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Published on: 13/05/2022
QB365 provides detailed and simple solution for every Book back Questions in class 7 Science Subject. It
will helps to get more idea about question pattern in every book back questions with solution.
Download Tamil Nadu 7th Standard Science question papers, model tests, one-mark questions, important questions, and public exam papers in PDF format. Free study materials and answer keys for TN State Board students.
Questions + Answers key
Take MCQ Science Test1.
The atomic number of an element is 9. It has 10 neutrons. Find the element from the periodic table. What will be its mass number?
2.
Differentiate mass number from atomic number.
3.
What are isotones? Give one example.
4.
Distinguish Isotopes from Isobar.
5.
An atom of an element has no electron, will that atom have any mass or not? Can an atom exist without electron? If so then give example.
1.
Atomic number Z = 9
No. of neutrons n = l0
Mass number A = ?
No. of neutrons n = A - Z
Mass number A = n + Z
= 10 + 9 = 19
The symbol of the element is 9Fe19 Fluorine
2.
| Atomic number | Mass number |
| Atomic number = No of protons (or) No of electrons | Mass number = No of protons + No of neutrons |
| Z = P or e | A = P+n |
| Ex: Atomic number (z) of helium is 2 | Ex: Mass nurnber (A) of helium is 4 |
3.
(i) Atoms of the different elements can have the same number of neutrons are called "Isotones".
(ii) Ex : 29Ca40 and 19K39
(iii) Numbers of neutrons = A - Z = 20
4.
| Isotopes | Isobar |
| i) Having same atomic number,different mass number. | i) Having same mass number, different atomic number. |
| ii) Atoms of same element Ex : 1H1, 1H2, 1H3 |
ii) Atoms of different elements Ex : 20Ca40, 18Ar40 |
5.
(i) Yes, an atom of an element has no electron will have the mass.
(ii) (Atomic mass, only depends on the mrmber of protons and the number of neutrons inside the nucleus. It is independent of number of electrons.)
(iii) Atom can exist with out electron and becomes a cation.
Ex:
1) Hydrogen atoms (Z = 1) has only one electrons.
2) It loses one electron and becomes H+ ion
3) H → H+ + 1e-
(atom) (Ion)
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Tamilnadu Stateboard 7th Standard Subjects
Tamilnadu Stateboard Standards
