Question

practice: isotope calculations #2

1. complete the following table

nuclear notation, atom or ion?, atomic #, mass #, # of protons, # of neutrons, # of electrons
24, 11, 11
³²s⁻², ion, 16, 32, 16
6, 14, 6
²⁴mg, atom
64, 34, 28
²⁰⁷pb, atom
53, 127, 53
²³⁸u, atom
20, 21, 20
20, 40, 18

1. explain the difference between mass number and average atomic mass.
2. which tells you the most common version of an element?
3. place a star next to each column that represents an isotope that is the most common for that element.
4. explain the difference between an atom and an ion.

Explanation:

Step1: Recall atomic structure relationships

Atomic number = number of protons. Mass number = number of protons + number of neutrons. In a neutral atom, number of electrons = number of protons. In an ion, adjust electrons based on charge.

Step2: First row

Atomic number is 11 (given number of protons). Mass number is 24. Number of neutrons = Mass number - Number of protons = 24 - 11 = 13. Nuclear notation: $^{24}_{11}X$ (where X is the element which is sodium, Na).

Step3: Second row (for $^{32}S^{- 2}$)

Number of neutrons = Mass number - Number of protons = 32 - 16 = 16. Since it is a - 2 ion, number of electrons = 16+2 = 18.

Step4: Third row

Atomic number is 6 (given). Element is carbon. Mass number is 14. Number of neutrons = 14 - 6 = 8. Nuclear notation: $^{14}_{6}C$.

Step5: Fourth row (for $^{24}Mg$)

Atomic number of Mg is 12. Mass number is 24. Number of neutrons = 24 - 12 = 12. Number of electrons in neutral atom = 12.

Step6: Fifth row

Atomic number = number of protons = 34. Element is selenium (Se). Mass number = 64. Number of neutrons = 64 - 34 = 30. Nuclear notation: $^{64}_{34}Se$.

Step7: Sixth row (for $^{207}Pb$)

Atomic number of Pb is 82. Mass number is 207. Number of neutrons = 207 - 82 = 125. Number of electrons in neutral atom = 82.

Step8: Seventh row

Atomic number is 53. Element is iodine (I). Mass number is 127. Number of neutrons = 127 - 53 = 74. Nuclear notation: $^{127}_{53}I$.

Step9: Eighth row (for $^{238}U$)

Atomic number of U is 92. Mass number is 238. Number of neutrons = 238 - 92 = 146. Number of electrons in neutral atom = 92.

Step10: Ninth row

Atomic number = number of protons = 20. Element is calcium (Ca). Mass number = 20 + 21 = 41. Nuclear notation: $^{41}_{20}Ca$.

Step11: Tenth row

Atomic number is 20. Element is calcium. Mass number is 40. Number of neutrons = 40 - 20 = 20. Since number of electrons is 18, it is a $Ca^{2 + }$ ion. Nuclear notation: $^{40}_{20}Ca^{2+}$.

1. Difference between mass number and average atomic mass:

• Mass number is the sum of protons and neutrons in a single isotope of an element. It is a whole - number value for a particular isotope.
• Average atomic mass is the weighted average of the masses of all naturally - occurring isotopes of an element, taking into account their relative abundances. It is usually a non - whole number.

1. Most common version of an element:

The most common version of an element is often referred to as the most abundant isotope. The average atomic mass is closest to the mass number of the most abundant isotope.

1. Without specific abundance data, we can't accurately place stars. But generally, for example, $^{12}C$ is the most common isotope of carbon, $^{24}Mg$ is a common isotope of magnesium, $^{32}S$ is a common isotope of sulfur etc.
2. Difference between an atom and an ion:

• An atom is a neutral particle where the number of protons is equal to the number of electrons.
• An ion is a charged particle. A cation has lost electrons (number of protons>number of electrons) and has a positive charge. An anion has gained electrons (number of protons<number of electrons) and has a negative charge.

Answer:

1.

Nuclear Notation	Atom or Ion?	Atomic #	Mass #	# of Protons	# of Neutrons	# of Electrons
$^{32}_{16}S^{-2}$	Ion	16	32	16	16	18
$^{14}_{6}C$	Atom	6	14	6	8	6
$^{24}_{12}Mg$	Atom	12	24	12	12	12
$^{64}_{34}Se$	Atom	34	64	34	30	34
$^{207}_{82}Pb$	Atom	82	207	82	125	82
$^{127}_{53}I$	Atom	53	127	53	74	53
$^{238}_{92}U$	Atom	92	238	92	146	92
$^{41}_{20}Ca$	Atom	20	41	20	21	20
$^{40}_{20}Ca^{2+}$	Ion	20	40	20	20	18

1. Mass number is for a single isotope (sum of protons and neutrons), average atomic mass is weighted average of all isotopes.
2. The most abundant isotope.
3. Varies by element, common isotopes like $^{12}C$, $^{24}Mg$ etc. (but specific answer needs abundance data).
4. Atom is neutral (protons = electrons), ion is charged (protons≠electrons).