Unit 3: Chemical Bonding
Why atoms give up, share, or pool their electrons, and how that single choice decides a compound's shape, polarity, and physical behavior.
13 topics · 44 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
3.1 Why Atoms Bond: The Octet Rule
- How it worksHow does reaching eight valence electrons make an atom's outer shell as stable as a noble gas's?
- Common mistakeWhy isn't hydrogen breaking the octet rule when it's satisfied with only two electrons?
- Going furtherWhat happens to an atom's stability once it achieves a full outer shell through bonding?
Your turn1 of 2
A sodium atom has just one lone electron in its outermost shell, and it reacts vigorously to get rid of that single electron rather than trying to gain seven more to fill the shell instead. Why would a sodium atom rather lose its one outer electron than keep it?3.2 Ionic Bonding: Electron Transfer
- How it worksHow does an electron actually jump from a sodium atom to a chlorine atom to form an ionic bond?
- Worked exampleWalk me through the electron transfer that turns neutral sodium and chlorine atoms into Na+ and Cl-.
- Common mistakeWhy isn't an ionic bond just two atoms sharing electrons unevenly?
- Going furtherWhat happens to the charges involved when magnesium bonds with chlorine instead of sodium bonding with chlorine?
Your turn1 of 2
Dropping a small piece of sodium metal into a container of chlorine gas triggers an immediate, vigorous, flame-producing reaction rather than a slow, gradual change. Why does sodium metal explode into flame the instant it touches chlorine gas?3.3 Properties of Ionic Compounds
- How it worksHow does a repeating lattice of alternating positive and negative ions hold an ionic solid together?
- Common mistakeWhy doesn't solid table salt conduct electricity even though it's made of charged ions?
- Going furtherWhat happens to an ionic compound's ability to conduct electricity once it dissolves in water?
Your turn1 of 2
Table salt requires heating to over 800 degrees Celsius before it finally melts, a far higher temperature than many other everyday solids need. Why does table salt need such an extremely high temperature to melt?3.4 Covalent Bonding: Electron Sharing
- How it worksHow do two atoms share a pair of electrons to complete both of their outer shells at once?
- Worked exampleWalk me through how two chlorine atoms share electrons to form a stable Cl2 molecule.
- Common mistakeWhy isn't a shared pair of electrons the same as a transferred pair of electrons?
- Going furtherWhat happens to the shared electron pair when the two bonded atoms are different elements?
Your turn1 of 2
Two hydrogen atoms bonding together each keep an equal claim on a shared pair of electrons, rather than one hydrogen atom fully taking the other's single electron for itself. Why do two hydrogen atoms bond together instead of one stealing the other's electron?3.5 Single, Double, and Triple Covalent Bonds
- How it worksHow does sharing two or three electron pairs instead of one change the strength of a covalent bond?
- Worked exampleFind the total number of shared electron pairs in one molecule of carbon dioxide, O=C=O.
- Common mistakeWhy doesn't a double bond act like two separate single bonds you could break one at a time?
Your turn1 of 2
A molecule contains 4 single bonds, 3 double bonds, and 2 triple bonds. A single bond is one shared electron pair, a double bond counts as two shared pairs, and a triple bond counts as three shared pairs. How many total shared electron pairs does the molecule contain?3.6 Properties of Molecular Compounds
- How it worksHow does the weak attraction between separate molecules explain why molecular compounds often melt easily?
- Common mistakeWhy doesn't a molecular compound conduct electricity in water the way an ionic compound does?
- Going furtherWhat happens to a molecular compound's melting point as its individual molecules get larger?
Your turn1 of 2
Ordinary table sugar melts at a comparatively low temperature you could reach on a kitchen stove, while table salt requires an industrial furnace reaching over 800 degrees Celsius to melt. Why does sugar melt at a much lower temperature than table salt?3.7 Metallic Bonding and the Electron Sea
- How it worksHow do delocalized valence electrons flow freely around fixed metal ions in the electron sea model?
- Common mistakeWhy isn't a metal's electrical conductivity explained by electrons locked to one nucleus?
- Going furtherWhat happens inside a metal's electron sea the instant you connect it to a battery?
Your turn1 of 2
A copper sheet can be hammered, bent, and reshaped repeatedly without cracking or shattering apart, unlike a brittle ionic crystal, which fractures cleanly when struck. Why can you hammer a piece of copper into a new shape without it shattering?3.8 Drawing Lewis Structures
- How it worksHow do you count total valence electrons and arrange them to build a molecule's Lewis structure?
- Worked exampleDraw the complete Lewis structure for a molecule of ammonia, NH3.
- Common mistakeWhy doesn't every atom in a Lewis structure need to be surrounded by exactly eight electrons?
- Going furtherWhat happens to a Lewis structure when a molecule doesn't have enough electrons to give every atom an octet?
Your turn1 of 2
An atom of a certain element contributes 5 valence electrons, and a molecule contains 4 atoms of that element, with no additional overall charge on the molecule. How many total valence electrons should be used when drawing this molecule's Lewis structure?3.9 VSEPR Theory and Molecular Shapes
- How it worksHow do lone pairs of electrons push bonded atoms into a specific molecular shape?
- How it worksWalk me through how four electron groups around carbon spread out into a tetrahedral shape.
- Worked exampleFind the molecular shape of a methane molecule, CH4, and its bond angle.
- Common mistakeWhy isn't a molecule's shape decided only by how many atoms are bonded to the center?
Your turn1 of 2
A water molecule has two hydrogen atoms bonded to a central oxygen atom, yet those two hydrogens sit at a bent angle to each other rather than in a straight line on opposite sides of the oxygen. Why does a water molecule bend instead of lying in a straight line?3.10 Bond Polarity and Electronegativity
- How it worksHow does a difference in electronegativity pull shared electrons closer to one atom than the other?
- Worked exampleFind whether the bond between hydrogen and chlorine in HCl is nonpolar, polar covalent, or ionic.
- Common mistakeWhy isn't a polar bond the same thing as a full ionic bond?
Your turn1 of 2
In a water molecule, the oxygen atom carries a slightly negative charge while the two hydrogen atoms each carry a slightly positive charge, even though the whole molecule overall has no net charge. Why does the oxygen end of a water molecule act more negative than the hydrogen ends?3.11 Polar and Nonpolar Molecules
- How it worksHow does a molecule's symmetric shape cancel out its individual bond polarities?
- Common mistakeWhy doesn't having polar bonds automatically make the whole molecule polar?
- Going furtherWhat happens to a molecule's overall polarity when you replace one hydrogen in methane with a chlorine atom?
Your turn1 of 2
Each individual carbon-oxygen bond in a carbon dioxide molecule is polar, with oxygen pulling shared electrons toward itself, yet the whole carbon dioxide molecule overall is classified as nonpolar. Why is carbon dioxide nonpolar even though each of its individual bonds is polar?3.12 Dispersion and Dipole-Dipole Forces
- How it worksHow does a momentary shift in electron position create a temporary dipole that attracts a neighboring molecule?
- How it worksHow do permanent dipoles line up their positive and negative ends between neighboring polar molecules?
- Common mistakeWhy isn't a dispersion force a real chemical bond between molecules?
- Going furtherWhat happens to the strength of dispersion forces as a molecule's electron cloud gets bigger?
Your turn1 of 2
Oxygen gas molecules have no permanent charge separation at all, no positive or negative end, yet oxygen still condenses into a liquid if cooled to a low enough temperature. Why can nonpolar molecules like oxygen gas still condense into a liquid at a low enough temperature?3.13 Hydrogen Bonding and Its Effects
- How it worksHow does a hydrogen atom bonded to oxygen, nitrogen, or fluorine create an unusually strong attraction to a neighboring molecule?
- Common mistakeWhy isn't a hydrogen bond a bond within a single molecule the way a covalent bond is?
- Going furtherWhat happens to a liquid's boiling point when its molecules can hydrogen bond to each other?
Your turn1 of 2
Water and methane have molecules of roughly similar small size, yet water boils at 100 degrees Celsius while methane boils at a frigid minus 161 degrees Celsius. Why does water boil at such a dramatically higher temperature than a similarly sized molecule like methane?