Physics, 19.04.2020 06:32 gonzalesalexiaouv1bg

1. How does the valence of an element relate to its chemical activity?
2. Identify the statements below as belonging to one of these laws: law of conservation of
matter, law of conversation of energy, or law of definite proportions,
a. Energy can be neither created nor destroyed by chemical means but can be changed
from one form to another.
b. The composition of a chemical compound never varies,
c. Matter can be neither created nor destroyed by chemical means but can be changed
from one form to another.
3. How was the Periodic Table of Elements developed and how are the elements arranged on
it?
4. Using the Periodic Table of Elements, fill in the chart below to identify and describe the
properties of the noble gases,
Element Name
Group Number
Period Number
Valence
Properties/Reactivity
Uses

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Answer from: yuvin

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 10 (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 20 (8 electrons in outermost shell) Used in electric lights

Argon (Ar) 18 30 (8 electrons in outermost shell) Used to fill electric light bulbs and in welding

Krypton (Kr) 18 40 (8 electrons in outermost shell) Used in flashbulbs and strobe lights

Xenon (Xe) 18 50 (8 electrons in outermost shell) Used in flashbulbs and strobe lights

Radon (Rn)1860 (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 elementsPrevents decay of teeth, used in manufacturing

Chlorine (Cl) 173 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 4Reddish-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 5Purplish-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 6Radioactive, 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) 142 +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

Answer from: kaliyaht01

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

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

Answer from: Quest

sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. these color-magnitude plots are known as hertzsprung–russell diagramsafter their co-developers, ejnar hertzsprungand henry norris russell. stars on this band are known as main-sequence stars or dwarf stars. these are the most numerous true stars in the universe, and include the earth's sun.after condensation and ignition of a star, it generates thermal energy in its dense core region through nuclear fusion of hydrogen into helium. during this stage of the star's lifetime, it is located on the main sequence at a position determined primarily by its mass, but also based upon its chemical composition and age. the cores of main-sequence stars are in hydrostatic equilibrium, where outward thermal pressure from the hot core is balanced by the inward pressure of gravitational collapse from the overlying layers. the strong dependence of the rate of energy generation on temperature and pressure to sustain this balance. energy generated at the core makes its way to the surface and is radiated away at the photosphere. the energy is carried by either radiation or convection, with the latter occurring in regions with steeper temperature gradients, higher opacity or both.the main sequence is sometimes divided into upper and lower parts, based on the dominant process that a star uses to generate energy. stars below about 1.5 times the mass of the sun (1.5 m☉) primarily fuse hydrogen atoms together in a series of stages to form helium, a sequence called the proton–proton chain. above this mass, in the upper main sequence, the nuclear fusion process mainly uses atoms of carbon, nitrogen and oxygen as intermediaries in the cno cycle that produces helium from hydrogen atoms. main-sequence stars with more than two solar masses undergo convection in their core regions, which acts to stir up the newly created helium and maintain the proportion of fuel needed for fusion to occur. below this mass, stars have cores that are entirely radiative with convective zones near the surface. with decreasing stellar mass, the proportion of the star forming a convective envelope steadily increases. main-sequence stars below 0.4 m☉undergo convection throughout their mass. when core convection does not occur, a helium-rich core develops surrounded by an outer layer of hydrogen.in general, the more massive a star is, the shorter its lifespan on the main sequence. after the hydrogen fuel at the core has been consumed, the star evolves away from the main sequence on the hr diagram, into a supergiant, red giant, or directly to a white dwarf.

Answer from: Quest

The answer is a 0.64 volts