Chemistry, 09.07.2019 04:00, savannahvargas512

Which phase change at standard temperature and pressure represents sublimation?

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Substances on Earth can exist in three phases namely, solid, liquid or gas. The phase can be changed from one to other by any of six changes of phase: melting, condensation, freezing, vaporization, decomposition or sublimation.

Chemical process in which a solid turns to a gas without going to liquid stage is known as sublimation. It is an endothermic (absorbs heat) process. For example: Transformation of dry ice (solid carbon dioxide) to vapors to form clouds.

Hence, phase change at standard temperature and pressure which represents sublimation is solid turns to a gas without going to liquid stage.

answered: Guest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

answered: Guest

What? i don’t understand

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