Chapter 2, Problem 2.26QP

Model of the Atom

Consider the following depictions of two atoms, which have been greatly enlarged so you can see the subatomic particles.

1. a How many protons are present in atom A?
2. b What is the significance of the number of protons depicted in atom A or any atom?
3. c Can you identify the real element represented by the drawing of atom A? If so, what element does it represent?
4. d What is the charge on atom A? Explain how you arrived at your answer.
5. e Write the nuclide symbol of atom A.
6. f Write the atomic symbol and the atomic number of atom B.
7. g What is the mass number of atom B? How does this mass number compare with that of atom A?
8. h What is the charge on atom B?
9. i Write the nuclide symbol of atom B.
10. j Draw pictures like those above of ${}_3^{6}L{i}^{+}$ and ${}_3^{6}L{i}^{-}$ atoms. What are the mass number and atomic number of each of these atoms?
11. k Consider the two atoms depicted in this problem and the two that you just drew. What is the total number of lithium isotopes depicted? How did you make your decision?
12. l Is the mass number of an isotope of an atom equal to the mass of the isotope of the atom? Be sure to explain your answer.

Interpretation Introduction

Interpretation:

The total number of protons in atom A has to be calculated.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.

Answer to Problem 2.26QP

The total number of protons in atom A was 3.

Explanation of Solution

In the given figure it is indicated that the blue sphere is proton.  In atom A, there are totally three blue spheres.  Hence, the total number of proton is three.

Conclusion

The total number of proton present in atom A was found out.

Interpretation Introduction

Interpretation:

The significance of the total number of protons has to be given.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.

Explanation of Solution

The important significance is that with the total number of protons that is present in the nucleus is known, we can find the element.  This is because, the total number of protons is the atomic number of element and it is unique for each element.

Conclusion

The significance of total number of proton present was given.

Interpretation Introduction

Interpretation:

The element that is represented in atom A has to be identified.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.  From the atomic number we can find the element.

Explanation of Solution

The important significance is that with the total number of protons that is present in the nucleus is known, we can find the element.  This is because, the total number of protons is the atomic number of element and it is unique for each element.  Here, the total number of protons in atom A is three.  This means, the atomic number of atom A is three.  The element which has atomic number three is Lithium.

Conclusion

The element was found to be lithium.

Interpretation Introduction

Interpretation:

The total charge on atom A has to be calculated.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.  If there is less or more electrons than the total number of protons means there is a net charge on the atom.

Answer to Problem 2.26QP

The charge on atom A is zero.

Explanation of Solution

In the given figure it is indicated that the blue sphere is proton and red spheres are electrons.  In atom A, there are totally three blue spheres and three red spheres.  Hence, the total number of proton is three and electron is also three.  Each proton carry a +1 charge and each electron carries as -1 charge.  As both protons and electrons are equal in numbers, the net charge on atom A is zero.

Conclusion

The net charge on atom A was found to be zero.

Interpretation Introduction

Interpretation:

The nuclide symbol for atom A has to be written.

Concept Introduction:

If the symbol of isotope of an element is represented using both mass number and atomic number, it is known as nuclide symbol.  The mass number is present in the left side superscript of the atomic symbol of element and the atomic number is present in the left side subscript.

Answer to Problem 2.26QP

The nuclide symbol for atom A was found to be ${}_3^7\text{Li}$.

Explanation of Solution

Mass number is the total number of protons and neutrons that is present in the nucleus of an atom.  Atomic number is the total number of protons that is present in the atom.  In a neutral atom the total number of electrons and total number of protons are same.

In atom A, the total number of protons and neutrons is found as 7.  The total number of protons is found as 3.  This means mass number is 7 and atomic number is 3.  The element which has atomic number 3 is Lithium.  The nuclide symbol can be given as ${}_3^7\text{Li}$.

Conclusion

The nuclide symbol for atom A was written.

Interpretation Introduction

Interpretation:

The atomic symbol and atomic number of atom B has to be written.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.  From the atomic number we can find the element.

Explanation of Solution

The important significance is that with the total number of protons that is present in the nucleus is known, we can find the element.  This is because, the total number of protons is the atomic number of element and it is unique for each element.  Here, the total number of protons in atom B is three.  This means, the atomic number of atom B is three.  The element which has atomic number three is Lithium.  The atomic symbol of Lithium is $\text{Li}$.

Conclusion

The atomic number and atomic symbol for atom B found as three and $\text{Li}$ respectively.

Interpretation Introduction

Interpretation:

The mass number of atom B has to be calculated and it has to compared with atom A.

Concept Introduction:

The total number of protons and neutrons present in the nucleus is known as the mass number of the atom.

Answer to Problem 2.26QP

The mass number of atom B is 6.  This is different from the mass number of atom A which is 7.

Explanation of Solution

In the given figure it is indicated that the blue sphere is proton and yellow sphere is neutron.  In atom B, there are totally three blue spheres and three yellow spheres.  Hence, the total number of proton is three and total number of neutron is three.  Mass number is the sum of total number of protons and neutrons.  Therefore, the mass number is 6.  For atom A, the mass number is 7.

Conclusion

The mass number of atom B was found and compared with the mass number of atom A.

Interpretation Introduction

Interpretation:

The total charge on atom B has to be calculated.

Concept Introduction:

The total number of protons present is the atomic number of the element.  Protons are present inside the nucleus.  They carry a positive charge.  To make the atom neutral, negatively charged electrons are present outside the nucleus.  If there is less or more electrons than the total number of protons means there is a net charge on the atom.

Answer to Problem 2.26QP

The charge on atom B is zero.

Explanation of Solution

In the given figure it is indicated that the blue sphere is proton and red spheres are electrons.  In atom B, there are totally three blue spheres and three red spheres.  Hence, the total number of proton is three and electron is also three.  Each proton carry a +1 charge and each electron carries as -1 charge.  As both protons and electrons are equal in numbers, the net charge on atom B is zero.

Conclusion

The net charge on atom B was found to be zero.

Interpretation Introduction

Interpretation:

The nuclide symbol for atom B has to be written.

Concept Introduction:

If the symbol of isotope of an element is represented using both mass number and atomic number, it is known as nuclide symbol.  The mass number is present in the left side superscript of the atomic symbol of element and the atomic number is present in the left side subscript.

Answer to Problem 2.26QP

The nuclide symbol for atom B was found to be ${}_3^6\text{Li}$.

Explanation of Solution

Mass number is the total number of protons and neutrons that is present in the nucleus of an atom.  Atomic number is the total number of protons that is present in the atom.  In a neutral atom the total number of electrons and total number of protons are same.

In atom B, the total number of protons and neutrons is found as 6.  The total number of protons is found as 3.  This means mass number is 6 and atomic number is 3.  The element which has atomic number 3 is Lithium.  The nuclide symbol can be given as ${}_3^6\text{Li}$.

Conclusion

The nuclide symbol for atom B was written.

Interpretation Introduction

Interpretation:

The figures that represent ${}_3^6{\text{Li}}^{\text{+}}$ and ${}_3^6{\text{Li}}^{\text{-}}$ has to be drawn.

Explanation of Solution

From the nuclide symbol, the figures that represent the same can be drawn.

For ${}_3^6{\text{Li}}^{\text{+}}$,

The mass number is 6 and atomic number is 3.  Hence, the total number of protons is found to be three.  Total number of neutrons is found to be three.  As there is a positive charge on the given nuclide symbol, there has to be an electron less.  This means there has to be only two electrons present.  This can be represented as,

For ${}_3^6{\text{Li}}^{\text{-}}$,

The mass number is 6 and atomic number is 3.  Hence, the total number of protons is found to be three.  Total number of neutrons is found to be three.  As there is a negative charge on the given nuclide symbol, there has to be an excess electron.  This means there has to be four electrons present.  This can be represented as,

Conclusion

The given nuclide symbols are represented as figures.

Interpretation Introduction

Interpretation:

The total number of lithium isotope depicted has to be given.

Answer to Problem 2.26QP

Two different isotopes of Lithium was depicted.

Explanation of Solution

Isotopes are the one which has same atomic number but different mass number.  The difference in mass number if due to the change in number of neutrons.  Atomic number is a characteristics of each element and it is unique to each element.  The isotopes of the elements are represented as the element name followed by the mass number.

The mass number of the Lithium isotopes depicted in the given figures were 6 and 7.  Atom A has mass number of 7 and atom B has mass number of 6.  The figures drawn in part (j) has mass number of 6.  The isotopes can be represented with the name of the element followed by the mass number.  Hence, in this case, the element is Lithium.  Therefore, the isotopes are Lithium-6 and Lithium-7.  Two isotopes are depicted.

Conclusion

The total number of isotopes that are depicted was given.

Interpretation Introduction

Interpretation:

Is mass number of an isotope of an atom is equal to the mass of isotope of the atom has to be explained.

Explanation of Solution

Mass number of an isotope of an atom is the total number of protons and total number of neutrons that is present in the nucleus.  This has an integer value.  This can be related to the mass of isotope but not the atomic weight.  This is because atomic weight is not an integer and it is the mass of each and every sub-atomic particle that is present.  The atomic weight is the weighted average over isotopic masses and fractional abundances.