4.4: The Elements

Learning Objectives

• Define a chemical element.
• Represent a chemical element with a chemical symbol.

An element is a substance that cannot be broken down into simpler chemical substances. There are about 90 naturally occurring elements known on Earth. Using technology, scientists have been able to create nearly 30 additional elements that do not occur in nature. Today, chemistry recognizes 118 elements—some of which were created an atom at a time. Figure \(\PageIndex{1}\) shows some of the chemical elements.

Figure \(\PageIndex{1}\): Samples of Elements. Gold is a yellowish solid, iron is a silvery solid, while mercury is a silvery liquid at room temperature. © Thinkstock

Abundance

The elements vary widely in abundance. In the universe as a whole, the most common element is hydrogen (about 90% of atoms), followed by helium (most of the remaining 10%). All other elements are present in relatively minuscule amounts, as far as we can detect.

Table \(\PageIndex{1}\): Elemental Composition of Earth

Earth’s Crust		Earth (overall)
Element	Percentage	Element	Percentage
oxygen	46.1	iron	34.6
silicon	28.2	oxygen	29.5
aluminum	8.23	silicon	15.2
iron	5.53	magnesium	12.7
calcium	4.15	nickel	2.4
sodium	2.36	sulfur	1.9
magnesium	2.33	all others	3.7
potassium	2.09
titanium	0.565
hydrogen	0.14
phosphorus	0.105
all others	0.174
Source: D. R. Lide, ed. CRC Handbook of Chemistry and Physics, 89th ed. (Boca Raton, FL: CRC Press, 2008–9), 14–17.

On the planet Earth, however, the situation is rather different. Oxygen makes up 46.1% of the mass of Earth’s crust (the relatively thin layer of rock forming Earth’s surface), mostly in combination with other elements, while silicon makes up 28.2%. Hydrogen, the most abundant element in the universe, makes up only 0.14% of Earth’s crust. Table \(\PageIndex{1}\) lists the relative abundances of elements on Earth as a whole and in Earth’s crust. Table \(\PageIndex{2}\) lists the relative abundances of elements in the human body. If you compare Table \(\PageIndex{1}\) and Table \(\PageIndex{2}\), you will find disparities between the percentage of each element in the human body and on Earth. Oxygen has the highest percentage in both cases, but carbon, the element with the second highest percentage in the body, is relatively rare on Earth and does not even appear as a separate entry in Table \(\PageIndex{1}\); carbon is part of the 0.174% representing “other” elements. How does the human body concentrate so many apparently rare elements?

Table \(\PageIndex{2}\): Elemental Composition of a Human Body

Element	Percentage by Mass
oxygen	61
carbon	23
hydrogen	10
nitrogen	2.6
calcium	1.4
phosphorus	1.1
sulfur	0.20
potassium	0.20
sodium	0.14
chlorine	0.12
magnesium	0.027
silicon	0.026
iron	0.006
fluorine	0.0037
zinc	0.0033
all others	0.174
Source: D. R. Lide, ed. CRC Handbook of Chemistry and Physics, 89th ed. (Boca Raton, FL: CRC Press, 2008–9), 7–24.

The relative amounts of elements in the body have less to do with their abundances on Earth than with their availability in a form we can assimilate. We obtain oxygen from the air we breathe and the water we drink. We also obtain hydrogen from water. On the other hand, although carbon is present in the atmosphere as carbon dioxide, and about 80% of the atmosphere is nitrogen, we obtain those two elements from the food we eat, not the air we breathe.

Names and Symbols

Each element has a name. Some of these names date from antiquity, while others are quite new. Today, the names for new elements are proposed by their discoverers but must be approved by the International Union of Pure and Applied Chemistry, an international organization that makes recommendations concerning all kinds of chemical terminology.

The names of the elements can be cumbersome to write in full, especially when combined to form the names of compounds. Therefore, each element name is abbreviated as a one- or two-letter chemical symbol. By convention, the first letter of a chemical symbol is a capital letter, while the second letter (if there is one) is a lowercase letter. The first letter of the symbol is usually the first letter of the element’s name, while the second letter is some other letter from the name. Some elements have symbols that derive from earlier, mostly Latin names, so the symbols may not contain any letters from the English name. Table \(\PageIndex{3}\) lists the names and symbols of some of the most familiar elements.

Table \(\PageIndex{3}\): Element Names and Symbols

aluminum	Al	magnesium	Mg
argon	Ar	manganese	Mn
arsenic	As	mercury	Hg*
barium	Ba	neon	Ne
bismuth	Bi	nickel	Ni
boron	B	nitrogen	N
bromine	Br	oxygen	O
calcium	Ca	phosphorus	P
carbon	C	platinum	Pt
chlorine	Cl	potassium	K*
chromium	Cr	silicon	Si
copper	Cu*	silver	Ag*
fluorine	F	sodium	Na*
gold	Au*	strontium	Sr
helium	He	sulfur	S
hydrogen	H	tin	Sn*
iron	Fe	tungsten	W^†
iodine	I	uranium	U
lead	Pb*	zinc	Zn
lithium	Li	zirconium	Zr
*The symbol comes from the Latin name of element.
^†The symbol for tungsten comes from its German name—wolfram.

Symbols for elements that seem odd for English speakers in many cases make sense to speakers of languages such as Spanish and French that are descended from Latin. For example, gold is oro in Spanish and or in French (close to the Latin aurum), tin is estaño in Spanish (compare to stannum), lead is plomo in Spanish and plomb in French (compare to plumbum), silver is argent in French (compare to argentum), and iron is fer in French and hierro in Spanish (compare to ferrum). The closeness is even more apparent in pronunciation than in spelling.

Example \(\PageIndex{1}\)

Write the chemical symbol for each element without consulting Table \(\PageIndex{3}\) "Element Names and Symbols".

1. bromine
2. boron
3. carbon
4. calcium
5. gold

Answer a

Br

Answer b

B

Answer c

C

Answer d

Ca

Answer e

Au

Exercise \(\PageIndex{1}\)

Write the chemical symbol for each element without consulting Table \(\PageIndex{3}\).

1. manganese
2. magnesium
3. neon
4. nitrogen
5. silver

Answer a

Mn

Answer b

Mg

Answer c

Ne

Answer d

N

Answer e

Ag

Example \(\PageIndex{2}\)

What element is represented by each chemical symbol?

1. Na
2. Hg
3. P
4. K
5. I

Answer a

sodium

Answer b

mercury

Answer c

phosphorus

Answer d

potassium

Answer e

iodine

Exercise \(\PageIndex{2}\)

What element is represented by each chemical symbol?

1. Pb
2. Sn
3. U
4. O
5. F

Answer a

lead

Answer b

tin

Answer c

uranium

Answer d

oxygen

Answer e

fluorine

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