Post on 25-Dec-2015
Mixtures and Pure Substances
• Matter that consists of two or more substances mixed together but not chemically combined is called a mixture.
• A pure substance is made of only one kind of material and has definite properties.
Elements
• Elements are the simplest pure substance. – Examples: hydrogen, carbon,
and oxygen.
• The smallest particle of an element that has the properties of that element is called an atom.
Compounds• A molecule is formed when two or
more atoms combine.
• Compounds are pure substances that are made of more than one element bound together.– Examples: water, table salt, and
carbon dioxide.
MIXTURESHeterogeneous vs. Homogeneous
• Homogeneous matter: matter that has identical properties throughout. – Examples: Sugar, salt, water, and whipped
cream
• Heterogeneous matter: matter that has parts with different properties. – Examples: granite, soil, potpourri
Conservation
• Law of Conservation of Matter (Mass): matter cannot be created or destroyed.
• Law of Conservation of Energy: Energy cannot be created or destroyed; it may only change from one form to another.
Making stuff nature
never dreamed of.
The Elements Song
Currently we have about 115 kinds of atoms. In the natural world there exists 88 different kinds of atoms.
The others have been artificially produced in laboratories.
Atoms are made up of protons, neutrons, and electrons.
Protons and neutrons are found in the nucleus of atoms -- roughly at the center
Electrons travel around the nucleus.
Of course real atoms don’t look anything
like this!
Different kinds of atoms, or elements, are different because they have different numbers of protons.
They don’t look anything like this either!
We list the elements by their atomic numbers - the number of protons
they have.
Hydrogen, number 1 Helium, number 2
Physical Properties
• Physical properties: characteristics that can be observed without changing the identity of the substance.
• Examples: – mass– volume– color – shape – texture– density
Physical Changes
• Physical change: a change in the physical form or properties of a substance that occurs without a change in composition.
• Examples:– melting– freezing– grinding– dissolving
Chemical Properties
• Chemical property: describes a substance’s ability to change into a different substance.
• Examples: – flammability– reactivity
Chemical Changes• Chemical change: occurs
when a substance changes composition by forming one or more new substances. (bonds are broken and bonds are formed)
• Example:– HCl + NaOH NaCl + H2O
Indications of a Chemical Change…
Flames
Gas is given off (not to be confused with boiling)
Color Change
Kinetic Theory
• All matter is made of atoms and molecules that act like tiny particles.
• These tiny particles are always in motion. The higher the temp., the faster the particles move.
• At the same temp., more massive (heavier) particles move slower than less massive (lighter) particles.
SOLIDS
• Definite shape?• YES
• Definite volume?• YES
• Molecules in a solid are tightly packed and constantly vibrating.
LIQUIDS
• Definite shape?• NO
• Definite volume?• YES
• Some liquids flow more easily than others. The resistance of a liquid to flow is called viscosity. – Honey has a high viscosity compared to water.
GASES
• Definite shape?• NO
• Definite volume?• NO
• The particles in a gas are spread very far apart, but can be compressed by pumping them into a restricted volume.
Phase Changes• Changes in phase are examples of
physical changes.
• Melting: solid liquid• Freezing: liquid solid• Vaporization: liquid gas• Condensation: gas liquid• Sublimation: solid gas
Changes of State
GAS
SOLID
Deposition
Sublimation
VaporizationCondensation
Melting
Freezing
LIQUID
Melting
• ENERGY is the ability to change or move matter.
• Energy is ABSORBED when substances melt or evaporate.– NOTE: our bodies cool down when our sweat
evaporates.
• Energy is RELEASED when substances freeze or condense.
Melting
• The change of state from solid to liquid.
• Energy (heat) is absorbed by the substance that is melting.
Freezing• The change of state from liquid to
solid. Opposite of melting. Energy (heat) is released by the substance undergoing freezing.
Evaporation• The change of state at the surface of a liquid as it passes to a vapor.
This results from the random motion of molecules that occasionally escape from the liquid surface. – Energy (heat) is released by the liquid (Cooling of the liquid results)
– Can happen at any temperature
Condensation
• The change of state from gas to liquid. The opposite of evaporation.– Energy (heat) is absorbed by the liquid (Warming of the
liquid results)
Boiling• Change from state from a liquid to a gas.• Occurs throughout the liquid.
– boiling point/temperature is determined by pressure
– Energy (heat) is released by the liquid.
*Boiling & freezing points depend on the pressure.*Boiling & freezing points depend on the pressure.
Water at normal pressure (1 atm):
• For water at normal (every day) pressures:
• Melting/freezing point:
• Condensing/boiling point:
0 oC (32oF)
100 oC (212oF)
Label the points & temperatures on your graph.
Phase Diagrams• a phase diagram shows the equilibria
pressure-temperature relationship among the different phases of a given substance
triple point = Point ______The point at which all 3 phases of a substance (solid, liquid, gas) can coexist at equilibrium.
critical point = Point ______The combination of critical temperature and critical pressure.
A
C
D
critical temp = temp. above which a gas cannot be liquefied. (H2O=374ºC)
critical pressure = press. required to liquefy a gas at its critical temperature. (H2O=218 atm)