Why did mendeleev leave blank spaces in his version of the periodic table? mendeleev’s periodic table arranged elements in order of increasing atomic mass; spaces were left for elements not having the correct atomic mass. mendeleev’s periodic table arranged elements in groups of similar chemical properties; spaces were left for elements not having a similar chemical property. mendeleev’s periodic table arranged elements in order of increasing atomic mass; it was noticed that chemical properties repeated. mendeleev predicted an element had not been discovered to fit the space.

The answer is Mendeleev’s periodic table arranged elements in order of increasing atomic mass; it was noticed that chemical properties repeated. Mendeleev predicted an element had not been discovered to fit the space.

the positions which points up in upward carbon and down in downward carbon are axial

and vice versa holds true for equatorial positions

so the correct answer with labelled diagram will be

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.