The elemental calcium in cheese, therefore, is the same as the calcium that forms your bones. Some other elements you might be familiar with are oxygen, sodium, and iron. The elements in the human body are shown in Table 1, beginning with the most abundant: oxygen O , carbon C , hydrogen H , and nitrogen N.
All the elements in your body are derived from the foods you eat and the air you breathe. In nature, elements rarely occur alone. Instead, they combine to form compounds. A compound is a substance composed of two or more elements joined by chemical bonds. For example, the compound glucose is an important body fuel.
It is always composed of the same three elements: carbon, hydrogen, and oxygen. Moreover, the elements that make up any given compound always occur in the same relative amounts. In glucose, there are always six carbon and six oxygen units for every twelve hydrogen units. An atom is the smallest quantity of an element that retains the unique properties of that element. In other words, an atom of hydrogen is a unit of hydrogen—the smallest amount of hydrogen that can exist.
As you might guess, atoms are almost unfathomably small. The period at the end of this sentence is millions of atoms wide. Atoms are made up of even smaller subatomic particles, three types of which are important: the proton , neutron , and electron.
Figure 1 shows two models that can help you imagine the structure of an atom—in this case, helium He. Although this model is helpful in visualizing atomic structure, in reality, electrons do not travel in fixed orbits, but whiz around the nucleus erratically in a so-called electron cloud. Figure 1. Two Models of Atomic Structure.
Electrons, which have a negative charge, are designated e —. Just as a magnet sticks to a steel refrigerator because their opposite charges attract, the positively charged protons attract the negatively charged electrons. This mutual attraction gives the atom some structural stability. The attraction by the positively charged nucleus helps keep electrons from straying far. An atom of carbon is unique to carbon, but a proton of carbon is not.
One proton is the same as another, whether it is found in an atom of carbon, sodium Na , or iron Fe. The same is true for neutrons and electrons. So, what gives an element its distinctive properties—what makes carbon so different from sodium or iron? The answer is the unique quantity of protons each contains. Carbon by definition is an element whose atoms contain six protons.
No other element has exactly six protons in its atoms. Moreover, all atoms of carbon, whether found in your liver or in a lump of coal, contain six protons.
Thus, the atomic number , which is the number of protons in the nucleus of the atom, identifies the element. Because an atom usually has the same number of electrons as protons, the atomic number identifies the usual number of electrons as well.
In their most common form, many elements also contain the same number of neutrons as protons. The most common form of carbon, for example, has six neutrons as well as six protons, for a total of 12 subatomic particles in its nucleus.
Electrons have so little mass that they do not appreciably contribute to the mass of an atom. Carbon is a relatively light element. Uranium U , in contrast, has a mass number of and is referred to as a heavy metal. Its atomic number is 92 it has 92 protons but it contains neutrons; it has the most mass of all the naturally occurring elements. The periodic table of the elements , shown in Figure 2, is a chart identifying the 92 elements found in nature, as well as several larger, unstable elements discovered experimentally.
The elements are arranged in order of their atomic number, with hydrogen and helium at the top of the table, and the more massive elements below. The periodic table is a useful device because for each element, it identifies the chemical symbol, the atomic number, and the mass number, while organizing elements according to their propensity to react with other elements.
The number of protons and electrons in an element are equal. The number of protons and neutrons may be equal for some elements, but are not equal for all. Figure 2. The Periodic Table of the Elements. The Main Difference Between the Two. Elements are the simplest form of any given substance. They are the purest form of a substance as they cannot be split or broken into sub-parts of a substance.
However, scientifically, an element can be made of smaller particles like ions, molecules or atoms. To be simpler, and in most cases, elements are made from only one type of atom. If an element comes from steel, it means it will contain steel atoms only.
Therefore, to be precise, atoms are the smallest part or amounts of elements. This is the primary difference between an atom and element. Atoms are the simplest unit of a matter. In their center, atoms have a closely packed nucleus. The nucleus in the center is surrounded by clouds of electrons. These electrons are negatively-charged particles of an atom.
However, Hydrogen is an exception as it is a form of nuclide that stays stable even without a single neutron. When atoms bind or combine together through chemical reactions, they together form molecules. Other elements include:. What makes something an element is the fact that all the atoms have the same number of protons in the nucleus.
Because like all things in the world, elements and molecules are both made of atoms. You know elements are all the different types of atoms on the periodic table. Molecules are what you get when those atoms are combined. Unlike elements, molecules can be made from the same or different elements. The key to a molecule is that two or more atoms are bonded together. For example, water is a molecule made of hydrogen and oxygen. You can also have molecules of a single atom bonded together like two oxygen atoms.
This makes up the oxygen humans breathe. It can be easy to see why elements and atoms get confused because elements are atoms. They are just a group of all the same kind of atoms. All the known elements on Earth can be found in the periodic table of elements. Science is fun right? Keep the chemistry fun going by exploring the difference between atoms and molecules. You can also have more chemistry fun by reading up on molecules and compounds.
0コメント