🧪 Chemistry

Introduction

The basic building blocks of our universe and at the same time the central point in chemistry are atoms and molecules. Chemistry has intersections with other disciplines: Mathematics, Biology, Physics and Earth Sciences.

Chemistry is divided into several areas: inorganic, organic, physical, applied, analytical chemistry or e.g. bio- or nuclear chemistry.

Atomic models

Because reality is very complex, one uses models (in chemistry => atomic models). There is no right or wrong, the models describe something good or bad. Many assumptions and theories are based on these models. Limits of models prevent wrong results. In inorganic chemistry the most important models to describe atoms are the shell model and the orbital model.

Atoms were once thought to be indivisible, but this is now disproved. An atom consists of three building blocks:

element	symbole	charge	position	purpose
proton	p / p^+	positive	Atomic nucleus	- Classification in periodic table - Number is the atomic number
electron	e / e^-	negative	Atomic shell	- takes over bonding of atoms - interacts with other electrons
neutron	n	neutral	Atomic nucleus	- stabilization of atomic nucleus - classification in periodic table - prevents repulsion of protons

Ordinal number

The atomic number describes the position in the periodic table and the properties of the element. It corresponds to the number of protons of an atom.

Ion

An ion exists when an atom has different numbers of electrons and protons. Ions can conduct electric current. One distinguishes between two variants of ions:

type of ion	number?	charge of ion	direction of the current flow
anion	electrons > protons	negative ion	to the anode (positive pole)
cation	electrons < protons	positive ion	to the cathode (negative pole)

Ions arrange themselves like a lattice in solids - in a kind of lattice structure: Space and spacing are fixed. The lattice structure creates the stability of the solid. Ions are water-soluble and therefore easily transportable in blood and drinking water. To balance charges, ions cluster together: Cation with positive charge seeks anion with negative charge. Ions usually occur as salts.

ion	searches for	ion
anion with ... two negative charges	--> -->	cation with ... two positive charges
anion with ... two negative charges	--> -->	two cation with ... one positive charge each

Isotope

An element can be either a pure element (no isotopes) or mixed element (more isotopes). In nature there are 22 pure elements. An isotope of an element has the following properties:

• always the same proton number, but different neutron number (different mass number)
• can be affected by radioactive decay (emission of radiation) (unstable) or not (stable)
• The following table shows the rough ratio of protons to neutrons for an isotope to be called "stable":

  ordinary number	Ratio of protons to neutrons
  low	1:1
  high	1:1,5

Radiocarbon method (C14-Methode)

Since some isotopes decay, this effect is used to determine the age of organisms.

Mass spectrometry

In mass spectrometry, particles are separated by mass in order to subsequently determine the dimensions.

The procedure is as follows:

• Introduce sample into gas phase (e.g. vaporize).
• Ionize gas molecules (electrically charge)
• Acceleration in electric field, thereby also deflected
• Depending on the mass, the trajectory or the velocity changes.

Note

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