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

Explanation:

9.

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

• Metals are generally solids (at room temperature, except mercury), conduct electricity, and are malleable (can be hammered into sheets).
• Element 1 is a gas (not a metal property).
• Element 2 is a solid that conducts electricity (a metal property).
• Element 3 is a gas (not a metal property, also effective nuclear charge of +7 is more characteristic of non - metals like halogens).
• Element 4 is malleable and can form a shiny solid sheet (metal properties).

Answer:

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

10.