$$(0.60 \times 10) + (0.40 \times 12) = 6 + 4.8 = 10.8$$ amu

$$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 26.50 + 8.96 = 35.46$$ amu

Question 1

Which statement best explains why a single pebble contains more atoms than you could count?

Accepted Answer

Atoms are so small that even a tiny object contains an enormous number of them.

Question 2

According to Dalton’s atomic theory, which of the following is NOT true?

Accepted Answer

Atoms of a given element can have different masses.

Question 3

Which experiment led to the discovery that atoms have a dense nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 4

What is the charge of an ion with 12 protons and 10 electrons?

Accepted Answer

$$12 - 10 = 2^+$$

Question 5

Which property is NOT typical of metals?

Accepted Answer

They tend to gain electrons during chemical changes.

Question 6

Which of the following elements is a metalloid and is widely used in electronics?

Accepted Answer

Silicon

Question 7

What is the atomic number ($$Z) of an $$element with 17 protons?

Accepted Answer

$$Z = 17$$

Question 8

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

Accepted Answer

11 electrons

Question 9

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

Accepted Answer

They have different numbers of neutrons.

Question 10

Calculate the atomic mass of an element with two isotopes: 60% $$A ($$mass = 10 amu) and 40% $$B ($$mass = 12 amu).

Accepted Answer

$$(0.60 	imes 10) + (0.40 	imes 12) = 6 + 4.8 = 10.8$$ amu

Question 11

Which group in the periodic table contains the noble gases?

Accepted Answer

Group 8A

Question 12

What is the mass number ($$A) of an $$isotope with 6 protons and 8 neutrons?

Accepted Answer

$$A = 6 + 8 = 14$$

Question 13

Which of the following is a correct isotope symbol for neon with 10 protons and 12 neutrons?

Accepted Answer

$$^{22}_{10}Ne$$

Question 14

Which of the following elements is most likely to form a $$1^+$$ ion?

Accepted Answer

Sodium (Na)

Question 15

Which statement about electrical charge is correct?

Accepted Answer

Positive and negative charges attract each other.

Question 16

A sample of chlorine contains 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu). What is the atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 26.50 + 8.96 = 35.46$$ amu

Question 17

Which of the following is a real-world application of a radioactive isotope?

Accepted Answer

Technetium-99 is used in medical imaging to diagnose disease.

Question 18

Which of the following best describes the distribution of mass in an atom?

Accepted Answer

Most of the mass is concentrated in the nucleus, which occupies a tiny fraction of the atom's volume.

Question 19

Which scientist is credited with arranging the periodic table by increasing atomic mass and observing recurring properties?

Accepted Answer

Dmitri Mendeleev

Atoms and Elements: Foundations of Matter

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