50 Fun Facts About Chemical Bonds

Which lizard's grip on glass has long been credited to van der Waals forces from tiny hairs on its feet?

Gecko footpads pack about 14,000 hair-like setae into every square millimeter. Forces this weak only add up to a firm grip over a very large contact area.

Which gemstone is pure carbon, each atom covalently bonded to its neighbors in a rigid 3D network?

Diamond has more atoms per unit volume than any other known substance, which is why it is both the hardest and the least compressible.

Which attraction between water molecules makes ice less dense than liquid water, so that it floats?

Hydrogen bonding locks the molecules of ice into an open hexagonal framework, so the solid is about 8% less dense than the liquid. Floating ice keeps lakes from freezing from the bottom up.

Which kitchen staple dissolves in water as whole molecules, not ions, because it is covalently bonded?

Table sugar is a non-electrolyte: its molecules stay whole in water instead of breaking into ions. Salt water conducts electricity because its dissolved ions are free to move.

Which metal, used in light-bulb filaments, owes its record-high melting point to strong bonds between its atoms?

Tungsten melts at 3,422 °C, hotter than any other metal, and has the highest tensile strength of any pure metal. That toughness puts it in heating elements and rocket engine nozzles.

Which bonds between protein chains in hair does a perm break and then re-form to hold a new curl?

Disulfide bridges give hair its elasticity. With the hair wound on rods, a perm lotion breaks them open and an oxidizing lotion closes them again in the rod's shape.

Which molecule's ring structure did August Kekulé say came to him in a daydream of a snake seizing its own tail?

Benzene is a ring of six carbon atoms, and Kekulé said the idea came from a reverie of a snake biting its tail. The image is an ancient symbol called the ouroboros.

Which American chemist won the 1954 Nobel Prize in Chemistry for research into the nature of the chemical bond?

Linus Pauling went on to win the 1962 Nobel Peace Prize as well, making him the only person to have been awarded two unshared Nobel Prizes.

Which metal is liquid at room temperature because its atoms bond to one another unusually weakly?

Mercury is the only metal that is liquid at standard temperature and pressure. Relativistic effects pull its outermost electrons in tight, which weakens the bonding between its atoms.

Which group of elements almost never forms bonds because their outer electron shells are already full?

Noble gases were once called the inert gases, but that label was dropped after chemists managed to make compounds of several of them.

Which model, refined by Gillespie and Nyholm in 1957, predicts a molecule's shape from repulsion between electron pairs?

VSEPR theory treats the electron pairs around an atom as pushing each other as far apart as possible. The core idea was first proposed in 1939 by Ryutaro Tsuchida in Japan.

What shape is a methane molecule, whose four hydrogen atoms sit 109.5 degrees apart around a central carbon?

Tetrahedral geometry puts the four hydrogen atoms as far apart in space as they can get. Laid flat in a square, they would be only 90 degrees apart.

What is the approximate angle between the two O–H bonds in a water molecule, squeezed by two lone pairs on oxygen?

104.5° is a little less than the 109.5° found in methane, because the two unshared pairs sit closer to the oxygen and push the O–H bonds toward each other.

Which gas that humans breathe out has a straight, linear molecule with a bond angle of 180 degrees?

Carbon dioxide is perfectly symmetrical, with the carbon in the middle, so the pull of one oxygen cancels the other and the molecule has no electric dipole.

What is the bond angle in boron trifluoride, a flat molecule with three fluorine atoms spaced evenly around boron?

120° is the angle that spreads three bonds evenly around a flat circle, a shape chemists call trigonal planar. Boron here has only six outer electrons, so the molecule is called electron deficient.

Which pungent gas has a trigonal pyramidal molecule, with three hydrogen atoms at bond angles of about 107 degrees?

Ammonia has a lone pair of electrons on its nitrogen atom that takes up the fourth corner and pushes the three bonds together. That same pair makes the gas a base.

What shape is sulfur hexafluoride, in which six fluorine atoms surround one sulfur atom at 90-degree angles?

Octahedral means eight faces, not eight atoms: the six fluorines sit at the six corners of the solid. The gas is so dense that breathing it makes a voice sound deeper.

What shape is an ozone molecule, whose three oxygen atoms meet at an angle of about 117 degrees?

Bent is also the shape of a water molecule. A ring-shaped form of ozone has been predicted by theory but never made in bulk.

Which American chemist, who sketched atoms as cubes, gives his name to the dot diagrams of bonding electrons?

Gilbert N. Lewis published the diagrams in 1916 and was nominated for a Nobel Prize 41 times without ever winning. He also coined the word photon.

Which property, highest of all in fluorine, measures how strongly an atom pulls shared electrons toward itself?

Electronegativity runs from about 0.8 for cesium to nearly 4 for fluorine on the usual scale. The wider the gap between two bonded atoms, the more lopsided their sharing becomes.

Which bonding guideline, ignored by hydrogen and helium, explains why sodium hands one electron to chlorine?

The octet rule says main-group atoms tend to bond until each has eight electrons in its outer shell. Sodium gets there by losing its single outer electron, chlorine by gaining one.

What name, from the Greek for down, is given to a positively charged ion such as sodium that has lost an electron?

Cation is one of the words the polymath William Whewell coined for Michael Faraday, along with anion, anode and cathode. A cation is smaller than the atom it came from.

Which electrons, the only ones drawn in an electron dot diagram, occupy a main-group atom's outermost shell?

Valence electrons are the ones that can take part in bonding, which is why the diagrams show only them. Transition metals break the pattern: theirs can also sit in an inner shell.

How many dots surround the symbol Cl in an electron dot diagram of chlorine, a group 17 halogen?

Seven dots stand for the seven electrons in chlorine's outer shell, one short of a full set. That single gap makes chlorine quick to take an electron from many other elements.

Which fiber used in bulletproof vests owes its strength to countless weak bonds linking its stiff chains side by side?

Kevlar is five times stronger than steel for its weight. The chemist Stephanie Kwolek invented it at DuPont, and it was first sold as a steel replacement in racing tires.

What is the formula of magnesium chloride, in which each magnesium atom gives up two electrons to chlorine atoms?

MgCl2 needs two chloride ions because each chlorine atom can take only one electron, while magnesium has two to give. The salt is extracted from seawater and brine.

Which pair of elements bonds ionically to form a salt once widely used as a sedative?

Potassium and bromine form potassium bromide, widely used as a sedative and epilepsy drug in the late 1800s. As a typical ionic salt, it splits fully into ions in water.

What holds the oppositely charged sodium and chloride ions together in an ionic bond?

Electrostatic attraction pulls on every nearby opposite charge, not just one partner. In solid sodium chloride each ion is surrounded by six ions of the opposite charge.

What name is given to the regular, repeating three-dimensional arrangement of ions in a crystal of table salt?

A lattice like this has no separate molecules in it, so chemists do not class ionic compounds as molecular at all.

In which state does solid table salt, normally an electrical insulator, become able to conduct electricity?

Molten salt conducts because its ions, fixed in place in the solid, become free to move and carry charge. Dissolving the salt in water frees them in the same way.

Which type of bonding is pictured as positive ions held together by a sea of freely moving electrons?

Metallic bonding lets those loose electrons carry current and heat through the solid, and it also accounts for the strength, ductility and luster of metals.

What word describes a covalent bond in which the electrons are shared unequally, leaving each end with a partial charge?

Polar bonds form when one atom pulls harder on the shared electrons, as oxygen does in water. The small charges are written δ+ and δ− because each is less than the charge of one electron.

What kind of covalent bond, made of six shared electrons, joins the two atoms in a molecule of nitrogen gas?

Triple bonds are short and very strong, which is why nitrogen gas is so unreactive even though it makes up about 78% of the air.

Which molecule's two strands are zipped together by weak bonds between paired bases, letting it unzip to be copied?

DNA strands can be pulled apart like a zipper because the links between bases are much weaker than covalent bonds. Adenine–thymine pairs have two such links and guanine–cytosine pairs three.

Which bond links one amino acid to the next in a protein chain, releasing a molecule of water as it forms?

Peptide bonds are covalent links between the carboxyl group of one amino acid and the amino group of the next. Cells build proteins by forming them on ribosomes.

Which form of carbon is soft and slippery because its flat sheets of atoms are held together only weakly?

Graphite layers glide past each other because only weak forces hold one sheet to the next. It also conducts electricity, mainly along the plane of its layers.

Which hard mineral, the main ingredient of most sand, is a covalent network of silicon and oxygen atoms?

Quartz is built from silicon atoms each bonded to four oxygens, with every oxygen shared between two silicons. It is the second most abundant mineral in Earth's rocky outer layer.

Which American architect of geodesic domes gives his name to a soccer-ball-shaped cage of 60 carbon atoms?

Buckminster Fuller designed domes that look like the molecule, a cage of twenty hexagons and twelve pentagons. Its discoverers won the 1996 Nobel Prize in Chemistry.

Which group of the periodic table, including sodium and lithium, forms 1+ ions by losing a single outer electron?

Alkali metals shed that lone electron so readily that they are never found as pure elements in nature. Cesium reacts explosively with water even at low temperatures.

What always happens to energy when a chemical bond is broken, even one of the so-called high-energy bonds in ATP?

It is absorbed every time, because pulling bonded atoms apart always costs energy. ATP pays out only because the new bonds formed afterward release more than the breaking took in.

Which American chemist, inventor of the gas-filled light bulb, coined the term covalence in a 1919 paper?

Irving Langmuir spent his career at General Electric, where studying light bulbs led him into surface chemistry and to the 1932 Nobel Prize in Chemistry.

Which approach to bonding, which won Robert Mulliken the 1966 Nobel Prize, spreads electrons over the whole molecule?

Molecular orbital theory explained what older bonding models could not: why oxygen is attracted to a magnet. Mulliken also introduced the word orbital in 1932.

What name is given to a covalent bond, drawn as an arrow, in which both shared electrons come from the same atom?

Dative bonds form when an atom with a spare pair of electrons meets one with an empty orbital, such as the boron in boron trifluoride. Once made, the bond is covalent like any other.

What is the mixing of one s and three p orbitals on carbon into four equal sp3 orbitals called?

Hybridization was proposed in 1931 to explain why the four bonds in methane are identical, even though the carbon orbitals that make them are not.

Which Greek letter names the covalent bond formed by head-on overlap of orbitals, the kind found in every single bond?

Sigma (σ) bonds are the strongest type of covalent bond because the orbitals overlap directly. A double bond is one sigma bond plus a pi bond.

What term describes a molecule such as ozone whose true bonding is an average of two or more electron dot diagrams?

Resonance does not mean the electrons flip back and forth between the drawings. The real molecule has one fixed structure, and in ozone both bonds come out identical.

Which weak attractions, named for physicist Fritz London, arise from fleeting shifts in the electron clouds of atoms?

Dispersion forces are the weakest of the intermolecular forces, yet they act even between atoms with perfectly even charge. London's 1930 theory first explained why such atoms attract at all.

What name is given to a molecule such as nitric oxide that has an unpaired electron in its dot diagram?

Free radical species are usually highly reactive because of that lone electron. The 1916 paper that introduced dot diagrams called them odd molecules.

Which fruit-ripening gas is the simplest molecule that contains a carbon–carbon double bond?

Ethylene is a natural plant hormone that farmers use to ripen fruit on demand. More than half of the world's supply goes into making polyethylene, the most widely used plastic.

What term describes different structural forms of one element, such as ozone and ordinary oxygen gas?

Allotropes differ only in how the atoms are bonded together, yet they can behave very differently: ozone is a much stronger oxidizing agent than ordinary oxygen.