TEKS 5 - Mrs. Knipp's Chemistry Course



TEKS 5B Use the Periodic Table to identify and explain the properties of chemical families, including alkali metals, alkaline earth metals, halogens, noble gases, and transition metals.

TEKS Lesson 5B: Chemical Families

How are elements arranged in the periodic table?

In the modern periodic table, which is shown below, elements are arranged in order of increasing atomic number, starting with hydrogen, which has atomic number 1. There are seven rows, or periods, in the periodic table. Each period corresponds to a principal energy level. The properties of the elements within a period change as you move across a period from left to right. However, the pattern of properties within a period repeats as you move from one period to the next. This pattern gives rise to the periodic law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. The arrangement of the elements into periods has an important consequence. Elements that have similar chemical and physical properties end up in the same column in the periodic table.

[pic]

The columns in the periodic table are also known as groups or families. Some groups of the periodic table have special names. The elements in Group 1A are called alkali metals, and the elements in Group 2A are called alkaline earth metals. The nonmetals of Group 7A are called halogens, and the elements of Group 8A are known as the noble gases.

What determines the properties of the chemical families?

Electrons play a key role in determining the properties of elements, so there should be a connection between an element’s electron configuration, its location in the periodic table, and its chemical and physical properties.

The Noble Gases Helium, neon, and argon, which are located in Group 8A of

the periodic table, are examples of noble gases. All of the Group 8A elements are monatomic gases at room temperature and are colorless, odorless, and tasteless. These nonmetals are sometimes called the inert gases because they rarely take part in a chemical reaction. The electron configurations for the first four noble gases are listed below.

|Helium (He) |1s2 |

|Neon (Ne) |1s22s22p6 |

|Argon (Ar) |1s22s22p63s23p6 |

|Krypton (Kr) |1s22s22p63s23p63d104s24p6 |

Look at the highest occupied energy level for each element. Except for helium, the s and p sublevels are completely filled with electrons—two electrons in the s sublevel and six electrons in the p sublevel. This arrangement of electrons is related to the relative inactivity of the noble gases.

The Representative Elements Elements in Groups 1A through 7A are often referred to as representative elements because they display a wide range of physical and chemical properties. Some elements in these groups are metals, some are nonmetals, and some are metalloids. Most of them are solids, but a few are gases at room temperature, and one, bromine, is a liquid. The portion of the periodic table that includes the representative elements is shown below.

In atoms of representative elements, the s and p sublevels of the highest occupied energy level are not filled. For any representative element, its group number equals the number of electrons in the highest occupied energy level.

Alkali metals, which are found in Group 1A of the periodic table, are silver-gray solids at room temperature, soft enough to cut with a knife, and have low melting points and boiling points. The alkali metals are the most reactive metals in the periodic table and do not occur uncombined in nature because they are so reactive. Look at the electron configurations for lithium, sodium, and potassium below.

|Lithium (Li) |1s22s1 |

|Sodium (Na) |1s22s22p63s1 |

|Potassium (K) |1s22s22p63s23p64s1 |

These are Group 1A elements, so there is only one electron in the highest occupied energy level. The electron is in an s sublevel. This configuration of electrons explains the reactivity of the alkali metals.

Alkaline earth metals, which are found in Group 2A of the periodic table, are relatively soft but are harder than the alkali metals. These metals have a gray-white luster when freshly cut, but when exposed to air, they quickly form a tough, thin coating. The density, melting point, and boiling point of a given alkaline earth metal tend to be higher than for the alkali metal in the same period. Alkaline earth metals are very reactive, though not as reactive as the alkali metals. Like alkali metals, alkaline earth metals are not found in nature in the elemental state. Look at the electron configurations below for beryllium, magnesium, and calcium.

|Beryllium (Be) |1s22s2 |

|Magnesium (Mg) |1s22s22p63s2 |

|Calcium (Ca) |1s22s22p63s23p64s2 |

The alkaline earth metals are in Group 2A and therefore have two electrons in the highest occupied energy level. The electrons are in an s sublevel.

The Group 7A elements, also known as the halogens, are all nonmetals and exist as diatomic molecules. At room temperature, fluorine and chlorine are gases and bromine is a liquid. Iodine and astatine are solids. Halogens are very reactive and thus do not exist in the elemental form in nature. The electron configurations for fluorine, chlorine, and bromine are listed below.

|Fluorine (F) |1s22s22p5 |

|Chlorine (Cl) |1s22s22p63s23p5 |

|Bromine (Br) |1s22s22p63s23p63d104s24p5 |

Halogens are in Group 7A of the periodic table, so atoms of the halogens have seven electrons in their highest occupied energy level. The s sublevel is completely filled with two electrons, and the p sublevel contains five electrons. This configuration of electrons explains the reactivity of the halogens.

Transition Elements In the periodic table, the B group elements separate the A groups on the left side of the table from the A groups on the right side. Elements in the B groups are referred to as transition elements. There are two types of transition elements—transition metals and inner transition metals. They are classified based on their electron configurations.

The transition metals are the Group B elements usually displayed in the main body of the periodic table. Most transition metals are ductile, malleable, and good conductors of heat and electric current. Copper, silver, and gold are transition metals, and their electron configurations are listed below.

|Copper (Cu) |1s22s22p63s23p63d104s1 |

|Silver (Ag) |1s22s22p63s23p63d104s24p64d105s1 |

|Gold (Au) |1s22s22p63s23p63d104s24p64d104f145s25p65d106s1 |

In atoms of a transition metal, the highest occupied s sublevel and a nearby d sublevel contain electrons. These elements are characterized by the presence of electrons in d orbitals. There is great variation in reactivity among transition metals. Scandium and yttrium are similar to Group 1A and 2A metals. They react easily with substances in the air and with water. Platinum and gold are extremely unreactive.

The inner transition metals are the elements that appear below the main body of the periodic table. In atoms of these elements, the highest occupied s sublevel and a nearby f sublevel generally contain electrons. The inner transition metals are characterized by the presence of electrons in f orbitals. Uranium is an example of an inner transition metal.

[pic]

Lesson Check

1. Identify Where are the following chemical families located on the periodic table?

a. alkali metals

b. alkaline earth metals

c. halogens

d. noble gases

e. transition metals

2. Identify Use the periodic table to identify the chemical family (alkali metals, alkaline earth metals, halogens, noble gases, or transition metals) to which each element belongs.

a. barium

b. chlorine

c. lithium

d. krypton

e. mercury

3. Explain Which of the following sets of elements have similar chemical and physical properties? Identify the chemical family (or families) to which the elements belong, and use the periodic table to explain why their properties are similar.

a. oxygen, nitrogen, carbon, boron

b. bromine, chlorine, fluorine, iodine

c. nitrogen, neon, nickel, niobium

4. Explain Sodium, an alkali metal, reacts with water to form a solution of sodium hydroxide and hydrogen gas:

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Name two elements that will react with water in the same way. Identify the chemical family (or families) to which these elements belong, and use the periodic table to explain your choices.

-----------------------

TEKS

Chemistry

Lesson 5B

[pic]

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download