In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?(1 point)

Question

Responses

The chemical formula for lithium sulfide is LiS2.
The chemical formula for lithium sulfide is LiS 2 .

Both lithium and sulfur form positive ions.
Both lithium and sulfur form positive ions.

A molecular model of lithium sulfide would have two spheres.
A molecular model of lithium sulfide would have two spheres.

The atoms in lithium sulfide are held together by bonds.

Answer 1

The correct statement about lithium sulfide is:

The atoms in lithium sulfide are held together by bonds.

In lithium sulfide (Li2S), lithium (Li) donates electrons to sulfur (S), resulting in the formation of ionic bonds. Thus, this statement accurately describes the nature of the interaction between the atoms in the molecule.

The other statements are incorrect:

• The chemical formula for lithium sulfide is not LiS2; it is Li2S.
• Lithium forms positive ions (Li⁺), but sulfur typically forms negative ions (S²⁻), not positive ions.
• A molecular model of lithium sulfide would actually have three spheres (two for lithium and one for sulfur), not two.

Thus, the correct answer is that the atoms in lithium sulfide are held together by bonds.

Answer 2

Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
Responses

They are both hard and brittle.
They are both hard and brittle.

They are both colorless.
They are both colorless.

They have similar reactivity.
They have similar reactivity.

They have similar atomic weights.

Answer 3

The correct response is:

They have similar reactivity.

Sodium (Na) and potassium (K) are both alkali metals found in Group 1 of the periodic table. Elements in the same group have similar chemical properties, including reactivity, due to having the same number of valence electrons. Both sodium and potassium react vigorously with water and exhibit similar behaviors in chemical reactions.

The other options are incorrect:

• They are not both hard and brittle; alkali metals are typically soft.
• They are not colorless; sodium and potassium can form colored compounds.
• While they may have some similarities in atomic weight, it is their reactivity that primarily defines their placement in the same group.

Answer 4

A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
Responses

It is a physical change because the process is reversible.
It is a physical change because the process is reversible.

It is a chemical change because there is no phase change.
It is a chemical change because there is no phase change.

It is a chemical change because the size changes.
It is a chemical change because the size changes.

It is a physical change because there is no reaction.

Answer 5

The correct response is:

It is a physical change because there is no reaction.

Cutting fabric into two pieces does not change the chemical composition of the fabric; it only changes its physical form (size and shape). Since no new substance is formed and there is no chemical reaction involved, this is classified as a physical change. Additionally, physical changes, such as cutting, can be reversible under certain conditions (e.g., sewing the pieces back together), further supporting this classification.

Answer 6

How are chemical changes different from physical changes?(1 point)
Responses

They form new substances.
They form new substances.

They are reversible.
They are reversible.

They include shifts in the phase of matter.
They include shifts in the phase of matter.

They involve heat.

Answer 7

The correct response is:

They form new substances.

Chemical changes involve the transformation of substances into different substances with distinct chemical properties. This often includes breaking and forming chemical bonds. In contrast, physical changes only alter the form or appearance of a substance without changing its chemical identity, so no new substances are formed.

While some chemical changes can be irreversible, and physical changes can be reversible, the key distinguishing factor between the two is the formation of new substances. Not all chemical changes involve heat, and phase changes (like melting or boiling) are purely physical changes. Therefore, "They form new substances" accurately captures the primary difference between chemical and physical changes.