A covalent bond is a type of chemical bond where two atoms are connected to each other by the sharing of two or more electrons
Covalent compounds have bonds where electrons are shared between atoms. These bonds mostly occur between nonmetals or between two of the same (or similar) elements. Two atoms with similar electronegativity will not exchange an electron from their outermost shell; the atoms instead share electrons so that their valence electron shell is filled. Due to the sharing of electrons, they exhibit characteristic physical properties that include lower melting points and electrical conductivity compared to ionic compounds.
Covalent bonds are characterized by the sharing of electrons between two or more atoms. These bonds mostly occur between nonmetals or between two of the same (or similar) elements. Two atoms with similar electronegativity will not exchange an electron from their outermost shell; the atoms instead share electrons so that their valence electron shell is filled.
Covalent bonds occur when electrons are shared between two atoms. A single covalent bond is when only one pair of electrons is shared between atoms. Double and triple covalent bonds are stronger than single covalent bonds and they are characterized by the sharing of four or six electrons between atoms, respectively. Experiments have shown that double bonds are stronger than single bonds, and triple bonds are stronger than double bonds. Therefore, it would take more energy to break the triple bond in N2 compared to the double bond in O2. Indeed, it takes 497 kcal/mol to break the O2 molecule, while it takes 945 kJ/mol to do the same to the N2 molecule.
Several physical properties of molecules/compounds are related to the presence of covalent bonds: Covalent bonds between atoms are quite strong, but attractions between molecules/compounds, or intermolecular forces, can be relatively weak. Covalent compounds generally have low boiling and melting points and are found in all three physical states at room temperature. Covalent compounds do not conduct electricity; this is because covalent compounds do not have charged particles capable of transporting electrons.
Practice Questions
MCAT Official Prep (AAMC)
Chemistry Online Flashcards Question 7
Practice Exam 1 C/P Section Passage 5 Question 22
Practice Exam 2 C/P Section Passage 7 Question 36
Practice Exam 2 C/P Section Passage 9 Question 48
Key Points
• Covalent bonds form between atoms of similar electronegativity when they share electrons form a complete octet of valence electrons
• Covalent bonds can be single, double or triple bonds depending on how many electrons are shared. With increasing bonds comes increasing bond strength and shortening of the bond length
• Covalent compounds generally have low melting and boiling points due to weak intermolecular forces, do not conduct electricity as electrons cannot move and tend to be liquids and gases at room temperature. They are also volatile and evaporate readily.
Key Terms
Valence electrons: Electrons in the outermost principal energy (valence) level of an atom that can participate in the formation of chemical bonds with other atoms.
Octet rule: Atoms lose, gain or share electrons to have a full valence level of eight electrons. Hydrogen and helium are exceptions because they can hold a maximum of two valence electrons.
Electronegativity: The tendency of an atom or molecule to attract electrons and form bonds.
Covalent bond: A type of chemical bond where two atoms are connected by the sharing of two or more electrons.
Bond strength: Directly related to the amount of energy required to break the bond between two atoms. The more energy required, the stronger the bond is said to be.
