Chemical Elements and the Periodic Table: Properties and Structure
Metals and Non-Metals
Since antiquity, items such as gold, silver, etc. have been discovered over time. Up to now, more than 100 have been identified. A first classification of items, focusing on appearance and physical properties, allows for 2 groups: metals and non-metals.
Metals and Non-Metals
To distinguish one from the other, we will name characteristics that make them different:
Metallic Elements
- Have a characteristic brightness.
- Are opaque and good conductors of heat and electricity.
- Are usually solid at room temperature and generally have high melting points.
Non-Metallic Elements
- Do not have metallic shine.
- Are poor conductors of electricity and heat.
- At room temperature, they can be solids, liquids, or gases, while the solids are quite fragile.
- Solids typically have low melting points, and liquids also have low boiling points.
Periodic Table Update
Elements are classified in the table or a periodic system, sorted according to the values of their atomic numbers, i.e., the positions depend on the number of protons. According to the periodic table, the elements are assigned to it in groups or columns (vertical rows, of which there are 18), which are groups of elements with the same number of electrons in the last orbit and also similar properties. On the other hand, elements that have the same number of layers in their orbits and electronic settings are located in the same horizontal row or period (there are 7).
Regularities in the Properties of Elements of the Periodic Table
Metallic Character
The metallic character of elements in the periodic table increases as the number of protons increases. If we take a group, the metallic character increases from top to bottom, i.e., it increases with the number of orbits.
Other Characteristics
- The number of protons and electrons increases in the table from left to right.
- The number of orbits increases from top to bottom.
- Some elements, as seen in the periodic table, have characteristics intermediate between the two groups and are called metalloids or semimetals.
Grouping of Atoms in Matter
The atoms that form different types of matter can appear isolated or united to form molecules or crystals.
Isolated Atoms
In general, atoms join together to form known substances, although there are elements whose isolated atoms are presented in nature. This is because their electronic configurations are more stable. Group 18 elements (helium, neon, argon, etc.) all have the last orbit full.
This group of elements has a very stable structure, and having the last orbit full causes spikes in natural gas that are isolated and at room temperature. The fact that they are so stable means that they do not tend to pair with other elements, or even themselves, hence this group is called noble gases or inert gases.
The other elements, however, try to find stability by joining with other elements to have the last orbit full, which gives rise to various molecules and crystals.
Molecules
All elements seek to fill their last orbit for stability, so the items that do not have it share electrons with others and thus fill it and stabilize, forming a molecule. For example, H (Z=1). The most common and stable form of hydrogen in nature is H2, where two atoms bind to stabilize. By sharing an electron, the atoms already have the last two full orbits, are more stable, and therefore hydrogen appears in nature as H2. By sharing electrons, chlorine stabilizes and already has the last full orbit with 8 electrons, so it appears in nature as Cl2.
In this union of atoms that share electrons to stabilize, it is said that the atoms are linked by an electrostatic bond, which is what keeps atoms together. This chemical bond linking atoms to stabilize is also called a covalent bond.
Characteristics of the Molecules Formed by Atoms
- They can be equal or different. In the first case, they are simple substances, and in the second, compounds.
- Normally, molecules are isolated or connected by very weak forces, so they are usually gaseous at room temperature, with the solids being quite fragile.
Crystals
Crystals are solid substances in their majority. Examples of crystals are salt, sugar, or ice. We have two types of crystals: covalent, ionic, and metallic.
Covalent Crystals
These are similar to molecules because they share electrons between different atoms; they are therefore covalent. Unlike molecules, covalent crystals are solid substances, in which atoms sharing electrons form highly resistant three-dimensional networks in all directions. The solids thus constituted are hard, and the networks they form are very large. This is because the electrons are shared by many atoms. For example, a three-dimensional network.
Metallic Crystals
Most of the items that contain metal atoms have 1, 2, or 3 electrons in the outer layer, so they are poorly bound to the nucleus and are not very stable. Metals are quite hard because the atoms are ordered in a very compact way, and since the electrons have enough mobility, metals are good conductors of electricity.
Ionic Crystals
The atoms of these crystals achieve stability by the loss or gain of electrons, which gives rise to the last full orbit. These atoms with negative or positive charges are called ions; if they have a positive charge, they are called cations (Na+), and if they have a negative charge, they are called anions (Cl-). The result of having a positive and a negative charge is an attraction between two opposite charges; the two ions tend to cluster together and form networks based on this attraction.
Molecular Mass
The molecular mass of a chemical or molecule equals the sum of the relative atomic masses of the atoms appearing in its formula.
Calculation of the Molecular Mass
To find the molecular mass of an element, we look at the mass number (protons + neutrons) of the element. If it is a molecule or compound, we simply add the mass numbers of the elements that compose it. For example, chlorine, which we saw previously, is found in nature as Cl2 to be stabilized. What will its molecular mass be? Cl2: Cl = Mass number = 35.5 x 2 = 71. For NaCl: Na = 23 + Cl = 35.5 = 58.5.
Percent Composition
The percent composition of a compound is calculated by finding the percentage of the total mass that corresponds to each element in the compound, i.e., dividing the mass of the element by the molecular mass of the compound. Then, multiply by 100 to know the percentage. To calculate the percent composition of NaCl, for example:
% = (Mass of element / Mass of compound) x 100
Amount of Substance: The Mol
Because atoms and molecules are very small, to count the number of atoms and molecules, we use a specific unit, the amount of substance (n), whose unit is the mol. It has been determined that a mole of any substance contains 6.022 x 1023 atoms, which can also be applied to other types of particles, such as molecules, ions, etc. That is, whenever we have a mole of any substance, it will mean that it contains 6.022 x 1023 elements.
For example, a mole of Fe atoms = 6.022 x 1023 Fe atoms; 1 mole of Na molecules = 6.022 x 1023 Na molecules; 2 moles of Li atoms = 2 x 6.022 x 1023 Li atoms.
Note that not all moles are equal, and not all have the same mass. A mole of iron atoms does not weigh the same as a mole of silver atoms because the atoms are different.
Equivalence with Mass
To convert between mass and moles, we use the following formula: amount of substance = mass / molecular mass, or n (mol) = mass / M.