Metals and Non-metals

Everything around you is made of matter, and some of that matter is made of a single kind of atom: the elements. Elements are sorted into three groups:

• Metals, such as iron, copper, aluminium, gold and sodium;
• Non-metals, such as carbon, sulphur, oxygen and chlorine;
• Metalloids, such as silicon and boron, which are in between: they behave partly like metals and partly like non-metals.

Of the 118 elements known, the great majority (more than 90) are metals. We use metals more than any other kind of element: for cooking pots, buses, bridges, coins, wires and phones.

A few metals, such as gold and platinum, are found in nature as the pure metal: we say they occur in the free state. Most metals have joined with other elements long ago, and are found in rocks as compounds, called ores; the metal has to be taken out of them.

Metals are not only around us but inside living things. Every red blood cell carries iron, which holds the oxygen you breathe. Every green leaf has a magnesium atom at the center of each molecule of chlorophyll, the green pigment that catches sunlight.

Activity 17.1: metals around you

The properties of metals are of two kinds:

• Physical properties: what a metal is like, and how it behaves when you hammer, stretch, heat or touch it. Nothing new is made.
• Chemical properties: how a metal reacts with other substances, such as air, water and acids, to make new substances.

What is inside a metal

Almost every property of a metal comes from one fact. In a metal, the atoms are packed closely together, and each atom lets go of its outermost electrons. Those electrons no longer belong to any one atom: they wander freely through the whole piece of metal, like a sea in which the atoms sit. These are the free electrons.

The atoms, having lost electrons, are positively charged; the sea of electrons is negative. The pull between them holds the metal together. This kind of bonding is called metallic bonding.

Keep this picture in mind. It explains why metals are malleable, ductile, good conductors and shiny.

A. Physical properties of metals

Most metals:

1. have a shine, called luster, when freshly cut or polished;
2. are hard;
3. are good conductors of heat and electricity;
4. are sonorous: they ring when struck;
5. are malleable: they can be beaten into thin sheets;
6. are ductile: they can be drawn into thin wires;
7. have high melting and boiling points.

Let’s test them one by one.

1. Metals are malleable

Metals such as iron, copper, aluminium, silver, tin and gold become flat sheets when hammered. Non-metals such as sulphur and carbon break into pieces. The property of being beaten into thin sheets without breaking is called malleability.

Why? Look again at Figure 17.1. When you hit a metal, rows of atoms slide over each other. The bonds don’t snap, because the free electrons were never tied to particular atoms: they simply flow along and hold the atoms in their new places. In sulphur or coal there are no free electrons to do this: the particles are locked in place, and when one layer is pushed past the next, the forces holding them together break instead of re-forming. So the solid cracks.

2. Metals are ductile

All these wires are made by pulling a metal through smaller and smaller holes until it is long and thin. The metal is still the same metal; only its shape has changed. The property of being drawn into thin wires is called ductility. The reason is the same as for malleability: the layers of atoms slide, and the free electrons hold them together.

Gold is again the champion: one gram of it can be drawn into a wire more than 2 km long.

3. Metals are good conductors of electricity

The bulb glows with aluminium, copper and iron wires, the coin and zinc, but not with sulphur, coal, wood or paper. So metals are good conductors of electricity, and most non-metals are not.

Why? An electric current is a flow of electric charge. In a metal, the free electrons are already loose. Connect a cell, and they all drift along the wire together: that drift is the current. In sulphur, every electron is held tightly in a bond, so there is nothing free to move.

The best conductor of all is silver; copper comes second. Silver is too costly for house wiring, so wires are made of copper, and the long overhead cables of aluminium, which is light and cheap.

4. Metals are good conductors of heat

Heat travels along a metal from the hot end to the cold end; it hardly travels through non-metals. So metals are good conductors of heat, and most non-metals are bad conductors (insulators). The free electrons help here too: at the hot end they gain energy, rush about faster, and carry that energy quickly through the metal.

That is why a cooking pot is made of aluminium or steel, but its handle is made of wood or plastic.

5. Metals are sonorous

Metal objects ring when they are struck. This property is called sonority, and we say metals are sonorous. When a metal is struck, it vibrates strongly and keeps vibrating for a long time, so the sound is loud and lasts. That is why bells, gongs, jhyali (cymbals) and the strings of musical instruments are made of metal, and why a school bell is a piece of iron.

6. Most metals are hard

Most metals are hard: they are not easily cut, scratched or broken. Most solid non-metals are soft or brittle, and can be scratched and broken easily.

7. Most metals have high melting and boiling points

The atoms of a metal are held together by strong forces. To melt a metal, those forces must be partly overcome; to boil it, overcome completely. That takes a lot of heat, so most metals have high melting and boiling points. Most non-metals have low melting and boiling points; many, like oxygen and nitrogen, are gases at room temperature.

Element	Metal or non-metal?	Melting point
tungsten	metal	3,422 °C (the highest of all metals)
iron	metal	1,538 °C
copper	metal	1,085 °C
aluminium	metal	660 °C
lead	metal	327 °C
sodium	metal	98 °C (melts in boiling water)
mercury	metal	−39 °C (liquid in your room)
sulphur	non-metal	115 °C
oxygen	non-metal	−218 °C (a gas in your room)
carbon (graphite)	non-metal	turns to gas at about 3,600 °C

B. Chemical properties of metals

1. Metals react with oxygen to form basic oxides

Metals combine with oxygen to form metal oxides, and these oxides are basic (a metal oxide that dissolves in water makes an alkali).

$$\text{metal} + \text{oxygen} \longrightarrow \text{metal oxide}$$

Reaction	Product
4Na + O₂ → 2Na₂O	sodium oxide
2Mg + O₂ → 2MgO	magnesium oxide
4Al + 3O₂ → 2Al₂O₃	aluminium oxide
4Fe + 3O₂ → 2Fe₂O₃	iron(III) oxide (ferric oxide)
2Cu + O₂ → 2CuO	copper(II) oxide (cupric oxide)

Some metals react with air at once: freshly cut sodium goes dull within seconds. Iron reacts slowly, and needs water as well: the brown rust on an old gate is mostly iron(III) oxide, Fe₂O₃, with water in it. (Iron heated in a flame gets a black coat of a different oxide, Fe₃O₄.) Copper turns black on top when heated in a flame. Gold doesn’t react with oxygen at all, which is why gold coins thousands of years old still shine.

Non-metals form oxides too, but theirs are acidic: carbon dioxide (CO₂) and sulphur dioxide (SO₂) dissolve in water to make acids. This is one of the clearest chemical differences between metals and non-metals.

2. Reactive metals react with dilute acids to give a salt and hydrogen

Reactive metals push the hydrogen out of an acid. The metal takes hydrogen’s place, forming a salt, and the hydrogen is set free as a gas.

$$\text{metal} + \text{dilute acid} \longrightarrow \text{salt} + \text{hydrogen}$$

Reaction	Salt formed
Mg + 2HCl → MgCl₂ + H₂	magnesium chloride
2Al + 6HCl → 2AlCl₃ + 3H₂	aluminium chloride
Fe + 2HCl → FeCl₂ + H₂	iron(II) chloride (ferrous chloride)
Zn + H₂SO₄ → ZnSO₄ + H₂	zinc sulphate
Mg + 2HNO₃ → Mg(NO₃)₂ + H₂	magnesium nitrate

Not every metal does this. Copper, silver and gold don’t react with dilute hydrochloric or sulphuric acid at all: they are less reactive than hydrogen. Acids still attack many everyday metals slowly. That is why sour foods such as pickles (achar) or tamarind should not be stored for long in aluminium or iron pots.

3. Very reactive metals react with water to give an alkali and hydrogen

The most reactive metals, lithium, sodium, potassium and calcium, push hydrogen out even from water. They form the metal hydroxide, which is an alkali.

$$\text{reactive metal} + \text{water} \longrightarrow \text{metal hydroxide} + \text{hydrogen}$$

Reaction	Hydroxide formed
2Li + 2H₂O → 2LiOH + H₂	lithium hydroxide
2Na + 2H₂O → 2NaOH + H₂	sodium hydroxide (caustic soda)
2K + 2H₂O → 2KOH + H₂	potassium hydroxide (caustic potash)
Ca + 2H₂O → Ca(OH)₂ + H₂	calcium hydroxide (slaked lime)

Potassium reacts so fast that the hydrogen catches fire with a lilac flame. Magnesium reacts with cold water only very slowly, iron not at all (iron reacts only with steam, at red heat), and copper, silver and gold never.

So metals are not all equally keen to react. Put them in order, from the most reactive to the least, and you get the reactivity series:

$$\text{K} > \text{Na} > \text{Ca} > \text{Mg} > \text{Al} > \text{Zn} > \text{Fe} > \text{Pb} > (\text{H}) > \text{Cu} > \text{Hg} > \text{Ag} > \text{Au}$$

The metals above hydrogen give hydrogen with dilute acids (lead only very slowly); those below it don’t.

Property	Metals	Non-metals
malleability	malleable: beaten into sheets	not malleable: brittle, break into pieces
ductility	ductile: drawn into wires	not ductile
electricity	good conductors	bad conductors (except graphite)
heat	good conductors: carry heat well	bad conductors (insulators)
melting and boiling points	mostly high	mostly low
hardness	mostly hard, don’t break easily	solid ones mostly soft or brittle (except diamond)
luster	shiny when fresh	mostly dull (except iodine and graphite)
sound	sonorous: ring when struck	not sonorous
state at room temperature	solid (except mercury, a liquid)	solid, liquid (bromine) or gas (oxygen, nitrogen…)
oxides	basic	acidic (or neutral)
with dilute acids	reactive metals give hydrogen	no hydrogen

Your body is mostly made of non-metals (oxygen, carbon, hydrogen, nitrogen). But it also needs small amounts of several metals to work properly: sodium, potassium, calcium, magnesium, iron and zinc among them. They take part in metabolism, the thousands of chemical reactions that keep you alive. The body can’t make these elements; they must come in food, and too little of any one causes illness. With too little iron, for example, the blood can’t carry enough oxygen (anemia); with too little sodium or potassium, the heart can beat unevenly.

These metals are not in your food as shiny lumps of metal! They are present as compounds and ions (charged atoms), such as the sodium in common salt (sodium chloride).

Metal	Sources in food	What it does in the body	Effects of too little
Zinc (Zn)	seeds (pumpkin, sunflower, flax or aalas), cereals, mushrooms, nuts (almonds, cashews); milk products, meat, fish, eggs	helps the body fight bacteria and viruses (immunity); needed to make proteins and DNA; helps wounds heal; needed for a baby’s growth in the womb	hair falls out; smell and taste become weaker; tiredness; loss of weight and diarrhea; wounds and injuries take longer to heal
Iron (Fe)	spinach and other green leafy vegetables, broccoli, cereals, seeds, beans and lentils; meat, fish and eggs	part of hemoglobin, which carries oxygen in the blood; needed for respiration in cells and to make energy; helps immunity	anemia: tiredness, pale skin, difficulty breathing when active
Sodium (Na)	common salt (the main source); meat, eggs, milk	keeps the right balance of water and salt inside and outside cells; needed for nerves and muscles to work	hyponatremia (too little sodium in the blood): muscle cramps, vomiting, confusion, fainting; in severe cases, death
Potassium (K)	fruits (banana, avocado), soybean, vegetables, bamboo shoots (tama), milk, curd	controls the water in cells, and the working of muscles and nerves; helps keep the heartbeat regular; helps keep bones strong and kidney stones away	hypokalemia (too little potassium in the blood): weakness, tired muscles, constipation, uneven heartbeat; a diet low in potassium also raises blood pressure

Two more metals the body needs in large amounts: calcium (from milk, curd, cheese, green vegetables and small fish eaten with their bones) builds bones and teeth and helps the blood clot and muscles contract; too little causes weak bones. Magnesium (from green vegetables, nuts, whole grains and beans) helps more than 300 enzymes work and keeps muscles and nerves healthy; too little causes cramps and tiredness.

Some metals do the body nothing but harm. The two most common in daily life are lead and mercury. They are called heavy metals: they are dense, they build up in the body over time, and the body has no good way to get rid of them.

Lead

Lead is used in vehicle batteries, paints, lead crystal glass, and sheets that shield people from X-rays and other radiation. In the past it was also added to petrol. Lead harms almost every part of the body.

Children are harmed most. Their bodies absorb lead more easily, and their brains are still growing. Lead can cause:

• headache and stomach ache;
• changes in behavior: irritability, trouble paying attention;
• anemia, because lead stops the body from making hemoglobin;
• slower development of the brain, and lower learning ability, which can’t be undone.

The body stores lead in the bones, in place of calcium. There it weakens the bones and interferes with the making of blood cells in the bone marrow. Doctors now say there is no safe level of lead in the body.

Mercury

Mercury is the only metal that is liquid at room temperature. It is used in thermometers, barometers and fluorescent tube lights. The harm that mercury does to the body is called mercury poisoning, also known as hydrargyria or mercurialism (mercury’s symbol, Hg, comes from its Latin name, hydrargyrum, “liquid silver”).

1. Mercury vapor, breathed in, passes easily from the lungs into the blood. (A drop of mercury that gets into a blood vessel could block it, which can be fatal.)
2. Mercury and its compounds damage the brain and nerves: they cause trembling hands, memory loss and changes in mood, and can weaken sight, hearing and speech.
3. They damage the kidneys and the lungs.
4. Mercury crosses the placenta easily, so it can harm a baby developing in the womb.
5. Mercury compounds harm the mental development of children.

1. Choose the correct answer

2. Differentiate between

3. Give reasons

4. Answer the following questions