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Valencies of each element refer to the number of electrons it acquires or loses in order to complete its outermost shell. Atoms become more stable when their outer shell, or octet, is completed (8 electrons ions in the outermost shell). As a result, the periodicity of element valence or oxidation states interacts with other atoms or participates in chemical interactions in which they can give or lose electrons to other atoms, or take or acquire electrons from other atoms to form a stable state.
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Key terms: Valency, oxidation, atom, electron, elements, valence
What is Valency?
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In chemistry, valence/valency is the characteristic of an element that influences how many other atoms it can combine with. The amount of hydrogen atoms that an atom of a specific element may combine determines its combining capacity or affinity.
What is the oxidation state of elements?
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The maximum number of electrons that an atom may lose or gain to establish a connection with another atom is known as the oxidation state. Diatomic molecules are diatomic elements with valency 1.
Valency and oxidation state
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- Oxidation State and valency are one amongst the foremost elementary properties of components and may be studied with the assistance of electron configuration or by the number of electrons that make up an atom's valence shell (outer shell).
- The number of valence electrons or eight minus the number of valence electrons is used to compute the valencies of elements in the s-block and p-block of the periodic table.
- Valency is governed for the d-block and f-block elements not only by valence electrons but also by d and f orbital electrons. These d-block and f-block components, on the other hand, have generic valencies of 2 and 3.
- Valence electrons are electrons that are located in the outermost shell of a molecule. At the same time, an atom's valency or valence was determined by the number of valences.
Valency of first 30 elements
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| Elements | Valency |
|---|---|
| Hydrogen | 1 |
| Helium | 0 |
| Lithium | 1 |
| Beryllium | 2 |
| Boron | 3 |
| Carbon | 4 |
| Nitrogen | 3 |
| Oxygen | 2 |
| Fluorine | 1 |
| Neon | 0 |
| Sodium | 1 |
| Magnesium | 2 |
| Aluminium | 3 |
| Silicon | 4 |
| Phosphorus | 3 |
| Sulphur | 2 |
| Chlorine | 1 |
| Argon | 0 |
| Potassium (K) | 1 |
| Calcium | 2 |
| Scandium | 3 |
| Titanium | 4 |
| Vanadium | 5,4 |
| Chromium | 2 |
| Manganese | 7,4,3 |
| Iron (Fe) | 2,3 |
| Cobalt | 3,2 |
| Nickel | 2 |
| Copper (Cu) | 2,1 |
| Zinc | 1 |
Periodic Trends in Elements' Oxidation States
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Variation of Oxidation State Over Time
The number of valence electrons in an element grows and changes from 1 to 8 as it moves from left to right throughout a period. When the elements are initially mixed with H or O, their valency increases from 1 to 4, then decreases to zero. Consider two oxygen-containing molecules, Na2O and F2o. F has a higher electronegativity than oxygen in the F2O molecule. As a result, one electron will be drawn from the oxygen molecule by each of the F atoms. It indicates that F will have a -1 oxidation state, while O will have a +2 oxidation state. In the case of Na2O, however, oxygen is significantly electronegative when compared to a sodium atom. As a result, oxygen will grab two electrons from each of the sodium atoms with a -2 oxidation state, resulting in a +1 oxidation state for the Na compound. The charge possessed by an atom as a result of the acquisition or loss of electrons (due to the electronegativity difference between the combining atoms) in the molecule is represented by the element's oxidation state.
Oxidation State Variation Within a Group
There is no change in the number of valence electrons as we travel down in a group. As a result, all elements of a group have the same valency.
In order to assign the Oxidation States, there are several rules to follow.
- The oxidation states of elements like S8, O2, H2, Fe, P4, and others are all zero.
- The oxidation state of oxygen is -2. In contrast, it has an oxidation state of -1 in its peroxides, such as H2O2 and Na2O2.
- Hydrogen, on the other hand, has +1. However, when it comes to Metal Hydrides, such as LiH, NaH, and others, it has a negative value.
Also, a few elements have comparable oxidation states in their compounds
- such as halogens, which have -1 unless they form a combination with Oxygen or another element.
- Alkali metals, such as K, Na, Rb, Cs, and -Li, have a positive charge.
- Alkali Earth Metals, on the other hand, contain +2 elements such as Ca, Mg, Ba, Sr, -Be, and others.
Things to remember
- The oxidation state is indicated by a number and a positive (+) or negative (-) sign.(click here for question)
- When considering the electron configurations of elements in the same group in the periodic table, the number of electrons present in the outermost shell is the same
- The valence electrons of an atom are denoted by the terms oxidation number and valency.
- A pure element's oxidation state is always zero.
Also read: Oxidation and Reduction
Sample Questions
Ques. What is the difference between valency and oxidation state? (2 marks)
Ans. The clear difference between valency and oxidation state is that valency refers to the number of electrons present in an atom's outermost shell, whereas oxidation state refers to the number of electrons lost or acquired by an element in a compound.
Ques. How do you find the valency of the element? (3 marks)
Ans. The simplest (and most straightforward) option is to examine the periodic table. The elements are classified into groups, with the items in groups 1–8 having the same valency as the other components in that group. All of the elements in group 8 contain eight electrons, (high stability). If the number of electrons in the outer shell is four or fewer, the valency of an atom is equal to that number. The valency is equal to eight minus the number of electrons in the outer shell if not specified. You can simply compute the valency once you know the number of electrons.
Ques. What is the distinction between oxidation state and oxidation number? (3 marks)
Ans. The main distinction between oxidation state and oxidation number is that oxidation number is the charge of the central atom of a coordination complex if all of the bonds around it were ionic bonds, whereas oxidation state is the number of electrons that a given atom can lose, gain, or share with another atom.
Ques. What do negative and positive oxidation states mean? (3 marks)
Ans. The oxidation state is the charge that an atom would have in a compound if the bonding electrons were obtained by the element with the greater electronegativity. The atom in the bond that acquires electron density (i.e., the more electronegative atom) is assigned a negative oxidation state, whereas the atom in the bond that loses electron density is assigned a positive oxidation state.
Ques. Name the elements which have more than one valency? (3 marks)
Ans. There are many valency’s for certain elements. They have varying valency. Copper, tin, iron, and mercury, for example, have varying valency’s. Cuprous oxide (Cu2O) and cupric oxide are formed when the copper reacts with oxygen (CuO). Mercury has two valency’s Mercurous (Hg+) Mercuric (Hg2+)
Ques. Which element has multiple oxidation states? Is it possible for valency to be negative? (4 marks)
Ans. Transition elements are elements that have several oxidation states and have coloured ions. Due to the abundance of unoccupied d-orbitals, they exhibit numerous oxidation states. Transition metals have several oxidation states because losing electrons is very simple for them compared to alkali metals.
The loss or gain of one electron is referred to as an atom charge. Donating an electron produces a positive charge, whereas receiving an electron produces a negative charge. Valency has no sign, whereas charge possesses both positive and negative signs
Ques. What are the guidelines in assigning the oxidation states? (3 marks)
Ans. Here are some guidelines.
- S8, O2, H2, Fe, P4, and other related elements have zero oxidation states.
- The oxidation state of oxygen is 2. It has an oxidation state of -1 in its peroxides, such as H2O2 and Na2O2.
- Hydrogen, on the other hand, has a +1. However, when it comes to metal hydrides such as LiH, NaH, and others, it has a negative value.
- A few elements, such as halogens, have comparable oxidation states in their compounds, with the exception of when they form a compound with Oxygen or one another.
- K, Na, Rb, Cs, and -Li are alkali metals with +1 oxidation state.
- Ca, Mg, Ba, Sr, -Be, and other Alkali Earth Metals have +2.
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