Answer:
1. fewer valence electrons generally means more reactivity
2. law of conservation of energy - a
law of definite proportions - b
law of conservation of matter - c
3. In 1869 Russian chemist Dimitri Mendeleev started the development of the periodic table, arranging chemical elements by atomic mass. He predicted the discovery of other elements and left spaces open in his periodic table for them.
4. Helium (He) 18 1 0 (2 electrons in outermost shell) The elements have full outermost shells and don't tend to gain or lose electrons. They're stable and don't form compounds readily. They're generally inert, or inactive. These are basically colorless gases that are abundant in the atmosphere.
Inflating airships and balloons
Neon (Ne) 18 2 0 (8 electrons in outermost shell) Used in electric lights
Argon (Ar) 18 3 0 (8 electrons in outermost shell) Used to fill electric light bulbs and in welding
Krypton (Kr) 18 4 0 (8 electrons in outermost shell) Used in flashbulbs and strobe lights
Xenon (Xe) 18 5 0 (8 electrons in outermost shell) Used in flashbulbs and strobe lights
Radon (Rn) 18 6 0 (8 electrons in outermost shell) Used in certain medical treatments, can be environmental hazard
5 Fluorine (F) 17 2 –1 (All halogens have seven electrons in their outer shells) Pale yellow gas, penetrating odor; most active of all elements Prevents decay of teeth, used in manufacturing
Chlorine (Cl) 17 3 Greenish-yellow gas, extremely poisonous and irritating; heavy, readily soluble in water, easily liquefied; forms chlorides with most metals Used as a bleaching agent and disinfectant, used in water purification, used in manufacture of chlorine compounds; used to make salt (rock salt, seasoning), used in electrolysis, used to make HCl
Bromine (Br) 17 4 Reddish-brown liquid with suffocating odor Used to make silver bromide used on photographic film, ingredient in an anti-knock constituent for gas
Iodine (I) 17 5 Purplish-black solid, boils at comparatively low temperatures, slightly soluble in water, unites with most metals and some nonmetals; sublimes Used as a disinfectant for cuts and lacerations; important to nutrition
Astatine (At) 17 6 Radioactive, occurs naturally but only in the smallest amounts Only for scientific research, no practical industrial uses currently
6. Hydrogen (H) 1 1 +1 (It has one valence electron) Colorless, odorless, and tasteless; lightest substance known; burns with colorless flame; rarely found in free condition; mostly found in water, with other elements, in animal and vegetable matter, and in energy sources (petroleum, coal, natural gas) Used industrially to form shortenings from animal and vegetable oils and to produce ammonia
Carbon (C) 14 2 +4/–4 (It has four valence electrons) Exists as diamond, graphite, or an amorphous form with various properties; as carbon monoxide, it's colorless, odorless, tasteless, and poisonous; as carbon dioxide, it's a colorless gas that is a product of fuel combustion, respiration, and decay or living matter As a diamond, it's used for cutting and industrial purposes; as graphite, it's used in pencils, making melting pots, used as a lubricant and in industry; as an amorphous material, it's used as fuel and as a coloring material; CO2 is used in making fire extinguishers, washing soda, and in manufacture of dry ice
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.
explaination ..................... YeS
