What Is the Trend of Valency and Oxidation States Across the Periodic Table?
Periodicity of Valence or Oxidation States of Elements is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Periodicity of Valence or Oxidation States of Elements in Chemistry?
The periodicity of valence or oxidation states refers to the repeating pattern in the valency and oxidation numbers of elements as you move across periods (rows) and groups (columns) in the periodic table.
This concept appears in chapters related to the periodic table, chemical bonding, and redox reactions, making it a foundational part of your chemistry syllabus.
Defining Valence, Valence Electrons, and Oxidation State
Valence electrons are the electrons present in the outermost shell of an atom. The valency of an element is its ability to combine with other atoms, often equal to the number of valence electrons (for metals) or eight minus the valence electrons (for non-metals).
The oxidation state is the effective charge an atom appears to have in a compound, defined by the gain or loss of electrons in chemical bonding.
Periodicity in the Periodic Table
As you move from left to right across a period in the periodic table, the number of valence electrons increases. This causes the valency (or oxidation state) to first increase, reach a maximum, and then decrease.
Down a group, the number of valence electrons generally remains the same, so elements in the same group have similar valency and oxidation state trends.
Valency and Oxidation States: Patterns and Chart (First 20 Elements)
The periodicity of valence or oxidation states can be seen clearly in the first 20 elements of the periodic table. Here is a sample chart you can use to quickly revise valency and oxidation number patterns:
| Element | Atomic No. | Valency | Common Oxidation State(s) |
|---|---|---|---|
| Hydrogen (H) | 1 | 1 | +1, -1 |
| Helium (He) | 2 | 0 | 0 |
| Lithium (Li) | 3 | 1 | +1 |
| Beryllium (Be) | 4 | 2 | +2 |
| Boron (B) | 5 | 3 | +3 |
| Carbon (C) | 6 | 4 | +4, +2, -4 |
| Nitrogen (N) | 7 | 3 | -3 to +5 |
| Oxygen (O) | 8 | 2 | -2, -1, 0, +2 |
| Fluorine (F) | 9 | 1 | -1 |
| Neon (Ne) | 10 | 0 | 0 |
| Sodium (Na) | 11 | 1 | +1 |
| Magnesium (Mg) | 12 | 2 | +2 |
| Aluminium (Al) | 13 | 3 | +3 |
| Silicon (Si) | 14 | 4 | +4, -4 |
| Phosphorus (P) | 15 | 3, 5 | -3, +3, +5 |
| Sulfur (S) | 16 | 2, 4, 6 | -2, +4, +6 |
| Chlorine (Cl) | 17 | 1, 3, 5, 7 | -1, +1, +3, +5, +7 |
| Argon (Ar) | 18 | 0 | 0 |
| Potassium (K) | 19 | 1 | +1 |
| Calcium (Ca) | 20 | 2 | +2 |
s-, p-, d-, and f-Block Trends in Periodicity of Valence and Oxidation States
For s- and p-block elements, the valency usually equals the group number (for s-block) or 8 minus the group number (for p-block non-metals).
d-block (transition) and f-block elements have variable or multiple oxidation states due to the similar energies of their outer and penultimate shells, making it easy for them to lose different numbers of electrons in bonding. Vedantu provides clear periodicity charts and explanations for quick revisions.
Relationship Between Valence and Oxidation State in Chemical Reactions
The valency of an element tells us how many bonds it usually forms. Oxidation state is more flexible—it can vary from one compound to another, even for the same element. For example, carbon has a valency of 4 but shows oxidation states from -4 (as in CH₄) to +4 (as in CO₂).
Step-by-Step Example: Finding Oxidation States
1. Write the chemical formula of the compound (e.g., Na₂O).2. Assign oxidation number to sodium (+1, always for alkali metals).
3. Balance the total oxidation numbers: 2 (Na, +1 each) + 1 (O, x) = 0.
4. Find x: 2(+1) + (x) = 0 → x = -2.
5. Final answer: Sodium = +1, Oxygen = -2.
Lab or Experimental Tips
Remember trends with the phrase "Across a period, valency and oxidation states go up, then down; down a group, they stay the same." Visualizing with colored periodic table charts can help. Vedantu often shares such memory aids in live online sessions.
Try This Yourself
- List the valency and oxidation states of magnesium and chlorine.
- Explain why iron shows +2 and +3 oxidation states in compounds.
- Draw a simple chart showing valency across period 2 elements.
Relation with Other Chemistry Concepts
Understanding the periodicity of valence or oxidation states helps connect chemical bonding, electronic configuration, and redox reactions. It is also useful in predicting the types of compounds formed by s-, p-, and d-block elements. Students can explore more about element trends on the Periodic Table and detailed transition element behavior on d-block elements pages.
Final Wrap-Up
We explored periodicity of valence or oxidation states of elements—its definition, patterns on the periodic table, and why these trends matter in chemical reactions and bonding. For more visual aids, examples, and live exam-prep help, explore Vedantu’s chemistry resources and online classes.
FAQs on Periodicity of Valence or Oxidation States of Elements
1. What is meant by periodicity of valence or oxidation states?
Periodicity of valence or oxidation states refers to the repeating trends in the valency (combining capacity) and oxidation numbers of elements as you move across a period or down a group in the periodic table.
• These trends help predict chemical bonding and the types of compounds elements can form.
• Periodicity is caused by the recurring pattern of electronic configuration in the periodic table.
2. How do valency and oxidation number differ?
Valency and oxidation number are related but different:
• Valency is the number of electrons an atom uses to bond with other atoms.
• Oxidation number is the apparent charge an atom has in a compound, based on electron gain or loss.
• An element can have multiple oxidation numbers, but usually a fixed valency in simple compounds.
3. Why do transition metals have variable oxidation states?
Transition metals have variable oxidation states because:
• Their ns and (n-1)d electrons have similar energies.
• They can lose different numbers of electrons for bonding.
• This property leads to multiple stable oxidation numbers in their chemical compounds.
4. What is the trend in oxidation states across periods?
Across a period, the maximum oxidation state of s- and p-block elements generally increases from left to right, reaching a maximum in the middle, and then decreases towards the right. This is due to the increase in the number of valence electrons.
5. What is the difference between periodicity of valence and periodicity of oxidation states?
Periodicity of valence refers to the regular change in the typical valency of elements as you move through the periodic table.
Periodicity of oxidation states highlights how possible positive and negative oxidation numbers vary and repeat periodically.
Both are linked to the arrangement of electrons, but oxidation states can be more variable, especially in transition elements.
6. Why do noble gases rarely show valency or oxidation states?
Noble gases are mostly inert because:
• They have a complete outermost electron shell.
• This stability gives them a valency of zero under normal conditions.
• However, heavier noble gases can form compounds in rare cases, displaying positive oxidation states.
7. What is the general trend of valency in the first 20 elements?
For the first 20 elements:
• Valency increases from 1 to 4 as you move from left to right.
• It then decreases from 4 to 0 across the period.
• This trend repeats for each period in the periodic table, following the number of valence electrons.
8. How does periodicity of oxidation states help in predicting redox reactions?
Knowing oxidation state trends allows for easy identification of which elements are likely to be oxidized or reduced in chemical reactions.
• Elements with higher possible oxidation states tend to be oxidizing agents.
• Elements with lower or negative states usually act as reducing agents.
9. Can an element have both positive and negative oxidation states?
Yes, some elements such as nitrogen and chlorine exhibit both positive and negative oxidation states, depending on the compounds they form.
• For example, nitrogen is -3 in NH3 and +5 in HNO3.
• These variations depend on the element’s position in the periodic table and its class (s-, p-, d-, or f-block).
10. How is the periodicity of valency and oxidation states related to electronic configuration?
The recurring electron configuration pattern in the periodic table causes elements in the same group to have similar valency and oxidation state trends.
• This determines an element’s chemical properties and typical reactivity.
• Similar configurations result in similar periodic behavior.
11. What are some examples of elements with multiple oxidation states?
Examples include:
• Iron (Fe): +2 and +3 in different compounds
• Copper (Cu): +1 and +2
• Manganese (Mn): +2, +4, +7
• Chlorine (Cl): -1, +1, +3, +5, +7
This variability is most common in transition and p-block elements due to their electronic structures.
12. What is the significance of periodicity of oxidation states in real-life chemistry?
Understanding periodicity of oxidation states is crucial for:
• Predicting the types of compounds an element forms
• Balancing redox reactions in chemistry
• Explaining biological, environmental, and industrial chemical processes that rely on changes in oxidation state
