9th Class (CBSE) Science: Structure of the Atom

Question: Draw the atomic structure of hydrogen atom.

Answer:

Question: Why are some elements chemically inert?

Answer: Because their outermost shell is completely filled.

Question: Why is atom electrically neutral?

Answer: It has same number of protons and electrons, (positive charge = negative charge).

Question: What is the charge and mass of a-particles?

Answer: Charge is + 2
Mass is 4 a.m.u.

Question: What are valence electrons?

Answer: Electrons present in the outermost shell of an atom are called valence electrons.

Question: An atom has atomic number 12, what is its valency and name the element?

Answer: Atomic number = 12
∴ Protons = Electrons = 12 Electrons Configuration = K L M -2 8 2
∴ Valency = 2
Element is magnesium.

Question: Find the number of neutrons in ²⁷₁₃X.

Answer: Mass number = 27
∴ p + n = 27 p = 13, (Atomic No. = Number of protons)
∴ 13 + n = 27
∴ n = 14
∴ Neutron =14

Question: Where is the mass of atoiji concentrated?

Answer: Mass of an atom is concentrated in nucleus.

Question: Name two elements with same number of protons and neutrons?

Answer: Carbon (Protons = Neutrons = 6)
Oxygen (Protons = Neutrons = 8)

Question: Draw the atomic structure of sodium atom.

Answer:

Question: Name the isotope used for treatment of cancer.

Answer: Isotope of cobalt.

Question: AZX What does this symbol represent?

Answer: X —> Symbol of element

A —> Mass number

Z —> Atomic number

Question: Can the value of ‘Z’ be same for two different atoms?

Answer: No, (Z = atomic number), two different atoms cannot have same atomic number.

Question: Can the value of A’ be same for two different atom?

Answer: Yes, it can be e.g. Ca and Ar has A-40 (i.e., mass number).