Chemical Elements

Structure of matter

Our earth, nature, all living things, objects, the continents, mountains, oceans and we ourselves are made of chemical elements that are connected in different ways. Life has come into being through the connection of elements. Chemical elements are atoms with the same number of protons in the nucleus. The number is called the atomic number (in English , atomic number). For example, carbon has atomic number 6 and consequently has 6 protons in its nucleus. The simplest element is hydrogen (H) with one proton and one electron (atomic number 1, without neutrons). Pure substances are also called elements, for example pure oxygen. They cannot be further divided by simple chemical and physical methods. Elements can be solid, gaseous or more rarely liquid (states of aggregation). Over 94 elements occur naturally and many more have been produced artificially.

Composition of the elements

The individual chemical elements are composed of positively charged protons, neutral neutrons, and negatively charged electrons. The nucleus of the atom consists of protons and neutrons which are collectively called nucleons, and the electrons are located in the atomic shell (electron shell).

  • Nucleons = protons + neutrons.

The number of protons and electrons equal each other in uncharged atoms. Because the charges balance, the elements are electrically neutral to the outside. However, if they give up an electron, they are positively charged (cations). If they accept one, they are negatively charged (anions). Charged atoms are called ions. Together they form salts. Atoms are often represented – also in this text – with the outdated Bohr atomic model, in which the electrons orbit the atomic nucleus on defined orbits, i.e. like the planets orbit the sun. Today, the quantum mechanical orbital model is usually used to represent electrons, in which the electrons have a definite probability of residence in the space around the nucleus.

Isotopes

Isotopes are atoms that differ only in the number of neutrons and therefore in mass. This is with the same number of protons. For example, deuterium (2H) is an isotope of hydrogen (1H) with one neutron. Because the mass is greater, deuterium (D) is called heavy hydrogen and deuterium oxide is called heavy water (D2O). Among the best-known isotopes are uranium isotopes, whose nuclei are fissile and are used in nuclear power plants and to make nuclear weapons and propulsion systems.

Origin of the elements

The simplest elements, hydrogen ( = 1) and helium ( = 2), were formed 13.8 billion years ago during the Big Bang shortly after the formation of our universe. Hydrogen remains the most abundant element in today’s vast universe, followed by helium. Most of the remaining elements were formed either in stars by nuclear fusion or in a supernova, in dying stars. A few have been formed by the influence of cosmic rays (lithium, beryllium, boron). Finally, elements with a high atomic number exist, which were produced artificially, by humans.

Examples

The following list shows a selection of elements. The (element symbol) is shown in the parentheses, for example C (carbon, from lat. , coal) for carbon. The abbreviation has either one or two letters.

  • Hydrogen (H) is a component of water, along with oxygen.
  • Carbon (C) is the basic building block for all life on earth.
  • Nitrogen (N) is the most important component of air.
  • Oxygen (O) is essential for energy production in the body.
  • Sodium (Na) is contained in table salt.
  • Magnesium (Mg) is found in chlorophyll (leaf green).
  • Aluminum (Al) is found in aluminum foil and car bodies.
  • Silicon (Si) is found in almost all minerals and rocks of the earth.
  • Phosphorus (P) is used for the production of matches.
  • Sulfur (S) is released by volcanoes.
  • Potassium (K) plays a central role in the function of the nerves.
  • Calcium (Ca) is contained in bones.
  • Iron (Fe) is the most abundant element on planet Earth.
  • Mercury (Hg), unlike other metals, is present as a liquid.
  • Nickel (Ni) is used for metal alloys.
  • Silver (Ag) and gold (Au) are included in the jewelry.

Mass and size

Almost all the mass of an atom is in the nucleus. The volume, on the other hand, is determined by the electron shell, because the nucleus is very small. The mass of atoms is given by the symbol u or Da (daltons). u stands for . It corresponds to the mass of protons, neutrons and electrons. 1 u is given as one-twelfth of the mass of carbon-12 (12C) and is 1.660 – 10-24 g. The mass of a proton and a neutron is about 1 u, which is one unit of mass. Because carbon-12 contains 6 protons and 6 neutrons and the electrons have a very small mass (1/1836 of a proton), its atomic mass is about 12 u (12.011 u). This number is called the mass number. Mass number = number of protons + number of neutrons The molecular mass of chemical compounds can be obtained by adding the atomic masses of the atoms of which they are composed. Atoms are unimaginably small – their diameter is in the range of 10-10 m (1 angstrom, 0.1 nm).

Chemical compounds

Chemical elements combine very readily with the same or other elements – pure or unbound they rarely occur. Only the electrons in the atomic shell are responsible for the chemical bonds, the atomic nuclei are not involved. The most important chemical compounds are:

  • Organic molecules with covalent bonds.
  • Salts with ionic bonds
  • Metals with the metallic bond

The special feature of chemical compounds is that their properties are completely different from those of the elements of which they are composed. For example, sodium chloride is composed of ionized sodium and chlorine atoms. Sodium as an element is a soft, silver-gray metal that is highly reactive, and chlorine exists (at room temperature) as a toxic gas. Together they form the crystalline table salt that we consume every day as a flavor enhancer in food. The same can be illustrated by the example of water, which is formed from the gases hydrogen and oxygen in the oxyhydrogen reaction.

Periodic table

The periodic table of the elements is a descriptive and practical overview of all the elements, first developed in the 1860s. It begins with hydrogen (1) and is arranged in order of increasing atomic number. By presenting them in horizontal periods and vertical groups, related elements with similar chemical and physical properties are grouped together. These include:

  • Alkali metals
  • Alkaline earth metals
  • Transition metals
  • Lanthanides
  • Actinoids
  • Metals
  • Semi-metals
  • Non-metals
  • Halogens
  • Noble gases

Link (English version): IUPAC periodic table with PDF download.

Indivisibility of the elements

Elements can be obtained from mixtures subjected to various chemical and physical separation processes, such as combustion, electric current, or acid addition. In the end, the common processes leave behind the pure elements. The term atom is derived from the Greek, which means indivisible. In fact, the elements are not further divisible by the usual chemical methods. With the discovery of radioactivity and radioactive decay, however, it has been shown that the term is inaccurate and that so-called nuclear fission into elements with a lower atomic number is possible. Conversely, nuclear fusion can produce elements with a higher atomic number. For example, the Sun forms helium from hydrogen in its core, which releases the energy and heat that is the basis of all life on Earth.

Structure of the human being

As mentioned at the beginning, we humans are also made up of the known elements. The most important representatives are oxygen (O), carbon (C), hydrogen (H), nitrogen (N), calcium (Ca) and phosphorus (P). These 6 elements together make up over 99% of the body mass! Other minerals such as potassium, magnesium and sodium, for example, as well as numerous trace elements such as chromium, iron, fluorine, selenium or copper are contained in a much smaller quantity, but have vital functions.

Origin of life on earth

The elements on earth originate, as already mentioned, on the one hand from the big bang, which took place about 13.8 billion years ago and with which the universe, the space and the time were created.Higher elements were formed mainly in active and dying stars (supernovae). The earth has an age of about 4.5 billion years. Life on Earth has emerged spontaneously from inanimate nature perhaps 4 billion years ago by the combination of elements into organic chemical compounds. These reactions have taken place with mainly in water, because chemical reactions take place inadequately in solids or gases. Studies such as the Miller-Urey experiment from the 1950s have shown that biomolecules such as amino acids or nucleic acids can form from simpler compounds in nature. Central to the transition from the inanimate to the animate Earth was the formation of proliferating polymeric molecules from monomers. These contain the information for the sequence in their structure. It is thought that this was first ribonucleic acid (RNA), which catalyzed its own replication. Once molecules self-replicated, evolution got underway, leading to increasing complexity, unicellular and multicellular organisms, plants, fungi, animals, and after an unimaginably long time, us humans.