Worksheet: Atomic Structure - Practice problems on atomic particles and isotope notation.

Worksheet: Atomic Structure

Let's solve each problem step by step.

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#### Problem 1:
A neutral atom has 54 protons and 70 neutrons.

- (a) What is its atomic number?
- The atomic number (Z) is equal to the number of protons in the nucleus.
- Answer: 54

- (b) What is its mass number?
- The mass number (A) is the sum of the number of protons and neutrons.
- Mass number = Number of protons + Number of neutrons
- Mass number = 54 + 70 = 124
- Answer: 124

- (c) How many electrons does the atom have?
- In a neutral atom, the number of electrons is equal to the number of protons.
- Answer: 54

- (d) What is the name of the atom?
- The element with atomic number 54 is Xenon (Xe).
- Answer: Xenon (Xe)

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#### Problem 2:
Give the symbol and number of protons in the following atoms:

- Lithium (Li):
- Symbol: Li
- Protons: 3
- Bromine (Br):
- Symbol: Br
- Protons: 35
- Iron (Fe):
- Symbol: Fe
- Protons: 26
- Copper (Cu):
- Symbol: Cu
- Protons: 29
- Oxygen (O):
- Symbol: O
- Protons: 8
- Mercury (Hg):
- Symbol: Hg
- Protons: 80
- Krypton (Kr):
- Symbol: Kr
- Protons: 36
- Helium (He):
- Symbol: He
- Protons: 2

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#### Problem 3:
Give the symbol and number of electrons in a neutral atom of:

- Uranium (U):
- Symbol: U
- Electrons: 92
- Chlorine (Cl):
- Symbol: Cl
- Electrons: 17
- Boron (B):
- Symbol: B
- Electrons: 5
- Iodine (I):
- Symbol: I
- Electrons: 53
- Antimony (Sb):
- Symbol: Sb
- Electrons: 51
- Argon (Ar):
- Symbol: Ar
- Electrons: 18
- Gold (Au):
- Symbol: Au
- Electrons: 79
- Silver (Ag):
- Symbol: Ag
- Electrons: 47

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#### Problem 4:
Give the isotope symbol and number of neutrons in the following elements. Show your calculations.

- Barium - 137:
- Atomic number (Z) of Barium (Ba) = 56
- Mass number (A) = 137
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 137 - 56 = 81
- Isotope symbol: $^{137}_{56}\text{Ba}$
- Answer: $^{137}_{56}\text{Ba}$, 81 neutrons

- Bismuth - 209:
- Atomic number (Z) of Bismuth (Bi) = 83
- Mass number (A) = 209
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 209 - 83 = 126
- Isotope symbol: $^{209}_{83}\text{Bi}$
- Answer: $^{209}_{83}\text{Bi}$, 126 neutrons

- Carbon - 12:
- Atomic number (Z) of Carbon (C) = 6
- Mass number (A) = 12
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 12 - 6 = 6
- Isotope symbol: $^{12}_{6}\text{C}$
- Answer: $^{12}_{6}\text{C}$, 6 neutrons

- Hydrogen - 1:
- Atomic number (Z) of Hydrogen (H) = 1
- Mass number (A) = 1
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 1 - 1 = 0
- Isotope symbol: $^{1}_{1}\text{H}$
- Answer: $^{1}_{1}\text{H}$, 0 neutrons

- Fluorine - 19:
- Atomic number (Z) of Fluorine (F) = 9
- Mass number (A) = 19
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 19 - 9 = 10
- Isotope symbol: $^{19}_{9}\text{F}$
- Answer: $^{19}_{9}\text{F}$, 10 neutrons

- Mercury - 201:
- Atomic number (Z) of Mercury (Hg) = 80
- Mass number (A) = 201
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 201 - 80 = 121
- Isotope symbol: $^{201}_{80}\text{Hg}$
- Answer: $^{201}_{80}\text{Hg}$, 121 neutrons

- Magnesium - 24:
- Atomic number (Z) of Magnesium (Mg) = 12
- Mass number (A) = 24
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 24 - 12 = 12
- Isotope symbol: $^{24}_{12}\text{Mg}$
- Answer: $^{24}_{12}\text{Mg}$, 12 neutrons

- Europium - 152:
- Atomic number (Z) of Europium (Eu) = 63
- Mass number (A) = 152
- Number of neutrons = Mass number - Atomic number
- Number of neutrons = 152 - 63 = 89
- Isotope symbol: $^{152}_{63}\text{Eu}$
- Answer: $^{152}_{63}\text{Eu}$, 89 neutrons

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#### Problem 5:
Give the symbols for the nuclides described by the following particles. Include the atomic number (A) and the mass number (M).

- (a) 92 protons, 145 neutrons:
- Atomic number (Z) = 92
- Mass number (A) = Number of protons + Number of neutrons = 92 + 145 = 237
- Element with Z = 92 is Uranium (U)
- Nuclide symbol: $^{237}_{92}\text{U}$
- Answer: $^{237}_{92}\text{U}$

- (b) 20 protons, 20 neutrons:
- Atomic number (Z) = 20
- Mass number (A) = Number of protons + Number of neutrons = 20 + 20 = 40
- Element with Z = 20 is Calcium (Ca)
- Nuclide symbol: $^{40}_{20}\text{Ca}$
- Answer: $^{40}_{20}\text{Ca}$

- (c) 8 protons, 10 neutrons:
- Atomic number (Z) = 8
- Mass number (A) = Number of protons + Number of neutrons = 8 + 10 = 18
- Element with Z = 8 is Oxygen (O)
- Nuclide symbol: $^{18}_{8}\text{O}$
- Answer: $^{18}_{8}\text{O}$

- (d) 22 protons, 23 neutrons:
- Atomic number (Z) = 22
- Mass number (A) = Number of protons + Number of neutrons = 22 + 23 = 45
- Element with Z = 22 is Titanium (Ti)
- Nuclide symbol: $^{45}_{22}\text{Ti}$
- Answer: $^{45}_{22}\text{Ti}$

- (e) 82 protons, 125 neutrons:
- Atomic number (Z) = 82
- Mass number (A) = Number of protons + Number of neutrons = 82 + 125 = 207
- Element with Z = 82 is Lead (Pb)
- Nuclide symbol: $^{207}_{82}\text{Pb}$
- Answer: $^{207}_{82}\text{Pb}$

- (f) 18 protons, 22 neutrons:
- Atomic number (Z) = 18
- Mass number (A) = Number of protons + Number of neutrons = 18 + 22 = 40
- Element with Z = 18 is Argon (Ar)
- Nuclide symbol: $^{40}_{18}\text{Ar}$
- Answer: $^{40}_{18}\text{Ar}$

- (g) 80 protons, 119 neutrons:
- Atomic number (Z) = 80
- Mass number (A) = Number of protons + Number of neutrons = 80 + 119 = 199
- Element with Z = 80 is Mercury (Hg)
- Nuclide symbol: $^{199}_{80}\text{Hg}$
- Answer: $^{199}_{80}\text{Hg}$

- (h) 25 protons, 32 neutrons:
- Atomic number (Z) = 25
- Mass number (A) = Number of protons + Number of neutrons = 25 + 32 = 57
- Element with Z = 25 is Manganese (Mn)
- Nuclide symbol: $^{57}_{25}\text{Mn}$
- Answer: $^{57}_{25}\text{Mn}$

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Final Answers:

1. (a) 54, (b) 124, (c) 54, (d) Xenon (Xe)
2. Lithium (Li): 3, Bromine (Br): 35, Iron (Fe): 26, Copper (Cu): 29, Oxygen (O): 8, Mercury (Hg): 80, Krypton (Kr): 36, Helium (He): 2
3. Uranium (U): 92, Chlorine (Cl): 17, Boron (B): 5, Iodine (I): 53, Antimony (Sb): 51, Argon (Ar): 18, Gold (Au): 79, Silver (Ag): 47
4. Barium - 137: $^{137}_{56}\text{Ba}$, 81 neutrons; Bismuth - 209: $^{209}_{83}\text{Bi}$, 126 neutrons; Carbon - 12: $^{12}_{6}\text{C}$, 6 neutrons; Hydrogen - 1: $^{1}_{1}\text{H}$, 0 neutrons; Fluorine - 19: $^{19}_{9}\text{F}$, 10 neutrons; Mercury - 201: $^{201}_{80}\text{Hg}$, 121 neutrons; Magnesium - 24: $^{24}_{12}\text{Mg}$, 12 neutrons; Europium - 152: $^{152}_{63}\text{Eu}$, 89 neutrons
5. (a) $^{237}_{92}\text{U}$, (b) $^{40}_{20}\text{Ca}$, (c) $^{18}_{8}\text{O}$, (d) $^{45}_{22}\text{Ti}$, (e) $^{207}_{82}\text{Pb}$, (f) $^{40}_{18}\text{Ar}$, (g) $^{199}_{80}\text{Hg}$, (h) $^{57}_{25}\text{Mn}$

Final Boxed Answer:
\[
\boxed{
\begin{array}{l}
\text{1. (a) 54, (b) 124, (c) 54, (d) Xenon (Xe)} \\
\text{2. Lithium (Li): 3, Bromine (Br): 35, Iron (Fe): 26, Copper (Cu): 29, Oxygen (O): 8, Mercury (Hg): 80, Krypton (Kr): 36, Helium (He): 2} \\
\text{3. Uranium (U): 92, Chlorine (Cl): 17, Boron (B): 5, Iodine (I): 53, Antimony (Sb): 51, Argon (Ar): 18, Gold (Au): 79, Silver (Ag): 47} \\
\text{4. Barium - 137: } ^{137}_{56}\text{Ba}, \text{ 81 neutrons; Bismuth - 209: } ^{209}_{83}\text{Bi}, \text{ 126 neutrons; Carbon - 12: } ^{12}_{6}\text{C}, \text{ 6 neutrons; Hydrogen - 1: } ^{1}_{1}\text{H}, \text{ 0 neutrons; Fluorine - 19: } ^{19}_{9}\text{F}, \text{ 10 neutrons; Mercury - 201: } ^{201}_{80}\text{Hg}, \text{ 121 neutrons; Magnesium - 24: } ^{24}_{12}\text{Mg}, \text{ 12 neutrons; Europium - 152: } ^{152}_{63}\text{Eu}, \text{ 89 neutrons} \\
\text{5. (a) } ^{237}_{92}\text{U}, \text{ (b) } ^{40}_{20}\text{Ca}, \text{ (c) } ^{18}_{8}\text{O}, \text{ (d) } ^{45}_{22}\text{Ti}, \text{ (e) } ^{207}_{82}\text{Pb}, \text{ (f) } ^{40}_{18}\text{Ar}, \text{ (g) } ^{199}_{80}\text{Hg}, \text{ (h) } ^{57}_{25}\text{Mn}
\end{array}
}
\]