State E: It two hydrogen atoms having electrons with parallel spins approach each other, potential energy of system increases and no bond is formed between the two hydrogen atoms. Science Chemistry Physical Chemistry Nature of Chemical Bond Valence Bond Theory. A hydrogen carbonate ion has the formula HCO3-, so the valency of a hydrogen carbonate ion is -1. Hydrogen carbonate is a group of atom having charge. Similarly, how do you write hco3? Description: Bicarbonate Ion is a polyatomic ion whose formula is HCO3.
- What Is Valence In Chemistry
- Hydrogen Valence Electron Dot Diagram
- Hydrogen Valence Electrons Number
- Hydrogen Valence Electrons
How hydrogen atoms share valence electrons to form covalent bond and hydrogen molecule (H2)
First, if we write the electron configuration of hydrogen, you will realize that hydrogen has only one valence electron in the one-s orbital (1s1). As a result, the hydrogen atom is unstable. Because it’s unstable, hydrogen will always bond with another atom so that it can become stable and achieve a stable electron configuration similar to that of helium (He): 1s2.
Where can hydrogen get this other electron?
One way hydrogen can get this other electron is to bond with another hydrogen atom. So, let’s imagine that we have two hydrogen atoms with their valence electrons depicted by these two circles.
As you can tell, the orange circle with the plus sign describes the nucleus, which usually carries a positive charge because of the protons in it. While the red circle with the minus sign describes the electron, which usually carries a negative charge.
To keep the hydrogen atom intact, its nucleus must attract its electron (opposite attract). Now, when the two separate hydrogen atoms are far apart, there is virtually no interaction between the two atoms. However, as the two hydrogen atoms gain energy and move toward each other, they reach a certain distance where the two hydrogen atoms feel the presence of each other.
That is the nucleus of the hydrogen atom on the left will attract the electron of the hydrogen atom on the right. Likewise, the nucleus of the hydrogen atom on the right will attract the electron of the hydrogen atom on the left. As the attractive force between the two atoms strengthens, the atoms pick up more speed and continue to move closer to each other. However, if these atoms suddenly become too close, they will immediately repel each other.
Why will the hydrogen atoms repel each other?
If they are too close, the nucleus of the left atom will repel the nucleus of the right atom. Likewise, the electron of the left atom will repel the electron of the right atom (like charges repel).
When’s the covalent bond formed between the two hydrogen atoms?
When the attractive and repulsive forces between the two hydrogen atoms is just right, they will form the covalent bond. Here is a model to help you visualize its creation.
Notice, because the electrons are equally attracted to the nuclei of both atoms, they are located between the two atoms. And these electrons hover and spend most of their time in the region once the covalent bond is created. The more covalent bonds atoms make, the stronger the force of attraction between them.
It’s tiring to keep drawing circles and pluses and minuses to explain covalent bonding. As a result, chemists have a shorthand for doing this. If we draw a line to connect the two dots depicting the two electrons shared by the hydrogen atoms, we will get something like a dash (__). The dash is a symbol chemist use to denote a covalent bond formed between two atoms.
What Is Valence In Chemistry
If we have three of these dashes between atoms, it follows that we have three pair of electrons (6 electrons) shared between them. So, we can depict the hydrogen molecule as a structural formula like this: H__H (read as single bond between hydrogen atoms). But it’s not always necessary to show the dash anytime we write the chemical formula for a molecule. As a result, chemists sometimes condense the H__H to H2.
If you want to learn more about chemical bonding, click here.
Science > Chemistry > Physical Chemistry > Nature of Chemical Bond > Valence Bond Theory
Valence bond theory was proposed by Heitler and London in (1927) and it was extended by Pauling and Slater (1931). It is based on the following concepts.
- The pairing of electrons.
- Neutralization of opposite electron spins.
- Overlapping of orbitals containing unpaired electrons to give a region of common electron density to the combining atoms.
Postulates of Valence Bond Theory:
Condition of bond formation:
A covalent bond is formed when the atomic orbital of one atom overlaps the atomic orbital of the other atom. The sharing of electrons takes place due to the overlapping of half-filled orbitals of the outermost shell of the two atoms. Only atomic orbital with unpaired electrons with opposite spin can participate in overlapping or bonding. They are known as Bonding Orbitals.
Binding force of covalent bond:
During theoverlapping of half-filled orbitals, spins get neutralized and electron densitybetween the two nuclei increases. As a result of this, the force of repulsionbetween the two nuclei decreases, while the force of attraction between thenucleus of one and the electron of other increases.
Strength of a bond:
Bond is formed when the system attains a stable lowest energy level. This occurs at a certain minimum equilibrium distance between two nuclei known as bond length. The strength of the covalent bond depends upon the extent of overlapping between two atoms. Greater the overlap, stronger is the bond. Complete overlapping is not possible as there are repulsive forces between two nuclei.
Number of covalent bonds:
One bonding orbital can form only one covalent bond. Hence the number of bonding orbitals restricts the number of covalent bonds that can be formed by an atom. The number of unpaired electrons possessed by an atom determines its valency.
Directional nature of covalent bond:
S- orbitalsare non-directional but p, d, and f – orbitals have a particulardirection. Due to their directional nature, the geometry of the moleculedepends upon the orientation of the overlapping of the orbitals.
Geometry of a Molecule on the Basis of Valence Bond Theory:
A covalent bond is formed when the atomic orbital of one atom overlaps the atomic orbital of the other atom. The bond has maximum electron density in the region of overlap. The line joining the nuclei of two atoms determines the direction of the bond.
‘S’ orbitals are spherical and non – directional, but p, d, f orbitals are directionally oriented and produce overlap in the internuclear axis resulting in a bond formation having s a specific direction. The geometry of molecules and bond angles therein are determined by the directional orientation of orbitals involved in the overlap. The electron pairs in the valence shell of the central atom arrange themselves symmetrically so as to get as far apart as possible due to repulsion between them.
e.g. Methane has tetrahedral geometry, Boron trifluoride has planar geometry while Beryllium difluoride has linear geometry, etc.
Energy Changes in Covalent Bond Formation on the Basis of Valence Bond Theory:
Interactive Force Between Approaching Molecules:
It must berealized that when any two atoms approach close to each other new forces ofattraction and repulsion set in.
The forces of attraction are between the nucleus of one atom and the electron of the other and vice – versa. The forces of repulsion are between two nuclei amongst themselves as well as between the electrons of the two atoms amongst themselves. The force of attraction and repulsion are represented in the figure.
If the netresult is attraction i.e. attractive forces are stronger than the repulsiveforces the total energy of the system decreases and a chemical bond results. If the net result is repulsion i.e. the repulsive forces are strongerthan attractive forces, the total energy of the system increases and nochemical bonding is not possible.
Variation in Energy of System Due to Approach of Orbitals for Overlapping:
Its plc professional edition keygen cracked. When two Hydrogen atoms with unpaired electrons with parallel spin approach each other, repulsion is greater than attraction and energy of system increases and bonding does not take place. In this case, the energy goes on increasing as inter-nuclear distance starts decreasing.
When twoHydrogen atoms with unpaired electrons with opposite spin approach each other,the attraction is greater than repulsion and energy of system continuouslydecreases till it becomes minimum at equilibrium distance between the twonuclei. There is overlap and leads to covalent bond formation between twohydrogens.
Formation of Hydrogen Molecule in terms of Decrease ofPotential Energy:
The way in which the potential energy of the system changes as two hydrogen atoms having electrons with opposite spins approaches each other to form a covalent bond is represented in the potential energy curve. Graphical representation of the change in potential energy as a function of internuclear distance is known as the Potential Energy Curve. The electronic configuration o the hydrogen atom is 1s1. It contains one unpaired electron in its valence shell.
Explanation of Curve – 1
- State A: When two hydrogen atoms are far apart from each other, then the potential energy of one atom is independent of the other. This potential energy is taken arbitrarily as zero
- State B: As the two hydrogen atoms having electrons with opposite spins approach each other, the electrons of one atom begin to feel the attractive forces of the nucleus of the other atom. The attractive force dominates the repulsive force between the electrons. Thus, as the distance between two hydrogen atoms decreases the potential energy of the system gradually decreases.
- State C: A state of minimum potential energy is reached when the forces of attraction are balanced by the forces of repulsion between two hydrogen atoms. At this stage orbital of two hydrogen atoms, overlap and spins of electrons are neutralized and a stable covalent bond is formed between hydrogen atoms, forming a hydrogen molecule. In this case, the overlap of orbitals is maximum. The minimum equilibrium distance between the two hydrogen nuclei at this stage is called bond length which is 74 picometer. The amount of energy released at this stage is called bond energy and it is equal to 431.8 kJ/mole.8.
- State D: When two hydrogen atoms are forced to come still closer, then the potential energy of the system shows a sharp rise. This is due to the increases of repulsive forces between the two nuclei at such small inter-nuclear distance and hence bond formed becomes unstable.
Hydrogen Valence Electron Dot Diagram
Explanation of Curve – 2
Hydrogen Valence Electrons Number
- State E: It two hydrogen atoms having electrons with parallel spins approach each other, potential energy of system increases and no bond is formed between the two hydrogen atoms.