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1.4: Chemical Elements and Symbols

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    258819
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    Learning Objectives

    • Identify names and symbols of common chemical elements.
    • Represent a chemical compound with a chemical formula.

    As described in the previous section, an element is a pure 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.

    2.1.jpg
    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

    Elemental 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.

    Today, new elements are usually named after famous scientists.

    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 \(\PageIndex{2}\) lists the names and symbols of some of the most familiar elements.

    Table \(\PageIndex{2}\): Element Names and Symbols
    Element Name Element Symbol Element Name Element Symbol
    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.

    Element names in languages other than English are often close to their Latin names. 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.

    Elements in Nature and the Human Body 

    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. On the planet Earth, however, the situation is rather different (Table \(\PageIndex{1}\)). 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 \(\PageIndex{1}\): Elemental Composition of Earth and the Human Body
    Earth’s Crust Human Body
    Element Percentage Element Percentage
    oxygen 46.1 oxygen 61
    silicon 28.2 carbon 23
    aluminum 8.23 hydrogen 10
    iron 5.53 nitrogen 2.6
    calcium 4.15 calcium 1.4
    sodium 2.36 phosphorus 1.1
    magnesium 2.33 sulfur 0.20
    potassium 2.09 potassium 0.20
    titanium 0.565 sodium 0.14
    hydrogen 0.14 chlorine 0.12
    phosphorus 0.105 magnesium 0.027
    all others 0.174 silicon 0.026
    Source: D. R. Lide, ed. CRC Handbook of Chemistry and Physics, 89th ed. (Boca Raton, FL: CRC Press, 2008–9), 14–17.

    Table \(\PageIndex{1}\) also lists the relative abundances of elements in the human body. If you compare both compositions, 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; carbon is part of the 0.174% representing “other” elements.

    How does the human body concentrate so many apparently rare elements? 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.

    Looking Closer: The Phosphorous Bottleneck

    There is an element that we need more of in our bodies than is proportionately present in Earth’s crust, and this element is not easily accessible. Phosphorus makes up 1.1% of the human body but only 0.105% of Earth’s crust. We need phosphorus for our bones and teeth, and it is a crucial component of all living cells. Unlike carbon, which can be obtained from carbon dioxide, there is no phosphorus compound present in our surroundings that can serve as a convenient source. Phosphorus, then, is nature’s bottleneck. Its availability limits the amount of life our planet can sustain.

    Higher forms of life, such as humans, can obtain phosphorus by selecting a proper diet (plenty of protein); but lower forms of life, such as algae, must absorb it from the environment. When phosphorus-containing detergents were introduced in the 1950s, wastewater from normal household activities greatly increased the amount of phosphorus available to algae and other plant life. Lakes receiving this wastewater experienced sudden increases in growth of algae. When the algae died, concentrations of bacteria that ate the dead algae increased. Because of the large bacterial concentrations, the oxygen content of the water dropped, causing fish to die in large numbers. This process, called eutrophication, is considered a negative environmental impact.

    800px-Potomac_green_water.jpg
    Figure \(\PageIndex{1}\): The eutrophication of the Potomac River is evident from the bright green water, caused by a dense bloom of cyanobacteria. (CC BY-SA 3.0; Alexandr Trubetskoy via Wikipedia)

    Today, many detergents are made without phosphorus so the detrimental effects of eutrophication are minimized. You may even see statements to that effect on detergent boxes. It can be sobering to realize how much impact a single element can have on life—or the ease with which human activity can affect the environment.

    Example \(\PageIndex{1}\)

    Write the chemical symbol for each element without consulting Table \(\PageIndex{2}\).

    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 \(\PageIndex{2}\).

    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

    Chemical Formulas

    A chemical formula is an expression that shows each of the elements in a compound and the relative proportions of those elements. Water is composed of hydrogen and oxygen in a 2:1 ratio and its chemical formula is \(\ce{H_2O}\). Sulfuric acid is one of the most widely produced chemicals in the United States and is composed of the elements hydrogen, sulfur, and oxygen; the chemical formula for sulfuric acid is \(\ce{H_2SO_4}\). Sucrose (table sugar) consists of carbon, hydrogen, and oxygen in a 12:22:11 ratio. The chemical formula of these are:

    \[ \underbrace{\color{red} {\ce{H2}} \color{blue} {\ce{O}}}_{\begin{aligned} & \color{red} {2\, \text{H atoms}} \\ & \color{blue} {1\, \text{O atom}} \end{aligned}} \quad \underbrace{\color{red} \ce{H2} \color{green} \ce{S} \color{blue} \ce{O4}}_{\begin{aligned} & \color{red} 2\, \text{H atoms} \\ \color{green} &1\, \text{S atom} \\ & \color{blue} 4\, \text{O atoms} \end{aligned}} \quad \underbrace{\color{red} \ce{C12} \color{black} \ce{H22} \color{blue} \ce{O11}}_{\begin{aligned} & \color{red} 12\, \text{H atoms} \\ & \color{black} 22\, \text{C atoms} \\ & \color{blue} 11\, \text{O atoms} \end{aligned}}\]

    Notice that the oxygen and sulfur in water and sulfuric acid, respectively, do not have a "1" subscripts - this is assumed.

    Sometimes certain groups of atoms are bonded together within the chemical and act as a single unit. Polyatomic ions will be discussed later and are enclosed in parenthesis followed by a subscript if more than one of the same ion exist in a chemical formula. For example, the formula \(\ce{Ca3(PO4)2}\) represents a compound with:

    • 3 \(\ce{Ca}\) atoms and
    • 2 \(\ce{PO_4^{3-}}\) polyatomic ions

    To count the total number of atoms for formulas with polyatomic ions enclosed in parenthesis, use the subscript as a multiplier for each atom or number of atoms.

    \[\ce{Ca_3(PO_4)} \color{red} \ce{_2} \nonumber\]

    and decomposing this to elements gives

    • 3 \(\ce{Ca}\) atoms
    • \(\color{red} 2 \color{black} \times 1\) \(\ce{P}\) atoms
    • \(\color{red} 2 \color{black} \times 4\) \(\ce{O}\) atoms

    That is, 3 \(\ce{Ca}\) atoms, 2 \(\ce{P}\) atoms, and 8 \(\ce{O}\) atoms

    Chemical formula can be used in chemical equations. For example, the reaction of hydrogen gas (\(\ce{H2}\)) burning with oxygen gas (\(\ce{O2}\)) to form water (\(\ce{H2O}\)) is written as:

    \[\ce{2H_2 + O_2 \rightarrow 2H_2O} \nonumber\]

    Exercise \(\PageIndex{3}\)

    Identify the elements in each of the following chemical formulas and what is the ratio of different elements in the chemical formulas:

    1. \(\ce{NaOH}\)
    2. \(\ce{NaCl}\)
    3. \(\ce{CaCl2}\)
    4. \(\ce{CH3COOH}\)
    Answer a

    Sodium \(\ce{Na}\), oxygen \(\ce{O}\), and hydrogen \(\ce{H}\) are present. This is sodium hydroxide and is also known as lye or caustic soda.

    This is a 1:1:1 ratio of sodium, oxygen, and hydrogen, respectively.

    Answer b

    Sodium \(\ce{Na}\) and chlorine \(\ce{O}\) are present. This is sodium chloride and is also known as table salt.

    This is a 1:1 ratio of sodium and chlorine, respectively.

    Answer c

    Calcium \(\ce{Ca}\) and Chlorine \(\ce{Cl}\) are present. This is calcium chloride and is a different type of salt than sodium chloride.

    This is a 1:2 ratio of calcium and chlorine, respectively.

    Answer d

    Carbon \(\ce{C}\), Oxygen \(\ce{O}\), and Hydrogen \(\ce{H}\) are present. This is acetic acid and is also known as vineger.

    This is a 2:2:4 (or 1:1:2) ratio of carbon, oxygen, and hydrogen, respectively.

    Key Takeaways

    • All matter is composed of elements.
    • Chemical elements are represented by a one- or two-letter symbol.

    Contributors and Attributions

    • Anonymous


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