Video: Identifying the Atomic Number of the Element Whose Atoms Are Most Likely to React with Atoms with a Given Electron Configuration

The elements whose atoms have an electron configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ will most probably combine with atoms of an element with an atomic number of _. [A] 13 [B] 31 [C] 35 [D] 54 [E] 56.

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Video Transcript

The elements whose atoms have an electron configuration of 1s2 2s2 2p6 3s2 3p6 4s1 will most probably combine with atoms of an element with an atomic number of space. (A) 13, (B) 31, (C) 35, (D) 54, (E) 56.

In this question, we’re given the electronic configuration of a mystery element. By simply adding together the number of electrons found in each subshell of this mystery element, we discover the element contains a total of 19 electrons. 19 electrons will be balanced by 19 protons in the nucleus of the atom of this element. So the atomic number is 19, and this identifies the mystery element as potassium, a metal in group one of the periodic table.

Using the periodic table, we can easily identify the other elements presented here as possible answers by using their atomic numbers. The possible answers give us the elements aluminum, gallium, bromine, xenon, and barium. These have atomic numbers 13, 31, 35, 54, and 56, respectively. We need to establish which one of these elements will combine with potassium to form a stable chemical compound. That is a chemical substance consisting of two or more chemically bonded chemical elements.

Aluminum, gallium, and barium are all metallic elements found within the periodic table, as is potassium in the question. What would happen if we were to mix atoms of potassium with atoms of these various different metals? By mixing different metal atoms together, frequently with heating, we often obtain alloys. An alloy is a substance made by melting two or more elements together, at least one of these elements being a metal. Often a solid solution or a mixture is formed upon cooling.

Alloys are not considered to be chemical compounds, even though it would be hard to separate the individual elements in the mixture. Potassium does form alloys with other metals. Some are rather unusual, having very, very low melting points. In fact, they’re liquids at room temperature. So there’s no reason why you wouldn’t expect potassium to form alloys with aluminum, gallium, and barium. Since these alloys are not strictly chemical compounds, aluminum, gallium, and barium are not the correct answers here.

Xenon is a noble gas, and it’s found in group 18 or zero of the periodic table. Like other noble gases, xenon is typically inert, that is, chemically unreactive. It has a full valence shell of electrons. This represents a stable arrangement. And it doesn’t form any compounds at all. Compounds of noble gases were thought not to exist at all until the early 1960s. One of the earliest xenon compounds discovered is xenon tetrafluoride shown here. However, xenon does not react with potassium under normal conditions. So it’s not the correct answer here.

Bromine is a halogen found within group 17 or seven of the periodic table. We can view bromine as having seven electrons in its valence shell. Being in group one, potassium only has one electron in its valence shell. In the diagrams here, only the valence-shell electrons are shown for clarity. Potassium metal will readily react with liquid bromine. A stable ionic salt is formed, which is potassium bromide. During this reaction, the potassium atoms lose one electron. The bromine atoms gain one electron into their valence shell. A pair of oppositely charged ions is formed. And the stable compound potassium bromide is made.

Therefore, bromine with atomic number 35 is the most likely element to combine with potassium here. It’s the correct answer.

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