Question

Among the elements W, X, Y and Z having atomic numbers \(9,10,11\) and 12 respectively, the correct order of ionization energies is: (a) \(\mathrm{W}>\mathrm{Y}>\mathrm{X}>\mathrm{Z}\) (b) \(\mathrm{X}>\mathrm{W}>\mathrm{Z}>\mathrm{Y}\) (c) \(X>Z>Y>W\) (d) \(\mathrm{Z}>\mathrm{Y}>\mathrm{X}>\mathrm{W}\)

Short answer

Option (b) \( \text{X > W > Z > Y} \) is the correct order of ionization energies.

Step-by-step solution

Identify the Elements

To determine the order of ionization energies, identify the elements based on atomic numbers. We have the following: - Atomic number 9 corresponds to Fluorine (W) - Atomic number 10 corresponds to Neon (X) - Atomic number 11 corresponds to Sodium (Y) - Atomic number 12 corresponds to Magnesium (Z)

Understand Ionization Energy Trend

Ionization energy generally increases across a period on the periodic table and decreases down a group. For elements with atomic numbers 9 to 12, they are in the same period (Period 2 and 3) and their ionization energies decrease as atomic number increases, except for noble gases.

Compare Ionization Energies

Neon (X) is a noble gas and has the highest ionization energy due to its full valence shell. Fluorine (W) follows, being very electronegative with an almost complete valence shell. Magnesium (Z), in the next period, has a lower ionization energy compared to Neon and Fluorine, as elements in the third period start to have available valence electrons that are more easily removed. Sodium (Y), being an alkali metal, has the lowest ionization energy among these.

Determine Order

Given that Neon (X) has the highest ionization energy, followed by Fluorine (W), then Magnesium (Z), and finally Sodium (Y), the correct order of ionization energies is: \[ \text{X > W > Z > Y} \]

Choose the Correct Option

Match \( \text{X > W > Z > Y} \) with the given options:- (a) \( \text{W > Y > X > Z} \)- (b) \( \text{X > W > Z > Y} \)- (c) \( \text{X > Z > Y > W} \)- (d) \( \text{Z > Y > X > W} \) Option (b) matches our determined order of ionization energies.

Key concepts

Periodic Table

The periodic table is like a map of elements organized by their properties. It helps predict how different elements will react and their general characteristics. The table is arranged in rows called periods and columns known as groups.
Each element is placed in a specific location because of its atomic structure. This periodic arrangement makes it easier to see the trends across different elements. For example, as you go across a period (left to right), the atomic number increases, and so does the ionization energy, generally.

• Periods: Horizontal rows that show elements with gradually changing properties.
• Groups: Vertical columns with elements that have similar chemical behaviors.

The periodic table is a powerful tool for chemists and students alike to understand how elements are related to each other.

Atomic Number

The atomic number is a fundamental property of an element. It tells us the number of protons in an atom's nucleus, which also determines the element's identity.
Because protons are positively charged, the atomic number also equals the number of electrons in a neutral atom. These electrons arrange themselves in shells around the nucleus.
The increase in atomic number as you move across a period explains the increase in ionization energy because more protons pull electrons closer, making them harder to remove. In our example:

• Fluorine (Atomic Number 9)
• Neon (Atomic Number 10)
• Sodium (Atomic Number 11)
• Magnesium (Atomic Number 12)

The atomic number uniquely categorizes these elements and helps predict their chemical behavior.

Noble Gases

Noble gases are a special group of elements found in Group 18 of the periodic table. They have interesting characteristics that make them unique. Their electron arrangements are very stable and complete, leading to very low chemical reactivity.
For example, Neon with an atomic number of 10 is a noble gas. It has a complete outer electron shell, making it very stable and giving it a high ionization energy.

• Generally unreactive due to full valence shells.
• Display high ionization energies compared to neighboring elements.

Noble gases are used in a variety of applications due to their inertness, like lighting and insulation gases.

Electron Configuration

Electron configuration refers to the arrangement of electrons around the nucleus of an atom. This setup affects each element's chemical properties and reactivity.
Electrons occupy energy levels or "shells." The number of electrons in the outermost shell, also known as the valence shell, plays a vital role in how elements interact with one another.
Fluorine, with electron configuration \[ 1s^2 2s^2 2p^5 \], is one electron short of a full shell, making it very reactive and giving it high ionization energy. On the other hand, Neon \[ 1s^2 2s^2 2p^6 \] has a completely filled outer shell, meaning it is a stable noble gas with very high ionization energy.

• Helps determine an element's reactivity by showing how full an atom's outer shell is.
• Directly related to the periodic trends in ionization energy.

Understanding electron configuration is key to predicting an element's chemical behavior in reactions.