Question

Referring to the periodic table, name (a) the halogen in the fourth period, (b) an element similar to phosphorus in chemical properties, \((\mathrm{c})\) the most reactive metal in the fifth period, (d) an element that has an atomic number smaller than 20 and is similar to strontium.

Short answer

(a) Bromine, (b) Arsenic, (c) Rubidium, (d) Calcium.

Step-by-step solution

Identifying the Fourth Period Halogen

Looking at the periodic table, the halogens are a group of elements in Group 17. The members of the halogen group in the fourth period include bromine. Thus, the halogen in the fourth period is bromine (Br).

Finding an Element Similar to Phosphorus

To find an element similar to phosphorus, we look within the same group (Group 15) as phosphorus. Elements in the same group have similar chemical properties. Nitrogen (N) and arsenic (As) are both similar in chemical properties to phosphorus (P). Arsenic is in the same group and period as phosphorus.

Determining the Most Reactive Metal in the Fifth Period

The fifth period includes the alkali metals and alkali earth metals, typically found in Groups 1 and 2. The most reactive metals are generally in Group 1. In the fifth period, rubidium (Rb) is the alkali metal, known for being highly reactive. Thus, rubidium is the most reactive metal in the fifth period.

Identifying an Element Similar to Strontium with Atomic Number < 20

Strontium (Sr) is in Group 2, known as the alkaline earth metals. To find an element similar to strontium with an atomic number less than 20, we look below calcium (Ca) in the periodic table. Ca, in Group 2, fits the criteria with an atomic number of 20.

Key concepts

Halogens

Halogens are an intriguing group of elements located in Group 17 of the periodic table. These elements include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). What's fascinating about halogens is their highly reactive nature, especially with alkali metals and alkaline earth metals.
This high reactivity is due to their seven valence electrons, meaning they need only one more to achieve a stable electronic configuration (like the noble gases in Group 18).
Characteristics of halogens include:

• High reactivity and formation of strong acids like hydrochloric acid.
• Existence in various physical states at room temperature: fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids.
• Usage in disinfection, medications, and even in the making of plastics.

Bromine, in particular, as identified in the exercise, is the halogen in the fourth period of the periodic table. It is known for its role in flame retardants and some types of medication.
Understanding halogens can help one appreciate the diverse roles elements play in both biological and industrial processes.

Group 15 Elements

Group 15 of the periodic table is a diverse group of elements, often referred to as the nitrogen group or pnictogens. This group includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). Group 15 elements display a variety of properties, both metallic and non-metallic.
Let’s explore some key characteristics:

• They have five valence electrons, leading to interesting bonding behavior, such as forming triple bonds in nitrogen gas \(N_2\).
• Nitrogen and phosphorus are essential for life. Nitrogen is crucial for amino acids, while phosphorus is part of DNA.
• Arsenic and antimony have more metallic characteristics and are used in semiconductors.

In the exercise, phosphorus and arsenic are noted for their similarities in chemical behavior. This similarity comes from being in the same group, sharing comparable electron configurations leading to similar types of chemical reactions.
Group 15 elements play a significant role in everything from agriculture to electronics, highlighting the importance of understanding these versatile elements.

Alkali Metals

Alkali metals, located in Group 1 of the periodic table, are known for their remarkable reactivity. This group of elements includes lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Each has a single electron in their outermost orbital, which they readily lose to form positive ions, making them highly reactive, especially with water.
Here are some noteworthy properties of alkali metals:

• Soft texture and can often be cut with a knife.
• Shiny appearance when freshly cut, which dulls quickly due to oxidation.
• Forming strongly alkaline hydroxides when reacting with water.

The exercise highlights rubidium, a highly reactive alkali metal in the fifth period. Rubidium's vigorous reactivity makes it a key player in various applications, such as photoelectric cells and research on ion propulsion.
Understanding alkali metals offers insights into fundamental chemical reactions and is vital for applications in both technology and industry.

Alkaline Earth Metals

Alkaline earth metals belong to Group 2 of the periodic table. This group includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Like alkali metals, alkaline earth metals are highly reactive, but their reactivity is a bit lower due to having two electrons in their outer shell.
Key characteristics of alkaline earth metals include:

• Higher melting points compared to alkali metals, making them more suitable for structural applications.
• Their compounds, like calcium carbonate and magnesium oxide, are widely used in construction and industry.
• Producing different oxide colors, such as the brilliant reds in fireworks from strontium compounds.

In the exercise, calcium is pointed out as an element similar to strontium with an atomic number less than 20. Calcium's properties make it essential in biological processes, such as bone formation.
Exploring alkaline earth metals helps in understanding their critical roles in industry and biology, offering a glimpse into their wide-ranging uses from building materials to nutritional supplements.