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The Magic of Chemical Reactions
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Wonders of Light 1
Wonders of Light 2
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- Definition: Periodic Trends
- Definition: valency
Definition: Periodic Trends
When the properties of elements in a period or a group of the modern periodic table are compared, certain regularity is observed in their variations. It is called the periodic trends in the modern periodic table.
Definition: Valency
The valency of an element is determined by the number of electrons present in the outermost shell of its atoms, that is, the valence electrons.
Valency Rules and Formula Formation
1. Valency: Valency is the combining capacity of an element and is determined by the number of electrons in the outermost shell (valence electrons) of an atom.
The electronic configuration of an element determines its valency. Let's take potassium (K) as an example:
- Symbol: K
- Electronic Configuration: 2, 8, 8, 1
- Valence Electron: 1 (in the outermost shell)
- Valency: 1 (since it loses 1 electron to attain stability like noble gas Argon)
2. Constant Valency: The valency of an element usually stays the same in different compounds. For example, hydrogen always has a valency of one.
3. Molecular Formulas and Valency: By analysing a compound’s molecular formula, we can determine the valencies of the elements involved. The univalency of hydrogen serves as a reference for calculating valencies.
4. Cross Multiplication: This method involves balancing the valencies of elements to create a stable compound formula, ensuring that the total number of bonds formed by each element is satisfied. Cross Multiplication Method for Writing the Molecular Formula of Simple Compounds:
Step 1: Write symbols of constituent elements.
C O
Step 2: Write the valency below the respective element.
C O
4 2
Step 3: Cross-multiply to obtain the number of atoms of the constituent elements in the molecule of the compound.
Step 4: To write the formula of the compound obtained by cross-multiplication.
C₂O₄
Step 5: To write the final molecular formula of the compound. The number of constituent atoms in the final molecular formula should be the smallest possible whole numbers.
To get this, divide the formula obtained in Step 4 by a suitable number.
Formula obtained by cross multiplication: C₂O₄
Final molecular formula obtained by dividing by ‘2’: CO₂
Shaalaa.com | Structure of Atom (Valency)
Related QuestionsVIEW ALL [26]
This question refers to the elements of the Periodic Table with atomic numbers from 3 to 18. Some of the elements are shown by letters, but the letters are not the usual symbols of the elements.
| 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| A | B | C | D | E | F | G | H |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| I | J | K | L | M | N | O | P |
Which of these is an element with valency 4?
