Which statement describes periodic trends across a period on the periodic table?

Which statement describes periodic trends across a period on the periodic table?

• A. Atomic radius increases from left to right.
• B. Ionization energy generally increases from left to right.
• C. Electronegativity decreases from left to right.
• D. Electron affinity becomes less negative across a period.

Answer: (C)

Across a period, the number of protons increases while shielding stays relatively similar, so the effective nuclear charge felt by valence electrons grows. This pulls electrons closer to the nucleus, causing atomic radius to decrease. Because the electrons are held more tightly, more energy is required to remove one, so ionization energy tends to rise from left to right. At the same time, atoms become more eager to attract additional electrons to complete a stable valence shell, so electronegativity increases across a period. Electron affinity generally becomes more negative as you move to the right, meaning adding an electron releases more energy, especially as you approach the highly reactive nonmetals. The statements that atomic radius increases, electronegativity decreases, or electron affinity becomes less negative do not match these trends.

Across a period, the number of protons increases while shielding stays relatively similar, so the effective nuclear charge felt by valence electrons grows. This pulls electrons closer to the nucleus, causing atomic radius to decrease. Because the electrons are held more tightly, more energy is required to remove one, so ionization energy tends to rise from left to right. At the same time, atoms become more eager to attract additional electrons to complete a stable valence shell, so electronegativity increases across a period. Electron affinity generally becomes more negative as you move to the right, meaning adding an electron releases more energy, especially as you approach the highly reactive nonmetals. The statements that atomic radius increases, electronegativity decreases, or electron affinity becomes less negative do not match these trends.