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Science Question Answer (5 Marks)

Structure of the Atom · Maharashtra Board STD 9 (MSBSHSE - English Medium). 6 questions.

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Question Answer (5 Marks)

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6 questions · self-marked practice — reveal the answer and mark yourself.

Question 15 Marks
Describe the Rutherford’s model of an atom. State one drawback of Rutherford’s model of the atom.
Answer
Rutherford's model of atom:
  1. An atom consists of positively charged, dense and very small nucleus containing all the protons and neutrons. Almost all the mass of atom is concentrated in the nucleus.
  2. The nucleus is surrounded by negatively charged electrons. The electrons are revolving at very high speed round the nucleus in fixed circular orbits.
  3. The electrostatic attraction between the positively charged nucleus and negatively charged electrons keep the atom held together.
  4. An atom is electrically neutral.
  5. Most of the space in an atom is empty.
The major drawback of Rutherford model of atom is that it does not explain the stability of the atom.
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Question 25 Marks
Describe Bohr’s model of the atom. How did Neils Bohr explain the stability of atom?
Answer
Bohr's model of atom:
  1. An atom is made up of three particles, namely electrons, protons and neutrons.
  2. The protons and neutrons are located in the small nucleus at the center of atom.
  3. Electrons revolve round the nucleus in fixed circular orbits.
  4. Maximum no. of electrons for any given shell is fixed. Any shell cannot exceed that maximum value.
  5. Each given shell is associated with fixed amount of energy.
  6. There is no change in energy of electrons as long as they keep revolving in the same energy level, and the atom remains stable.
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Question 35 Marks
The atom of an element $X$ has $7$ electrons in its $M$ shell:
a. Write the electronic configuration of element X .
b. What is the atomic number of element $X$ ?
c. Is it a metal or a non-metal?
d. What type of ion will be formed by an atom of element $X$ ? Write the symbol of the ion formed.
e. What could element $X$ be?
Answer
  1. Electronic configuration of the element $X$ is,
Element X: $\text{K}\ \ \ \ \ \ \text{L}\ \ \ \ \ \ \text{M}\\2\ \ \ \ \ \ \ 8\ \ \ \ \ \ \ 7$
  1. Atomic number of the element $X$ will be $17$
  2. Element $X$ is a non-metal because there are $7$ electrons in its outermost orbit. In order to complete its octet (to get $8$ electrons), it will gain one electron. An element which gains electrons in order to complete its octet is a non-metal.
  3. The element will form an anion by gaining an extra electron in order to complete its octet. Symbol of an ion of $X$ will be $X^-$
  4. $X$ is Chlorine.
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Question 45 Marks
The electronic configuration of an element Z is 2, 8, 8.
  1. What is the atomic number of the element?
  2. State whether element Z is a metal or a non-metal.
  3. What type of ion (if any) will be formed by an atom of element Z? Why?
  4. What is special about the outermost electron shell or the atom of this element?
  5. Give the name and symbol of element Z.
  6. Name the group of elements to which Z belongs.
Answer
  1. Atomic no. of the element = 18
  2. Element Z is a non-metal
  3. Element Z will not form any ion because its outermost shell is complete.
  4. Outermost electronic shell of the atom of this element is completely filled with electrons.
  5. Name of element Z is Argon Symbol is Ar.
  6. Z belongs to the noble gases group or the zero group of the periodic table.
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Question 55 Marks
An atom of element E contains $3$ protons, $3$ electrons and $4$ neutrons:
  1. What is its atomic number?
  2. What is its mass number?
  3. Write the electronic configuration of the element E.
  4. State whether element E is a metal or non-metal. Why?
  5. What type of ion, cation or anion, will be formed by an atom of element E? Why?
  6. Write the symbol of the ion formed by an atom of element E.
  7. What could element X be?
Answer
  1. Its atomic number is $3$
  2. Mass no. $= 3 + 4 = 7$
  3. Electronic configuration is
$\text{K}\ \ \ \ \ \text{L}\\2\ \ \ \ \ \ 1$
  1. Element E is a metal because in order to complete its octet, the element loses $1$ electron from its outermost orbit and attains a stable configuration with $2$ electrons in its first shell. Elements which lose electrons to attain stability are called metals.
  2. A Cation will be formed by an atom of element A because its outermost single electron can be easily donated.
  3. $E^+$
  4. Element $X$ is lithium.
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Question 65 Marks
An atom of an element $X$ may be written as ${ }_4^9 X$
a. What does the figure $9$ indicate?
b. What does the figure $4$ indicate?
c. What is the number of protons in atom $X $?
d. What is the number of neutrons in atom $X$ ?
e. What is the number of electrons in atom $X$ ?
f. How many electrons are there in the outermost shell of an atom of element $X$ ?
g. Write the symbol of ion formed by an element $Z$ is $2,8,8$.
Answer
a. Figure $9$ indicates the mass number.
b. Figure $4$ indicates the atomic number.
c. No. of protons in atom $X=4$
d. No. of neutrons in atom $X=9-4=5$
e. No. of electrons in atom $X=4$
f. Electrons in the outermost shell of an atom of element $X=2$
g. $X ^{2+}$
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