Notes

across the period, the number of protons increases. this would also mean that the number of electrons is also increasing. with the increasing number of electrons residing in the same shell, the nuclear charge of the atom ? also increases. This causes the atomic radius to decrease due to the stronger pull of electrons towards the nucleus? this, in overall, causes the size of the particle to shrink in size, as per seen in the diagram. However, down the group, the number of shells increases.( down the period, the number of electron shells increases). though the number of protons are more, the number of electron shells is more. Thus, the element would need to exert a nuclear charge over the increased number of electron shells causing the atomic radius to increase.


Ethane molecule is ditetrahedral and has a bond angle of 109*
Ethene molecule is a planar molecule with a bond angle of 120* ( all of them differ from each other in geometry and bond angle due to the difference in the state of hybridization of carbon atom in them )
Ethyne is a linear molecule with a bond angle of 180*

A sigma bond is a chemical bond formed by orbital overlap along the internuclear axis ( eg. ethane has 7 axes and there is an overlap of s orbital and the p orbital at each interface?)
Each carbon atom is surrounded by 3 hydrogen sigma bond and one carbon carbon sigma bond

in my simplistic brain, the overlap at each 'junction' is considered a sigma bond ohhh