Structure of Atoms: solved exercise and Think Tank

  Structure of Atoms: solved exercise and Think Tank

Question 2. Give short answers. 

I. Distinguish between shell and aub shell.

In an atom, the circular path around the nucleus in which electron revolves is called shell or an orbit. According to Bohr atomic theory, each shell has fixed energy. For example  K shell , L shell, M shell etc.

Sub-shell:

The space around the nucleus, in which probability of finding electron is maximum is called sub shell. A shell is sub divided into sub shells. 

K shell has one sub-shells 1s.

L shell has two sub-shells 2s and 2p.

M shell has three sub shells 3s, 3p and 3d.

Why an atom is electrical neutral.

Answer.

An atom is electrical neutral because it has same number of positively charged protons and negative charged  electrons. Oppositely charge balance each other and there is no net charge. Neutron has also no charge, so atom is electrical neutral.

How many sub-shells are there in N shell.

Answer. 

For Nshell, n =4, so N shell has four sub-shells.

Give notation for sub-shells of M shell.

Answer. For M shell, n = 3  so M has three sub shells. 3s, 3p and 3d.

List the sub-shells of M shell in order of increasing energy.

Answer. 3s < 3p<3d

Can you identify an item without knowing number of neutron in it.

Question 3. The electronic configuration listed are correct explain what mistake have been made in each and right correct electronic configuration.

X = 1s2, 2s2, 2p4, 3p2.

Y= 1s2, 2s1, 2p1

Z = 1s2, 2s2, 2p5,3s1

Question 4. Which orbital in each of the following pairs is lower in energy?

a. 2s,20  

b. 3p, 2p

c. 3s,4s

Question 5.Draw Bohr's atomic model for the following atoms indicating the location for electrin, protons and neutrons.

a. Potassium (Atomic number =19, Mass No. 39)

b. Silicon (Atomic No. 14, Mass No. 28

c. Argon (Atomic No. 18, Mass No. 39)

Question 6: right electronic configuration for the farming elements.

a. Si      b. Mg        c.  Al       d.  Ar

Question 7: Describe the contribution that Rutherford made to the development of atomic theory.

Answer.

Rutherford the first scientist who proposed first atomic model of an atom.

He suggested that all of the positive charge and most of the ma’s of atom is concentrated in the nucleus.

The remaining volume is occupied by electrons that revolve around the nucleus in orbits. These suggestions remain unchallenged.

But this model could not explain the stability of an atom and line spectrum for an atom.

Question 8:  Explain how atomic theory different from ratherford atomic theory. 

Answer.

Bohr’s leaped over the difficulty by using by using quantum theory of radiation that was proposed by Max Plank.  Bohr proposed that electron moves the nucleus in well defined paths called orbits. Electrons present in an orbit does not radiate energy. Bohr’s atomic theory nicely explains the stability of atom and also explains why atom gives line sspectrum.

Question 9: Describe the presence of shells in a shell.

Answer. 

A shell or energy level is sub divided into sub shells or sub energy levels. N value of shell is placed before the symbol of sub shell For example,

N = 1, for K shell. It has only one sub-shell which is represented by 1s

For L shell, n = 2, L has two sub-shells which are represented by 2s, and 2p

For M shell, n = 3, M has three sub-shells which are represented by 3s, 3p and 3d

For N shell, n = 4 N has four sub-shells which are represented by 4s, 4p, 4d and 4f

S sub- shellcan accommodate maximum 2 electrons.

p sub- shell can accommodate maximum 6 electrons.

d sub- shell can accommodate maximum 10 electrons. 

F sub- shell can accommodate maximum 14 electrons. 

 Question 10: State the importance and uses of various field of life. 

Question 11:  The atomic number of element is 23 and its mass number is 56.

a How many protons and electron does an atom of this element have?

 b How many neutron does this atom have?

Answer. 

a. An atom of this element has 23 protons and 23 electrons.

b. This atom has 33 protons. I.e., 

Number of neutrons present in this Atom is = mass number- Atomic number

                                                                             = 56 -23

                                                                               = 33

Question 12. The atomic symbol of alumium is written as written as Al. What information do you get from it?

Answer.  

From this symbol, we get the information that Al has:

1. 13 protons

2. 13 electrons

3. 14 neutrons

4. Atomic number =13

5. Mass number = 56

Question 13: How the prevailing theories about testing bring changes in atomic theories?

Answer.

Dalton’s Atomic theory explained data from many experiments. So it was widely accepted. However, discovery of sub Atomic particles and isotopes proved that some of Dalton’s idea about atom was not correct. Scientists did not discarded his theory(  سائنسدانوں نے اس کے نظریے کو رد نہیں کیا۔) . Instead, they revised the theory to take into account new discoveries(انہوں نے نئی دریافتوں کو مدنظر رکھنے کے لیے پرانے نظریہ پر نظر ثانی کی۔). This shows how prevailing theories bring about changes in atomic theories.

Question 14. How experimental results of some scientist help chemist to formulate new theories and new explanation?

Answer. Experimental results of some scientists create certain questions which require answers. For this purpose, first a hypothesis is developed and then eexperiments are performed  to test hypothesis. Finally, analysis of results of an experiment will either accept or reject the hypothesis. If hypothesis is accepted,  then it leads to a new theory and explanation. 

Think Tank

Question15: M-24 Is a radioactive isotope used to diagnose the restrictec blood circulation, for example in legs. How many electrons, protons and neutrons are there in this isotope. Valence shell electronic configuration of MS3 S1.

Question16: to as a tropes of chlorine are CL how do these isotopes differ how are they alike?

Question 17. How many electrons can be placed in all of the sub-shells in the n =2 shell?

Question 18. Mass number of an atom indicates total number of protons and neutrons in the nucleus. Can you identify an atom without any neutron?

Question 19: The table shows the nuclei of five different atoms?

Name of atom      No. Of protons        No. Of neutrons

A                                  5                                     6

B                                  6                                     6

C                                  6                                     7

D                                 7                                      7

E                                  8                                      8

a. Which atom has the highest mass number?

b. Which two atoms are isotopes?

c. Which atom has the least number of electrons?

d. Which atom will have electronic configuration 1 is to 2s to 2p3?

e. Which of atom contain the most number of electrons