Question

3 multiple choice 1 point dmitri mendeleev’s version of the periodic table was used to predict the properties of undiscovered elements. one example of this was... silicon. cobalt. aluminum. gallium 4 multiple choice 1 point zirconium is a strong, durable material that is often used in jewelry such as wedding rings. what is the correct electron configuration for a zirconium ion, zr²⁺? ar 4d⁴ 5s⁰ kr 4d² kr 4d⁵ 5s² ar 4d⁵

Explanation:

Question 3

Mendeleev's periodic table predicted properties of undiscovered elements. Gallium was one such element (predicted as eka - aluminum) before its discovery. Silicon, cobalt, and aluminum were already known, so gallium is the correct example.

Step 1: Determine Zirconium's Atomic Number and Electron Configuration

Zirconium (Zr) has an atomic number of 40. The electron configuration of neutral Zr is $[Kr]4d^{2}5s^{2}$ (or $[Ar]3d^{10}4s^{2}4p^{6}4d^{2}5s^{2}$). When Zr forms $Zr^{2 + }$, it loses 2 electrons. These electrons are lost from the outermost shell, which is the 5s orbital (since s electrons are lost before d electrons in transition metals). So, the electron configuration of $Zr^{2+}$ is $[Kr]4d^{2}$ (or $[Ar]3d^{10}4s^{2}4p^{6}4d^{2}$). Let's check the options:

• Option 1: $[Ar]4d^{2}5s^{2}$ is the configuration of neutral Zr (or a mis - written version), not $Zr^{2+}$.
• Option 2: $[Kr]4d^{2}$ matches our calculation as we lost 2 electrons from the 5s orbital of Zr's neutral configuration.
• Option 3: $[Kr]4d^{2}5s^{2}$ is the neutral Zr configuration, not $Zr^{2+}$.
• Option 4: $[Ar]4d^{2}$ is incorrect because Zr is in the period after Ar, and its noble gas core should be Kr (or Ar with the next shells filled), but the electron count would be wrong here.

Step 2: Confirm the Correct Option

Based on the electron configuration rules for transition metal ions (losing s electrons first), the correct electron configuration for $Zr^{2+}$ is $[Kr]4d^{2}$.

Answer:

D. gallium

Question 4