The valency of an element with atomic number 4 is 2. This element is Beryllium (Be).
Valency refers to the combining capacity of an element, indicating the number of chemical bonds an atom can form. It is primarily determined by the number of electrons an atom needs to gain, lose, or share to achieve a stable outer electron shell, typically an octet (eight electrons) or a duplet (two electrons for very light elements like hydrogen, lithium, and beryllium).
Understanding Beryllium (Atomic Number 4)
Beryllium (symbol: Be) is an alkaline earth metal, known for its light weight and high melting point. Its atomic number is 4, which means it has 4 protons in its nucleus and 4 electrons orbiting the nucleus in a neutral atom.
Electron Configuration and Valency
To understand Beryllium's valency, we look at its electron configuration:
- Electron Configuration: 1s² 2s²
- Valence Electrons: The outermost shell (the second shell, 2s) contains 2 electrons. These are its valence electrons.
- Stability: To achieve a stable electron configuration, Beryllium readily loses these 2 valence electrons. By doing so, it attains the stable electron configuration of Helium (1s²), which has a full outermost shell (duplet).
- Ion Formation: When Beryllium loses 2 electrons, it forms a positively charged ion, Be²⁺.
Because Beryllium consistently loses two electrons to form chemical bonds and achieve stability, its combining capacity, or valency, is 2.
Valency of Elements: A Quick Reference
Understanding the valency of common elements is crucial for predicting how they will combine to form compounds. Here's a brief table illustrating the valency of elements around Beryllium, showcasing how atomic number relates to this property:
| Element | Atomic Number | Valency |
|---|---|---|
| Helium | 2 | 0 |
| Lithium | 3 | 1 |
| Beryllium | 4 | 2 |
| Boron | 5 | 3 |
(For a more comprehensive understanding of valency and electron configurations, refer to reliable chemistry resources such as the Royal Society of Chemistry periodic table.)
Practical Insights into Valency
Valency is a fundamental concept in chemistry with several practical applications:
- Predicting Chemical Formulas: Knowing the valency of elements allows us to predict the formulas of compounds. For example, Beryllium (valency 2) combines with Oxygen (valency 2) to form Beryllium Oxide (BeO), and with Chlorine (valency 1) to form Beryllium Chloride (BeCl₂).
- Understanding Reactivity: Elements with low valency (like Group 1 and 2 metals) tend to be highly reactive because they easily lose electrons to achieve stability.
- Compound Formation: Valency helps explain why certain elements combine in specific ratios to form stable chemical compounds, following the principles of chemical bonding.
