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Chapter 3: Problem 139

Postulate a reason why the first ionization energy increases as we progress from left to right across a period.

Short Answer

Expert verified
The first ionization energy increases from left to right across a period in the periodic table due to the increase in effective nuclear charge and the relatively constant shielding effect. This results in a stronger attraction between electrons and the nucleus, making it more difficult to remove the outermost electron, hence requiring more energy.

Step by step solution

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1. Introduction to Ionization Energy

Ionization energy is the amount of energy required to remove an electron from an isolated gaseous atom or ion in its ground state. The first ionization energy refers to the energy required to remove the outermost electron, or in other words, the closest electron to the nucleus.
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2. Recognizing the trend in the periodic table

As we move from left to right across a period in the periodic table, the first ionization energy generally increases. That is, more energy is required to remove an electron from the atoms of elements located further to the right.
03

3. Increase of effective nuclear charge

The increase in ionization energy across a period can be attributed to the increase in effective nuclear charge experienced by the electrons. As we move from left to right, the atomic number increases, meaning there are more protons in the nucleus, resulting in a stronger positive charge. Along with this, the increase in the positive charge is not fully countered by the increase in electron-electron repulsion, since electrons are added to the same energy level or shell.
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4. The shielding effect

As we move across a period, the shielding effect remains relatively constant. Shielding refers to the ability of inner electrons to repel outer electrons, reducing the effective nuclear charge experienced by outer electrons. Since the electrons are added to the same shell, there is minimal change in the shielding effect from the inner electrons.
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5. Attraction between electrons and the nucleus

Due to the increase in effective nuclear charge and minimal change in shielding, the attraction between negatively charged electrons and the positively charged nucleus increases. The stronger the attraction, the more energy is required to remove an electron from the atom.
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6. Conclusion and reasoning

In conclusion, the first ionization energy increases as we progress from left to right across a period in the periodic table due to the increase in the effective nuclear charge and the relatively constant shielding effect. This leads to a stronger attraction between electrons and the nucleus, increasing the amount of energy required to remove the outermost electron.

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Most popular questions from this chapter

Suppose you added one electron and one proton to an atom somewhere in the middle of a period. Which way would this move you on the periodic table and by how many places?

Write the name of each element: (a) \(\mathrm{Be}\) (b) \(\mathrm{Mg}\) (c) \(\mathrm{Fe}\) (d) \(S\) (e) \(\mathrm{Ar}\) (f) \(\mathrm{Cu}\)

Explain why Rutherford expected all alpha particles to go through the gold foil undisturbed.

While an atom's mass number and its atomic mass are not the same, they are often quite close to one another. Consider the following: Uranium- 235 has an atomic mass of \(235.04393\) amu and a percent abundance of \(0.73 \%\). Uranium-238 has an atomic mass of \(238.0508\) amu and a percent abundance of \(99.27 \%\). Without doing any calculations or consulting any other sources, which of the following do you think represents the atomic mass of naturally occurring uranium? (a) \(234.04 \mathrm{amu}\) (b) \(236.03 \mathrm{amu}\) (c) \(237.03\) amu (d) \(238.03\) amu (e) \(238.07\) amu Explain how you made your choice.

How did Mendeleev's discovery aid in discovering additional elements?
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