QUESTION IMAGE
Question
the mendeleev lab of 1869
introduction:
the elements had been listed and carefully arranged before dmitri mendeleev. they had even been organized by similar properties before. so why is mendeleev’s periodic table the one that has endured? the answer to that question lies in the fact that mendeleev purposefully left “gaps” in his arrangement and boldly predicted the existence of elements there with specific properties.
your task:
you are given “tiles” of known element and 7 unknown elements with various properties about each of them. use your knowledge of the periodic table to determine the identity of each of the seven unknown elements.
□ all the elements (known and unknown are from family a only groups 1, 2,13-18).
□ none of the known elements serve as one of the seven unknown elements.
□ no radioactive elements are used during this experiment. the relevant radioactive elements include fr, ra, at, and rn.
□ you may not use your textbook nor other reference materials. you have been provided with enough information to determine each of the unknown elements.
the guiding question for this investigation is, “what is the identity of each of the seven unknown elements?”
procedure:
- the element tiles have already been arranged for the known elements in a crude representation of the periodic table.
- the spot for the seven unknown elements have been identified by the green “?” tiles. inspect the properties of the unknowns to see where their properties would best “fit” the trends of the elements of each group.
- in your data table, assign the proper element name to each of the unknowns. you may use a modern periodic table to accomplish this. record the symbol for each of the “unknowns” in your data table.
- provide sufficient evidence and reasoning to support each of your claim with regards to the identity of each unknown.
data and results:
| unknown | identity | evidence and reasoning |
|---|---|---|
| unknown #2<br>atomic number ?<br>physical state solid<br>density 1.74 g/cm³<br>conductivity good<br>melting point 651°c<br>color silvery white<br>reactivity reactive<br>ionization energy 7.646 | ||
| unknown #3<br>atomic number ?<br>physical state solid<br>density 1.90 g/cm³<br>conductivity poor<br>melting point 115°c<br>color yellow<br>reactivity reactive<br>ionization energy 10.36 |
To solve for the identity of each unknown element, we analyze their properties and match them to the periodic table trends (e.g., group/period trends for physical state, density, conductivity, melting point, color, reactivity, ionization energy). Here's the breakdown for each unknown:
Unknown #1
Step 1: Analyze Properties
- Physical State: Gas
- Density: \( 0.00374 \, \text{g/cm}^3 \) (very low, typical of noble gases)
- Conductivity: Very poor (noble gases are non-conductive)
- Melting Point: \( -158.6^\circ \text{C} \) (low, consistent with noble gases)
- Color: Colorless
- Reactivity: Almost none (noble gases are inert)
- Ionization Energy: \( 13.000 \) (high, characteristic of noble gases)
Step 2: Match to Periodic Table
Noble gases (Group 18) have these properties. The density, melting point, and ionization energy match Neon (Ne) or a similar noble gas, but given the low density and melting point, it is most consistent with Neon (Ne) (or another noble gas like Argon, but Neon’s properties align closely with the low density and melting point here).
Unknown #2
Step 1: Analyze Properties
- Physical State: Solid
- Density: \( 1.74 \, \text{g/cm}^3 \)
- Conductivity: Good (metallic)
- Melting Point: \( 651^\circ \text{C} \)
- Color: Silvery white
- Reactivity: Reactive
- Ionization Energy: \( 7.646 \) (moderate, typical of Group 1 or 2 metals)
Step 2: Match to Periodic Table
Group 1 (alkali metals) or Group 2 (alkaline earth metals) have metallic properties. The density, melting point, and reactivity suggest a Group 1 metal. Sodium (Na) or Potassium (K)? Wait, density \( 1.74 \, \text{g/cm}^3 \) and melting point \( 651^\circ \text{C} \) match Sodium (Na) (density ~0.97, no—wait, maybe Lithium (Li)? No, density of Li is ~0.53. Wait, maybe Group 2: Magnesium (Mg)? Density ~1.74, melting point ~650°C, silvery white, reactive, good conductor. Yes! Magnesium (Mg) fits: density \( 1.74 \, \text{g/cm}^3 \), melting point \( 650^\circ \text{C} \) (close to 651), reactive, good conductor.
Unknown #3
Step 1: Analyze Properties
- Physical State: Solid
- Density: \( 1.90 \, \text{g/cm}^3 \)
- Conductivity: Poor (non-metal or metalloid)
- Melting Point: \( 115^\circ \text{C} \) (low for a solid)
- Color: Yellow
- Reactivity: Reactive
- Ionization Energy: \( 10.36 \) (moderate-high)
Step 2: Match to Periodic Table
Yellow, reactive solid with poor conductivity: Sulfur (S). Sulfur is a non-metal, yellow, solid at room temp, melts at ~115°C, reactive, poor conductor, density ~2.07 (close to 1.90, slight variation possible).
Final Identities (Example for 3 Unknowns; Full 7 Would Follow Similar Trend Analysis)
| Unknown | Identity | Evidence & Reasoning |
|---|---|---|
| #2 | Magnesium (Mg) | Solid, good conductor, silvery white, reactive, density/melting point (Group 2 trends). |
| #3 | Sulfur (S) | Yellow solid, poor conductor, reactive, melting point/density (Group 16 trends). |
(For the full 7 unknowns, repeat this process for each, using periodic table trends for groups 1, 2, 13–18, excluding radioactive elements like Fr, Ra, At, Rn.)
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To solve for the identity of each unknown element, we analyze their properties and match them to the periodic table trends (e.g., group/period trends for physical state, density, conductivity, melting point, color, reactivity, ionization energy). Here's the breakdown for each unknown:
Unknown #1
Step 1: Analyze Properties
- Physical State: Gas
- Density: \( 0.00374 \, \text{g/cm}^3 \) (very low, typical of noble gases)
- Conductivity: Very poor (noble gases are non-conductive)
- Melting Point: \( -158.6^\circ \text{C} \) (low, consistent with noble gases)
- Color: Colorless
- Reactivity: Almost none (noble gases are inert)
- Ionization Energy: \( 13.000 \) (high, characteristic of noble gases)
Step 2: Match to Periodic Table
Noble gases (Group 18) have these properties. The density, melting point, and ionization energy match Neon (Ne) or a similar noble gas, but given the low density and melting point, it is most consistent with Neon (Ne) (or another noble gas like Argon, but Neon’s properties align closely with the low density and melting point here).
Unknown #2
Step 1: Analyze Properties
- Physical State: Solid
- Density: \( 1.74 \, \text{g/cm}^3 \)
- Conductivity: Good (metallic)
- Melting Point: \( 651^\circ \text{C} \)
- Color: Silvery white
- Reactivity: Reactive
- Ionization Energy: \( 7.646 \) (moderate, typical of Group 1 or 2 metals)
Step 2: Match to Periodic Table
Group 1 (alkali metals) or Group 2 (alkaline earth metals) have metallic properties. The density, melting point, and reactivity suggest a Group 1 metal. Sodium (Na) or Potassium (K)? Wait, density \( 1.74 \, \text{g/cm}^3 \) and melting point \( 651^\circ \text{C} \) match Sodium (Na) (density ~0.97, no—wait, maybe Lithium (Li)? No, density of Li is ~0.53. Wait, maybe Group 2: Magnesium (Mg)? Density ~1.74, melting point ~650°C, silvery white, reactive, good conductor. Yes! Magnesium (Mg) fits: density \( 1.74 \, \text{g/cm}^3 \), melting point \( 650^\circ \text{C} \) (close to 651), reactive, good conductor.
Unknown #3
Step 1: Analyze Properties
- Physical State: Solid
- Density: \( 1.90 \, \text{g/cm}^3 \)
- Conductivity: Poor (non-metal or metalloid)
- Melting Point: \( 115^\circ \text{C} \) (low for a solid)
- Color: Yellow
- Reactivity: Reactive
- Ionization Energy: \( 10.36 \) (moderate-high)
Step 2: Match to Periodic Table
Yellow, reactive solid with poor conductivity: Sulfur (S). Sulfur is a non-metal, yellow, solid at room temp, melts at ~115°C, reactive, poor conductor, density ~2.07 (close to 1.90, slight variation possible).
Final Identities (Example for 3 Unknowns; Full 7 Would Follow Similar Trend Analysis)
| Unknown | Identity | Evidence & Reasoning |
|---|---|---|
| #2 | Magnesium (Mg) | Solid, good conductor, silvery white, reactive, density/melting point (Group 2 trends). |
| #3 | Sulfur (S) | Yellow solid, poor conductor, reactive, melting point/density (Group 16 trends). |
(For the full 7 unknowns, repeat this process for each, using periodic table trends for groups 1, 2, 13–18, excluding radioactive elements like Fr, Ra, At, Rn.)