Question

1. a mystery element has 18 protons. which one of the following statements is true about the element?

a. the element belongs in row 2 of the periodic table and is classified as a halogen.
b. the element belongs in row 3 of the periodic table and is classified as a noble gas.
c. the element belongs in row 4 of the periodic table and is classified as an alkali metal.
d. the element belongs in row 5 of the periodic table and is classified as an alkaline earth metal.

1. the list identifies various properties of four elements:

element 1 is a gas at room temperature.
element 2 is a solid which conducts electricity.
element 3 is a gas with an effective nuclear charge of +7.
element 4 is malleable and can take the form of a shiny solid sheet.
based on this list, which elements are metals?
a. elements 1 and 3
b. elements 1 and 4
c. elements 2 and 3
d. elements 2 and 4

1. which pair of words correctly completes the statement?

alkali metals are highly _ since they _ easily to form ions.
a. nonreactive; lose 1 electron
b. nonreactive; lose 2 electrons
c. reactive; lose 1 electron
d. reactive; gain 1 electron

Explanation:

Question 9

• The number of protons in an atom is equal to its atomic number. An element with 18 protons is argon (\(Ar\)).
• In the periodic table, argon is in row 3 (period 3) and is a noble gas (group 18).
• Halogens are in group 17, alkali metals in group 1, and alkaline earth metals in group 2.

• Metals are good conductors of electricity, malleable (can be hammered into sheets), and ductile (can be drawn into wires).
• Element 2 is a solid that conducts electricity - a property of metals.
• Element 4 is malleable and can form a shiny solid sheet - typical metal properties.
• Element 1 (gas at room temperature) and Element 3 (gas with effective nuclear charge +7, likely a non - metal like \(Cl\)) are not metals.

• Alkali metals (group 1 elements like \(Li\), \(Na\), \(K\) etc.) have 1 valence electron.
• They are highly reactive because they can easily lose this 1 valence electron to achieve a stable electron configuration (like a noble gas).
• Non - reactive is incorrect as they react readily (e.g., with water). Gaining an electron is not typical for alkali metals as they tend to lose electrons.

Answer:

B. The element belongs in row 3 of the periodic table and is classified as a noble gas.

Question 10