General about the chemical bond - Factors that determine the chemical behavior of the individual. Types of chemical bonds (ionic - covalent)

  General about the chemical bond - Factors that determine the chemical behavior of the individual. Types of chemical bonds (ionic - covalent)

What is a chemical bond? When and why is it created?

The chemical bond:

 Simply put, it is the "glue" that binds atoms (or other building blocks of matter, e.g. ions) to form compounds or even other groups of atoms, such as polyatomic elements.

Chemical bond is created:

 When the building blocks of matter (atoms, molecules or ions) are close enough that the gravitational forces that develop between them exceed the repulsive forces that develop. These connections of atoms are made through the valence electrons,which is the electrons of the outer layer.

The creation of the chemical bond leads the system to lower energy, that is, it makes it more stable.

Factors that determine the chemical behavior of atoms:

The chemical behavior of the elements is determined primarily by two parameters. These are:

1. the valence electrons

2. atom size

valence electrons:

Responsible for atomic chemical behavior.

 Elements that have completed the outer layer of their atom with eight electrons (except for layer K supplemented by two), do not tend to form chemical compounds. Noble gases belong to this category. The atoms of these elements are in a very stable energy state and this stability is attributed to the completeness of their outer layer, tend to acquire this structure, i.e. to "look" like noble gases. Thus they are chemically bonded together, eliminating or absorbing or contributing electrons to obtain the stable electronic structure of noble gases (rule of eight).

Atomic radius (the size of the atom):

The size of an atom determines the force with which the electrons of the outer layer are held by the nucleus, since between the positively charged nucleus and the negatively charged electrons forces of electrostatic nature (Coulomb) are exerted.  

The smaller it is an atom, the harder it is to lose electrons or the easier it takes electrons (large attraction from the nucleus). 

Conversely, the larger an atom, the easier it is to lose electrons or the more difficult it is to gain electrons(small attraction from the nucleus).

During a period the atomic radius decreases from left to right.

This is

because As we move to the right, the atomic number increases, thus increasing the positive charge of the nucleus, resulting in a decrease in radius, due to greater attraction of electrons from the nucleus.

In a group the atomic radius increases from top to bottom

This happens:

Because as we go down layers are added to the atom, so as the distance of valence electrons from the nucleus increases, the attraction decreases, so the atomic radius increases.

Types of chemical bonds:

Covalent bond:

A compound between two non-metals.

Covalent bond properties:

• are solid, liquid or gaseous

• In pure state they are poor conductors of electricity, while aqueous solutions of some covalent compounds (e.g. acids) conduct electricity.

• have low melting point and heat

• do not dissolve easily in water

Heteropolar bond:

A compound between a metal and a non-metal.

During the formation of an ionic (heteropolar) bond between two atoms, one atom removes 1 to 3 electrons, thus taking the form of a cation (positive ion). Instead, the other person receives 1 to 3 electrons, thus taking the form of an anion (negative ion).

Properties of heteropolar compounds: 

• are solid.

• crystals are formed, which are hard and brittle

• have a high melting point and heat

• dissolve in water and other polar solvents

• aqueous solutions are good conductors of electricity

in solid state are poor conductors of electricity