Q: A chlorine atom has two main isotopes: $$^{35}Cl (75$$% abundance) and $$^{37}Cl (25$$% abundance). What is the average atomic mass of chlorine?

$$35 \times 0.75 + 37 \times 0.25 = 35.5$$

Question 1

Which of the following best describes the difference between an element and a compound?

Accepted Answer

An element is a substance that contains only one type of atom, while a compound is a substance composed of two or more different types of atoms chemically bonded together.

Question 2

Which of the following is a heterogeneous mixture?

Accepted Answer

Sand and water

Question 3

Which experiment led to the discovery that atoms have a small, dense, positively charged nucleus?

Accepted Answer

Rutherford's gold foil experiment

Question 4

A neutral atom of potassium has an atomic number of 19 and a mass number of 39. How many neutrons does it have?

Accepted Answer

$$39 - 19 = 20$$ neutrons

Question 5

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 6

Which of the following best explains why burning fossil fuels can lead to acid rain?

Accepted Answer

Burning fossil fuels releases sulfur compounds, which react with water in the atmosphere to form acids.

Question 7

Which of the following is the correct electron arrangement for a neutral sodium atom ($$Na$$, atomic number 11) according to the Bohr model?

Accepted Answer

2 electrons in the first shell, 8 in the second, 1 in the third: $$2, 8, 1$$

Question 8

Which of the following is a correct chemical formula for an ionic compound formed between magnesium and chlorine?

Accepted Answer

$$MgCl_2$$

Question 9

A sample contains only $$S_8$$ molecules. Which classification best describes this sample?

Accepted Answer

Element

Question 10

Which of the following best describes the process of bioaccumulation of heavy metals in fish?

Accepted Answer

Heavy metal atoms accumulate in the tissues of fish over time, potentially causing toxic effects in organisms that consume the fish.

Question 11

Which of the following is a correct statement about the periodic table?

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 12

Which of the following is a polyatomic ion?

Accepted Answer

$$OH^-$$

Question 13

Which of the following best describes a cation?

Accepted Answer

A positively charged ion formed by removing electron(s) from an atom.

Question 14

Which of the following is the correct formula for aluminum sulfate?

Accepted Answer

$$Al_2$$($$SO_4)_3$

Question 15

A chlorine atom has two main isotopes: $$^{35}Cl (75$$% abundance) and $$^{37}Cl (25$$% abundance). What is the average atomic mass of chlorine?

Accepted Answer

$$35 	imes 0.75 + 37 	imes 0.25 = 35.5$$

Question 16

Which of the following best describes the difference between a molecule and a compound?

Accepted Answer

A molecule is two or more atoms joined in a specific arrangement, while a compound is a molecule that contains at least two different types of atoms.

Question 17

Which of the following is a real-world example of a homogeneous mixture?

Accepted Answer

Salt dissolved in water

Question 18

Which of the following statements about Bohr’s atomic model is correct?

Accepted Answer

Electrons orbit the nucleus in specific shells, and moving between shells requires absorption or release of energy.

Question 19

Which of the following is the correct chemical formula for iron(III) oxide?

Accepted Answer

$$Fe_2O_3$$

Question 20

Which of the following best explains why helium was first discovered in the Sun before it was found on Earth?

Accepted Answer

Helium was identified by its unique spectrum in sunlight, which did not match any known element on Earth.

Atoms, Elements, and Atomic Structure: General Chemistry Study Notes

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