Question

Identify the group or period number described by each of the following: a. contains \(\mathrm{Na}, \mathrm{K}\), and \(\mathrm{Rb}\) \(\mathrm{b}\), the row that begins with \(\mathrm{Li}\) c. the noble gases d. contains \(\mathrm{F}, \mathrm{Cl}, \mathrm{Br}\), and \(\mathrm{L}\)

Short answer

a. Group 1 b. Period 2 c. Group 18 d. Group 17

Step-by-step solution

- Identify the group for Na, K, and Rb

Locate sodium (Na), potassium (K), and rubidium (Rb) on the periodic table. These elements are all in the same vertical column. The group number for these elements is Group 1, also known as the alkali metals.

- Identify the period that begins with Li

Find lithium (Li) on the periodic table. Lithium is the first element in its row. Determine the period number by counting the rows from the top. Lithium belongs to Period 2.

- Identify the group for noble gases

Noble gases are located in the last column of the periodic table. Identify the group number. The noble gases belong to Group 18.

- Identify the group for F, Cl, Br, and I

Find fluorine (F), chlorine (Cl), bromine (Br), and iodine (I) on the periodic table. These elements are all in the same vertical column. The group number for these elements is Group 17, known as the halogens.

Key concepts

Group 1 elements

Group 1 elements on the periodic table are also called alkali metals. These include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Alkali metals are known for being very reactive, especially with water. That's why they are not found freely in nature but in compounds.
Alkali metals have one electron in their outer shell, which makes them highly likely to lose that electron to achieve a stable noble gas configuration. This property leads to their reactivity.

• Lithium (Li) is light and used in batteries.
• Sodium (Na) is found in table salt (sodium chloride).
• Potassium (K) is essential for the human body.

Group 18 elements

Group 18 elements are known as noble gases. These gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Noble gases are known for being extremely unreactive due to their complete outer electron shells.
This stability makes them very useful in several applications. For example:

• Helium (He) is used in balloons because it is lighter than air and non-flammable.
• Neon (Ne) is used in neon lights for advertising.
• Argon (Ar) is used as an inert gas shield for arc welding and cutting.

Because of their lack of reactivity, noble gases were historically termed ‘inert gases’.

Period 2 elements

Period 2 elements are the elements in the second row of the periodic table. This period includes lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen (N), oxygen (O), fluorine (F), and neon (Ne). These elements are characterized by having two energy levels, or electron shells.
Each element in Period 2 has unique properties:

• Lithium (Li) is an alkali metal and highly reactive.
• Beryllium (Be) is a metal with a high melting point.
• Boron (B) is a metalloid used in glass and ceramics.
• Carbon (C) is essential to life and forms organic compounds.
• Nitrogen (N) is a major component of Earth's atmosphere.
• Oxygen (O) is crucial for respiration.
• Fluorine (F) is highly reactive and found in toothpaste.
• Neon (Ne) is a noble gas used in lighting.

Group 17 elements

Group 17 elements are known as halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Halogens are highly reactive nonmetals, especially with alkali metals and alkaline earth metals to form salts.
These elements have seven electrons in their outermost shell, so they are eager to gain one electron to achieve a stable noble gas electron configuration.

• Fluorine (F) is the most reactive and is used in toothpaste to prevent cavities.
• Chlorine (Cl) is used in disinfectants and in the treatment of drinking and swimming pool water.
• Bromine (Br) is used in flame retardants and certain types of medication.
• Iodine (I) is essential for thyroid function and is added to table salt as a supplement.