Question

According to the general trend, the atomic radius for a period of elements (increases/decreases) proceeding from left to right in the periodic table.

Short answer

The atomic radius decreases from left to right in a period.

Step-by-step solution

Recognize Periodic Table Trends

First, recall that the atomic radius is a periodic trend observed across the periodic table. Generally, the atomic radius tends to decrease as you move from left to right across a period.

Understanding the Concept

Understand that as you move left to right within a period, the number of protons in the nucleus increases. This increase in positive nuclear charge pulls the electron cloud closer to the nucleus, resulting in a smaller atomic radius.

Apply the Concept

Apply this concept to the elements in a period on the periodic table. As each element adds another proton and electron, the effective nuclear charge increases, further reducing the atomic radius.

Key concepts

Atomic Radius

The atomic radius is a key concept in chemistry, describing the size of an atom. It is the distance from the center of the nucleus to the outermost shell of electrons. Understanding the atomic radius provides insights into the behavior and reactivity of different elements.
As you move across a period from left to right on the periodic table, the atomic radius decreases. This happens because, even though electrons are added to the same energy level, the number of protons in the nucleus increases.
The increased positive charge pulls the electron cloud closer, reducing the size of the atom. Thus, with a greater pull on the electrons by the nucleus, the atomic radius naturally becomes smaller.

Effective Nuclear Charge

Effective nuclear charge is the net positive charge experienced by valence electrons in an atom. It considers both the total positive charge from protons and the shielding effect caused by inner electrons. The effective nuclear charge can be thought of as the net pull from the nucleus that a valence electron 'feels'.

Moving across a period, the effective nuclear charge increases. More protons in the nucleus provide a stronger pull on the outer electrons, while the number of inner shielding electrons remains essentially constant.

• Shielding effect: Inner electrons repel outer electrons, which diminishes the pull of the nucleus on valence electrons.
• Increasing protons: Each new proton adds to the pulling force, shrinking the atomic radius.

Understanding effective nuclear charge helps explain many periodic trends, including atomic radii and ionization energies.

Periodic Table

The periodic table is an essential tool in chemistry, organizing the elements in a way that reflects periodic trends. These trends help predict and explain the chemical behavior of elements. By laying out elements in rows (periods) and columns (groups), the table showcases patterns such as the change in atomic radius or effective nuclear charge.

The periodic table reveals how properties change as elements progress across a period or down a group. Key trends include

• Atomic size (radius) decreases across a period as effective nuclear charge increases.
• Reactivity varies; metals become less reactive across a period, while nonmetals become more reactive.
• Direction down a group saw an increase in atomic size due to higher energy levels.

Utilizing these trends, chemists can predict how different elements might react with one another and understand the structure of matter.