定义Definition
直线形分子的所有原子在一条直线上，中心原子两侧的键角为 180°。中心原子有两个电子区域且没有孤电子对时形成直线形，如 CO₂、BeCl₂、HCN 和乙炔。双原子分子也都是直线形。
In a linear molecule all the atoms lie on a straight line, with a bond angle of 180° at the central atom. It arises when the central atom has two electron regions and no lone pairs, as in CO₂, BeCl₂, HCN and ethyne. All diatomic molecules are linear too.
价层电子对互斥理论的解释VSEPR explanation
两个电子区域互相排斥，在中心原子两侧相距最远，夹角 180°。双键或三键按一个电子区域计算，所以 O=C=O 是直线形，中心碳为 sp 杂化。
Two electron regions repel and sit on opposite sides of the central atom, 180° apart. Double and triple bonds count as one region each, so O=C=O is linear and its carbon is sp hybridised.
带孤电子对的直线形Linear with lone pairs
XeF₂ 和 I₃⁻ 中心原子周围有五个电子区域（两个成键对和三对孤电子对），孤电子对占据三角双锥的三个赤道位置，两个成键原子在轴向，分子仍为直线形。
In XeF₂ and I₃⁻ the central atom has five electron regions, two bonding pairs and three lone pairs. The lone pairs take the three equatorial positions of a trigonal bipyramid and the bonded atoms the axial ones, so the molecule is still linear.
极性Polarity
对称的直线形分子（CO₂、BeCl₂）中键的偶极相互抵消，是非极性分子；两端不同的直线形分子（HCN）是极性分子。
In symmetrical linear molecules (CO₂, BeCl₂) the bond dipoles cancel and the molecule is non-polar; linear molecules with different ends (HCN) are polar.