Conceptual MCQs

Mendeleev did not always arrange elements by increasing atomic mass because he wanted to group elements with similar

• properties.

• atomic numbers.

• isotopes.

• charges.

Answer explanation

Mendeleev prioritized grouping elements with similar properties over strictly following atomic mass. This approach allowed him to better organize the periodic table and highlight relationships between elements.

As the atomic number increases in a group, the atomic radius

• generally increases.

• remains constant.

• decreases.

• varies unpredictably.

Answer explanation

As the atomic number increases in a group, additional electron shells are added, leading to a larger atomic radius. Therefore, the atomic radius generally increases.

If a compound forms by ionic bonding, which is not true?

• A positively charged atom or group attracts a negatively charged atom or group.

• The net charge of the compound is zero.

• The compound contains just two atoms of opposite charge.

• Several ions group together in a tightly packed structure.

Answer explanation

The statement 'The compound contains just two atoms of opposite charge' is not true because ionic compounds can consist of multiple ions, forming a lattice structure, not just two atoms.

Tags

NGSS.HS-PS2-4

Which of the following is not a property of ionic compounds?

• high melting point.

• hardness.

• lack of crystal structure.

• brittleness.

Answer explanation

Ionic compounds are characterized by high melting points, hardness, and brittleness due to their strong ionic bonds and crystal lattice structure. Therefore, the statement 'lack of crystal structure' is incorrect.

Tags

NGSS.HS-PS1-3

Ionic compounds have higher melting points than molecular compounds because

• ionic substances tend to vaporize at room temperature.

• ionic substances are brittle.

• attractive forces between ions are greater than those between molecules.

• the numbers of positive and negative charges are equal in an ionic compound.

Answer explanation

Ionic compounds have higher melting points because the attractive forces between ions are stronger than those between molecules. This strong ionic bonding requires more energy to break, resulting in higher melting points.

Water (H₂O) has a higher boiling point than hydrogen sulfide (H₂S) because water molecules are

• less polar and form hydrogen bonds.

• more covalent and form hydrogen bonds.

• ionic and form hydrogen bonds.

• more polar and form hydrogen bonds.

Answer explanation

Water (H₂O) is more polar than hydrogen sulfide (H₂S), allowing it to form stronger hydrogen bonds. These bonds require more energy to break, resulting in a higher boiling point for water compared to H₂S.

A covalent bond where atoms have unequal attraction for shared electrons is called a(n) _____________________________.

• polar covalent bond

• nonpolar covalent bond

• ionic bond

• metallic bond

Answer explanation

A polar covalent bond occurs when two atoms share electrons unequally due to differing electronegativities, resulting in a partial charge. This distinguishes it from nonpolar covalent bonds, where electrons are shared equally.

Tags

NGSS.HS-PS1-1

A molecule with two atoms is called a(n) _____________________________.

• diatomic molecule

• monatomic molecule

• polyatomic ion

• isotope

Answer explanation

A molecule with two atoms is specifically called a diatomic molecule. This term distinguishes it from monatomic molecules, which consist of a single atom, and polyatomic ions, which contain more than two atoms.

Tags

NGSS.MS-PS1-1

The simplest collection of atoms that defines an ionic compound is called a(n) _____________________________.

• formula unit

• molecule

• atom group

• elemental cell

Answer explanation

The simplest collection of atoms in an ionic compound is called a formula unit. It represents the ratio of ions in the compound, distinguishing it from a molecule, which is used for covalent compounds.

The property of being able to be drawn into a wire is called ________________________________.

• ductility

• malleability

• brittleness

• elasticity

Answer explanation

The property of being able to be drawn into a wire is known as ductility. This characteristic is crucial for materials like metals, allowing them to be stretched without breaking.