Chemistry, 04.07.2019 05:30 junior2461

Asolution of salt water is boiled. the water evaporates and solid salt remains. which statement is true? a. the salt and the water have both undergone chemical changes. b. the salt has undergone a physical change, and the water has undergone a chemical change. c. the salt and the water have both undergone physical changes. d. the salt has undergone a chemical change, and the water has undergone a physical change.

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Answer from: mladyrj5338

C because neither the water or salt have changed their molecular structure. H2O is still H2O and NaCl is still NaCl.

Answer from: joshua1255

The salt and the water have both undergone physical changes.

Explanation:

A physical change occurs when the appearance of a substance changes, but its chemical identity does not. In this case, the water has changed its appearance by changing from a liquid to a gas, while the salt has changed its appearance by changing from a dissolved substance to a solid. However, no chemical reactions have taken place and so only physical changes have occurred.

Answer from: Quest

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.

Answer from: Quest

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Asolution of salt water is boiled. the water evaporates and solid salt remains. which statement is t...