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Chapter 8: Problem 42

Use the second period of the periodic table as an example to show that the size of atoms decreases as we move from left to right. Explain the trend.

Short Answer

Expert verified
In the second period of the periodic table, as we move from left to right, the atomic size decreases. This decision is due to the increasing number of protons, which create a larger positive nuclear charge. This increased charge attracts the electrons more strongly, pulling them closer to the nucleus and thereby decreasing the atomic radius.

Step by step solution

01

Understand the Atomic Structure

First, it's important to understand the atomic structure. An atom consists of a nucleus, which contains protons and neutrons, and shells with electrons around the nucleus. The number of protons is the atomic number, which increases as we move from left to right across a period.
02

Analyze the Second Period of the Periodic Table

In the second period of the periodic table, there are eight elements from Lithium (Li) to Neon (Ne). As we move from left to right, the atomic number increases, which means that the number of protons in the nucleus and the number of electrons in the shells increase.
03

Explain the Decrease in Atomic Size

As we move from left to right across the period, each atom has one more proton and one more electron than its predecessor. However, these additional electrons are added to the same shell, so they are approximately at the same distance from the nucleus. The increase in the number of protons means the positive charge of the nucleus also increases. The larger nuclear charge attracts the electrons more strongly, pulling them closer to the nucleus, which results in a smaller atomic radius.
04

Detail the Trend

The trend observed is that the atomic size decreases as we move from left to right in a period. This is because the increasing nuclear charge due to the addition of protons draws the electrons closer to the nucleus, reducing the atomic size despite an increase in the number of subatomic particles.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Periodic Table
The periodic table is a system that categorizes the elements based on their chemical properties and atomic numbers. It is arranged in rows, known as periods, and columns, known as groups or families. As you look across the second period of the periodic table, from Lithium (Li) to Neon (Ne), a clear pattern emerges: the atomic size decreases from left to right.

Why does this happen? To answer that, we look at other concepts like atomic structure, atomic radius, and electron shells, all influencing this trend. Understanding the layout and logic behind the periodic table is crucial because it reflects the systematic organization that dictates the behavior and reactions of elements.
Atomic Structure
The atomic structure is at the heart of understanding the properties of different elements. An atom is essentially a building block of matter, consisting of a nucleus surrounded by electrons that orbit in electron shells. The nucleus houses protons, which are positively charged, and neutrons, which have no charge. As elements are organized in the periodic table based on their atomic numbers (the number of protons in the nucleus), we see that this number gradually increases from left to right. This change has a crucial impact on the atomic size, as we'll explore next with the concept of atomic radius.
Atomic Radius
The atomic radius is a measure of the size of an atom, typically the distance from the center of the nucleus to the outer boundary of the electron cloud. In the second period of the periodic table, although the number of electron shells remains the same, the atomic radius decreases from Lithium to Neon. This is because the growing number of protons in the nucleus exerts a stronger pull on the electrons, drawing them in closer and reducing the overall size of the atom. This trend provides us with valuable insights into how atomic size can be affected by changes within the atom's core structure.
Electron Shell
The electron shell is like an orbit followed by electrons around an atom's nucleus. These shells can hold a certain number of electrons and are filled from the innermost shell outward. In a period, as we move from one element to the next, an additional electron is added to the same shell, not creating a new layer but increasing the electron count in the existing shell. This addition does not significantly increase the size of the electron cloud, but it does have implications for the attractive force that the nucleus can exert on the electrons, an idea closely tied to the concept of nuclear charge.
Nuclear Charge
Nuclear charge is the total charge of the nucleus, equal to the number of protons it contains. It is responsible for the electrostatic pull that the nucleus exerts on the electrons. As the atomic number increases along a period, the higher nuclear charge pulls the electrons closer to the nucleus. This greater attraction is effective at shrinking the atomic radius, leading to smaller atomic sizes despite an increasing number of electrons and protons. Understanding the effect of nuclear charge on atomic size is key to understanding the trends observed in the periodic table.

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Most popular questions from this chapter

Which elements are more likely to form acidic oxides? Basic oxides? Amphoteric oxides?

Using the following boiling-point data, estimate the boiling point of francium: $$ \begin{array}{l|l|l|l|l|l|l} \text { Metal } & \mathrm{Li} & \mathrm{Na} & \mathrm{K} & \mathrm{Rb} & \mathrm{Cs} & \mathrm{Fr} \\ \hline \text { B.p. }\left({ }^{\circ} \mathrm{C}\right) & 1347 & 882.9 & 774 & 688 & 678.4 & ? \end{array} $$

One allotropic form of an element \(X\) is a colorless crystalline solid. The reaction of \(\mathrm{X}\) with an excess amount of oxygen produces a colorless gas. This gas dissolves in water to yield an acidic solution. Choose one of the following elements that matches \(\mathrm{X}:\) (a) sulfur, (b) phosphorus, (c) carbon, (d) boron, and (e) silicon.

An element X reacts with hydrogen gas at \(200^{\circ} \mathrm{C}\) to form compound Y. When \(Y\) is heated to a higher temperature, it decomposes to the element \(X\) and hydrogen gas in the ratio of \(559 \mathrm{~mL}\) of \(\mathrm{H}_{2}\) (measured at STP) for \(1.00 \mathrm{~g}\) of \(\mathrm{X}\) reacted. \(\mathrm{X}\) also combines with chlorine to form a compound \(Z,\) which contains 63.89 percent by mass of chlorine. Deduce the identity of \(X\).

How does atomic radius change (a) from left to right across a period and (b) from top to bottom in a group?
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