HESI A2 · Chemistry · 5 min read
Chemical Bonds and Naming Compounds
- Distinguish between ionic and covalent bonds by examining valence electron behavior, electronegativity differences, and characteristic physical properties.
- Apply systematic naming rules and formula-writing conventions to binary ionic compounds, variable-charge metals using the Stock system, and polyatomic ions.
- Name binary covalent compounds using Greek numerical prefixes and compare single, double, and triple covalent bonds in terms of shared electrons, length, and strength.
Chemical Bonding, Electronegativity, and the Octet Rule
Chemical bonds are the fundamental forces that hold atoms together to create stable substances. Atoms interact through their valence electrons, which are the electrons involved in chemical bonding. The octet rule states that atoms generally gain, lose, or share electrons to attain eight valence electrons. By transferring or sharing these valence electrons, atoms achieve ionic and covalent bonds, respectively, often resulting in more stable electron configurations.
The type of bond that forms depends largely on electronegativity, which measures an atom's ability to attract shared electrons within a chemical bond. When two bonding atoms have identical or very similar electronegativities, they share electrons equally or nearly equally, resulting in a nonpolar covalent bond. A moderate electronegativity difference produces unequal sharing and a polar covalent bond; very small differences are usually classified as nonpolar, while very large differences favor ionic bonding.
In a polar covalent bond, the atom with higher electronegativity pulls electron density toward itself and develops a partial negative charge. In contrast, the atom with lower electronegativity develops a partial positive charge. An everyday example of this phenomenon is water, which is a molecular compound composed of polar covalent bonds between oxygen and hydrogen. If the electronegativity difference is very large, bonding is predominantly ionic and is commonly described as involving electron transfer, although ionic bonds can retain some covalent character.
Common mistakes
- Applying the prefix mono- to the first element when naming binary covalent compounds, such as incorrectly writing monocarbon monoxide instead of carbon monoxide.
- Assuming solid ionic compounds conduct electricity; solid ionic compounds are poor conductors because their ions are locked in fixed positions, only conducting when melted into a liquid or dissolved in water.
- Forgetting to place parentheses around a polyatomic ion in a chemical formula when more than one unit of that polyatomic ion is needed to balance charge.
- Confusing bond strength and length across bond orders by failing to recognize that triple covalent bonds are shorter and stronger than single covalent bonds between the same two atoms.
Key points
- Ionic and covalent bonding are commonly described in terms of electron transfer and sharing, respectively; the octet rule is a useful guideline for predicting many bonding patterns, not the force that drives bonding.
- Electronegativity measures an atom's ability to attract shared electrons; equal sharing creates nonpolar covalent bonds, unequal sharing creates polar covalent bonds with partial charges (such as in water), and very large differences produce ionic bonds.
- Ionic compounds consist of cations and anions, which may be monatomic or polyatomic; they typically form crystal lattices and conduct electricity when molten or when dissolved sufficiently in water.
- Binary ionic compounds are named with the metal cation first and nonmetal anion ending in -ide, using the Stock system of Roman numerals for metals with variable charges, and parentheses for multiple units of polyatomic ions.
- Important polyatomic ions include the ammonium cation (NH4+) and anions such as hydroxide (OH-, -1), nitrate (NO3-, -1), carbonate (CO3 2-, -2), sulfate (SO4 2-, -2), and phosphate (PO4 3-, -3).
- Covalent bonds involve sharing one (single), two (double), or three (triple) electron pairs; triple bonds are shorter and stronger than single bonds between the same two atoms, and the seven homonuclear diatomic molecules are hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine.
- Binary covalent compounds use prefixes (mono- through hexa-) to denote atom counts, omitting mono- on the first element and adding -ide to the second, as illustrated by carbon dioxide (CO2), carbon monoxide (CO), and dinitrogen tetroxide (N2O4).
Practice this section
Explained HESI Chemistry questions, no account needed. HESI Chemistry practice test
The full lesson continues with 4 more sections with exam tips, audio in English and Spanish, 5 Check yourself questions and 20 flashcards.
- 1 month
$53.99$26.99 - 3 months
$158.99$79.49 - Lifetime
$323.99$161.99
One payment, no subscription.
See HESI plansAlready a member? Log in
Sample lesson: Atomic Structure and Isotopes25 practice questions on this exam
Each HESI practice test has 25 original questions with the answers explained. No account needed.
Open the HESI practice testsOriginal lesson written for HESI A2 practice · updated October 30, 2026. Exam names are trademarks of their owners; tests.global is not affiliated with them.