Question

a student chemist set out to identify three unknown elements by comparing it with the properties of known elements. below is a table of the known elements. the empty tiles represent the unknown elements.

element al si p
atomic number 13 14 15
physical state solid solid solid
density 2.7 g/cm³ 2.33 g/cm³ 1.823 g/cm³
conductivity medium intermediate poor
melting point 303°c 1410°c 44.2°c
color silvery white gray white
ionization energy 5.986 8.151 10.486

element ga as se
atomic number 31 33 34
physical state solid solid solid
density 5.904 g/cm³ 5.776 g/cm³ 4.81 g/cm³
conductivity medium poor semi-
melting point 30°c 817°c 221°c
color silvery gray gray/red/black
ionization energy 5.999 9.81 9.752

element in sn te
atomic number 49 50 52
physical state solid solid solid
density 7.31 g/cm³ 7.31 g/cm³ 6.24 g/cm³
conductivity medium good varies
melting point 157°c 232°c 450°c
color silvery white silver silvery gray
ionization energy 5.786 7.344 9.009

the table below represents the properties of each unknown element.

element unknown #1 unknown #2 unknown #3
atomic number ? ? ?
physical state solid solid solid
density 5.32 g/cm³ 6.69 g/cm³ 1.96 g/cm³
conductivity fair to poor poor poor
melting point 937°c 631°c 115°c
color gray bluish - white yellow
ionization energy 7.899 8.641 10.36

Explanation:

Step1: Compare Unknown #1 properties

Compare density ($5.32\ g/cm^3$), conductivity (fair - to - poor), melting point ($937^{\circ}C$), color (gray), ionization energy ($7.899$) with known elements. As has density $5.776\ g/cm^3$, poor conductivity, gray color and ionization energy close to Unknown #1. So Unknown #1 is likely As.

Step2: Compare Unknown #2 properties

Compare density ($6.69\ g/cm^3$), conductivity (poor), melting point ($631^{\circ}C$), color (bluish - white), ionization energy ($8.641$) with known elements. Te has density $6.24\ g/cm^3$, varies conductivity, melting point and ionization energy values close to Unknown #2. So Unknown #2 is likely Te.

Step3: Compare Unknown #3 properties

Compare density ($1.96\ g/cm^3$), conductivity (poor), melting point ($115^{\circ}C$), color (yellow), ionization energy ($10.36$) with known elements. P has density $1.823\ g/cm^3$, poor conductivity, melting point and ionization energy values close to Unknown #3. So Unknown #3 is likely P.

Answer:

Unknown #1: As
Unknown #2: Te
Unknown #3: P