Periodic Table

An element with a common ion charge of zero means that it typically forms neutral atoms. This means that the number of protons in the nucleus is equal to the number of electrons surrounding the nucleus, resulting in a stable, electrically neutral element.

The two metals with the lowest Mohs hardness scale values are cesium, with hardness 0.2, and rubidium, with hardness 0.3. Lithium, sodium, and potassium metals have values near 0.5-0.6.

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Cesium and rubidium are liquids at or near room temperature--cesium undergoes phase change at 28C, rubidium undergoes phase change at 39C. I knew they were the softest metals on the Mohs scale, but didn't list them because of this low melt point.

So...after the liquid metals (there are five--mercury, francium and gallium plus the two already named), you could pick any of the three low-mass alkali metals as the "softest."

tin

The atomic mass is the can be determined by the number of protons in an atom. Remember that a proton has an atomic mas number of 1 AMU (atomic mass unit).

(The total mass of an atom is the protons, neutrons and electrons combined.)

Two families ??

Calcium is an alkaline earth metal; located in group 2 and period 4 in the periodic table of Mendeleev.

There are 11: Name: Nitrogen Symbol: N

Type: Non-Metal Atomic weight: 14.0067

Density @ 293 K: 0.0012506 g/cm3 Atomic volume: 17.3 cm3/mol

Discovered: Nitrogen was discovered by Daniel Rutherford in Scotland in 1772. Rutherford removed oxygen and carbon dioxide from air and showed that the residual gas could not support combustion or living organisms. He called his discovery noxious air.

Name: Oxygen Symbol: O

Type: Non-Metal, Chalcogen Atomic weight: 15.9994

Density @ 293 K: 0.001429 g/cm3 Atomic volume: 14.0 cm3/mol

Discovered: Oxygen was discovered in 1774 by J. Priestley in England and independently by C. W. Scheele in Sweden. The word oxygen is derived from the Greek words 'oxys' meaning acid and 'genes' meaning forming.

Name: Fluorine Symbol: F

Group: Halogen Atomic weight: 18.998403

Density @ 293 K: 0.001696 g/cm3 Atomic volume: 17.1 cm3/mol

Group: Halogen Discovered: 1886

Name: Chlorine Symbol: Cl

Type: Halogen Atomic weight: 35.453

Density @ 293 K: 0.003214 g/cm3 Atomic volume: 22.7 cm3/mol

Discovered: Chlorine was produced first in 1774 by Carl Wilhelm Scheele, who observed the greenish-yellow gas released by the reaction of pyrolusite (manganese dioxide) with the substance we now call hydrochloric acid. Scheele mistakenly thought the resulting gas contained oxygen. In 1810, Sir Humphry Davy confirmed this gas was an element, not a compound. He named it chlorine, from the Greek word 'chloros', meaning pale green.

Name: Helium Symbol: He

Group: Noble Gas Atomic weight: 4.00260

Density @ 293 K: 0.0001787 g/cm3 Atomic volume: ?

Group: Noble Gas Discovered: 1895

Name: Neon Symbol: Ne

Type: Noble Gas Atomic weight: 20.179

Density @ 293 K: 0.0009 g/cm3 Atomic volume: 16.7 cm3/mol

Discovered: Neon was discovered in 1898 by William Ramsay and Morris Travers during experiments with liquid air. The name comes from the Greek word 'neon', meaning new.

Name: Argon Symbol: Ar

Type: Noble Gas Atomic weight: 39.948

Density @ 293 K: 0.001784 g/cm3 Atomic volume: 22.4 dm3/mol at 0 oC, 101.325 kPa.

Discovered: 1894 by Lord Rayleigh and Sir William Ramsay who sought to explain why nitrogen from air appeared to be heavier than nitrogen released from compounds. They discovered that air-sourced nitrogen contained another gas that is nearly one-and-a-half times denser than nitrogen. After isolating the new gas, the first of the noble gases to be discovered, the scientists named it argon ("the inactive one") and found it made up almost one percent of air. Rayleigh said, "Argon must not be deemed rare. A large hall may easily contain a greater weight of it than a man can carry."

Name: Krypton Symbol: Kr

Group: Noble Gas Atomic weight: 83.80

Density @ 293 K: 0.003708 g/cm3 Atomic volume: 38.9 cm3/mol

Group: Noble Gas Discovered: 1898

Name: Xenon Symbol: Xe

Group: Noble Gas Atomic weight: 131.30

Density @ 293 K: 0.00588 g/cm3 Atomic volume: 37.3 cm3/mol

Group: Noble Gas Discovered: 1898

Name: Radon Symbol: Rn

Group: Noble Gas Atomic weight: 222

Density @ 293 K: 0.00973 g/cm3 Atomic volume: 50.5 cm3/mol

Group: Noble Gas Discovered: 1900

Source: http://www.chemicool.com/

Air is roughly 21% O2 and 79% N2. Those two molecules have approximate Molecular Weights of 32 grams per mole and 28 grams per mole, respectively. So if you take a weighted average:

(.21)(32 g/mol) + (.79)(28 g/mol) = 28.84 g/mol

So 28.84 is my estimation of the average MW of air. If you used more accurate values for atomic molecular weights, the percents, and added the additional species which make up "air" then you may come up with a value closer to 28.966.

Please note, however, that there really can't be as hard and fast a definition of the MW of air as there can of H2 for example. This is because the concentration of gases in the atmosphere (and around you, more specifically) is constantly changing, minute to minute, day to day, and year to year.

The molar mass of the empirical formula is calculated by summing up the molar masses of the elements in the given composition (which gives a molar mass of 281.6 g/mol). To find the empirical formula, divide the molar mass of the compound (245.8 g/mol) by the molar mass of the empirical formula (281.6 g/mol), which gives approximately 0.873. This means the empirical formula is BrC₆H₈O₃.

Potassium hydroxide (KOH) is the strong base formed by the 5th group element potassium (K).

In the U.S., zinc is the lightest metal currently used. Cents are 97.5% zinc with only a small amount of copper plating.

However worldwide, aluminum is the lightest metal used for coinage.

Alkali metals generally form cations by losing their outermost electron to achieve a stable electron configuration.

The combining ratio for Group II elements with Group VII elements is 1:2. For example, calcium (Group II) will combine with chlorine (Group VII) to form calcium chloride with a ratio of 1 calcium atom to 2 chlorine atoms.

He could not because it had not yet been discovered when he created the table. However he was able to determine that an element was missing at that location and predict the properties it would have when it was discovered. When germanium was discovered and named, his predictions were found to be very accurate.

The five named groups from the periodic table are the alkali metals, alkaline earth metals, halogens, noble gases, and transition metals. Each group has unique properties and characteristics based on their electron configurations.

Water is not an element. It is a compound composed of hydrogen and oxygen atoms.

The representative elements belong to the s-block and p-block in the periodic table. These elements are also known as the main group elements and are found in groups 1, 2, and 13-18. They have properties like forming ionic compounds and covalent bonds easily compared to transition metals.

It's not better to do that for everyone, but it certainly is for chemists, since the electron structure of atoms is the building blocks for pretty much...everything they study. Nuclear physicists would surely rather arrange the elements based on atomic masses, for...something I'm sure. Fortunately, the Periodic Table of the Elements has them arranged both ways at the same time, whew!

The combined weight of all particles in an atomic nucleus is typically less than the combined weight of the individual particles due to the binding energy that holds the nucleus together. This is described by Einstein's mass-energy equivalence principle, E=mc^2, where a small amount of mass is converted to energy to hold the nucleus together.

Planes are not made from copper alone because copper is heavy, can be prone to corrosion, and lacks the necessary strength and stiffness required for structural components of an aircraft. Instead, airplanes are made from lighter and stronger materials such as aluminum, titanium, and composite materials to ensure optimal performance and safety.

I believe that the appropriate property to explain this is electronegativity, which is the amount of attraction that an atom has for electrons. Compared to other elements, that number is huge for oxygen.

Why that number is huge is a little difficult to explain, but basically it's because oxygen atoms by themselves have two empty "holes" of energy that electrons could fit in. It turns out that all atoms having these empty "holes" are much more stable when they're filled rather than empty. Therefore, one oxygen atom will often find another and they will share two of their electrons with each other, effectively filling each others energy "holes" and therefore becoming more stable. By joining forces in this way, the now labeled O2 molecule has all of its energy "holes" filled and will therefore be quite reluctant to empty them back out. That's why they're hard to break apart.

Oxygen is nonmetal because since oxygen isn't visable it's not solid so oxygen is nonmetal.

Elements are not intrinsically either bad or good, though I've never trusted samarium. Oh yeah, it wants you to think "hey, good samarium, I think I heard a story about that" but then you're just playing right into its hands. Many elements are toxic. Some of the ones that are toxic in large quantities are essentially to the proper functioning of your body in small quantities... potassium, for example. Potassium is absolutely essential to proper brain and nerve function. It's also part of what they give criminals executed by lethal injection, to stop their hearts. Also, just because an element is toxic doesn't mean it's "bad". Uranium is toxic, but the lights wouldn't be on at my house without it.

Of the elements listed by atomic symbol, Cs has the largest atoms.

PbO2 is the chemical formula for lead dioxide. It is a dark brown solid commonly used as a precursor for the production of other lead compounds and as a catalyst in chemical reactions.