A compound is a substance formed by two or more elements combined. The chemical and physical properties of the compound do not have to be the same, or even similar, in fact, more often than not, the properties of the compounds are very different from the properties of the elements separately.
Most substances found in nature are compounds, pure elements are clearly much less abundant. Furthermore, there are only about 100 elements that exist naturally and are stable, but when combined they give rise to millions of different compounds.
The union between atoms to form a compound can be produced in several ways, including by ionic bonding and covalent bonding, therefore, the resulting compounds are known as ionic compounds and covalent compounds, respectively.
While it is common for covalent compounds to be also known as molecular compounds, it should be clear that all compounds are made up of molecules. The difference is in the type of chemical bond.
When an atom loses electrons it gains a positive charge and vice versa, when it gains electrons it acquires a negative charge. These charged atoms are known as ions. the cation is the positively charged ion and the anion is the negatively charged ion.
As with any type of charged particle, between the negative ions and the positive ions there is a force of electromagnetic attraction, and it is this force that holds the atoms together to form the ionic compound.
One of the most common examples of an ionic compound is Sodium Chloride (common salt), formula NaCl. In this compound, chlorine, which is further to the left of the periodic table and more electronegative, retains an electron from the sodium atom. Thus, the chlorine atom becomes negatively charged and the sodium atom positively and form the ionic compound.
Ionic compounds are generally known as you leave. Other examples may be sodium bromide (NaBr) or calcium chloride (CaCl22).
Ionic compounds are generally solid at room temperature and have a high melting and boiling point, since the ionic bond is usually very strong. Although not all ionic compounds are soluble in water, they generally have high solubility because the dipole of the water molecule can interact with the charges on the ions and dissolve them.
Ionic compounds are not good conductors of electricity in the solid state, but in solution they have good conductivity. Dissolved ions can move and carry electrical charges. Negative ions will move to the positive electrical pole and positive ions to the negative electrical pole.
Covalent or molecular compounds are formed by covalent bonds between atoms. Unlike ionic bonding, covalent bonding electrons are neither lost nor gained, they are shared the atoms involved in the bond.
Although there is no net electrical charge in a covalent bond, there can be polarity in the bond if one of the atoms attracts electrons with more or less force than the other.
An example of a polar covalent compound is water (HtwoANY). Oxygen bonds with two hydrogen atoms and shares a pair of electrons with each. Because oxygen has a higher electronegativity, electrons are much more strongly attracted to the oxygen atom, and the electrical charge is shifted toward the oxygen, even though the molecule has no net electrical charge.
Other examples of covalent compounds are hydrogen chloride (HCl), methane (CH4), ethanol (C22H5OH) or carbon dioxide (CO2).
Within covalent compounds, two types of substances can be distinguished:molecular covalent substances lattice covalent substances
Molecular covalent substances are made up of individual molecules and are generally compounds with low melting and boiling temperatures, although solids, liquids and gases exist under normal conditions of pressure and temperature (1 atm, 25 °C). Solids are generally soft and poor electrical and thermal conductors. For example, carbon or molecular oxygen (Otwo).
Covalent lattice substances form a crystal lattice in which there is not a single molecule, but an indefinite number of atoms bonded to each other. They are usually solid under normal conditions, have high melting and boiling temperatures, are very hard, insoluble in water and are good thermal and electrical insulators. For example, quartz and graphite.