If you were to design a timeline of atomic models for a museum display, which model would best show electrons orbiting around a nucleus?

• Dalton’s Solid Sphere Model

• Thomson’s Plum Pudding Model

• Rutherford’s Nuclear Model

• Democritus’ Particle Model

Answer explanation

Rutherford’s Nuclear Model best illustrates electrons orbiting a nucleus, depicting a central nucleus surrounded by orbiting electrons, unlike the other models which do not represent this structure.

A scientist adds one proton to a neutral nitrogen atom. Which element is now formed?

• Neon

• Oxygen

• Fluorine

• Carbon

Answer explanation

A neutral nitrogen atom has 7 protons. Adding one proton increases the count to 8, which corresponds to oxygen on the periodic table. Therefore, the element formed is oxygen.

Two isotopes of chlorine are found in nature: chlorine-35 and chlorine-37. Why are these atoms considered isotopes of the same element?

• They have the same mass number.

• They have identical atomic masses.

• They have the same number of protons but different numbers of neutrons.

• They have the same number of neutrons but different numbers of electrons.

Answer explanation

Chlorine-35 and chlorine-37 are isotopes because they have the same number of protons (17), which defines them as chlorine, but differ in the number of neutrons (18 and 20, respectively). This difference in neutrons leads to different mass numbers.

If you were to create an infographic distinguishing elements from compounds, which example pair correctly shows a pure element and a compound?

• Air and milk

• Bronze and vinegar

• Gold and water

• Salt and air

Answer explanation

Gold is a pure element, while water is a compound made of hydrogen and oxygen. The other options either contain mixtures or do not correctly represent an element and a compound.

If you were creating a classroom poster showing Mendeleev’s arrangement, which guiding principle should you display?

• Grouped elements alphabetically

• Arranged elements by atomic number

• Arranged elements by color and density

• Arranged elements by increasing atomic mass and recurring properties

Answer explanation

Mendeleev arranged elements by increasing atomic mass and noted recurring properties, which helped predict the existence of undiscovered elements. This principle is key to understanding his periodic table.

Imagine you are designing a color-coded periodic table for your classroom. Which grouping best highlights metallic properties?

• Alternating rows by color

• Random colors for each group

• Red for nonmetals, blue for metalloids, yellow for metals

• Metals on the left, nonmetals on the right, metalloids along the zigzag line

Answer explanation

The correct choice organizes the periodic table by placing metals on the left, which emphasizes their metallic properties, while nonmetals are on the right and metalloids along the zigzag line, clearly distinguishing these groups.

If your science club creates a 3D model of an atom, what feature should be emphasized to represent chemical reactivity?

• The innermost electron shells

• The nucleus with protons and neutrons

• The relative atomic mass of each element

• The outermost energy level containing valence electrons

Answer explanation

To represent chemical reactivity, emphasize the outermost energy level containing valence electrons, as these electrons are involved in bonding and reactions, determining how an atom interacts with others.

When two elements are placed in the same group of the periodic table, what can you infer about their Lewis dot structures?

• Their chemical reactivity is unrelated.

• Their symbols will appear side by side.

• They have the same number of valence electrons.

• They have a different number of valence electrons.

Answer explanation

When elements are in the same group of the periodic table, they have the same number of valence electrons, which is reflected in their Lewis dot structures. This similarity influences their chemical properties.

A student argues that the nucleus of an atom has the least importance since electrons determine behavior. Evaluate this statement.

• Correct, because electrons orbit freely.

• Incorrect, because protons have no charge.

• Correct, because electrons are farther from the nucleus.

• Incorrect, because the nucleus defines the atom’s identity through its protons.

Answer explanation

The statement is incorrect because the nucleus, containing protons and neutrons, defines the atom's identity. Protons determine the element, while electrons influence behavior, but the nucleus is crucial for the atom's fundamental properties.

What is the common characteristic among all isotopes of a given element?

• Same number of neutrons

• Same number of protons

• Same atomic mass

• Same number of electrons in each shell

Answer explanation

All isotopes of a given element have the same number of protons, which defines the element itself. They differ in the number of neutrons, leading to different atomic masses.