Q: How many atoms are present in 24.02 grams of carbon? (Molar mass of carbon = 12.01 g/mol, Avogadro's number $$= 6.022 \times 10$$^{23}$$)

$$2 \times 6.022 \times 10$$^{23}$$ = 1.2044 \times 10$$^{24}$$ atoms

Q: A metal surface has a binding energy of $$2.0 \times 10$$^{-19}$$ J. If it is irradiated with light of frequency 1.0$$ \times $$10^{15} Hz$$ ($$h = 6.626 \times 10$$^{-34}$$ J·s), what is the maximum kinetic energy of the emitted electron?

$$6.626 \times 10$$^{-19}$$ - 2.0 \times 10$$^{-19}$$ = 4.626 \times 10$$^{-19}$$ J

Question 1

Which of the following best illustrates the law of multiple proportions as described by John Dalton?

Accepted Answer

When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a simple whole-number ratio.

Question 2

Given that carbon monoxide (CO) has a mass ratio of oxygen to carbon of 1.33:1 and carbon dioxide (CO$$_2) $$has a ratio of 2.67:1, what is the ratio of the masses of oxygen that combine with 1 g of carbon in these two compounds?

Accepted Answer

$$\frac{2.67}{1.33} = 2.01$$

Question 3

Which experiment led to the discovery of the electron and what was a key observation?

Accepted Answer

J.J. Thomson's cathode ray experiment; cathode rays were deflected by electric and magnetic fields, indicating they were negatively charged particles.

Question 4

According to Dalton's atomic theory, which statement is INCORRECT based on modern understanding?

Accepted Answer

Atoms of the same element have the same mass and other properties.

Question 5

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many protons, neutrons, and electrons does it have?

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 6

Which of the following statements about isotopes is TRUE?

Accepted Answer

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

Question 7

A lithium ion has 3 protons and 2 electrons. What is its charge and why?

Accepted Answer

$$+1$$; it has lost one electron, resulting in more protons than electrons.

Question 8

How many atoms are present in 24.02 grams of carbon? (Molar mass of carbon = 12.01 g/mol, Avogadro's number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$2 	imes 6.022 	imes 10$$^{23}$$ = 1.2044 	imes 10$$^{24}$$ atoms

Question 9

Which statement best describes the quantum mechanical model of the atom?

Accepted Answer

It describes electrons as existing in a cloud of probability rather than fixed orbits.

Question 10

Which equation correctly relates the energy of a photon to its frequency?

Accepted Answer

$$E = h 
u$$

Question 11

A metal surface has a binding energy of $$2.0 	imes 10$$^{-19}$$ J. If it is irradiated with light of frequency 1.0$$ 	imes $$10^{15} Hz$$ ($$h = 6.626 	imes 10$$^{-34}$$ J·s), what is the maximum kinetic energy of the emitted electron?

Accepted Answer

$$6.626 	imes 10$$^{-19}$$ - 2.0 	imes 10$$^{-19}$$ = 4.626 	imes 10$$^{-19}$$ J

Question 12

Which property of light determines its color in the visible spectrum?

Accepted Answer

Wavelength ($$\lambda)$$

Question 13

According to the Heisenberg uncertainty principle, which of the following is TRUE?

Accepted Answer

The more precisely the position of an electron is known, the less precisely its momentum can be known.

Question 14

Which of the following best explains why atomic emission spectra are unique for each element?

Accepted Answer

Each element has a unique set of energy levels, so the wavelengths of emitted light are unique.

Question 15

Which quantum number determines the energy level of an electron in an atom?

Accepted Answer

$$n$$

Question 16

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

Accepted Answer

$$-3$$; P$$^{3-}$$

Question 17

Which of the following best describes constructive interference in the context of wave behavior?

Accepted Answer

Two waves in phase combine to produce a wave with greater amplitude.

Question 18

Which statement about the Bohr model of the atom is correct?

Accepted Answer

Electrons emit radiation only when they jump from a higher to a lower energy orbit.

Question 19

Which formula correctly relates the speed of light ($$c$$), wavelength ($$\lambda$$), and frequency ($$
u$$)?

Accepted Answer

$$c = \lambda 
u$$

Question 20

Which of the following is a direct consequence of the wave-particle duality of electrons?

Accepted Answer

Electrons can produce interference patterns in a double-slit experiment.

Atoms and the Quantum-Mechanical Model: Foundations of Modern Chemistry

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