Chemi Groups And Period Comparison.docx

Melting and boiling points

Atomic radius

Group 1

Group 17

Group 18

Period 3

DECREASE. The atomic radius increases. The distance between the positive nucleus and valence electrons increases. The attractive forces between the positive nucleus and valence electrons decreases. The metallic bond is weaker. Less heat energy is needed to overcome the forces of attraction between atoms when melting or boiling. INCREASE. Because the distance between the positive nucleus and the outermost shell filled with electron increases.

INCREASE. The atomic radius increases. The Van der Waals’ forces between the molecules increase. More heat energy is needed to overcome the intermolecular forces when melting or boiling.

INCREASE. The atomic radius increases. The Van der Waals’ forces between the neighbouring atoms increase. More heat energy is needed to overcome the forces of attraction between atoms when melting or boiling.

INCREASE from Na to Al because the metallic bonds in these metals get stronger. DECREASE from Si to Ar because the Van der Waals’ forces of attraction between the molecules get weaker. Melting point of Si is the highest because of strong threedimensional covalent bonds.

INCREASE. Because the number of electron-filled shells in the atom increases.

DECREASE. Because the proton number increases. The number of protons in the nucleus increases but all the atoms have 3 shells occupied with electrons. The number of positive charges in the nucleus increases. The attractive forces between the

Changes in reactivity

INCREASE. The atomic radius increases. The distance between the positive nucleus and valence electrons increases. The attractive forces between the positive nucleus and valence electrons decreases. The metallic bond is weaker. It is easier for bigger atoms to lose valence electrons to form positive ions.

Density

INCREASE. Because the increase of atomic mass is bigger than the increase of atomic radius.

DECREASE. x The atomic radius increases. The distance between the positive nucleus and valence electrons increases. The attractive forces between the positive nucleus and valence electrons decreases. It is more difficult for the nucleus of an atom to attract an electron to form negative ions.

INCREASE. Because the increase of atomic mass is bigger than the increase of atomic radius.

positive nucleus and the electrons is stronger. The electrons in each shell of the atom are more strongly attracted to the nucleus and pulled closer to the nucleus. INCREASE. The atomic radius decreases. The distance between the positive nucleus and valence electrons decreases. The positive charges in the nucleus increases. The attractive forces between the nucleus and the electrons in the electron shells become stronger. The atoms have high tendency to attract electrons to form negative ions.