ACT Science Chemical Bonds: Predict Bond Type From Electronegativity Differences

Electronegativity: An atom's tendency to attract electron pairs. Ionic bonds form between atoms with large electronegativity difference (one atom pulls electrons completely). Example: Na (low) and Cl (high) form NaCl ionic bond. Covalent bonds form between atoms with small electronegativity difference (atoms share electrons). Example: H and Cl form HCl covalent bond. Larger difference (>1.8) usually indicates ionic. Smaller difference (<1.8) usually indicates covalent. Use electronegativity trends: metals have low values; nonmetals have high values. Metals bonded to nonmetals tend to be ionic. Nonmetals bonded to nonmetals tend to be covalent.

Example: C and H bonding. Both are nonmetals with similar electronegativity. Covalent bond (C-H). Na and O bonding. Na is metal (low), O is nonmetal (high). Ionic bond (Na2O).

Mistake 1: Forgetting electronegativity trends. F is most electronegative; metals are least electronegative. Mistake 2: Using precise cutoff (>1.8 ionic, <1.8 covalent) when real chemistry is more nuanced. ACT uses this as a guideline, not absolute rule. Mistake 3: Not recognizing polar covalent bonds (between covalent atoms with different electronegativity). Bonds exist on a spectrum: purely ionic → polar covalent → nonpolar covalent. For ACT, focus on large vs. small electronegativity differences.

During practice, predict bond type before looking at the answer, using electronegativity trends. This habit trains reasoning.

Pair 1: Na and Cl. Na is metal (low EN), Cl is nonmetal (high EN). Large difference. Ionic bond. Pair 2: C and O. Both nonmetals, C is low-moderate, O is high. Moderate difference. Polar covalent. Pair 3: C and H. Both nonmetals, similar EN. Small difference. Nonpolar covalent. Pair 4: Mg and O. Mg is metal (low), O is nonmetal (high). Large difference. Ionic. Pair 5: N and N. Same atom, no difference. Pure nonpolar covalent (N2 gas). Predict bond type for each pair based on electronegativity logic.

Find three ACT Science passages with bond type questions. Predict bond types before reading answers. By the third passage, prediction will be reliable.

Bond type questions appear on some ACT Science sections. They test whether you apply electronegativity concepts. Students who predict bond types using electronegativity logic pick up 1 point because the reasoning is reliable and generalizable.

Drill bond type prediction daily this week. For each element pair, predict the bond type based on electronegativity trends. By test day, you should predict bond types confidently.