First and Second Ionization Energies

What is meant by first ionization energy?

• The energy required to remove the first electron from an atom

• The energy required to remove the second electron from an atom

• The energy required to add an electron to an atom

• The energy required to split an atom

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Which element has the smallest first ionization energy? The largest? What are their values?

• Small: He, 10 kJ/mol

  Large: Na, 520 kJ/mol

• Small: H, 10 kJ/mol

  Large: Ne, 2080 kJ/mol

• Small: Li, 520 kJ/mol

  Large: Ne, 2080 kJ/mol

• Small: He, 10 kJ/mol

  Large: Ne, 2080 kJ/mol

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What generally happens to the first ionization energy of the elements within a period as the atomic number of the elements increases?

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What accounts for the general trend in the first ionization energy of the elements within a period?

• Atomic mass

• Atomic radius

• Number of valence electrons

• Number of protons

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How is a jump in ionization energy related to the valence electrons of the element?

• A jump occurs when valence electrons are added

• A jump occurs when valence electrons are removed

• A jump occurs when valence electrons change energy levels

• A jump occurs when valence electrons are shared

Answer explanation

The jump refers to the general increase in successive ionization energies. Notice that from H to He, there's a major jump. This occurs as we try to remove electrons from stable orbitals.

A dip occurs (e.g., from Be to B) when valence electrons are removed from unstable orbitals (s² vs p¹).

A big dip occurs (e.g., from Ne to Na) when valence electrons are removed from unstable orbitals (s¹ vs p⁶).

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Based on the graph, rank the group 2 elements in periods 1-5 in decreasing order of first ionization energy.

• Be, Mg, Ca, Sr

• Ba, Sr, Ca, Mg

• Mg, Ca, Sr, Ba

• Ca, Sr, Ba, Mg

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With increasing ​ (a)   , the size of the atom ​ (b)   and the valence electron are​ (c)   from the nucleus. Consequently, ​ (d)   energy is needed to remove them, and the first ionization energy decreases.

• atomic number
• increases
• farther
• less
• mass number
• decreases
• closer
• more

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