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 .

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.
The atoms in lithium sulfide are held together by bonds.

Both lithium and sulfur form positive ions.

Answer 1

The correct statement about lithium sulfide is:

The atoms in lithium sulfide are held together by bonds.

To elaborate on other options:

1. The chemical formula for lithium sulfide is Li2S (not LiS2 or LiS).
2. A molecular model of lithium sulfide would not specifically have "two spheres" since the structure is ionic, not molecular, but you might represent lithium ions and a sulfur ion.
3. Lithium forms positive ions (Li⁺), while sulfur typically forms negative ions (S²⁻), contradicting the statement that both form positive ions.

Thus, the most accurate and universally correct statement is about the bonds holding the atoms together.

Answer 2

Which element has the same number of valence electrons as bromine (Br)?

(1 point)
Responses

selenium (Se)
selenium (Se)

krypton (Kr)
krypton (Kr)

potassium (K)
potassium (K)

chlorine (Cl)

Answer 3

Bromine (Br) is in Group 17 of the periodic table and has 7 valence electrons. The element that has the same number of valence electrons as bromine is:

Chlorine (Cl)

Chlorine is also in Group 17 and has 7 valence electrons, just like bromine.

For clarity:

• Selenium (Se) has 6 valence electrons (Group 16).
• Krypton (Kr) has 8 valence electrons (Group 18).
• Potassium (K) has 1 valence electron (Group 1).

Therefore, the correct answer is chlorine (Cl).

Answer 4

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

They have similar atomic weights.
They have similar atomic weights.

They are both colorless.
They are both colorless.

They have similar reactivity.
They have similar reactivity.

They are both hard and brittle.

Answer 5

Sodium (Na) and potassium (K) are in the same group (Group 1, also known as the alkali metals) on the periodic table because:

They have similar reactivity.

Alkali metals have similar chemical properties due to having the same number of valence electrons (one electron in their outer shell). This similarity in electron configuration leads to comparable reactivity and behavior in chemical reactions.

The other options are not correct:

• They do not have similar atomic weights (potassium is heavier than sodium).
• While sodium and potassium are metals, they are not colorless in their elemental form.
• Both are soft metals but not hard and brittle; they are actually quite the opposite.

Thus, the statement regarding similar reactivity is the most appropriate.

Answer 6

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

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

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 7

The correct response is:

It is a physical change because there is no reaction.

When fabric is cut into pieces, the composition of the fabric remains the same; no new substances are formed, and therefore, it is a physical change. Physical changes can often be reversed, such as sewing the pieces back together, but the defining feature here is that no chemical reaction occurs during the cutting process.

Answer 8

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

They involve heat.
They involve heat.

They are reversible.
They are reversible.

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

They form new substances.

Answer 9

The correct response is:

They form new substances.

Chemical changes result in the formation of new substances with different chemical properties from the original substances, whereas physical changes do not result in the creation of new substances; the original substances remain the same even if they undergo changes in physical state, shape, or size.

The other options provided (heat involvement, reversibility, phase shifts) can occur in both physical and chemical changes and are not distinguishing characteristics of the two types of changes.

Answer 10

How does a balanced chemical equation demonstrate the Law of Conservation of Mass?(1 point)
Responses

it shows that no atoms have been gained or lost during the reaction
it shows that no atoms have been gained or lost during the reaction

it shows that only physical changes follow the Law of Conservation of Mass
it shows that only physical changes follow the Law of Conservation of Mass

it shows that all compounds remain bonded after the reaction
it shows that all compounds remain bonded after the reaction

it shows that the properties of the elements stay the same after the reaction

Answer 11

The correct response is:

It shows that no atoms have been gained or lost during the reaction.

A balanced chemical equation demonstrates the Law of Conservation of Mass by ensuring that the number of atoms of each element is the same on both sides of the equation. This reflects the principle that in a chemical reaction, atoms are neither created nor destroyed; they are simply rearranged to form new substances.

The other options do not accurately describe how a balanced chemical equation relates to the Law of Conservation of Mass.