Question

Which of the following statement is wrong? (1) In the sixth period the orbitals being filled arc \(6 \mathrm{~s}\), \(4 \mathrm{f}, 5 \mathrm{~d}\), and \(6 \mathrm{p}\). (2) All the elements in a group in the periodic table have the same number of electrons in the outer most shell of their atoms. (3) Periodicity in the properties of elements when elements are arranged in increasing order of their atomic weights is that elements with similar nature repeat after certain fixed interval. (4) The last member in each period of the periodic table is an inert gas.

Short answer

Statement (3) is wrong because periodicity is based on atomic number, not atomic weight.

Step-by-step solution

- Understanding the Periodic Table

Review the principles behind the structure of the periodic table. Each period corresponds to the filling of a set of orbitals.

- Checking Orbital Filling in Sixth Period

Validate the orbital filling sequence for the sixth period. The orbitals are filled in the following order: Start with 6s, followed by 4f, then 5d, and finally 6p.

- Analyzing Group Properties

Recall that elements in the same group (vertical columns) have the same number of electrons in their outermost shell, which gives them similar chemical properties.

- Periodicity and Atomic Weight

Understand the concept of periodicity: When elements are arranged by increasing atomic number, elements with similar properties appear at regular intervals. The periodic table should be arranged based on atomic number rather than atomic weights due to discrepancies in atomic weight-based ordering.

- Final Element in Period

Remember that each period ends with a noble gas, which is an inert gas.

- Identifying the Wrong Statement

Statement (3) is wrong. The periodicity in the properties of elements is due to their atomic number, not their atomic weight.

Key concepts

orbital filling

Orbital filling refers to the order in which electrons occupy the atomic orbitals. According to the Aufbau principle, electrons fill orbitals starting with the lowest energy level first.
In the sixth period of the periodic table, the orbitals are filled as follows:

• First, the 6s orbital is filled with two electrons.
• Next, the 4f orbitals are filled with fourteen electrons.
• Following that, the 5d orbitals are filled with ten electrons.
• Finally, the 6p orbitals fill with six electrons.

This sequence is critical for understanding the electron configuration of elements, which influences their chemical properties.

group properties

Elements in the same group of the periodic table share similar chemical properties.
This similarity arises because they have the same number of electrons in their outermost shell (valence electrons). Here are some group property highlights:

• Group 1: Alkali Metals - These elements have one valence electron and are highly reactive, especially with water.
• Group 2: Alkaline Earth Metals - These elements have two valence electrons and are also quite reactive.
• Group 17: Halogens - These nonmetals have seven valence electrons and are very reactive, especially with alkali metals to form salts.
• Group 18: Noble Gases - These elements have a full valence shell, making them very stable and inert.

Understanding these patterns helps predict the behavior of elements in reactions.

periodicity

Periodicity is the recurring trend in the properties of elements when they are arranged by increasing atomic number.
These trends are visible across different periods (rows) of the periodic table and can be predicted based on an element's position in the table.

• Atomic Radius: Generally decreases across a period from left to right and increases down a group.
• Ionization Energy: Tends to increase across a period and decrease down a group.
• Electronegativity: Increases across a period and decreases down a group.
• Electron Affinity: More negative across a period and less negative down a group.

These periodic trends are essential for understanding and predicting chemical reactions and bonding patterns.

noble gases

Noble gases, found in Group 18 of the periodic table, are a unique group of elements with distinct properties.
These gases include helium, neon, argon, krypton, xenon, and radon. Here’s what makes noble gases special:

• Inertness: They are very stable and unreactive due to their full valence shell of electrons.
• Monatomic: They exist as single atoms rather than molecules under standard conditions.
• Low Boiling and Melting Points: These are characteristics of gases.
• Applications: Commonly used in lighting, welding, and as inert environments for chemical reactions.

Understanding the properties of noble gases explains their limited reactivity and their various uses in industry and research.