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Section 1

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Hydrogen Bonding

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Chemistry Science

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Date created

Mar 1, 2020

Cards (22)

Section 1

(22 cards)

Hydrogen Bonding

Front

The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong We call these interactions hydrogen bonds Typical Bond Energies 5-30 kJ/mol (compare with ionic and covalent bonds at 100-300kJ/mol) Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.

Back

The States of Matter

Front

The state a substance is in at a particular temperature and pressure depends on two antagonistic entities The kinetic energy of the particles The strength of the attractions between the particles

Back

States of Matter

Front

The fundamental differences between states of matter is the distance between particles and the arrangement of the particles.

Back

Intermolecular Forces Affect Many Physical Properties

Front

The strength of the attractions between particles can greatly affect the properties of a substance or solution

Back

Phase Diagram of Water

Front

Note the high critical temperature and critical pressure These are due to the strong van der Waals forces between water molecules

Back

At that instant, then, the helium atom is polar, with an excess of electrons on the left side and a shortage on the right side. These forces are present in all molecules, whether they are polar or nonpolar.

Front

London Dispersion Forces

Back

Factors Affecting London Forces

Front

The shape of the molecule affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger dispersion forces than short, fat ones (like neopentane) This is due to the increased surface area in n-pentane The strength of dispersion forces tends to increase with increased molecular weight

Back

Viscosity

Front

Resistance of a liquid to flow is called viscosity It is related to the ease with which molecules can move past each other Viscosity increases with stronger intermolecular forces and decreases with higher temperature

Back

Energy Changes Associated with Changes of State

Front

The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other. The temperature of the substance does not rise during the phase change

Back

London Dispersion Forces

Front

While the electrons in the 1s orbital of helium would repel each other (and, therefore, tend to stay far away from each other), it does happen that they occasionally wind up on the same side of the atom London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

Back

States of Matter depend on

Front

Temperature and Pressure

Back

Phase Diagram of Carbon Dioxide

Front

Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; CO2 sublimes at normal pressures The low critical temperature and critical pressure for CO2 make supercritical CO2 a good solvent for extracting nonpolar substances (such as caffeine)

Back

Surface Tension

Front

Surface tension results from the net inward force experienced by the molecules on the surface of a liquid

Back

Intermolecular Forces

Front

They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.

Back

Kinetic Energy

Front

movement of molecules

Back

Dipole-Dipole Interactions

Front

Molecules that have permanent dipoles are attracted to each other The positive end of one is attracted to the negative end of the other and vice-versa. These forces are only important when the molecules are close to each other. The more polar the molecule, the higher its boiling point

Back

Van der Waals Forces

Front

Dipole-dipole interactions Hydrogen bonding London dispersion forces

Back

Which Have a Greater Effect: Dipole-Dipole Interactions or Dispersion Forces?

Front

If two molecules are of comparable size and shape, dipole-dipole interactions will likely be the dominating force If one molecule is much larger than another, dispersion forces will likely determine its physical properties

Back

Temperature

Front

average kinetic energy of a molecule

Back

Phase Diagrams

Front

Phase diagrams display the state of a substance at various pressures and temperatures and the places where equilibria exist between phasesThe AB line is the liquid-vapor interface. It starts at the triple point (A), the point at which all three states are in equilibrium. It ends at the critical point (B); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other

Back

Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1

Front

more london dispersion forces

Back

Intermolecular Forces also called

Front

These intermolecular forces as a group are referred to as van der Waals forces.

Back