Final answer:
The symbols (+) and (-) on atoms in molecules represent partial positive and negative charges, respectively, which occur due to unequal electron sharing in polar covalent bonds. Oxidation numbers additionally convey the electron status of an atom in a compound, and adjustments to valence electrons are made for ions.
Step-by-step explanation:
The symbols (+) and (-) on atoms in molecules indicate the presence of a partial positive charge (delta plus or δ+) or a partial negative charge (delta minus or δ-), respectively. These symbols are used in the context of polar covalent bonds, where the unequal sharing of electrons results in one atom having a slight positive charge and the other a slight negative charge. For example, in an H-Cl molecule, the chlorine atom would carry a δ- because it is more electronegative and thus attracts the shared electrons more strongly than hydrogen, which would carry a δ+.
Oxidation numbers are another way to keep track of the electrons associated with an atom, indicating how many electrons an atom has gained or lost compared to its neutral state. Positive oxidation numbers correspond to a loss of electrons (δ+), while negative oxidation numbers correspond to a gain of electrons (δ-).
Understanding valence electrons is crucial for determining the stability of ions and forming ionic bonds. For ions, the number of valence electrons is adjusted by adding one for each negative charge in anions or subtracting one for each positive charge in cations.