Answer: Periodic Trends
Zeff increases because the positive charge of the nucleus increases while the outermost electrons stay the same distance from the nucleus (filling the same orbital). In other words, going across a period, the outermost electrons are more tightly held. This explains the trend in atomic radius.
It refers to how strongly an atom attracts electrons from other atoms. Electronegativity is a measure of an atom's ability to draw electrons towards itself, or the ability of the nucleus to hold electrons tightly
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