Intermolecular Forces

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Intermolecular Forces Noun

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[in-ter-muh-lek-yuh-ler for-sez]

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Intermolecular Forces

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Electrostatic forces of attraction or repulsion that exist between two or more separate molecules, influencing a substance's physical state.

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Example: The dotted lines show intermolecular forces, called hydrogen bonds, which are attractions between the slightly positive hydrogen atoms and slightly negative oxygen atoms of different water molecules.

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Intramolecular Forces Noun

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[in-truh-muh-lek-yuh-ler for-sez]

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Intramolecular Forces

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The strong forces, such as ionic or covalent bonds, that hold the atoms together within a single molecule.

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Example: This diagram shows that an intramolecular force is the strong bond holding atoms together *within* a single molecule, like the bond between H and Cl.

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Kinetic Energy Noun

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[ki-net-ik en-er-jee]

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Kinetic Energy

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The energy that a substance's molecules possess due to their constant, random motion, which increases with temperature.

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Example: Heating a solid increases the kinetic energy of its particles, causing them to vibrate more and spread apart, which demonstrates thermal expansion.

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Polarity Noun

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[poh-lar-i-tee]

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Polarity

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A molecular property resulting from the unequal sharing of electrons, creating distinct positive and negative poles within the molecule.

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Example: A water molecule has polarity because its oxygen atom pulls electrons more strongly, creating a partial negative charge, while the hydrogen atoms have partial positive charges.

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Electronegativity Noun

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[ih-lek-troh-neg-uh-tiv-i-tee]

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Electronegativity

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A chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

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Example: The highly electronegative chlorine atom pulls an electron from the less electronegative sodium atom, forming positive and negative ions.

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Dipole Moment Noun

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[dy-pohl moh-muhnt]

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Dipole Moment

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A quantitative measurement of the separation of two opposite electrical charges, indicating the overall polarity of a molecule.

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Example: In a water molecule, the oxygen atom pulls electrons more strongly, creating a slightly negative side (δ⁻) and leaving the hydrogen side slightly positive (δ⁺), resulting in an overall dipole moment.

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Van der Waals Forces Noun

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[van der wawlz for-sez]

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Van der Waals Forces

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A general term for the weak, distance-dependent intermolecular attractions between atoms or molecules, including dispersion and dipole-dipole forces.

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Example: This image shows how a gecko's foot has millions of tiny hairs (nanostructures), creating a huge surface area that allows weak Van der Waals forces to add up and let the gecko stick to walls.

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London Dispersion Forces Noun

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[lun-duhn dis-pur-zhuhn for-sez]

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London Dispersion Forces

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The weakest intermolecular force, caused by temporary dipoles induced in molecules due to the random movement of electrons.

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Example: The random movement of electrons in a molecule creates a temporary area of positive and negative charge (a temporary dipole), which attracts a neighboring molecule.

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Dipole-Dipole Forces Noun

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[dy-pohl dy-pohl for-sez]

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Dipole-Dipole Forces

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Attractive forces that occur between the positive end of one polar molecule and the negative end of another polar molecule.

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Example: The image shows how polar molecules, which have a partially positive (δ+) end and a partially negative (δ-) end, attract each other like tiny magnets.

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Hydrogen Bonding Noun

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[hy-druh-jen bon-ding]

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Hydrogen Bonding

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A strong type of dipole-dipole attraction occurring when hydrogen is bonded to a highly electronegative atom like N, O, or F.

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Example: This diagram shows a hydrogen bond as the weak attraction between a hydrogen atom of one water molecule and the oxygen atom of another.