Question

Moseley's experiments on \(\mathrm{X}\) rays emitted from atoms led to the concept of atomic numbers. (a) If arranged in order of increasing atomic mass, which element would come after chlorine? (b) Describe two ways in which the properties of this element differ from the other elements in group \(8 \mathrm{~A}\).

Short answer

The element that comes after Chlorine when arranged in order of increasing atomic mass is Argon (Ar). Argon differs from other elements in group 8A in terms of its lower atomic mass and lower boiling point.

Step-by-step solution

From the periodic table, we can find the atomic mass of Chlorine (Cl), which is approximately 35.5 atomic mass units (amu). ##Step 2: Identify the element after Chlorine##

After identifying Chlorine's atomic mass, we need to look for the next element in the periodic table with a higher atomic mass. The next element with higher atomic mass is Argon (Ar) with an atomic mass of approximately 39.95 amu. ##Step 3: Identify Argon's properties##

Argon (Ar) is a noble gas and belongs to the 8A group in the periodic table. It has an electron configuration of \(1s^2 2s^2 2p^6 3s^2 3p^6\). Argon is colorless, odorless, and an inert gas. ##Step 4: Compare Argon's properties with other elements in group 8A##

We need to describe two ways in which Argon's properties differ from other elements in group 8A. Difference 1:

Argon has a lower atomic mass compared to other elements in group 8A. The atomic masses of the elements in group 8A increase as we go down the periodic table (e.g., Krypton, Xenon, and Radon). Difference 2:

Argon has the lowest boiling point (-302.6°F or -185.9°C) among the elements in group 8A. As we go down the group, the boiling points of the elements increase (Krypton's boiling point: -244.2°F or -153.4°C, Xenon's boiling point: -162.2°F or -108.1°C, and Radon's boiling point: - 81.8°F or -63.1°C). In conclusion, the element which comes after Chlorine when arranged in order of increasing atomic mass is Argon (Ar), and it differs from other elements in group 8A in terms of its lower atomic mass and lower boiling point.

Key concepts

Periodic Table

The periodic table is an organized chart that arranges all known elements in order of increasing atomic number, which is the number of protons in an atom's nucleus. Each element has a unique atomic number and characteristic properties.
The table is structured into rows called periods and columns known as groups or families. These groups contain elements with similar chemical behaviors.
Understanding the layout of the periodic table can help in identifying patterns in element properties:

• Vertical columns (groups) contain elements that often behave similarly, known as chemical families.
• Horizontal rows (periods) represent elements with the same number of electron shells.
• The transition from left to right across a period brings a change from metallic to non-metallic characteristics.

A key point to remember is that moving down a group increases atomic mass and atomic radius. However, the reactivity of elements can either increase or decrease depending on whether you are considering metals or non-metals.

Noble Gases

Noble gases are a group of elements found in Group 8A (or Group 18) of the periodic table, known for their lack of reactivity. This property stems from having a complete valence electron shell. In simple terms, their outermost electron shell is full, making them stable and unlikely to form chemical bonds with other elements.
Some key characteristics of noble gases include:

• They are colorless, odorless, and tasteless in their natural state.
• They are non-reactive, or inert, which makes them useful in applications requiring a non-flammable and stable atmosphere, such as filling light bulbs or creating protective environments for arc welding.
• The noble gases include Helium, Neon, Argon, Krypton, Xenon, and Radon. They are often used in lighting, laser technologies, and for cooling purposes.
• Noble gases are unique because their boiling and melting points are extremely low compared to other elements. As a result, they are monatomic gases under standard conditions.

Their unique properties make them invaluable in many industrial applications, despite being chemically unreactive.

Argon Properties

Argon is a noble gas, positioned right after Chlorine on the periodic table with an atomic number of 18 and a symbol 'Ar'. One of its significant properties is being entirely inert under most conditions, which means it doesn’t easily participate in chemical reactions.
Here are some specific characteristics of Argon:

• Argon is colorless, tasteless, and odorless, like other noble gases.
• Its electron configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6\), giving it a stable octet that doesn't require any additional electrons or involve sharing via chemical bonding.
• Argon is the third most abundant gas in the Earth's atmosphere, making up about 0.93% by volume, which makes it readily available.
• Its low boiling point of -185.9°C means it can remain gaseous at very low temperatures, which is useful in cryogenic applications.
• Because of its inertness, Argon is extensively used in applications such as providing a non-reactive atmosphere for welding, in incandescent and fluorescent lighting, and in growing crystals for silicon wafers in electronics.

Being versatile and safe due to its non-reactive nature, Argon is a valuable element in various technological and industrial processes.