What Is an Element

An element is a substance made up entirely of atoms of one single kind. This chunk of bismuth, for example, contains only bismuth atoms, all of them chemically identical. We can break it in two, smash it with a sledgehammer, and then grind it to dust. Each piece, each separate flake of dust, is still bismuth. We can heat it until it flows like water, or until it boils and every atom flies away into the air as a gas. We still have identical bismuth atoms and nothing else. 

Most atoms can combine with others to form molecules. 

An atom of one element may combine with other identical atoms, as when two oxygen atoms form an oxygen molecule. An atom may also combine with one or more atoms of other, different, elements to form molecules or chemical compounds. 

An astonishing thing about chemistry is that an element usually becomes completely unrecognizable when combined with another element. A highly flammable gas, hydrogen, combines with oxygen to form the chemical compound, water. 

Two poisons, chlorine gas and the soft, silver-white metal, sodium, combine to form table salt. 

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What is needed now (1913) is an answer to the question what is an element Up to this time elements had been characterized by their respective masses. But now different masses (isotopes) all correspond to the same element. As already noted, Mendeleev had assembled the elements into a table by writing down the elements in order of increasing mass and had found, by making the table two dimensional through the introduction of rows and columns, that he was able to construct the table so that elements in given columns had similar properties. The similarities included physical properties as well as chemical properties. The table was therefore called a periodic table (there was periodicity). However, Mendeleev noted immediately that, in order to make his table work , he needed to introduce blank spaces for missing elements. This was fine because it led to the prediction of new elements which were later actually found. However, there were also places in the table where he had to reverse the ordering demanded by the masses in order to obtain periodicity (e.g. Co and Ni). 

What is an element A compound Give an example of each. 

What is an element To the ancient Greeks, everything on Earth was made from only four elements—earth, air, fire, and water. Celestial bodies—the Sun, moon, planets, and stars—were made of a fifth element ether. Only gradually did the concept of an element become more specific. 

What is an element and what is a compound Give examples of each. What does it mean to say that a com-poimd has a constant composition Would samples of a particular compoimd here and in another part of the world have the same composition and properties ... 

What is an element Which elements are most abundant on the earth Which elements are most abundant in the human body ... 

What is an element Elements are all around us. The element iron is in everything from bridges to safety pins. Electric wire is made from the element copper. Cans are made from the element aluminum. The lead in pencils is not really lead. It is graphite. This is the element carbon. Even the air we breathe is made of elements. It is mostly nitrogen and oxygen. 

What is an element Is it possible to prove rigorously by chemical methods that a substance is an element Is it possible to prove rigorously by chemical methods that a substance is a compound ... 

Present-day chemists describe elements as matter composed of atoms. Each atom is built up of a nucleus surrounded by electrons in one or more orbits or waves. In the nucleus there are a number of protons with positive charge and neutrons without charge. The number of protons is the atomic number. What is an element in the light of these facts The answer is that an element is a piece of matter built up of atoms, every one with the same atomic number. (Atoms of one element can, however, contain different numbers of neutrons and thus have different atomic masses. These different atoms are isotopes of the specific element). 

Suppose that 10.0 g of an organic compound used as a component of mothballs is dissolved in 80.0 g of benzene. The freezing point of the solution is 1.20°C. (a) What is an approximate molar mass of the organic compound (b) An elemental analysis of that substance indicated that the empirical formula is C3H2C1. What is its molecular formula (c) Using the atomic molar masses from the periodic table, calculate a more accurate molar mass of the compound. 

C02-0037. Iodine is an element whose molecules can move directly from the solid to the gas phase. A sample of solid iodine in a stoppered flask stood undisturbed for several years. As the photo shows, crystals of solid iodine grew on the sides of the flask. Use the principle of dynamic equilibrium to explain at the molecular level what happened. Include an observation about the color of the atmosphere inside the flask. 

Can an open-loop be still a loop You may wonder what is an open-loop Often, we loosely refer elements or properties of part of a system as open-loop, as opposed to a complete closed-loop system. You ll see more of this language in Chapter 7. 

The elements Si and Ge of group 14 act as semiconductors. A semiconductor is an element that can, to some extent, conduct electricity and heat, meaning it has the properties of both metal and nonmetals. The abihty of semiconductors to transmit variable electrical currents can be enhanced by controlling the type and amount of impurities. This is what makes them act as on-ofF circuits to control electrical impulses. This property is valuable in the electronics industry for the production of transistors, computer chips, integrated circuits, and so on. In other words, how well a semiconductor conducts electricity is not entirely dependent on the pure element itself, but also depends on the degree of its impurities and how they are controlled. 

An ionic bond results from the electrostatic attraction of oppositely charged ions. Once we know what ions an element is likely to form, we shall be able to predict the formulas of its compounds and explain some of their properties. 

On the basis of the work of Dalton, Gay-Lussac, Avogadro, Cannizzaro, and others, chemistry was beginning to make sense. The concept of atoms was clearly a good idea. Inevitably, scientists began to wonder about the nature of the atom. What is an atom made of, and how do the atoms of the various elements differ ... 

What is an isotope Give an example of an element with isotopes. 

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