sun is the centre of the solar system while the nucleus is the centre of an atom.
Solution 1(c):
Planets are rotating around the sun in the solar system while electrons are rotating around the nucleus in an atom.
Exercise 16:
Solution 1(a):
Element | Symbol | Atomic Number | No. of Protons | Electrons |
Beryllium | Be | 4 | 4 | 4 |
Boron | B | 5 | 5 | 5 |
Carbon | C | 6 | 6 | 6 |
Nitrogen | N | 7 | 7 | 7 |
Oxygen | O | 8 | 8 | 8 |
Fluorine | F | 9 | 9 | 9 |
Neon | Ne | 10 | 10 | 10 |
Sodium | Na | 11 | 11 | 11 |
Magnesium | Mg | 12 | 12 | 12 |
Aluminium | Al | 13 | 13 | 13 |
Silicon | Si | 14 | 14 | 14 |
Phosphorus | P | 15 | 15 | 15 |
Sulphur | S | 16 | 16 | 16 |
Chlorine | Cl | 17 | 17 | 17 |
Argon | Ar | 18 | 18 | 18 |
Potassium | K | 19 | 19 | 19 |
Exercise 20:
Solution 1.1:
- Electron.
Electrons revolve around the nucleus in orbits.
Solution 1.2:
- Electron.
Electrons revolve around the nucleus in orbits.
Exercise 21:
Solution 1.3:
- Neutron.
Neutrons are electrically neutral; so, they do not carry any charge.
Solution 1.4:
- 18.
Third energy level can accommodate maximum 18 electrons.
Solution 2:
- Molecule – Atom:
Atom | Molecule |
Atom is the smallest particle in an element. | Molecules are formed by the combination of two or more atoms. |
It is not possible to breakdown the atom further. | Molecules can be subdivided to individual atoms. |
- Atom – Ion:
Atom | Ion |
An atom is neutral. | An ion has positive or negative charge. |
An atom has same number of protons as electrons. | An ion has different number of protons and electrons. |
Solution 3.1:
In an atom, the number of protons and electrons are equal. Since the positive and negative charges are equal, an atom is neutral with respect to the electrical charge.
Solution 3.2:
Elements consist of individual atoms. Each element always consists of the same type of atom which imparts its own unique properties to that element; so, basic unit for an element is atom. Compound consists of the smallest unit which contains at least two different types of atoms joint together by chemical bonds; so, the basic unit for compound is molecule.