Sugar (A) is a compound that can be easily decomposed to simpler substances by heating. (B) One of the simpler substances is the black element carbon, which cannot be further decomposed by chemical or physical means.
The phlogiston theory. (A) In this theory, burning was considered to be the escape of phlogiston into the air. (B) Smelting combined phlogiston-poor ore with phlogiston from a fire to make a metal. (C) Metal rusting was considered to be the slow escape of phlogiston from a metal into the air.
Priestley produced a gas (oxygen) by using sunlight to heat mercuric oxide kept in a closed container. The oxygen forced some of the mercury out of the jar as it was produced, increasing the volume about five times.
Lavoisier heated a measured amount of mercury to form the red oxide of mercury. He measured the amount of oxygen removed from the jar and the amount of red oxide formed. When the reaction was reversed, he found the original amounts of mercury and oxygen.
Here are some of the symbols Dalton used for atoms of elements and molecules of compounds. He probably used a circle for each because, like the ancient Greeks, he thought of atoms as tiny, round hard spheres.
The elements of aluminum, Iron, Oxygen, and Silicon make up about 88 percent of the earth's solid surface. Water on the surface and in the air as clouds and fog is made up of hydrogen and oxygen. The air is 99 percent nitrogen and oxygen. Hydrogen, oxygen, and carbon make up 97 percent of a person. Thus almost everything you see in this picture us made up of just six elements.
“ Any given compound always consists of the same atoms and the same ratio of atoms. For example, water always consists of oxygen and hydrogen atoms, and it is always 89 percent oxygen by mass and 11 percent hydrogen by mass”
2. The Law of Conservation of Mass:
“ The total mass of materials before and after a chemical
reaction must be the same. For example, if we combine
89 grams of oxygen with 11 grams of hydrogen under
the appropriate conditions, 100 grams of water will be
produced—no more and no less.”
Dalton’s Laws 3. The Law of Multiple Proportions: “ If two elements combine to form more than one compound, the masses of one of the elements that can combine with a given mass of the other element are related by factors of small whole numbers” For example, water has an oxygen-to-hydrogen mass ratio of 7.9:1. Hydrogen peroxide, another compound consisting of oxygen and hydrogen, has an oxygen-to-hydrogen mass ratio of 15.8:1. The ratio of these two ratios gives a small whole number.
EXAMPLE How many protons, neutrons and electrons are found in an atom of Cs Atomic number = protons and electrons There are 55 protons and 55 electrons Mass number = sum of protons and neutrons 133 – 55 = 78 There are 78 neutrons 133 55
Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.
Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).
Metal: Elements that are usually solids at room temperature. Most elements are metals. Non-Metal: Elements in the upper right corner of the periodic Table. Their chemical and physical properties are different from metals. Metalloid: Elements that lie on a diagonal line between the Metals and non-metals. Their chemical and physical properties are intermediate between the two.
Elements with 1, 2, or 3 electrons in their outer shell tend to lose electrons to fill their outer shell and become cations.
These are the metals which always tend to lose electrons.
Elements with 5 to 7 electrons in their outer shell tend to gain electrons to fill their outer shell and become anions.
These are the nonmetals which always tend to gain electrons.
Semiconductors (metalloids) occur at the dividing line between metals and nonmetals.
What would the charge be on a sodium ion? EXAMPLE Since sodium in in Group IA it is a metal and so would LOSE an electron You can tell how many would be lost by the group number Group 1A elements lose 1 electron So the charge would be +1 Remember an electron is negatively charged. When you lose them atom becomes positively charged… when you gain them it becomes negatively charged
How would you right the symbol for the sodium CATION? EXAMPLE Na +1 How many outer electrons does sodium have before it loses one? It has 1…remember the group number!