How can we know which elements are more electronegative than others? I’ve never come across any such formula or trick for this, except learning it by practice. Please tell if you know any.

Electronegativity is a property that indicates the tendency of an atom to attract a shared pair of electrons in a chemical bond. While there isn't a single formula or trick that can definitively determine the electronegativity of elements, there are some trends and patterns that you can use to make educated guesses. Here are a few methods and concepts that can help you understand and predict electronegativity:

Periodic Table Trends: Electronegativity generally increases as you move across a period from left to right and decreases as you move down a group. This trend is primarily due to the effective nuclear charge and atomic size. Elements on the right side of the periodic table tend to have higher electronegativities because they have more protons and a smaller atomic size, which leads to stronger attraction for electrons.

Pauling Electronegativity Scale: Linus Pauling devised a widely used electronegativity scale. Fluorine is assigned the highest value of 3.98, and all other elements are ranked relative to fluorine. You can use the Pauling scale to compare the electronegativity of different elements.

Electronegativity Difference: When two atoms are bonded together, the electronegativity difference between them can help predict the type of bond that will form. If the difference is small, a nonpolar covalent bond is likely to form, where electrons are shared relatively equally. If the difference is large, an ionic or polar covalent bond is more likely, where one atom has a stronger pull on the electrons.

Group Trends: Within a group, electronegativity tends to decrease as you move down. This is due to the increase in atomic size and the shielding effect of inner electron shells. As you move down a group, the valence electrons are farther from the nucleus and experience less effective nuclear charge.

Dipole Moments: In molecules with polar covalent bonds, you can look at the dipole moments to determine the relative electronegativity of the atoms involved. The direction of the dipole moment points towards the more electronegative atom.

Common Knowledge: Over time, as you practice and study chemistry, you'll become familiar with certain patterns of electronegativity. For example, you'll learn that fluorine is highly electronegative, and elements like oxygen, nitrogen, and chlorine are also relatively electronegative.

While there's no definitive formula or trick to memorize electronegativity values for all elements, understanding the underlying trends and using resources like electronegativity scales and periodic table trends will help you make informed predictions about the relative electronegativities of different elements. Over time, practice and exposure to chemistry will enhance your ability to gauge electronegativity intuitively.