Matter, elements, and atoms | Chemistry of life (article) | Khan Academy
Atoms, elements, molecules, compounds, and mixtures are all forms of matter. Matter is defined as anything that has mass and volume. Atoms, elements. Learn about the structure of the atom, and how atoms make up matter. An atom is the smallest unit of matter that retains all of the chemical properties of an. An answer to the question: Atoms, elements, compounds and mixtures. Atoms are the smallest bits of ordinary matter and are made from particles called.
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.
Elements and Compounds
Thus, the atomic number, which is the number of protons in the nucleus of the atom, identifies the element. Since 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 Uin 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 [link], 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.
The Periodic Table of the Elements Figure 2. Martin External Website Visit this website to view the periodic table. In the periodic table of the elements, elements in a single column have the same number of electrons that can participate in a chemical reaction. What is the meaning of a mass number shown in parentheses? Isotopes Although each element has a unique number of protons, it can exist as different isotopes. An isotope is one of the different forms of an element, distinguished from one another by different numbers of neutrons.
The standard isotope of carbon is 12C, commonly called carbon twelve. All of the isotopes of carbon have the same number of protons; therefore, 13C has seven neutrons, and 14C has eight neutrons. The different isotopes of an element can also be indicated with the mass number hyphenated for example, C instead of 12C. Hydrogen has three common isotopes, shown in [link]. Isotopes of Hydrogen Figure 2. Protium, designated 1H, has one proton and no neutrons. It is by far the most abundant isotope of hydrogen in nature.
Deuterium, designated 2H, has one proton and one neutron. Tritium, designated 3H, has two neutrons. An isotope that contains more than the usual number of neutrons is referred to as a heavy isotope.
An example is 14C. Heavy isotopes tend to be unstable, and unstable isotopes are radioactive. A radioactive isotope is an isotope whose nucleus readily decays, giving off subatomic particles and electromagnetic energy. Different radioactive isotopes also called radioisotopes differ in their half-life, the time it takes for half of any size sample of an isotope to decay. For example, the half-life of tritium—a radioisotope of hydrogen—is about 12 years, indicating it takes 12 years for half of the tritium nuclei in a sample to decay.
Excessive exposure to radioactive isotopes can damage human cells and even cause cancer and birth defects, but when exposure is controlled, some radioactive isotopes can be useful in medicine.
For more information, see the Career Connections. Career Connections — Interventional Radiologist The controlled use of radioisotopes has advanced medical diagnosis and treatment of disease. Interventional radiologists are physicians who treat disease by using minimally invasive techniques involving radiation. Many conditions that could once only be treated with a lengthy and traumatic operation can now be treated non-surgically, reducing the cost, pain, length of hospital stay, and recovery time for patients.
For example, in the past, the only options for a patient with one or more tumors in the liver were surgery and chemotherapy the administration of drugs to treat cancer. Some liver tumors, however, are difficult to access surgically, and others could require the surgeon to remove too much of the liver; chemotherapy is highly toxic to the liver, and certain tumors do not respond well to it.
In some such cases, an interventional radiologist can treat the tumors by disrupting their blood supply, which they need if they are to continue to grow. In the days and weeks following the procedure, the radiation emitted from the seeds destroys the vessels and directly kills the tumor cells in the vicinity of the treatment. Radioisotopes emit subatomic particles that can be detected and tracked by imaging technologies.
One of the most advanced uses of radioisotopes in medicine is the positron emission tomography PET scanner, which detects the activity in the body of a very small injection of radioactive glucose, the simple sugar that cells use for energy.
Matter, elements, and atoms
PET can reveal some cancerous masses because cancer cells consume glucose at a high rate to fuel their rapid reproduction. Pet Scan Figure 2. PET highlights areas in the body where there is relatively high glucose use, which is characteristic of cancerous tissue. This PET scan shows sites of the spread of a large primary tumor to other sites. The Behavior of Electrons In the human body, atoms do not exist as independent entities. Rather, they are constantly reacting with other atoms to form and to break down more complex substances.
To fully understand anatomy and physiology you must grasp how atoms participate in such reactions. The key is understanding the behavior of electrons. An electron shell is a layer of electrons that encircle the nucleus at a distinct energy level. The atoms of the elements found in the human body have from one to five electron shells, and all electron shells hold eight electrons except the first shell, which can only hold two. This configuration of electron shells is the same for all atoms.
The precise number of shells depends on the number of electrons in the atom. Hydrogen and helium have just one and two electrons, respectively. If you take a look at the periodic table of the elements, you will notice that hydrogen and helium are placed alone on either sides of the top row; they are the only elements that have just one electron shell [link]. A second shell is necessary to hold the electrons in all elements larger than hydrogen and helium.What's the Difference between an Atom and a Molecule?
Lithium Liwhose atomic number is 3, has three electrons. Two of these fill the first electron shell, and the third spills over into a second shell. The second electron shell can accommodate as many as eight electrons.
Carbon, with its six electrons, entirely fills its first shell, and half-fills its second.
Relationships Between Matter, Atoms, Elements, and Molecules by on Prezi
With ten electrons, neon Ne entirely fills its two electron shells. Again, a look at the periodic table reveals that all of the elements in the second row, from lithium to neon, have just two electron shells.
Oxygen stoms are joined in pairs. To write a pair of oxygen atoms using symbols, we use the symbol O and the number 2. Oxygen would be O2. The 2 is a subscript. The 2 is written to the right of and below the O. A pair of oxygen atoms is a molecule of oxygen.
A molecule is the smallest particle of a substance that exists independently. Molecules of most elements are made up of only one of atom of that element.
Oxygen, along with nitrogen, hydrogen, and chlorine are made up of two atoms. Look at the model of oxygen above. The two balls represents the two oxygen molecules. The oxygen molecules are bonded or stuck together.
We will learn about bonds later. Compounds A compound is a substance formed when two or more elements are chemically joined. Water, salt, and sugar are examples of compounds. When the elements are joined, the atoms lose their individual properties and have different properties from the elements they are composed of. A chemical formula is used a quick way to show the composition of compounds. Letters, numbers, and symbols are used to represent elements and the number of elements in each compound.
Mixtures Mixtures are two or more substances that are mixed together but not chemically joined.
A good example of a mixture is a salad. There are tomatoes, lettuce, cucumbers, and salad dressing all mixed together.