arrange these seven substances in order from highest melting point to lowest melting point.
H2O, MgO, CCl4, CH2Cl2, CaCl2, N2, PF3
yes
To determine the order of melting points for these substances, we need to consider the types of bonds and intermolecular forces present in each compound.
1. N2 (Nitrogen Gas): Nitrogen gas consists of nonpolar covalent bonds. Since it is a diatomic molecule, the intermolecular forces are weak London dispersion forces. These forces arise due to temporary fluctuations in electron distribution, and they are relatively weak compared to other types of bonds and forces. Consequently, N2 has the lowest melting point among the given substances.
2. CCl4 (Carbon Tetrachloride): Carbon tetrachloride consists of nonpolar covalent bonds as well. Similar to N2, it experiences weak London dispersion forces. However, CCl4 has a higher molecular weight compared to N2, which usually results in stronger intermolecular forces. Therefore, CCl4 has a slightly higher melting point than N2.
3. CH2Cl2 (Dichloromethane): Dichloromethane has similar characteristics to carbon tetrachloride because it also has nonpolar covalent bonds and exhibits London dispersion forces. However, it has a lower molecular weight than CCl4. Thus, CH2Cl2 is expected to have a lower melting point than CCl4.
4. H2O (Water): Water is a polar molecule that forms strong hydrogen bonds. Hydrogen bonds are relatively much stronger than London dispersion forces. Consequently, water has a higher melting point compared to substances with only dispersion forces.
5. PF3 (Phosphorus Trifluoride): Phosphorus trifluoride consists of polar covalent bonds. Although it does not have hydrogen bonding like water, it has dipole-dipole intermolecular forces. These forces are stronger than London dispersion forces but weaker than hydrogen bonding. Hence, PF3 has a higher melting point than compounds with only dispersion forces.
6. CaCl2 (Calcium Chloride): Calcium chloride is an ionic compound. It consists of strongly charged ions, which are held together by ionic bonds. Ionic bonds are typically much stronger than any type of covalent bond or intermolecular force. Consequently, CaCl2 has a considerably higher melting point than compounds with covalent bonds.
7. MgO (Magnesium Oxide): Magnesium oxide is another ionic compound. Similar to calcium chloride, it has strong ionic bonds. However, magnesium oxide has a higher melting point than calcium chloride due to the higher charge and smaller size of magnesium ions compared to calcium ions.
Considering the above information, the order of the substances from highest melting point to lowest melting point is:
MgO > CaCl2 > H2O > PF3 > CH2Cl2 > CCl4 > N2