Define covalent bond according to orbital concept.

Answer

### Step-by-Step Text Solution:

1. **Understanding Orbitals**:
- An orbital is a region in an atom where there is a high probability of finding electrons. The simplest type of orbital is the s-orbital, which can hold a maximum of two electrons.

2. **Hydrogen Atom Configuration**:
- Take the hydrogen atom as an example. The electronic configuration of hydrogen is 1s¹, meaning it has one electron in its 1s orbital.

3. **Pairing of Electrons**:
- When two hydrogen atoms come close to each other, each atom has one electron in its 1s orbital. For a covalent bond to form, the electrons from each hydrogen atom must have opposite spins (one electron spins up, and the other spins down).

4. **Orbital Overlapping**:
- As the two hydrogen atoms approach each other, their 1s orbitals overlap. This overlap allows the electrons to interact and pair up, which is essential for bond formation.

5. **Formation of Covalent Bond**:
- The overlapping of the two 1s orbitals leads to the formation of a covalent bond. This bond can be represented as H-H, indicating that a bond has formed between the two hydrogen atoms.

6. **Definition of Covalent Bond**:
- According to the orbital concept, a covalent bond is defined as the result of the overlap of half-filled orbitals from two atoms, where the electrons in these orbitals have opposite spins. This pairing of electrons in the overlapping orbitals leads to bond formation.

### Final Definition:
A covalent bond, according to the orbital concept, is formed when half-filled orbitals from two atoms overlap and the electrons in these orbitals have opposite spins, resulting in a stable bond.

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