The Matter

The matter The Atom Structure of the Atom The atom is the smallest unit of matter that retains the chemical properties of an element. It consists of two main regions: a central nucleus and surrounding electron clouds. Atomic Components The nucleus contains: ● Protons (positive charge) ● Neutrons (neutral charge) Outside the nucleus: ● Electrons (negative charge) exist in regions called orbitals, which are probability clouds where electrons are likely to be found. Elements in Nature Of the 118 known elements, 90 occur naturally while the remainder have been synthesized in laboratories through various nuclear processes Atomic and Mass Number Each chemical element corresponds to an atom. Some parameters are used to distinguish one atom from another: - Atomic number: is the number of protons (indicated by the letter Z) that has an atom inside its nucleus. In a neutral (or isolated) atom it also corresponds to the number of electrons; - Mass number: is the sum of protons and neutrons (indicated by the letter A). Atoms with the same atomic number have similar chemical properties, therefore they are united under the name of the same chemical element. There are cases where atoms of the same element have the same atomic number (Z) but different mass number (A). These atoms are called isotopes. Periodic Table of Elements The periodic table of elements is a scheme in which the elements are sorted according to their atomic number. The columns of the table are called GROUPS, while the rows are called PERIODS. Looking at the image, the elements with the blue background are called semi-metals (or metalloids), those on the left of these are the metals, while on the right are the non-metals. In the image, the pink column on the left is the alkali metal group. The orange column is the alkali earth metal group. The last column on the right is formed by noble gases. The penultimate column represents the halogen group. The yellow elements in the middle of the table are called transition metals (they range from the third to the thirteenth group). The blue elements are the metalloids, or transition elements, which have intermediate chemical properties between metals and non-metals. Metals are elements with few valence electrons, low ionization energy and therefore low electron affinity, so they tend to yield electrons more easily when they have to react with non-metals or metalloids, forming cations. They are generally in the solid state at room temperature, although there are exceptions such as Mercury. They are also generally ductile, malleable, shiny electrical conductors, very dense and with high melting points. The characteristics of metals become less marked when proceeding along a PERIOD (row) and are more marked when descending along a GROUP (column). Non-metals are elements with characteristics opposite to those of metals, in fact they have many valence electrons, have high ionization energy and high electron affinity, so they tend to buy electrons more easily, forming anions. These substances are not ductile, malleable, good conductors or shiny. lons lons are monatomic or polyatomic compounds (molecule or group of atoms bound together). Ions have a positive or negative charge. A negative ion, or anion, has more electrons than its atomic number, while a positive ion, or cation, has fewer electrons than its atomic number. These charged atoms are formed due to chemical reactions between several atoms having different electronegativity. The electronegativity is born in order to reach a stable electronic situation in the outermost atomic orbital of the atoms bound by a covalent bond.