Download
1 / 8
490 likes | 1.83k Views
Periodic Table Trends Melting & Boiling Point. Melting point(K): Definition. The temperature at which the crystal lattice of a solid collapses and solid is converted to liquid. Melting point: Trends Down the Groups.
E N D
Melting point(K): Definition The temperature at which the crystal lattice of a solid collapses and solid is converted to liquid.
Melting point: Trends Down the Groups Main Group Metals- Melting point generally decreases as it goes down the group. Non-metals- Melting point generally increases as it goes down the group. Transition Metals- Melting point generally increases as it goes down the group. Metalloids- melting point generally decreases as it goes down diagonally (along the "staircase") Melting Point: Trends Across the Period Excluding metalloids, melting point generally increases until group 6 and then decreases as you continue across the period.
Boiling Point(K): Definition The temperature at which the vapor pressure of a liquid is equal to the external pressure on the liquid.
Boiling Point: Trends Down the Groups Main Group Metals- Boiling point generally decreases as it goes down the group. Non-metals- Boiling point generally increases as it goes down the group. Transition Metals- Boiling point generally increases as it goes down the group. Metalloids- Boiling point generally decreases as it goes down diagonally (along the "staircase") Boiling Point: Trends Across the Period Excluding metalloids, the boiling point generally increases until group 5 (middle of transition metals) and then decreases as you continue across the period.
Explanation of Melting and Boiling Point Trends Across a Period High Z* (effective nuclear charge) means higher intermolecular forces within the atom. When there is the same amount of core electrons shielding an increasing positive charge of the nucleus from the outermost electrons, less energy is required to overcome weak attractive forces on the outermost electrons. Therefore, as a general rule, as Z* increases, melting & boiling point increases. Z* increases across a period because you add more protons (stronger positive charge) and more outer-shell electrons, but no additional core electrons. Also, there are stronger metallic bonds in the middle of a period (for example carbon and transition metals). The more bonds there are, the more energy is required to break them.
Explanation of Melting and Boiling Points Down a Group For nonmetals: as an atom gets larger (more electrons) Van der Waals forces increase. The more forces there are, the more energy is needed to overcome them. For main group metals: When an atom is larger, it is easier to break its metallic bonds. There are weaker bonds between the outermost electrons of larger atoms because they are increasingly far away from the positively charged nucleus. For transition metals: Metallic bonds are strongest on the bottom and near the middle of the transition metals. Since they're the strongest, they're the hardest to break.
Exceptions: Groups 11 and 12-The elements in groups 11 and 12 form intermolecular bonds in the way that elements in groups 1 and 2 form intermolecular bonds. (Groups 11 and 12 are sometimes called groups 1B and 2B) Their melting and boiling points generally decrease as you go down the group. Period 3- Out of phosphorus, sulfur, chlorine, and argon, sulfur has the highest melting and boiling point due to its molecular structure. Phosphorus exists as P4 molecules, sulfur exists as S8 molecules, chlorine exists as Cl2 molecules, and argon exists as Ar. The larger the nonmetal molecule, the stronger the Van der Waals force will be. Therefore, the melting and boiling point of sulfur are higher.
