Different groups exhibit different trends in boiling and melting points. For Groups 1 and 2, the boiling and melting points decrease as you move down the group. For the transition metals, boiling and melting points mostly increase as you move down the group, but they decrease for the zinc family.
The melting points and boiling points of the halogens increase going down group 7. This is because, going down group 7: the molecules become larger. the intermolecular forces become stronger.
Group 2 Elements are called Alkali Earth Metals. Generally the melting point of the metals decreases down the group. This is because as the metal ions get larger the distance between the bonding electrons and the positive nucleus gets larger and reduces the overall attraction between the two.
Melting and boiling points increase across the three metals because of the increasing strength of their metallic bonds. The number of electrons which each atom can contribute to the delocalized "sea of electrons" increases.
There does not appear to be a trend in boiling points going down the group. Again magnesium is an anomaly. If you exclude it, the boiling points decrease from beryllium to strontium, then increase to radium.
The densities of the Group 1 elements increase down the group (except for a downward fluctuation at potassium). The metals in this series are relatively light—?lithium, sodium, and potassium are less dense than water (less than 1 g cm-3).
All the group 4 hydrides have a regular tetrahedral shape and are non-polar. The only intermolecular forces between such molecules are weak van der Waals' forces. These generally increase with increasing relative molecular mass.
The group VIA elements are called chalcogens because most ores of copper (Greek chalkos) are oxides or sulfides, and such ores contain traces of selenium and tellurium.
Therefore the
melting point of H
2O
(s)is greater than the
melting points of the other
Group 16 hydrides.
Melting Points of the Group 16 Hydrides.
| Name | hydrogen telluride |
|---|
| Molecular Formula | H2Te |
|---|
| Relative Molecular Mass 1 | 129.616 |
|---|
| MeltingPoint / °C | -49.00 |
|---|
Oxygen group element, also called chalcogen, any of the six chemical elements making up Group 16 (VIa) of the periodic classification—namely, oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and livermorium (Lv).
Since the lone pair on these molecules is more repulsive than bonded groups, the decrease in steric interactions between bonded groups results in a decrease in bond angles.
Preparation and General Properties of the Group 16 Elements
| Property | Oxygen | Polonium |
|---|
| valence electron configuration* | 2s 22p 4 | 6s 26p 4 |
| melting point/boiling point (°C) | −219/−183 | 254/962 |
| density (g/cm 3) at 25°C | 1.31 | 9.20 |
| atomic radius (pm) | 48 | 135 |
Preparation and General Properties of the Group 16 Elements
| Property | Oxygen | Sulfur |
|---|
| *The configuration shown does not include filled d and f subshells. |
|---|
| melting point/boiling point (°C) | −219/−183 | 115/445 |
| normal oxidation state(s) | −2 | +6, +4, −2 |
| product of reaction with H2 | H2O | H2S |
Nitrogen group element, any of the chemical elements that constitute Group 15 (Va) of the periodic table. The group consists of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc).
Members of group 15 of the periodic table (15th vertical column) are summarised as group 15 elements (or the nitrogen group) consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi).
The main
group (s- and p-block)
elements are among the most diverse in the Periodic Table.
Isotopes.
| Isotope | Natural abundance (%) |
|---|
| Nitrogen-15 | 0.0366 |
| Phosphorus-31 | 100 |
| Arsenic-75 | 100 |
| Antimony-121 | 57.36 |
Group 15 elements are also known as pnictogens because in Greek pigeon means to cholk or stifle. In the absence of the oxygen, molecular nitrogen has this property. That's why group 15 elements are known as either nitrogen family or pnictogens.
Hydrogen is not an alkali metal itself, but has some similar properties due to its simple one proton (loctated in the nucleus), one electron arrangement. The lone electron exists in a s -orbital around the nucleus. For lithium, there are two 1 s electrons in an inner orbit and one 2 s electron in the outer orbit.
Mnemonic for Group 14: Chemistry Sir Gives Sanki Problems. Group 15 is known as the group of Pnictogens or Nitrogen group. It includes Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), and Bismuth (Bi). Mnemonic for Group 15: Nahi Pasand Aise Sab Bhai.
The number of valence electrons
| Periodic table block | Periodic table group | Valence electrons |
|---|
| p | Group 15 (V) (pnictogens or nitrogen group) | 5 |
| Group 16 (VI) (chalcogens or oxygen group) | 6 |
| Group 17 (VII) (halogens) | 7 |
| Group 18 (VIII or 0) (noble gases) except helium | 8 |
∴ Generally mass increases then boiling point increases. The higher point of NH3 is due to excessive hydrogen bonding, so PH3 have lowest boiling point among hydrides of group number 15, i.e, nitrogen family.
However, boiling point of NH3>PH3 even though NH3 has lower molecular mass than PH3, due to the intermolecular hydrogen bonding in Ammonia that is not present in PH3 and other hydrides in Group-15.
The boiling point of H2S is lowest.
An ideal gas has no intermolecular forces. The low boiling point shows that the intermolecular forces in nitrogen are quite weak, but they still exist. Thus nitrogen is not an ideal gas.
a) Among H2O, H2S, H2Se, H2Te. 1) As we go down the group, size of the atom increases, it becomes easier for the hydrogen to get departed. 2) Oxygen being smallest in group, has lone pairs more closely attached, this creates repulsions, leading to maximum bond angle.
Which of the following has the highest boiling point? The compound with the highest intermolecular forces will have the highest boiling point. Only choice C is capable of hydrogen bonding (having an O-H bond) and has the highest overall intermolecular forces and therefore the highest boiling pt.
