Use delta ( + or - ) to show direction of expected polarity?

for each of the bonds indicated.

do you use electronegative numbers? how? I know the answers (i have the book) i just want to know how im supposed to know it for a test.

a) H3C - CL

b) H3C - NH2

c) H2N - H

d) H3C - SH

e) H3C - MgBr

f) H3C - F

Yes, use electronegativities.

Cl is -, C is +.
The more EN element will be -, the less EN element will be +.

To determine the expected direction of polarity for each of the given bonds, you can use electronegativity values. Electronegativity is the ability of an atom to attract electrons towards itself in a chemical bond.

The higher the electronegativity difference between atoms in a bond, the more polar the bond becomes.

In general, electronegativity increases across a period from left to right in the periodic table, and decreases down a group.

For each bond:

a) H3C-Cl: Chlorine (Cl) has a higher electronegativity than carbon (C), so the bond is polarized towards chlorine. You can represent this as H3C-δ+Cl-δ-.

b) H3C-NH2: Nitrogen (N) has a higher electronegativity than carbon (C), so the bond is polarized towards nitrogen. You can represent this as H3C-δ+N-δ-.

c) H2N-H: Nitrogen (N) and hydrogen (H) have similar electronegativities, so the bond between them is considered nonpolar. It does not have a significant direction of polarity, so you can represent it as H2N-H.

d) H3C-SH: Sulfur (S) has a higher electronegativity than carbon (C), so the bond is polarized towards sulfur. You can represent this as H3C-δ+S-δ-.

e) H3C-MgBr: Magnesium (Mg) is a metal, and bromine (Br) is a nonmetal. The bond between them is considered ionic, so the direction of polarity is towards the more electronegative atom. You can represent this as H3C-δ+MgBr-δ-.

f) H3C-F: Fluorine (F) has a higher electronegativity than carbon (C), so the bond is polarized towards fluorine. You can represent this as H3C-δ+F-δ-.

To determine the direction of expected polarity using delta ( + or - ) for each bond indicated, you need to consider electronegativity differences between the atoms involved. Electronegativity is a measure of an atom's ability to attract shared electrons towards itself in a covalent bond.

Here's how you can determine the expected direction of polarity for each bond:

a) H3C-CL:
Compare the electronegativity of carbon (C) and chlorine (Cl). Chlorine is more electronegative than carbon, so the electron density in the bond is expected to be shifted towards chlorine. Represent this by placing a delta negative (-) sign on chlorine (Cl) and a delta positive (+) sign on carbon (C).

b) H3C-NH2:
Compare the electronegativity of carbon (C) and nitrogen (N). Nitrogen is more electronegative than carbon, so the electron density in the bond is expected to be shifted towards nitrogen. Place a delta negative (-) sign on nitrogen (N) and a delta positive (+) sign on carbon (C).

c) H2N-H:
Compare the electronegativity of nitrogen (N) and hydrogen (H). Hydrogen is less electronegative than nitrogen, so the electron density in the bond is expected to be shifted towards nitrogen. Place a delta negative (-) sign on nitrogen (N) and a delta positive (+) sign on hydrogen (H).

d) H3C-SH:
Compare the electronegativity of carbon (C) and sulfur (S). Sulfur is more electronegative than carbon, so the electron density in the bond is expected to be shifted towards sulfur. Place a delta negative (-) sign on sulfur (S) and a delta positive (+) sign on carbon (C).

e) H3C-MgBr:
In this case, an ionic bond is formed between carbon (C) and magnesium (Mg), resulting in a complete transfer of the electron from carbon to magnesium. So, a delta positive (+) sign is placed on carbon (C) to signify its electron deficiency and a delta negative (-) sign is placed on magnesium (Mg) to signify its electron abundance.

f) H3C-F:
Fluorine (F) is the most electronegative element. Therefore, the electron density in the bond is expected to be shifted towards fluorine. Place a delta negative (-) sign on fluorine (F) and a delta positive (+) sign on carbon (C).

Remember that the electronegativity value can vary depending on the periodic table or resource you consult. It's always a good idea to refer to your textbook or notes for the exact electronegativity values in your specific study material.