Question

choose the correct trend in ionization energy
ionization energies decrease going across a row in the periodic table from left to right. it increases going down a column
ionization energies increase going across a row in the periodic table from left to right; it increases going down a column
ionization energies decrease going across a row in the periodic table from left to right. it decreases going down a column
ionization energies increase going across a row in the periodic table from left to right; it decreases going down a column
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part b
choose the correct trend in atomic size.
atomic size decreases down a group; it decreases across a period from left to right
atomic size increases down a group; it decreases across a period from left to right
atomic size decreases down a group; it increases across a period from left to right
atomic size increases down a group; it increases across a period from left to right

Explanation:

• Ionization energy:
• Across a period (left - right): As the atomic number increases, the nuclear charge increases while the shielding effect remains relatively constant. This stronger nuclear - electron attraction makes it harder to remove an electron, so ionization energy increases.
• Down a group: The number of electron shells increases. The outermost electrons are further from the nucleus and more shielded. So, it is easier to remove an electron, and ionization energy decreases.
• Atomic size:
• Down a group: New electron shells are added. The outermost electrons are in higher - energy levels, farther from the nucleus, so atomic size increases.
• Across a period (left - right): The nuclear charge increases. Electrons are added to the same shell. The increased nuclear attraction pulls the electrons closer to the nucleus, so atomic size decreases.

Answer:

• For ionization energy: Ionization energies increase going across a row in the periodic table from left to right; it decreases going down a column.
• For atomic size: atomic size increases down a group; it decreases across a period from left to right.