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Polarity: Bonds and Molecule

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Created on February 6, 2024

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Review of Electronegativity

Electronegativity is the measure of the ability of an atom in a bond to attract electrons to itself.Electronegativity increases across a period and decreases down a group.

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Electronegativity in Bonding

The chemical bonding behavior of elements is significantly influenced by electronegativity. The differential electronegativity between two interacting atoms controls the nature of the resulting bond. A large electronegativity difference results in a mostly ionic bond, while a small electrongativity differnce results in a covalent bond.

  • Types of Boding:
  • Convalent Bond
    • Nonpolar Covalent
    • Polar Covalent
  • Ionic Bond

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Covalent Bonds

Polar Covalent bonds are a type of chemical bond formed between two atoms where the electrons are shared, but the sharing is unequal. This unequal sharing is a result of electrons being more attracted to one atom over another (electronegativity). Polar covalent bonds are characterized by a partial positive charge on one atom while the other now has a partial negative charge. This is known as a dipole.

Nonpolar Covalent bonds are a type of chemical bond formed between two atoms when they share electrons almost equally. This equal sharing results in no significant separation of electrical charge within the molecule. Electrons within a nonpolar covalent bond have equal probability of being near the nucleus of each atom in the bond.

Example: H2, 02, Cl2

Dipole

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Dipole

A dipole is a molecule with a permanent separation of electrical charge. This separation arises when atoms within the molecule share electrons unequally due to differences in their electronegativity. A dipole moment is the measure of the polarity of the molecule. Dipoles go from the slightly positive charged (δ+) atom to the slightly negative charged atom(δ−). This is indicated by an arrow.

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Bond Polarity

Electronegativity table

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Self Check

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Self Check

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Self Check

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Polar Molecules

Individual atoms within a polar molecule can have a partial positive charge (δ+) and while the other atom will with a partial negative charge (δ–). An entire molecule may also have a separation of charge depending on the molecular shape and polarity of the overall bonds.
If all bonds are non-polar, the molecule is automatically non-polar. If some or all bonds are polar, you have to look at the shape of the module.

In general, symmetrical molecules are non-polar because dipoles cancel and asymmetrical molecules are polar because they do not cancel.

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Self Check

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Solution

Self Check

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Solution

Ionic Bonds

Ionic bonds are a type of chemical bond that occurs when there is an electrostatic attraction between two atoms. The bond occurs when the valence electron of one atom is transferred to the other, allowing both to possibly fulfill the Octet Rule. That atom receiving the electron(s) is given a negative charge and the atom losing the electron becomes positively charged.

Reminder of the Octet Rule

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What is an Ion?

An ion is an atom or molecule that has gained or lost one or more electrons, resulting in a net positive or negative electrical charge.
Types of ions: There are two main types:
  • Cations: Positively charged ions (e.g., Na+, Ca2+).
  • Anions: Negatively charged ions (e.g., Cl-, SO42-).
When atoms form an ionic bond, this means electrons are moved from one atom to another. The Proton never leaves the atom.

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Drag each infromation to the drawer of the corresponding concept

valence electron(s) are either lost or gained by an atom forming a positive or negative charge. 3
bond formed from an sharing of electrons. 2
a dipole forms between the atoms in the bond. 4
bond formed from an electrostatic attraction between two atoms. 1
Ionic Bonds
Covalent Bonds

1 & 3

2 & 4

Solution

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Attributions

Periodic Table: Periodic table large.svg (CC BY-SA 4.0; 2012rc via Wikipedia)

Periodic table Energy Levels 1-20 Copied with permission from middleschoolchemistry.com

MASTERING Periodic Trends and corresponding images copied with premission from ACS

By Mirek2 - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=14923345

“Electronegativity-Example.” Chemistry Learner , www.chemistrylearner.com/. Accessed 06 Feb. 2026.

Clark, Adelaide E. General Chemistry II. Open Oregon Educational Resources, 2019.

“Electronegativity and Bonding: Chemical Bonds: Chemistry: Khan Academy.” YouTube, 29 Oct. 2013, youtu.be/126N4hox9YA?si=rI3n4vLCtKYrLF4i. Accessed 08 Feb. 2024.

CNX OpenStax, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons

H Padleckas, vectorized by MaxDZ8, Public domain, via Wikimedia Commons

Radio89, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Yikrazuul, Public domain, via Wikimedia Commons

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Dipole:

a dipole is a molecule with a permanent separation of electrical charge. This separation arises when atoms within the molecule share electrons unequally due to differences in their electronegativity. A dipole moment is the measure of the polarity of the molecule.

Dipoles are often shown with the positive and negative atoms in a polar covalent bond using a lowercase Greek letter “delta,”δ, with a plus sign or minus sign to indicate whether the atom has a partial positive charge (δ+) or a partial negative charge (δ−).

Example of a Cation:
NH3 is considered a polar molecule because a dipole moment occurs between the slightly more electronegative nitrogen atom and the three hydrogens. There is an asymmetrical shape between the pair electrons of nitrogen and the three hydrogens.
Electronagtivity Difference Chart and the Pauling Scale for Electronegativity
CCl4 is nonpolar because the chlorine atoms are arranged in a way that the electrical charge from each individual atom is canceled out by the other.

Octet Rule

The octet rule is a guide that explains how atoms tend to bond with each other. It states that atoms generally achieve stability (nuetral charge) by having eight electrons in their outermost energy level (valence shell), similar to the electronic configuration of noble gases. This stability arises from a filled or closed-shell configuration, which lowers the atom's potential energy.

Example of an Anion:
CH3Cl Polar molecule: asymmetrical
CO2 Nonpolar molecule: symmetrical