Definition: Electronegativity is a measure of an atom’s ability to attract electrons from a chemical bond to itself. It is used to determine how strongly an atom will attract electrons from another atom in a chemical bond.

Trends in the periodic table:

• Electronegativity decreases down a group.
• Electronegativity increases across a period.

Why does this happen?

• Smaller atoms with nearly complete valence shells will attract electrons more easily than larger atoms with fewer valence electrons. The smaller the atomic radius, the closer the valence electrons are to the nucleus, and the stronger the pull on the electrons in a bond.

Real-world example: The Carbon-Fluorine (C-F) bond is highly polar due to the difference in electronegativity between carbon and fluorine. Fluorine is more electronegative than carbon because fluorine has a smaller atomic radius and higher nuclear charge. This causes fluorine to attract bonded electrons more strongly.

Activity Overview: In this activity, you will follow the work of Julius Lothar Meyer, an 18th-century chemist, who explored the periodicity of the known chemical elements.

Skills Required

• Use spreadsheets to manipulate and represent data.
• Use and interpret scientific notation.
• Apply and use SI prefixes and units.
• Identify, describe, and explain patterns, trends, and relationships.

Steps

• Collect data: In a spreadsheet, collect atomic mass and atomic radius data for the elements from hydrogen to strontium.
• Calculate atomic volume: Use the equation for the volume of a sphere to calculate the volume of a single hydrogen atom. Then, calculate the volume of a single atom of the other elements by copying and pasting the formula down the column.
• Calculate atomic volume of hydrogen: Atomic volume is the volume taken up by one mole of an element, in m³ mol–1. Copy and paste the formula down the column to obtain data for the other elements.
• Plot a graph: Plot a graph of atomic volume vs atomic mass. Analyze the graph to identify the periodicity of elements and discuss how well it supports the law of octaves.

Real-world example: The periodic trend in atomic volume helps chemists predict the behavior and properties of elements. For example, elements with larger atomic volumes tend to have lower densities and may be less reactive than elements with smaller atomic volumes.