Chapter 3: Chemical Bonding - Electronegativity, Dipole Moment, and Bond Nature

Practice flashcards covering Chapter 3: Chemical Bonding, including electronegativity trends, factors affecting electronegativity, Pauling bond type classifications, cation polarizing power and covalent character, and dipole moments.

What is the definition of electronegativity?

Electronegativity is the power of a covalently bonded atom to attract a shared pair of electrons towards itself in a molecule.

Why is electronegativity a dimensionless property without units, and which scale is most commonly used to measure it?

It is a dimensionless property without units because it is only a tendency representing the net attraction for bond-forming electron pairs; the most commonly used scale was designed by Linus Pauling.

What three main factors affect the electronegativity of an atom?

Electronegativity depends on the size of the atom, the nuclear charge, and screening by inner electrons.

How does electronegativity change down a group in the periodic table, and what causes this trend?

Electronegativity decreases from top to bottom in groups because the addition of extra shells (an increase in shielding effect) overcomes the increase in nuclear charge, weakening the attraction of shared electrons to the nucleus.

How does electronegativity change across a period from left to right, and why?

Electronegativity increases from left to right across a period because the effective nuclear charge increases while the shielding effect remains constant, which decreases atomic size and increases the atom's power to attract shared electron pairs.

According to Pauling electronegativity values, what difference thresholds define ionic, polar covalent, and nonpolar covalent bonds?

An electronegativity difference higher than $1.8$ produces an ionic bond; a difference between $0.4$ and $1.8$ produces a polar covalent bond; and a difference of $0.4$ or lower produces a nonpolar covalent bond.

Why does an oxygen molecule ($O_2$) contain a nonpolar covalent bond?

Each oxygen atom has an electronegativity of $3.44$, making the difference in electronegativity $0$, which means electrons are shared equally.

Why is the chemical bond in potassium chloride ($KCl$) ionic?

Potassium has an electronegativity of $0.82$ and chlorine has $3.16$, yielding an electronegativity difference of $2.34$, which is greater than $1.8$.

Why is the bond in hydrogen chloride ($HCl$) classified as polar covalent?

Hydrogen has an electronegativity of $2.20$ and chlorine has $3.16$, giving an electronegativity difference of $0.96$, which falls between $0.4$ and $1.8$.

What factors govern the covalent character of a compound?

Covalent character depends on the polarizing power of the cation, which is determined by the cation's oxidation state; a higher polarizing power induces greater covalent character.

Why is aluminium chloride ($AlCl_3$) more covalent in nature than magnesium chloride ($MgCl_2$)?

Aluminium has an oxidation state of $+3$ compared to magnesium's $+2$, giving $Al^{3+}$ higher polarizing power to polarize the anion and cause electron sharing.

What is dipole moment, and what is its mathematical formula?

Dipole moment is the product of the magnitude of positive or negative charges and the distance between them, expressed as $\mu = q \times r$.

What is the SI unit of dipole moment, and what is its equivalence in coulomb meters ($C\,m$)?

The SI unit of dipole moment is the debye, where $1\,\text{Debye} = 3.335 \times 10^{-30}\,C\,m$.

Why is carbon dioxide ($CO_2$) considered nonpolar despite containing polar $C=O$ bonds?

Carbon dioxide is a symmetrical linear molecule where the equal and opposite bond dipoles cancel each other out, yielding a net dipole moment of $0$.

Which molecular shapes typically make symmetrical polyatomic molecules nonpolar?

Linear, trigonal planar, and tetrahedral molecular geometries.