Periodic Table Trends (Electronegativity, Ionization energy, and Atomic radius)

The periodic table arranges elements to reveal predictable patterns in their properties, known as periodic trends. These trends are primarily governed by two factors: the number of electron shells (energy levels) and the effective nuclear charge, which is the pull that the outermost electrons feel from the nucleus. Understanding these core principles allows us to predict an element's behavior based on its position on the table. Three of the most important trends are atomic radius, ionization energy, and electronegativity.

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Atomic Radius 

Atomic radius is a measure of the size of an atom. As you move down a group on the periodic table, the atomic radius increases. This is because each step down adds a new electron shell, placing the outermost electrons further from the nucleus. Moving from left to right across a period, the atomic radius decreases. Although electrons are being added, they are filling the same energy level, while protons are also being added to the nucleus. This stronger nuclear charge pulls the electron cloud in more tightly, shrinking the atom.

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Ionization Energy 

Ionization energy is the energy required to remove an electron from an atom. This trend is inversely related to atomic radius. As you move down a group, the ionization energy decreases. The outermost electrons are farther from the nucleus and are shielded by inner electrons, making them easier to remove. Conversely, moving across a period, ionization energy increases. The greater effective nuclear charge holds the electrons more tightly, so it takes significantly more energy to strip one away.

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Electronegativity 

Electronegativity describes an atom's ability to attract shared electrons in a chemical bond. Moving down a group, electronegativity decreases. With more electron shells, the nucleus is farther from the shared bonding electrons and has a weaker pull on them. As you move across a period, electronegativity increases due to the rising nuclear charge, which more powerfully attracts the bonding electrons. Fluorine is the most electronegative element, while noble gases are typically assigned an electronegativity of zero as they rarely form bonds.

You can also find this explained in this video.