1. The number of valence electrons that an atom has dictates its ability to react chemically. The closer an atom is to achieving a full outermost shell, the more likely it will be to borrow electrons. Atoms are paired in a way that allows both to achieve a full stable outermost shell. For example, one atom of silicon has 14 electrons, four of which are valence electrons in the outermost shell. Silicon can lend, share, or gain four electrons to achieve a full outermost shell.
2.
a. Law of conservation of energy
b. Law of definite proportions
c. Law of conservation of matter
3. Mendeleev first published a table of elements arranged according to increasing atomic masses. He noticed that some elements near each other had differing properties, but elements in vertical columns had similar properties. Moseley then rearranged the table according to atomic numbers and this eliminated the discrepancies found in Mendeleev’s attempt. Today’s version of the periodic table displays elements in order based on their atomic number; the atomic number indicates the number of protons within the atoms of a particular element. Rows are called periods and columns are called groups. Elements in the same group have similar properties. Elements are grouped into nine categories: noble gases, halogens, nonmetals, alkali metals, alkaline earth metals, transition metals, other metals, metalloids, and rare earth elements.
4. 1st pic
5. 2nd pic
6. 3rd, 4th, 5th pic
7. Water is colorless, odorless, and tasteless. It's the chief substance of living material. It has a specific gravity of 1.0 at 4° Celsius. It freezes at 0° Celsius and boils at 100° Celsius. Water is a powerful solvent. Distillation is needed to remove impurities. Purification methods include
Aeration (water is sprayed into the air so that light and oxygen can kill bacteria)
Filtration (water is passed through a filter to remove impurities)
Chlorination (chlorine is added to water to destroy bacteria)
Coagulation (chemicals are added to water to cause organic matter with bacteria
to settle out)
8. Air contains nitrogen (78%), oxygen (21%), carbon dioxide (0.04%), and rare gases (less than 1%). It also contains water, dust, bacteria, and other materials.
The atmosphere supports life via two cycles. In the carbon dioxide cycle, carbon dioxide is taken in by plants and used in photosynthesis. From here, oxygen is released to the atmosphere and taken in by animals; it fuels combustion and is needed for fermentation and decay. These processes convert it back to carbon dioxide.
In the nitrogen cycle, nitrogen is fixed by bacteria in the soil into usable nitrogen compounds absorbed by plants. Plants use these to form proteins, which are used as food by animals. Decaying plants and animal wastes return the nitrogen to the soil and ammonia to air. Without atmospheric nitrogen, rust and decay of living material would happen more quickly.
Explanation:
From PennFoster
