中三化學題目

Question

x and y are elements.

chloride of X -- melting point 772 C
chloride of Y -- melting point -68 C

1 ) 想問下點睇x同y係咪金屬??
2 ) 點睇佢地係咩compound??

Answer 1

There are 4 types of structure : giant metal structure, giant covalent structure, giant ionic structure, simple molecular structure.

Chlorides would NOT have giant metal structure or giant covalent structure.

Metal chlorides have giant ionic structure, and their melting points are high, because the opposite ions are held together by strong electrostatic forces (or strong ionic bonds).
Non-metal chlorides have simple molecular structure, and their melting point are low, because the molecules are held together by weak van der Waals forces.

Therefore, we can determine whether it is a metal chloride or a non-metal chloride by the melting point.

Since the chloride of X has a high melting point, it is a metal chloride and X is a metal.
Since the chloride of Y has a low melting point, it is a non-metal chloride and Y is a non-metal.

Answer 2

x is metal, since chloride of X has a high melting point, therefore it is an ionic compound
chloride of Y has a low melting point( being a liquid/gas in room condition) therefore y is non-metal

x is usually Na or Mg as NaCl and MgCl has a melting point around 700C
y is H(most common) as HCl is covalent, bonded by weak van der waals' force, therefore it has low melting point.