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214 Unit B Atoms, Elements, and Compounds NEL
7. The Modern Periodic Table
There are many different ways that scientists can classify the elements. One way is to separate them by their physical properties into metals, metalloids, and non-metals. As you have learned, in general, most metals conduct electricity, have a shiny lustre, and are malleable and ductile. Most non-metals do not conduct electricity, do not have a shiny lustre, and are gases at room temperature or brittle if solid. Metalloids have some of the properties of metals and some of the properties of non-metals. In the Periodic Table in Figure 1, the metal elements are shaded blue, the non-metal elements are shaded pink, and the metalloid elements are shaded green.
Li Be
Sc Ti Zr Hf Rf Ce Th
V
Nb Ta Db Pr Pa
Cr Mo W Sg Nd U
Mn Tc Re Bh Pm Np
Fe Ru Os Hs Sm Pu
Co Rh Ir Mt Eu Am
Cu Ag Au Rg Tb Bk
Zn
B
Al Ga In Tl Uut Ho Es
C
Si Ge Sn Pb Uuq Uup Uuh Uus Uuo Er Fm
N
P
As Sb Bi
Tm Md
O
S
Se Te Po
F
H
Cl Br I At
Ne
He
Ar Kr Xe Rn
Yb Lu No Lr
Cd Hg Uub Dy Cf
Ni Pd Pt Ds Gd Cm
Y
La Ac
Mg Ca Sr Ba Ra
Na K Rb Cs Fr
1 18 2 13 14 15 16 17
3 4 5 6 7 8 9 10 11 12
Li Be
Sc Ti Zr Hf Rf
V
Nb Ta Db
Cr Mo W Sg
Mn Tc Re Bh
Fe Ru Os Hs
Co Rh Ir Mt
Cu Ag Au Rg
Zn
B
Al Ga In Tl Uut
C
Si Ge Sn Pb Uuq Uup Uuh Uus Uuo
N
P
As Sb Bi
O
S
Se Te Po
F
H
Cl Br I At
Ne
He
Ar Kr Xe Rn
Cd Hg Uub
Ni Pd Pt Ds
Y
La Ac
Mg Ca Sr Ba Ra
Na K Rb Cs Fr
alkaline earth metals
halogens noble gases
alkali metals rare earth metals
transition metals
Ce Th
Pr Pa
Nd U
Pm Np
Sm Pu
Eu Am
Tb Bk
Ho Es
Er Fm
Tm Md
Yb Lu No Lr
Dy Cf
Gd Cm
Figure 1 Periodic Table showing metal
(blue), non-metal (pink), and metalloid
elements (green)
Figure 2 Periodic Table showing major
families of elements and group numbers
LEARNING TIP
What does Figure 2 tell you? Try
reading the Periodic Table up and
down (in columns), rather than left
to right (in rows). Ask yourself, “How
many groups are there? How are the
elements in each group like members
of a family?”
Another way to classify the elements is by family, based on common physical and chemical properties. The Periodic Table in Figure 2 shows the major families highlighted in different colours. A third way to classify the elements is by group. The groups are the columns in the Periodic Table, and are numbered from 1 to 18, starting at the left.
NEL 7.3 The Modern Periodic Table 215
The elements can also be classified according to their ion charges, atomic number, or electron arrangement. The modern Periodic Table, based on Mendeleev’s design, allows us to include all of these classifications in one model. It is a model that chemists use to explain and predict the chemical and physical behaviour of the elements.
Finding Information in the Periodic Table Examine the following sample entry below from the Periodic Table (Figure 3). Note the location of the element name, chemical symbol, atomic number, ion charge, and atomic mass.
What do the different parts of the entry tell you? The element name and chemical symbol tell you that Al is the chemical symbol for aluminum. The atomic number tells you the number of protons in the nucleus of the atom (13). Since the number of electrons in a neutral atom is equal to the number of protons, the atomic number also tells you the number of electrons. The ion charge of 3 tells you that the aluminum atom will form an ion that has 3 fewer electrons than protons. Unlike the mass number, the atomic mass is not an integer. Many elements have more than one isotope—an atom with the same number of protons, but a different number of neutrons. Therefore, the mass numbers of isotopes are different, but the atomic numbers are the same. The atomic mass of an element is the average of the mass numbers of all the naturally occurring isotopes. The mass number is the mass of one particular isotope of an element. You can determine the mass number of the most common form of an element by rounding the atomic mass to the nearest whole number. The mass number of the most common form of aluminum is 27 (26.98 rounded up), so the number of neutrons in the most common form of the element is 14.
Calculating the Number of Electrons in an Ion The number of protons in the nucleus of an atom does not change when the atom forms an ion—only the number of electrons orbiting the nucleus can change. Aluminum’s atomic number is 13, so its atoms have 13 protons. Aluminum’s ion charge is 3. Therefore, an atom of aluminum has 13 electrons. An ion of aluminum will have only 10 electrons, 3 fewer electrons than protons. Oxygen’s atomic number is 8, and its ion charge is 2. Oxygen atoms have 8 electrons, but oxygen ions have 2 more electrons than protons or 10 electrons.
atomic number
most common ion charge
density at SATP
symbol of element name of element atomic mass
Al
aluminum 26.
13 2.
Figure 3 The entry for aluminum
in the Periodic Table
To learn more about isotopes,
go to
GOGO www.science.nelson.com GOGO
LEARNING TIP
Check your understanding. Examine
Figure 3 closely. Then cover the labels.
What vital information can you learn
from Figure 3? Identify the element’s
name, symbol, atomic number, ion
charge, and atomic mass.
Mass of Ions
The mass spectrometer is used to
measure the mass of ions using electric
and magnetic fields. Thomson’s
student, Francis Aston, constructed
the first mass spectrometer in 1919
and used it (and later versions) to
identify 212 of the 287 naturally
occurring isotopes.
KNOW
Did You
7.3 (^) CHECK YOUR Understanding
NEL 7.3 The Modern Periodic Table 217
Refer to the modern Periodic Table at the back of the book to answer questions 1 to 9.
1. Where on the Periodic Table are the elements that form ions with a positive charge? 2. Where are the metals? 3. Where are the elements that form ions with a negative charge? 4. Where are the non-metals? 5. Where are the metalloids? 6. What shape does the arrangement of the metalloids form in the Periodic Table? 7. Starting from carbon, what happens to the ion charge as you move to the right? 8. Starting from carbon, what happens to the ion charge as you move to the left? 9. As you move to the right, and down, what happens to the atomic mass and the atomic number? Are there any exceptions to your answers? 10. What is the relationship between the number of protons in the nucleus of an atom and the atomic number of the element? 11. Describe how to determine the number of electrons in the atom of an element. 12. Describe how to determine the number of electrons in the ion of an element. 13. A certain element has 12 protons and 14 electrons. (a) Is the element an atom or an ion? (b) Which element is it? (c) What charge, if any, does it have? 14. A certain element has 34 protons and 36 electrons. (a) Is the element an atom or an ion? (b) Which element is it? (c) What charge, if any, does it have? 15. A certain element has 24 protons and a charge of 3+. (a) Is the element an atom or an ion? (b) How many electrons does the element have in this form? (c) Which element is it? 16. Look at the Periodic Table entry for sulfur in Figure 4.
(a) What is the atomic number? (b) What is the atomic mass? (c) What is the ion charge? (d) How many electrons does the sulfur atom have? (e) How many electrons does the sulfur ion have?
17. Look at the Periodic Table entry for calcium in Figure 5.
(a) What is the atomic number? (b) What is the atomic mass? (c) What is the ion charge? (d) How many electrons does the calcium atom have? (e) How many electrons does the calcium ion have?
18. Look up each of the following elements in the Periodic Table, list its atomic number and atomic mass, and state if it is a metal, non-metal, or metalloid. (a) tellurium (e) manganese (b) osmium (f) silicon (c) arsenic (g) phosphorous (d) yttrium
S
sulfur
2
Ca
calcium
Figure 4
Figure 5
