Which of the following is a dipole?

KrF2, NH2Cl, CH2Br2, and SCN^-
I'm pretty sure that KrF2 and NH2Cl are not dipoles, but why? also, what makes something be a dipole?

If KrF2 is linear and symmetric, it is not a dipole. The others probably are. a molecule needs symmetry about a plane to avoid being a dipole. You can't always tell that from the chemical formula.

CH2Br2 is a molecule

Br-CH2-Br, linear almost, no dipole

SCN-

::S=C=N: triple bond between C,N

most definitely has dipole moment

I take the CH2Br2 back. It is a bent tetrahedral, so the Br side gives it a dipole moment.

To determine if a molecule is a dipole, we need to examine its molecular geometry and the electronegativity difference between its atoms.

First, let's understand what makes a molecule a dipole. A dipole molecule is one that has a separation of positive and negative charges, creating a positive end and a negative end. This occurs when there is an unequal distribution of electrons within the molecule.

To determine if a molecule is a dipole, we need to consider two factors: molecular geometry and the electronegativity difference between its atoms.

1. Molecular Geometry:
Molecular geometry refers to the arrangement of atoms in a molecule. If a molecule's geometry is symmetrical, it tends to cancel out any dipole moments. This means the molecule will not be a dipole. On the other hand, if the molecule's geometry is asymmetrical, it is more likely to have a dipole moment.

2. Electronegativity Difference:
Electronegativity is the measure of an atom's ability to attract bonding electrons towards itself. In a polar bond, the atom with the higher electronegativity will draw the electron density away from the other atom, creating a partial positive charge on one atom and a partial negative charge on the other. The greater the electronegativity difference, the stronger the dipole moment.

Now, let's analyze the given molecules:

1. KrF2:
Krypton tetrafluoride (KrF2) has a linear molecular geometry, with the two fluorine atoms located on opposite sides of the central krypton atom. The molecular geometry is symmetrical, meaning the dipole moments of the two Kr-F bonds cancel each other out. Therefore, KrF2 is not a dipole.

2. NH2Cl:
Ammonia chloride (NH2Cl) has a pyramidal molecular geometry, with the chlorine atom and two hydrogen atoms positioned around the central nitrogen atom. The molecule is asymmetrical, which indicates that it may have a dipole moment. However, to determine if it truly is a dipole, we need to examine the electronegativity difference between the atoms.

Nitrogen has an electronegativity of 3.04, while chlorine has an electronegativity of 3.16. Although there is a slight difference, it is not significant enough to create a strong dipole moment. Therefore, NH2Cl is not considered a dipole.

3. CH2Br2:
Dibromomethane (CH2Br2) has a tetrahedral molecular geometry, with the two bromine atoms and two hydrogen atoms arranged around the central carbon atom. Similar to NH2Cl, the molecular geometry is asymmetrical, suggesting the possibility of a dipole moment. We need to consider the electronegativity difference between the atoms.

Carbon has an electronegativity of 2.55, while bromine has an electronegativity of 2.96. There is a significant difference in electronegativity, indicating that there will be a strong dipole moment in the CH2Br2 molecule. Therefore, CH2Br2 is a dipole.

4. SCN^-
Thiocyanate ion (SCN^-) has a linear molecular geometry, with the carbon atom bonded to the nitrogen and sulfur atoms. As mentioned earlier, a linear molecular geometry tends to cancel out dipole moments. Additionally, the electronegativity difference between sulfur (2.58) and carbon (2.55) is negligible. Therefore, SCN^- is not considered a dipole.

In summary, KrF2 and SCN^- are not dipoles because their molecular geometries cancel out any dipole moments. NH2Cl has a slight difference in electronegativity, but it is not significant enough to create a strong dipole moment. CH2Br2 has both an asymmetrical molecular geometry and a noticeable electronegativity difference, making it a dipole.