Question

Describe the trend in electronegativity going from left to right across a period.

Short answer

Electronegativity increases from left to right across a period due to increasing nuclear charge.

Step-by-step solution

Identify the Periodic Trend

Understand that electronegativity is a measure of an atom's ability to attract and hold electrons in a chemical bond.

Analyze the Periodic Table

Locate a period (horizontal row) on the periodic table. Periods run from left to right.

Observe Atomic Structure Changes

As you move from left to right across a period, the number of protons in the nucleus increases. This increase in positive charge attracts electrons more strongly.

Consider the Principal Energy Levels

Across a period, electrons are added to the same principal energy level. There is little change in shielding effect, but nuclear charge increases, pulling the electron cloud closer to the nucleus and increasing electronegativity.

Summarize the Trend

Due to the increasing nuclear charge with little increase in shielding, electronegativity increases from left to right across a period.

Key concepts

Periodic Table

The periodic table is an organized chart of elements based on their atomic number, electron configurations, and recurring chemical properties.

Elements are arranged in rows called periods and columns called groups.

As you move from left to right across a period, properties of elements gradually change. This layout helps predict and understand various elemental trends, such as electronegativity, by examining the periodic table's structure.

Atomic Structure

Atomic structure refers to the organization of subatomic particles—protons, neutrons, and electrons.

Protons, which have a positive charge, and neutrons, which are neutral, reside in the nucleus. Electrons, with a negative charge, orbit the nucleus in various energy levels.

The number of protons (atomic number) defines the element and influences how strongly an atom attracts electrons. This attraction is measured by electronegativity.

Nuclear Charge

Nuclear charge refers to the total charge of the nucleus, calculated as the number of protons in an atom.

As you move across a period from left to right, the nuclear charge increases because more protons are added to the nucleus.

This increased charge pulls electrons closer to the nucleus, enhancing the atom's ability to attract electrons and hence increasing its electronegativity.

The more protons there are, the stronger the pull on the electrons.

Principal Energy Levels

Principal energy levels are the fixed distances from the nucleus where electrons may be found.

As electrons are added to the same energy level when moving across a period, the principal energy level remains unchanged.

Despite increasing nuclear charge, these energy levels limit the variation in electron distancing from the nucleus.

It's within these levels that the balance of charge and distance impacts an element’s electronegativity.

Shielding Effect

The shielding effect refers to the ability of inner-shell electrons to reduce the effective nuclear charge felt by the outer-shell (valence) electrons.

As you move across a period, the shielding effect generally remains constant because electrons are added to the same principal energy level.

The minimal change in shielding allows the increasing nuclear charge to exert a stronger pull on the valence electrons, thus increasing electronegativity.

This explains why elements on the right of a period usually have higher electronegativity values.