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Which trends are observed when the elements in Period 3 on the Periodic Table are considered in order of increasing atomic number?

(1) The atomic radius decreases, and the first ionization energy generally increases.

(2) The atomic radius decreases, and the first ionization energy generally decreases.

(3) The atomic radius increases, and the first ionization energy generally increases.

(4) The atomic radius increases, and the first ionization energy generally decreases.

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5 answers

  1. What do you think and why?

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  2. i know its either 1 or 2 because i know the radius will decrease but i don't know about the ionization energy..

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  3. You are right. The radius decreases. But we can figures out the why for both parts by the following:
    Think about this. Let's pick the first element in the period (Na) and the last element in the period (Cl).
    Na has 11 protons (+ charge) in the nucleus. Cl has 17 + charges in the nucleus. Which will pull harder on trying to get those electrons (remember + charges attract negative charges) to come in with them. Of course, the 17+ charges will pull harder; therefore, the Cl is smaller than the Na.
    Now for ionization potential.
    If we are trying to pull the outside electron away, which will be harder? To pull an electron (with a negative charge) away from 11+ charges or to pull an electron away from 17+ charges. Of course it will be harder to pull an electron away from 17+ charges won't it. So the ionization potential generall increases as we go from left to right.

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  4. so that mean the answer is number 1?

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  5. yes

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