Compare the values of the partial charges on the nitrogen atom in ammonia and on the nitrogen atom in nitrogen trifluoride. Rationalize the positive and negative aspects of these charges.

Electronegativity is a measure of an atom's ability to attract and hold onto electrons when it forms a chemical bond. Imagine it as a kind of 'tug-of-war' where the strength of each player is measured by their electronegativity. The higher the value, the stronger the atom's pulling power on the electrons.

When atoms with different electronegativities form a bond, the electrons are not shared equally. The atom with the higher electronegativity will draw more electron density towards itself, resulting in a partial negative charge (δ-), while the other atom acquires a partial positive charge (δ+).

Using the ammonia (NH₃) example, nitrogen has an electronegativity of 3.04 and easily 'wins the tug-of-war' against hydrogen's 2.20, pulling the electrons closer and becoming slightly negative. This concept is fundamental in understanding the distribution of charge within a molecule and the resulting chemical behaviors.

Covalent bonding is the sharing of electron pairs between atoms. These bonds are what hold molecules together. The shared electrons are what cause molecules to have shapes, and they roughly orbit both the nuclei of the atoms involved.

But not all covalent bonds are created equal. When atoms with equal electronegativity share electrons, the electrons are distributed evenly, resulting in a nonpolar covalent bond. On the other hand, atoms with differing electronegativities share electrons unevenly, and the bond is considered polar.

In both ammonia and nitrogen trifluoride (NF₃), nitrogen forms three covalent bonds. However, the differing electronegativity values between nitrogen and its bonding partners lead to different charge distributions in the molecules - this change in electronegativity and therefore in charge is what makes understanding covalent bonding essential to the study of chemistry.

Molecular polarity is a concept that describes how unevenly electric charge is distributed across a molecule. This uneven distribution arises from both the molecular shape and the polarity of the individual bonds within the molecule.

If we use the see-saw analogy, imagine each bonded atom has a 'weight' equal to its electronegativity. If one side has a heavier 'weight' (higher electronegativity), that side of the see-saw will tip, indicating that the side is more negative.

The polarity of a molecule affects its physical properties, such as boiling and melting points, solubility, and reactivity. Polar molecules, like water (H₂O), are often soluble in other polar substances, while nonpolar molecules are soluble in nonpolar substances. Understanding molecular polarity is thus crucial for predicting the behavior of substances in different chemical reactions and environments.