Question 1

Which of the following statements best explains why different elements have different chemical properties?

Accepted Answer

Because each element has a unique number of protons, which determines its atomic structure and properties.

Question 2

According to Dalton’s Atomic Theory, which of the following is FALSE?

Accepted Answer

Atoms of a given element can have different numbers of neutrons.

Question 3

Which scientist is credited with discovering the electron?

Accepted Answer

J.J. Thomson

Question 4

A neutral atom of sodium ($$Na) $$has an atomic number of 11. How many electrons does it have?

Accepted Answer

$$11$$

Question 5

Which of the following best describes the Law of Conservation of Mass?

Accepted Answer

Atoms are neither created nor destroyed in chemical reactions.

Question 6

Which subatomic particle has the least mass?

Accepted Answer

Electron

Question 7

An atom has 17 protons, 18 neutrons, and 17 electrons. What is its mass number ($$A$$)?

Accepted Answer

$$35$$

Question 8

Which of the following ions has 12 protons and 10 electrons? What is its symbol?

Accepted Answer

$$Mg^{2+}$$

Question 9

Which of the following pairs of ions have the same number of electrons?

Accepted Answer

$$Cl^-$$ 	ext{ and } Br^-$

Question 10

Which of the following statements about metals is TRUE?

Accepted Answer

Metals tend to lose electrons during chemical changes.

Question 11

Which of the following best describes the Bohr model of the atom?

Accepted Answer

Electrons orbit the nucleus in defined energy levels.

Question 12

A certain isotope of carbon has 6 protons and 8 neutrons. What is its atomic mass number ($$A$$)?

Accepted Answer

$$14$$

Question 13

Which of the following is the correct relationship between wavelength ($$\lambda$$), frequency ($$
u$$), and the speed of light ($$c$$)?

Accepted Answer

$$c = \lambda 
u$$

Question 14

Which type of electromagnetic radiation has the highest energy photons?

Accepted Answer

Gamma rays

Question 15

If an atom has 15 protons, 16 neutrons, and 18 electrons, what is the symbol for this ion?

Accepted Answer

$$P^{3-}$$

Question 16

Which of the following best explains why the emission spectrum of hydrogen contains only specific wavelengths?

Accepted Answer

Electrons in hydrogen atoms can only occupy certain energy levels, so they emit photons of specific energies when transitioning between these levels.

Question 17

Which of the following is a property of nonmetals?

Accepted Answer

They tend to gain electrons during chemical changes.

Question 18

A sample contains $$2.0 	imes 10$$^{23}$$ atoms of magnesium (Mg$). How many moles of magnesium are present? (1$ mole = 6.022$$ 	imes $$10^{23}$$ atoms)

Accepted Answer

$$0.33$$ 	ext{ moles}$

Question 19

Which of the following best describes the difference between isotopes of the same element?

Accepted Answer

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

Question 20

Which of the following equations correctly expresses the energy ($$E) of a $$photon in terms of Planck’s constant ($$h) $$and frequency ($$
u$$)?

Accepted Answer

$$E = h 
u$$

Atoms and Elements: Foundations of Chemistry

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