Section K Test Review Matter and the many wonders it contains.
Review properties • Physical properties describe—solid, gas, color, shape, liquid, etc. Often used to classify matter. • Every form of matter has two kinds of properties—physical and chemical. • Chemical properties-what the potential of a reaction may bring—example—ability to change the substance into a different substance- –natural gas to heat, light, and smoke.
Elements • A pure substance that cannot be broken down into any other substances by physical or chemical means. It is the atom of that element. • Molecules have more than one element. • Elements in them—like H2O • Which is water.
What about compounds? • These are pure substances made of two or more elements chemically combined in a set ratio. • Example of this could be CO2 which is carbon dioxide—we breath it out of our bodies. It is a 1 to 2 ratio. • A different ratio would be carbon monoxide—this is the fumes from car exhaust. CO-That is a 1 to 1 ration
Physical change • A substance that undergoes a physical change is still the same substance after the change. • Good example is the phase changes of water or salt/sugar water that can evaporate and still leave the salt and sugar in the container after the water has gone bye-bye into the air.
Some physical changes in shape or form- - - • You know that you can separate some mixtures so many of those are physical changes also and not a chemical change. These can be separated with filtration and distillation methods. • So, bending, crushing, breaking, and chopping are all a physical change.
Chemical change • Chemical changes produce a new substance with properties different from those of the original substances. • Example: Gas burned in your car changes to movement, light, heat—sometimes flames.
Temperature • Temperature is a measure of the average energy of random motion of particles of matter. • You know then that a solid’s particles are moving very slowly compared to a gases molecules. Your liquid state of matter is in between the gas and solid particle movement. • If I continue to add heat then the • molecules of that substance will • go faster and faster and faster!
Speaking of solids: • They have a definite shape and a definite volume. Solids keeps theirshape and volume in any position or in any container. • Each shape of these solids--- • keep their shape and • volume.
How are the particles in a solid? • Close and tightly packed. • Do they move---?? Yes, vibrate. • Types of solids: crystalline—examples would be salt, sugar and snow. They melt at a distinct temperature.
What about the amorphous solids? • These are arranged in a regular pattern but they do not melt at distinct temperatures. They may become softer and softer or change into other substances. Examples would be glass, plastics, and rubber.
Liquids • Liquids have a definite volume but no shape of their own. • Thus—no container--?—liquids go everywhere!
Liquids keep their volume so. . . • If the container is too small the volume of the liquid spills everywhere and if the container is larger than the volume you will see the container as only partially full.
What else about liquids? • The particles in a liquid are packed almost as closely as in a solid. However, the particles move around one another freely—”kinda” like a rolling motion. Like a hand-full of marbles—you can slide them around one another but they stay in contact. • Because of this particle motion, • liquids have a definite volume • but remember NO definite shape.
Liquids also have many other cool traits—here are two of them: • 1. They have surface tension which is the result of an inward pull among the molecules of a liquid—it holds the surface together and it forms droplets on surfaces and can “bead up” when it falls. It is the water in the liquids that give this property. It almost acts like “skin”!
Remember the word “viscosity”? • This is a liquid’s resistance to flowing. This depends on the size and shape of the liquid’s particles. You can think of it as the “thickness” of a liquid. • Honey has a high viscosity--- Soda has a low viscosity.
So for liquids remember: • Has definite volume • Does NOT have a definite shape—takes on the shape of it’s container • Has viscosity—high (runs slow) or low (runs fast) • Has cohesion abilities—remember the water skeeter insect? Also the droplets on the leaf? • GOT IT? • Of Course!
Now—on to Gas!! • OOPS!! So Sorry!
OK!! Gases. . . . • Gas is like a fluid, however, a gas can change volume very easily. • Put a gas into a container and it will either spread apart or be squeezed together as the gas particles fill that container
So the particles of gas move as far as they are allowed. • As gas particles move and spread apart, they will fill all the space available—hence---a gas has neither definite shape nor definite volume.
Changes of State • Solids are frozen and then they • MELT into a liquid. • Liquids can absorb heat and then they • Become gases
By the way—what is the freezing point? • O degrees celsius • What is the boiling point of water? • 100 degrees celsius!
So what is evaporation? • The gradual turning of a liquid to a gas. Things that evaporate are open containers, lakes, puddles of water, etc.
What about sublimation? • This is the process of particles of a solid that do not pass through the liquid state at all. They go from a solid to a gas immediately. • Can you think of an example? • Dry ice! • Snow on a very cold day
Atoms----again!!!! • Atoms have how many parts? • Three—protons, neutrons, and electrons • What charge is a proton? (nucleus) • Positive • What charge is a neutron? (nucleus) • None ---it is neutral! • What charge is an electron? • Negative and it is buzzing around the nucleus on the outside of the atom
Models of atoms • 1808 Dalton model • John Dalton (chemist) though that each element were atoms all made alike. He therefore thought atoms were tiny, solid spheres.
1897 Thomson Model • As a scientist, J.J. Thomson discovered the electron. He suggested that an atom is positively charged sphere with electrons embedded in it.
1904 Nagaoka Model • A Japanese physicist, Nagaoka proposed a model of the atom that had a large sphere in the center with a positive charge and electrons revolving around the sphere like the planets around the sun.
1911 Rutherford model • Ernest Rutherford was a British physicist who concluded that the atom is mostly empty space. Electrons orbit randomly around a small, positively charged nucleus.
1913-Bohr Model • Niels was a Danish physicist who proposed a model that showed electrons moving in specific layers or shells rather than randomly. He said the atoms would give off energy when the electrons move from one shell to another.
1932- Chadwick Model • British physicist James Chadwick discovered the neutron. The existence of neutrons explained why atoms were heavier than the total mass of their protons and electrons. • Remember the mass is actually the proton and neutrons. Electrons are too small to make much of a difference.
Present Modern Model of the Atom • The current model results from work done from the 1920’s to the present. Electrons form a negatively charged cloud around the nucleus. It is impossible to determine exactly where an electron is at a given point.
What is an isotope? • An atom which has the same number of protons but a different number of neutrons. Example in your book was the carbon atoms. It had Carbon 12, Carbon 13, and Carbon 14
Mendeleev’s Work • By 1869, 63 elements had been discovered. Some were gases, liquids, solid metals, some reacted explosively as they formed compounds and others reacted more slowly. • Dmitri Mendeleev was a Russian scientist who put the periodic table together.
How did Mendeleev arrange the periodic table? • In the order of increasing *atomic mass. • *Remember that the atomic mass of an element is the average mass of ALL the isotopes of that element. • Most of the elements that were close together seemed to share the same properties, but not all-- so Mendeleev moved a few elements into groups where the elements did have similar properties.
Bly the way—what is the atomic number? • It tells you how many protons are in the nucleus of the atom. • Well how many electrons are there? • The same number as protons.
How accurate was Mendeleev?—Pretty darn accurate!!! • There were three blank spaces left and Mendeleev predicted that the blank spaces would be filled by elements that had not yet been discovered—he even predicted the properties of those missing elements. • The periodic table has not changed much, new elements were added as they were discovered. • Now the modern PERIODIC TABLE has the table arranged in order of the ATOMIC NUMBER NOT THE ATOMIC MASS.
What pages in the book did we cover? • All from “K” section: • 6-12 • 22-27 • 40-47 • 48-53 • 74-87 • Think back to all the new words you learned—we only had you write down about 8 of them. You also had many on your yellow packet that you are keeping to study until the test. Many are in this review power point also. Go home and review it.