Covalent Bond Basics
Definition of Covalent Bond: A covalent bond happens when two atoms, usually non-metal atoms, decide to share electrons from their outermost shells. These shared electrons help both atoms feel more stable because it fills up their outer shells, making them more like noble gases.
Electrostatic Attraction: This type of bond forms because the negatively charged electrons that are shared are pulled toward the positively charged centers (nuclei) of both atoms. This attraction between the electrons and both nuclei holds the atoms together.
Formation Through Electron Sharing
Sharing Not Transfer: In covalent bonding, electrons are not given away or taken like in ionic bonding. Instead, the atoms work together and agree to share their electrons, so each can feel like it has a full outer shell.
Contribution by Both Atoms: To form a covalent bond, each atom gives at least one electron to be shared. These electrons form a shared pair that both atoms use, helping them become more stable together.
Achieving Stable Configurations
Octet or Duplet Rule: Atoms share electrons so that they can have a full outer shell of electrons. Most atoms want 8 electrons in their outer shell (octet), but very small atoms like hydrogen only need 2 (duplet) to be stable.
Hydrogen Molecule Example: When two hydrogen atoms come close, they each share one electron with the other. Now both feel like they have two electrons, which is a full shell for hydrogen. This forms a molecule of H₂.
Water Molecule Example: In a water molecule (H₂O), one oxygen atom shares electrons with two hydrogen atoms. Oxygen ends up with 8 electrons (an octet), and each hydrogen gets 2 (a duplet), so all the atoms feel stable.
Single Covalent Bonds
One Electron Pair Shared: When only one pair of electrons is shared between two atoms, it is called a single covalent bond. In drawings called Lewis structures, this bond is shown as a single line (–).
Examples of Single Bonds: Hydrogen gas (H₂) is made by two hydrogen atoms sharing a pair of electrons. Another example is the carbon-hydrogen (C–H) bond found in fuels like methane.
Multiple Covalent Bonds
Double Bonds: In a double bond, two atoms share two pairs of electrons. This makes the bond stronger and shorter than a single bond. Oxygen gas (O₂) is an example where each oxygen shares two pairs of electrons.
Triple Bonds: When three pairs of electrons are shared, we get a triple bond. This is even stronger and shorter than a double bond. Nitrogen gas (N₂) has a triple bond between the two nitrogen atoms.
Covalent Molecule Examples
Diatomic Molecules: Some elements naturally form pairs of atoms with covalent bonds. These include hydrogen (H₂), chlorine (Cl₂), oxygen (O₂), and nitrogen (N₂).
Water (H₂O): A water molecule forms when one oxygen atom makes two single bonds by sharing electrons with two hydrogen atoms. This makes all the atoms stable.
Carbon Dioxide (CO₂): In this molecule, a carbon atom forms two double bonds with two oxygen atoms. This way, carbon gets 8 electrons and each oxygen also gets 8.
Methane (CH₄): One carbon atom shares electrons with four hydrogen atoms, forming four single covalent bonds. All atoms reach stable configurations.
Ammonia (NH₃): In ammonia, nitrogen forms three single covalent bonds by sharing electrons with three hydrogen atoms.
Hydrogen Halides (HF & HCl): Hydrogen bonds with halogens like fluorine (F) or chlorine (Cl) by sharing one pair of electrons.
Tetrachloromethane (CCl₄): This molecule has one carbon atom bonded to four chlorine atoms, all through single covalent bonds formed by sharing electrons.
Ethanol (C₂H₅OH): Ethanol has different covalent bonds, including carbon-carbon (C–C), carbon-hydrogen (C–H), and carbon-oxygen (C–O) bonds. Each atom shares electrons to stay stable.
Representing Covalent Bonds: Lewis Structures
Electron Dot Diagrams: Lewis structures are drawings that use dots to show electrons and lines to show bonds. They help us see how atoms are connected in a molecule.
Components of the Structure: In these diagrams, letters like H, O, or C represent atoms. Dots show unshared electrons, and lines show shared electron pairs between atoms.
Visualization Purpose: Lewis structures are useful because they show how atoms share electrons and help us figure out the shape and structure of molecules.
Properties of Covalent Compounds
Lower Melting/Boiling Points: Covalent compounds usually don’t have strong forces holding them together like ionic compounds do. This means they melt and boil at lower temperatures
Poor Electrical Conductivity: These compounds do not have free-moving charged particles (like ions), so they usually cannot carry electricity.
Variable Solubility: Some covalent compounds dissolve well in water if they are polar (like water itself), but others that are non-polar only dissolve in non-polar liquids like oil.
Comparison with Ionic Bonds
Covalent vs Ionic Formation: Covalent bonds form when two non-metals share electrons. Ionic bonds happen when a metal gives electrons to a non-metal.
Resulting Species: Covalent bonding creates neutral molecules. Ionic bonding creates charged particles (ions) that stick together because of opposite charges.
Different Properties: Because of how they form, covalent and ionic bonds lead to different kinds of substances with different properties, such as melting point, conductivity, and solubility.