Water is made of two hydrogen atoms and one oxygen atom bonded together. julia is describing how water undergoes a physical change when it boils. she says that the particles shift to be farther apart and that the oxygen and hydrogen separate. she also says that the total mass of the steam is the same as the initial water, and that heat energy was required to cause the change. she finishes her description by saying that the steam can be turned back into water if it is cooled.
which is the mistake in her description?
1 .the total mass remains the same in physical changes.
2.the arrangement of particles may change in physical changes.
3.atoms remain bonded to each other in physical changes.
4.energy changes may occur in physical changes.
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Ответ:
Ответ:
Answer is: the two electrons in the fourth shell.
Atomic number of calcium is 20, it means that it has 20 protons and 20 electrons, so atom of calcium is neutral.
Electron configuration of calcium atom: ₂₀Ca 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²; calcium has two valence electrons (4s²).
In reactions it lose those two electrons ang form cation with positive charge 2+.
Atomic number is the number of protons, which is characteristic of a chemical element.
Beryllium, magnesium,calcium and strontium are alkaline earth metals. The elements have very similar properties.
Alkaline earth metals have in common an outer s- electron shell (two electrons).