Look around a kitchen and nearly everything in it, from the steel knife to the nonstick pan to the plastic wrap, was designed by chemists. A material's properties come from two things: which atoms it contains and how they are arranged. The arrangement can matter as much as the atoms themselves.

Same atoms, different materials

Diamond and graphite are both pure carbon. In diamond each atom is locked into a rigid three-dimensional network, while in graphite the atoms lie in flat sheets that slide over one another. So diamond is the hardest natural material, used to cut stone, while graphite is soft enough to leave marks on paper as pencil lead. Different structural forms of the same element are called allotropes. In 2004 Andre Geim and Konstantin Novoselov isolated graphene, a single sheet of graphite one atom thick, which turned out to be extraordinarily strong and conductive and won them a Nobel Prize in 2010.

Metals and alloys

Pure metals are often too soft or too weak for use. Pure gold can be dented with a fingernail, so jewelry gold is usually mixed with copper or silver. An alloy is a mixture of a metal with other elements, and it is often harder or stronger than the pure metal. Bronze, copper mixed with tin, gave its name to an age of human history. Steel is iron with a small amount of carbon, usually well under two percent; the carbon atoms wedge between iron atoms and stop the layers sliding past each other.

Ordinary steel rusts, as iron oxidizes in moist air and the flaky rust falls away to expose fresh metal. Stainless steel resists this because the chromium in stainless steel forms a thin, tough oxide layer on the surface that shields the metal beneath. If the layer is scratched, it forms again.

Glass

Window glass is made mostly from sand, which is silica, melted with soda and lime and cooled quickly. The atoms have no time to line up. Glass is an amorphous solid: its atoms lack the regular repeating pattern of a crystal. A popular story claims that old cathedral windows are thicker at the bottom because glass slowly flows over centuries. It does not, at least not at any rate that could be seen. Old panes are uneven because of how glass was made at the time, and glaziers often set the thicker edge at the bottom.

Plastics

Plastics are polymers, long chains of repeating units. In 1907 Leo Baekeland, a Belgian-born chemist working in New York, made Bakelite, often called the first fully synthetic plastic. In 1935 Wallace Carothers and his team at DuPont made nylon, which soon replaced silk in stockings and parachutes. Plastics divide into two broad kinds. Thermoplastics soften when heated and can be remelted and reshaped, while thermosets, such as Bakelite, set permanently once cured. Drink bottles are thermoplastic; the handles of old saucepans were often thermoset.

Plastics are cheap, light and durable, and durability is their problem. The strong carbon chains that make plastics durable also mean that few natural organisms can break them down, so discarded plastic can last for centuries, breaking into smaller and smaller fragments. Recycling helps less than many people assume. One widely cited 2017 study estimated that only about 9 percent of all plastic ever made had been recycled. Melting and reprocessing also shortens the chains, so recycled plastic is often turned into lower grade products.

Kitchen chemistry

Cooking is chemistry you can eat. The brown crust on bread, roasted coffee and seared meat all come from the Maillard reaction, named after the French chemist Louis-Camille Maillard, who described it in 1912. Browning in cooked food comes from reactions between sugars and amino acids at high heat, which create hundreds of flavor compounds. Boiling food never gets hot enough for much browning, which is why boiled meat tastes so different from grilled.

Worked example: washing a greasy pan

Run water over a pan coated in grease and the water beads up and slides off. The grease is nonpolar, the water polar, and like dissolves like. Add a drop of soap or dish detergent and the grease lifts away.

The trick lies in the shape of the soap molecule. One end is charged and attracts water. The other end is a long hydrocarbon tail that attracts oils. The tails burrow into the grease while the charged heads stay in the water. Soon the grease breaks into tiny droplets, each wrapped in a ball of soap molecules with their heads facing out. These balls, called micelles, mix with water and rinse away.

People have made soap for thousands of years by heating fats with ashes or lye. Soap has a weakness: in hard water, calcium ions bind to it and form scum. During the First World War, fat shortages in Germany helped push the development of synthetic detergents, which work in hard water too. The washing up liquid by the sink is a direct descendant.