Phases of Matter: are determined by the energy content and movement of the particles
What keeps the particles in liquids and solids together? The movement of particles is directly related to the temperature of the substance, as the temperature cools the movement of the molecules slows and the molecules maybe attracted to each other. This is referred to as INTERMOLECULAR FORCES. Intermolecular forces are the attraction between molecules. These attractions are weaker than intramolecular forces like ionic and covalent bonds. The intermolecular forces can determine many of the physical properties of the substance. The stronger the intermolecular forces the higher the melting and boiling points of the substance. Why do you think this might be?
Why? The stronger the intermolecular forces the higher the energy required to disturb or break the attractions.
Types of intermolecular forces: Dispersion Forces (Van der Waals): Temporary attraction created as electrons orbit the nucleus. (-) Positive nuclei will repel each other. + +
Types of intermolecular forces: Dispersion Forces (Van der Waals): Temporary attraction created as electrons orbit the nucleus. (-)+ (-) + When the electrons are concentrated on the same side as an exposed positive nuclei there will be an attraction. Creating a temporary bond between the two atoms.
Types of intermolecular forces: Dispersion Forces (Van der Waals): Temporary attraction created as electrons orbit the nucleus. (weak attraction) Dipole – Dipole: The attraction between the oppositely charged ends of polar molecules. N H H H δ+δ+δ-δ- N H H H δ+δ+δ-δ- (-)+ (-) + Hydrogen Bonding: The attraction created when a hydrogen atom is bonded to a highly Elecronegative atom (F, O, N). This attraction causes a higher than expected boiling point. (strong attraction) H H O H H O
How do substances change state? Beginning StateEnding StateProcess of Change SolidLiquidMelting SolidGasSubliming LiquidSolidFreezing LiquidGasEvaporating/Boiling Gas Solid LiquidCondensing Deposition
Boiling Points The temperature at which a substance turns from liquid to vapor Thought question: Is the boiling point of a liquid the same in every location? Boiling point is directly related to atmospheric pressure, and indirectly related to altitude! LocationAltitude (ft)PressureBoiling Point Sea Level0760 mmHg100 ºC (373 K) Mt. Everest29,028240 mmHg70 ºC (343 K)
Boiling vs. Evaporation Occurs below the boiling point, only at the surface of the liquid. Occurs at the boiling point, throughout the entire liquid. Heat of vaporization: the amount of heat required to vaporize a liquid. Normal Boiling Point: the temperature at which vapor pressure of a liquid is equal to atmospheric pressure.
Freezing and Melting Points At what temperature does water freeze? At what temperature does ice melt? (Freezing point) (Melting point) Heat of Fusion: the amount of heat required to melt a solid to liquid
We often use graphs to show the correlation between vapor pressure and boiling. The graph below is the vapor pressure curve for four different substances. Using this graph we can find the “Normal boiling point” for any substance by observing its boiling point at standard pressure (101.3 kPa, 1 atm, 760 mmHg). For example the “normal boiling point” of substance A would be 35°C. What would the normal boiling of substance D be? 100°CBased on this information, what do you think substance D might be?
Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?
Do the practice graph in your packet. Answers: 1. ~32kPa, ~7kPa (your answer may differ by +/- 1) 2. 70ºC 3. ~21kPa 4. ~74ºC, ~115ºC
Particles are Always in Motion GASES 1.Gases are composed of tiny particles 2.Particles are in constant motion 3.Elastic collisions occur between particles 4.There are no attractive forces between particles 5.Kinetic Energy increases when temperature increases.
Particles are Always in Motion LIQUIDS 1.Viscosity: the friction or resistance to motion that exists between the molecules of a liquid 2.Surface Tension: the imbalance of forces at the surface of a liquid
Particles are Always in Motion SOLIDS 1.Particles are “locked” in position and can only vibrate 2.Can be classified by three main characteristics: Hardness Electrical Conductivity Melting Point
How do we classify solids? Crystalline Solids: organized, repetitive unit cells, sharp melting point metallic: conduct electricity well molecular: soft, low melting point ionic: hard, brittle covalent-network: conduct electricity at high temperatures Amorphous Solids: not “true” solids because molecules do move some high viscosities make them appear solid they soften before melting
For Next Class: Complete homework page of packet.