Explain why methane has a tetrahedral shape while ammonia has a trigonal pyramidal shape even though they both have the same number of electrons

:Ammonia has a Central N atom which is attached to 3 H atoms

:Methane has a central c atom with 4 H atoms attached to it .

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

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