Question

for each statement below, write (t) true or (f) false.

1. the number of neutrons in an atom is referred to as its atomic number.
2. the periodic table is arranged by increasing atomic number.
3. atomic number is equal to the number of electrons in an atom.
4. the number of protons in an atom identifies it as an atom of a particular element.
5. most atoms have either a positive or a negative charge.

label the mass number and the atomic number on the following isotope notation.
6.
7.
write each isotope below in symbolic notation. use the periodic table to determine the atomic number of each isotope.

1. neon - 22
2. uranium - 234

answer the following questions.

1. lead has an atomic number of 82. how many protons and electrons does lead have if its neutral?
2. oxygen has 10 electrons. how many protons does oxygen have if it has a \ - 2\ charge?
3. polonium has an atomic number of 84. how many protons and electrons does it have if its neutral?
4. how many protons and electrons does calcium have if its got a \2 + \ charge?
5. calculate the atomic mass of the element x. then use the periodic table to identify the element. show all your work.

Explanation:

Step1: Determine the number of protons and electrons for neutral atoms

• For a neutral atom, the number of protons is equal to the atomic number, and the number of electrons is equal to the number of protons.
• For lead with atomic number \(82\): Protons \(= 82\), Electrons \(= 82\)
• For polonium with atomic number \(84\): Protons \(= 84\), Electrons \(= 84\)

Step2: Determine the number of protons for an ion with charge

• The charge of an ion is given by \(Charge=Protons - Electrons\)
• For oxygen with \(10\) electrons and \(- 2\) charge: \(-2=Protons - 10\), so \(Protons=10 - 2=8\)
• For calcium with \(2+\) charge: Calcium has atomic number \(20\) (from periodic table), so Protons \(=20\), and \(2 = 20 - Electrons\), so \(Electrons=20 - 2=18\)

Step3: Calculate atomic mass of element X

• The formula for average atomic mass is \(\bar{M}=\sum_{i}(M_{i}\times A_{i})\) where \(M_{i}\) is the mass of isotope \(i\) and \(A_{i}\) is the percent abundance (in decimal) of isotope \(i\)
• For \(^{27}X\): \(M_{1} = 27.977\), \(A_{1}=0.9223\)
• For \(^{28}X\): \(M_{2}=28.976\), \(A_{2}=0.0467\)
• For \(^{29}X\): \(M_{3}=29.974\), \(A_{3}=0.0310\)
• \(\bar{M}=(27.977\times0.9223)+(28.976\times0.0467)+(29.974\times0.0310)\)
• \(27.977\times0.9223 = 27.977\times(1 - 0.0777)=27.977-27.977\times0.0777\approx27.977 - 2.174=25.803\)
• \(28.976\times0.0467\approx1.353\)
• \(29.974\times0.0310\approx0.929\)
• \(\bar{M}\approx25.803 + 1.353+0.929=28.085\) (using more precise calculation: \(27.977\times0.9223=27.977\times\frac{92.23}{100}=27.977\times0.9223 = 25.803\), \(28.976\times0.0467 = 28.976\times\frac{4.67}{100}=1.353\), \(29.974\times0.0310=29.974\times\frac{3.10}{100}=0.929\), sum \(25.803+1.353 + 0.929=28.085\))
• From periodic table, the element with atomic mass approximately \(28.085\) is silicon (\(Si\))

Answer:

1. \(F\)
2. \(T\)
3. \(T\) (for neutral atom)
4. \(T\)
5. \(F\) (most atoms are neutral)
6. Mass number (\(24\))
7. Atomic number (\(12\))
8. \(_{10}^{22}Ne\)
9. \(_{92}^{234}U\)
10. Protons: \(82\), Electrons: \(82\)
11. Protons: \(8\)
12. Protons: \(84\), Electrons: \(84\)
13. Protons: \(20\), Electrons: \(18\)
14. Atomic mass of \(X\approx28.085\), element is \(Si\) (silicon)