The periodic table common mistakes

Common mistakes

• Relative Molecular Mass Confusion

  Students often confuse the trend in relative molecular mass with the trend in atomic number down Group 7.

  Fix itFocus on understanding that relative molecular mass increases due to the addition of more atoms and their respective masses, while atomic number relates to the number of protons.

• Melting and Boiling Points Confusion

  Students often confuse the trends in melting point and boiling point down Group 7, thinking both increase instead of recognizing that melting points increase while boiling points also increase but at a different rate.

  Fix itTo fix this, students should create a table comparing the melting and boiling points of Group 7 elements, noting the specific values and trends to visualize how each property changes down the group.

• Reactivity Misunderstanding

  Students often think that reactivity increases down Group 7 instead of decreases.

  Fix itFocus on the concept that as you move down Group 7, the outer electrons are further from the nucleus, making it harder for the atom to attract additional electrons, thus decreasing reactivity.

• Misunderstanding Displacement Reactions

  Students often think that halogens can displace any halide salt regardless of their reactivity.

  Fix itRemember that a more reactive halogen can displace a less reactive halide from its salt, while a less reactive halogen cannot displace a more reactive one.

• Misunderstanding Reactivity Trends

  Students often think that reactivity increases down Group 7 instead of decreases.

  Fix itRemember that as you move down Group 7, the outer electrons are further from the nucleus, making it harder for the atom to attract electrons and thus decreasing reactivity.