1.7 The Periodic Table
Learning Objectives
Explain how elements are organized into the periodic table.
Describe how some characteristics of elements relate to their positions on the periodic table.
In the nineteenth century, many previously unknown elements were discovered, and scientists noted that certain sets of elements had similar chemical properties. For example, chlorine, bromine, and iodine react with other elements (such as sodium) to make similar compounds. Likewise, lithium, sodium, and potassium react with other elements (such as oxygen) to make similar compounds. Why is this so?
In 1864, Julius Lothar Meyer, a German chemist, organized the elements by atomic mass and grouped them according to their chemical properties. Later that decade, Dmitri Mendeleev, a Russian chemist, organized all the known elements according to similar properties. He left gaps in his table for what he thought were undiscovered elements, and he made some bold predictions regarding the properties of those undiscovered elements. When elements were later discovered whose properties closely matched Mendeleev’s predictions, his version of the table gained favor in the scientific community. Because certain chemical properties of the elements repeat on a regular basis throughout the table (that is, they are periodic), it became known as the periodic tableA chart of elements that groups the elements by some of their properties..
Note
Mendeleev had to list some elements out of the order of their atomic masses to group them with other elements that had similar properties.
The periodic table is one of the cornerstones of chemistry because it organizes all the known elements on the basis of their chemical properties. A modern version is shown in Figure 1.7. Most periodic tables provide additional data (such as atomic mass) in a box that contains each element’s symbol. The elements are listed in order of atomic number.
Figure 1.7 A Modern Periodic Table
A modern periodic table lists elements left to right, top to bottom, by atomic number.
Source: Reproduced by permission of International Union of Pure and Applied Chemistry.
Features of the Periodic Table
Elements that have similar chemical properties are organized in columns called groups (or families)A column of elements on the periodic table.. As well as being numbered, some of these groups have names—for example, alkali metals (the first column of elements), alkaline earth metals (the second column of elements), halogens (the next-to-last column of elements), and noble gases (the last column of elements).
Note
The word halogen comes from the Greek word for “salt maker” because these elements combine with other elements to form a group of compounds called salts.
To Your Health: Radon
Radon is an invisible, odorless noble gas that is slowly released from the ground, particularly from rocks and soils whose uranium content is high. Because it is a noble gas, radon is not chemically reactive. Unfortunately, it is radioactive, and increased exposure to it has been correlated with an increased lung cancer risk.
Because radon comes from the ground, we cannot avoid it entirely. Moreover, because it is denser than air, radon tends to accumulate in basements, which if improperly ventilated can be hazardous to a building’s inhabitants. Fortunately, specialized ventilation minimizes the amount of radon that might collect. Special fan-and-vent systems are available that draw air from below the basement floor, before it can enter the living space, and vent it above the roof of a house.
After smoking, radon is thought to be the second-biggest preventable cause of lung cancer in the United States. The American Cancer Society estimates that 10% of all lung cancers are related to radon exposure. There is uncertainty regarding what levels of exposure cause cancer, as well as what the exact causal agent might be (either radon or one of its breakdown products, many of which are also radioactive and, unlike radon, not gases). The U.S. Environmental Protection Agency recommends testing every floor below the third floor for radon levels to guard against long-term health effects.
Each row of elements going across the periodic table is called a periodA row of elements on the periodic table.. Periods have different lengths; the first period has only 2 elements (hydrogen and helium), while the second and third periods have 8 elements each. The fourth and fifth periods have 18 elements each, and later periods are so long that a segment from each is removed and placed beneath the main body of the table.
Certain elemental properties become apparent in a survey of the periodic table as a whole. Every element can be classified as either a metal, a nonmetal, or a semimetal, as shown in Figure 1.8. A metalAn element that is shiny, typically silvery in color, an excellent conductor of heat and electricity, malleable, and ductile. is a substance that is shiny, typically (but not always) silvery in color, and an excellent conductor of electricity and heat. Metals are also malleable (they can be beaten into thin sheets) and ductile (they can be drawn into thin wires). A nonmetalAn element that is typically dull, not a good conductor of heat and electricity, and brittle. is typically dull and a poor conductor of electricity and heat. Solid nonmetals are also very brittle. As shown in Figure 1.8, metals occupy the left three-fourths of the periodic table, while nonmetals (except for hydrogen) are clustered in the upper right-hand corner of the periodic table. The elements with properties intermediate between those of metals and nonmetals are called semimetals (or metalloids)An element whose properties are intermediate between metals and nonmetals..
Figure 1.8 Types of Elements
Elements are either metals, nonmetals, or semimetals. Each category is located in a different part of the periodic table.
Source: FlatWorld
Another way to categorize the elements of the periodic table is shown in Figure 1.9. The first two columns on the left and the last six columns on the right are called the main group elementsAn element in the first two or the last six columns on the periodic table.. The ten-column block between these columns contains the transition metalsAn element between the main group elements on the periodic table.. The two rows beneath the main body of the periodic table contain the inner transition metalsAn element in the two rows beneath the main body on the periodic table. Such metals are also called the lanthanide and actinide metals.. The elements in these two rows are also referred to as, respectively, the lanthanide metalsThe first row of the inner transition metal elements in the periodic table. and the actinide metalsThe second row of the inner transition metal elements in the periodic table..
Figure 1.9 Special Names for Sections of the Periodic Table
Some sections of the periodic table have special names.
Source: FlatWorld
To Your Health: Transition Metals in the Body
According to Table 1.2, most of the elemental composition of the human body consists of main group elements. The first element appearing on the list that is not a main group element is iron, at 0.006 percentage by mass. Because iron has relatively massive atoms, it would appear even lower on a list organized in terms of percent by atoms rather than percent by mass.
Iron is a transition metal. Transition metals have interesting chemical properties, partially because some of their electrons are in d subshells. (For more information about electron shells, refer to Chapter 1, Section 6 “Arrangements of Electrons”.) The chemistry of iron makes it a key component in the proper functioning of red blood cells.
Red blood cells are cells that transport oxygen from the lungs to cells of the body and then transport carbon dioxide from the cells to the lungs. Without red blood cells, animal respiration as we know it would not exist. The critical part of the red blood cell is a protein called hemoglobin. Hemoglobin combines with oxygen and carbon dioxide, transporting these gases from one location to another in the body. Hemoglobin is a relatively large molecule, with a mass of about 65,000 u.
The crucial atom in the hemoglobin protein is iron. Each hemoglobin molecule has four iron atoms, which act as binding sites for oxygen. It is the presence of this particular transition metal in your red blood cells that allows you to use the oxygen you inhale.
Other transition metals have important functions in the body, despite being present in low amounts. Zinc is needed for the body’s immune system to function properly, as well as for protein synthesis and tissue and cell growth. Copper is also needed for several proteins to function properly in the body. Manganese is needed for the body to metabolize oxygen. Cobalt is a necessary component of vitamin B-12, a vital nutrient. (For more information about proteins and vitamins, refer to Chapter 13 “Amino Acids, Proteins, and Enzymes”.) These last three metals are not listed explicitly in Table 1.2, so they are present in the body in very small quantities. However, even these small quantities are required for the body to function properly; without them, illness, disease, and even death can result.
The periodic table is organized on the basis of similarities in elemental properties, but what explains these similarities? It turns out that the shape of the periodic table reflects the filling of subshells with electrons, as shown in Figure 1.10. Starting with the first period and going from left to right, the table reproduces the order of filling of the electron subshells in atoms. Furthermore, elements in the same column share the same valence shell electron configuration. For example, all elements in the first column have a single s electron in their valence shells, so their electron configurations can be described as ns1 (where n represents the shell number). This last observation is crucial. Chemistry is largely the result of interactions between the valence electrons of different atoms. Thus, atoms that have the same valence shell electron configuration will have similar chemistry.
Figure 1.10 The Shape of the Periodic Table
The shape of the periodic table reflects the order in which electron shells and subshells fill with electrons.
Source: FlatWorld
Example 1.9: Using the Periodic Table to Understand Valence Shell Electron Configurations
Using the variable n to represent the number of the valence electron shell, write the valence shell electron configuration for each group.
the alkaline earth metals
the column of elements headed by carbon
Solution
The alkaline earth metals are in the second column of the periodic table. This column corresponds to the s subshell being filled with 2 electrons. Therefore, the valence shell electron configuration is ns2.
The electron configuration of carbon is 1s22s22p2. Its valence shell electron configuration is 2s22p2. Every element in the same column should have a similar valence shell electron configuration, which we can represent as ns2np2.
Skill-Building Exercise 1.9
Using the variable n to represent the number of the valence electron shell, write the valence shell electron configuration for each group.
the halogens
the column of elements headed by oxygen
Atomic Radius
The periodic table is useful for understanding atomic properties that show periodic trends. One such property is the atomic radiusThe approximate size of an atom. (refer to Figure 1.11). As mentioned earlier, the higher the shell number, the farther from the nucleus the electrons in that shell are likely to be. In other words, the size of an atom is generally determined by the number of the valence electron shell. Therefore, as we go down a column on the periodic table, the atomic radius increases.
As we go across a period on the periodic table, however, electrons are being added to the same valence shell; meanwhile, more protons are being added to the nucleus, so the positive charge of the nucleus is increasing. The increasing positive charge attracts the electrons more strongly, pulling them closer to the nucleus. Consequently, as we go across a period, the atomic radius decreases. These trends are seen clearly in Figure 1.11.
Figure 1.11 Trends on the Periodic Table
The relative sizes of the atoms show several trends with regard to the structure of the periodic table. Atoms become larger going down a column and smaller going across a period.
Source: FlatWorld
Example 1.10: Atomic Radii
Using the periodic table (rather than Figure 1.11), which atom is larger?
N or Bi
Mg or Cl
Solution
Because Bi is below N on the periodic table and has electrons in higher-numbered shells, we expect that Bi atoms are larger than N atoms.
Both Mg and Cl are in period 3 of the periodic table, but Cl lies farther to the right. Therefore we expect Mg atoms to be larger than Cl atoms.
Skill-Building Exercise 1.10
Using the periodic table (rather than Figure 1.11), which atom is larger?
Li or F
Na or K
Career Focus: Clinical Chemist
Clinical chemistry is the area of chemistry concerned with the analysis of body fluids to determine the health status of the human body. Clinical chemists measure a variety of substances, ranging from simple elements such as sodium and potassium to complex molecules such as proteins and enzymes, in blood, urine, and other body fluids. The absence or presence, or abnormally low or high amounts, of a substance can be a sign of some disease or an indication of health. Many clinical chemists use sophisticated equipment and complex chemical reactions in their work, so they not only need to understand basic chemistry, but also be familiar with special instrumentation and how to interpret test results.
A Visit to a Clinical Hospital Lab
| 11.85 to 15.15 | Hello, I'm Lauren. Welcome to Pathology. |
| 15.54 to 19.17 | This is the Blood Sciences Lab. So yeah, come on in. |
| 24.06 to 28.23 | So this is the main corridor. We've got a lot of offices down here. |
| 28.23 to 31.32 | So we've got clinical scientists, medics, |
| 31.56 to 34.14 | a whole host of different people in these offices. |
| 34.38 to 35.67 | But through here is the main lab. |
| 38.015 to 40.44 | So this is specimen reception. |
| 40.95 to 44.61 | So here we get a lot of the samples coming through. |
| 44.94 to 49.5 | So all over the hospital have pod systems so they can |
| 49.68 to 54.18 | shoot any samples that they want to send to us down through the pod. |
| 55.2 to 57.27 | So they'll have pods like this, |
| 57.33 to 62.16 | they put the samples in and it comes through the air pod system all |
| 62.16 to 65.46 | through the hospital. We've also over here, got the hatch. |
| 66.84 to 69.9 | So people also drop a lot of different samples off here. |
| 70.29 to 73.74 | And then over here's the main sorting area. |
| 73.77 to 78.03 | So here samples will get sorted into whether they're for blood sciences, |
| 78.09 to 82.8 | microbiology, cell path, which are on the floors above us. |
| 83.76 to 88.5 | And then all of these people here are booking in and sorting samples out. |
| 88.5 to 91.92 | So they're booking them in for whatever blood sciences tests that they need. |
| 95.43 to 100.02 | So there's three departments down here in blood sciences. We've got immunology, |
| 100.02 to 101.94 | hematology, and biochemistry. |
| 102.78 to 106.62 | So they'll book them in for the tests and make sure they're going to the right |
| 106.62 to 107.453 | department. |
| 109.86 to 113.43 | So over here is the main biochemistry section. |
| 113.43 to 116.73 | So this is where the bulk of the tests get processed. |
| 117.72 to 122.67 | So a lot of the samples will go in here and |
| 123.03 to 127.68 | they all have a barcode on and the barcode gets read and that tells them where |
| 127.68 to 130.77 | they need to go and what they need to do and what tests they need doing on the |
| 130.77 to 131.603 | main track. |
| 133.44 to 137.67 | It'll get red here and then it'll go along and go to where it needs to go. |
| 138.21 to 142.59 | We'll go this way. So first of all, |
| 142.59 to 146.16 | a lot of the samples will get centrifuged in these machines here |
| 147.96 to 152.73 | and then they'll get the taken off them and then it'll go to one of the |
| 152.73 to 153.36 | analyzers. |
| 153.36 to 158.34 | So different analyzers do different tests and the track will take the |
| 158.34 to 161.58 | sample to whichever analyzer it needs to do the correct test. |
| 161.7 to 165.33 | Some samples might need to go to multiple analyzers and the track will do that. |
| 165.36 to 167.31 | It'll take them to the different analyzers. |
| 168.06 to 170.88 | And then when the results have been done, |
| 171.84 to 175.89 | they'll come to this desk here where they'll get technically validated by one of |
| 175.89 to 177.42 | the biomedical scientists. |
| 181.75 to 183.82 | So over here you've got hematology. |
| 184.18 to 186.52 | So this is where you'll do things like your full blood count, |
| 186.52 to 190.45 | your clotting screens, blood films, |
| 190.78 to 193.63 | a lot of things like that. So that's over in this section. |
| 194.8 to 198.55 | So these analyzers here are a bit more manual and they're part of biochemistry |
| 198.55 to 202.6 | as well. So they run things like hemoglobin A1C, |
| 202.69 to 205.6 | which is used for diagnosis and monitoring of diabetes, |
| 206.14 to 210.22 | and also it does the protein electrophoresis |
| 210.67 to 215.5 | and things like that. And this section over here is immunology. |
| 218.23 to 222.1 | So this is one of our chemistry analyzers. We have four in total. |
| 222.76 to 225.07 | This is running a variety of different samples. |
| 225.49 to 229.09 | There's two cover cells in total, |
| 229.09 to 233.47 | which and a variety of different samples to specify what needs to be run. |
| 233.74 to 238.51 | And we do regular checks each day to ensure that these tests are run |
| 238.51 to 241.81 | correctly and efficiently. As you can see here, |
| 242.56 to 244.72 | we have 320 wells in total, |
| 244.72 to 248.11 | which means that at any one time we can have 320 samples running. |
| 248.47 to 253.06 | So this sample would run along and this one of our pipe |
| 253.06 to 256.63 | competitors would move around, pick it up, and then inject it into the well. |
| 256.84 to 261.43 | And then it will go around to the corresponding sections, |
| 261.64 to 266.44 | mix it up at the back and then test it via infra fluorescent. |
| 266.44 to 269.26 | So we shine a light through it and measure the absorbance taken from it. |
| 269.62 to 271.06 | And that's what the chemist analyzers would do. |
| 273.545 to 278.47 | So over here we have got around the edges away from |
| 278.47 to 281.98 | the main analyzers. We've got a lot of manual tests that we run. |
| 282.64 to 287.47 | So here we've got one of Urey machines. |
| 287.98 to 290.89 | These also might be in some places on the wards as well. |
| 290.98 to 294.19 | This is a point of care testing machine, but we do do it in the lab as well. |
| 295.21 to 297.64 | Here we've got the sweat test machines, |
| 297.64 to 300.43 | so we measure sweat chloride and sweat conductivity, |
| 301.12 to 304.69 | and we do that to diagnose cystic fibrosis. |
| 305.86 to 307.57 | Here we've got an OSM monitor. |
| 307.57 to 312.19 | So this is using serum and urine as modality. |
| 312.97 to 315.34 | They can both be measured using this machine here. |
| 316.9 to 321.46 | Here we've got a blood gas machine. These are also in place around the hospital. |
| 321.46 to 325.03 | This is another point of care testing machine, but we also have one in the lab. |
| 325.03 to 329.32 | So if someone around the hospital doesn't have a blood gas machine near them, |
| 329.32 to 332.02 | they can bring their blood gas samples here for analysis. |
| 333.16 to 335.32 | And here's another standalone analyzer. |
| 335.32 to 339.01 | So this runs some of the things that aren't on the main tracked machines. |
| 339.31 to 342.88 | So we run NT Pro BMP on here, |
| 343.66 to 345.31 | which is a marker of heart failure. |
| 345.94 to 349.965 | And we also do things like IGF one and |
| 350.805 to 354.01 | HCG Srin on this analyzer. |
| 361.34 to 364.58 | Thank you very much for coming to have a look round by chemistry in the Blood |
| 364.58 to 367.16 | Sciences Lab today, and hopefully we'll see you soon. |
Concept-Review Exercises
How are the elements ordered into the periodic table?
Looking at the periodic table, where do the following elements appear?
the metals
the nonmetals
the halogens
the transition metals
Describe the trends in atomic radii as related to an element’s position on the periodic table.
Answers
Elements are ordered by atomic number.
the left three-quarters of the periodic table
the right quarter of the periodic table
the next-to-last column of the periodic table
the middle section of the periodic table
As you go across the periodic table, atomic radii decrease; as you go down the periodic table, atomic radii increase.
Key Takeaways
The chemical elements are arranged in a chart called the periodic table.
Many characteristics of the elements are related to their position on the periodic table.
Exercises
Which elements have chemical properties similar to those of magnesium?
sodium
fluorine
calcium
barium
selenium
Which elements have chemical properties similar to those of lithium?
sodium
calcium
beryllium
barium
potassium
Which elements have chemical properties similar to those of chlorine?
sodium
fluorine
calcium
iodine
sulfur
Which elements have chemical properties similar to those of carbon?
silicon
oxygen
germanium
barium
argon
Which elements are alkali metals?
sodium
magnesium
aluminum
potassium
calcium
Which elements are alkaline earth metals?
sodium
magnesium
aluminum
potassium
calcium
Which elements are halogens?
oxygen
fluorine
chlorine
sulfur
carbon
Which elements are noble gases?
helium
hydrogen
oxygen
neon
chlorine
Which pairs of elements are located in the same period?
H and Li
H and He
Na and S
Na and Rb
Which pairs of elements are located in the same period?
V and Nb
K and Br
Na and P
Li and Mg
In each pair of atoms, which atom has the greater atomic radius?
H and Li
N and P
Cl and Ar
Al and Cl
In each pair of atoms, which atom has the greater atomic radius?
H and He
N and F
Cl and Br
Al and B
Scandium is a (metal, nonmetal, semimetal) and is a member of the (main group elements, transition metals).
Silicon is a (metal, nonmetal, semimetal) and is a member of the (main group elements, transition metals).