Question 1

Which statement best describes Dalton’s Atomic Theory as originally proposed?

Accepted Answer

Atoms are indivisible particles that cannot be created or destroyed in chemical reactions.

Question 2

According to the Law of Definite Composition, which of the following is true for a pure chemical compound?

Accepted Answer

It always contains the same elements in the same proportion by mass.

Question 3

A sample of water is decomposed into hydrogen and oxygen. If 18 g of water produces 2 g of hydrogen and 16 g of oxygen, which law does this experiment illustrate?

Accepted Answer

Law of Conservation of Mass

Question 4

Which of the following discoveries led to the modification of Dalton’s Atomic Theory?

Accepted Answer

Discovery of the electron, proton, and neutron

Question 5

Which experiment provided evidence for the existence of negatively charged particles in atoms?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 6

What is the charge and relative mass of a proton?

Accepted Answer

Charge: $$+1$$, Relative mass: $$1$$

Question 7

Which of the following best describes the nucleus of an atom?

Accepted Answer

It is small, dense, and contains protons and neutrons.

Question 8

An isotope of carbon has 6 protons and 8 neutrons. What is its mass number and how is it represented?

Accepted Answer

Mass number: $$14$$, Representation: $$^{14}\mathrm{C}$$

Question 9

Which of the following is true about ions?

Accepted Answer

Anions have more electrons than protons.

Question 10

If an atom has an atomic number $$Z = 17$$ and a mass number $$A = 35$$, how many neutrons does it have?

Accepted Answer

$$18$$

Question 11

Which scientist is credited with discovering the neutron?

Accepted Answer

James Chadwick

Question 12

What is the average atomic mass of an element with two isotopes: $$^{10}\mathrm{X} (20$$% abundance, mass = 10 u) and $$^{11}\mathrm{X} (80$$% abundance, mass = 11 u)?

Accepted Answer

$$10.8\ \mathrm{u}$$

Question 13

Which of the following best explains why atoms are electrically neutral?

Accepted Answer

The number of protons equals the number of electrons.

Question 14

Which model of the atom was described as 'positive pudding with electrons embedded'?

Accepted Answer

Thomson’s plum pudding model

Question 15

A molecule of carbon dioxide ($$\mathrm{CO}_2) $$contains how many atoms in total?

Accepted Answer

$$3$$

Question 16

Calculate the molecular mass of $$\mathrm{CO}_2$$ using the atomic masses: C = $$12.01\ \mathrm{u}$$, O = $$16.00\ \mathrm{u}.$$

Accepted Answer

$$44.01\ \mathrm{u}$$

Question 17

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 18

Which of the following best describes the space outside the nucleus in an atom?

Accepted Answer

It is mostly empty space populated by electrons.

Question 19

If a sodium atom ($$Z = 11) $$loses one electron, what is the resulting ion called and what is its charge?

Accepted Answer

Cation, $$+1$$

Question 20

Which instrument is used to measure the relative atomic mass of atoms?

Accepted Answer

Mass spectrometer

Atoms and Elements: Foundations of Atomic Theory

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