Q: Calculate the atomic mass of chlorine given the following isotope data: $^{35}$Cl (75.77%, 34.97 u) and $^{37}$Cl (24.23%, 36.97 u).

$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45\ \mathrm{u}$

Q: What is Avogadro’s number and what does it represent?

$6.022 \times 10^{23}$, the number of units (atoms, molecules, etc.) in one mole of substance

Q: How many atoms are present in $2.00\ \mathrm{mol}$ of carbon?

$2.00 \times 6.022 \times 10^{23} = 1.2044 \times 10^{24}$ atoms

Q: A sample contains $3.00\ \mathrm{mol}$ of sodium atoms. What is the mass of sodium in the sample? (Atomic mass of Na = $22.99\ \mathrm{g/mol}$)

$3.00 \times 22.99 = 68.97\ \mathrm{g}$

Question 1

Which instrument is capable of imaging individual atoms on conductive surfaces, and what principle does it use to achieve atomic resolution?

Accepted Answer

Scanning Tunneling Microscope (STM), which uses tunneling current sensitive to tip height changes.

Question 2

According to the law of conservation of mass, what will be the total mass of products if 7.7 g of Na(s) reacts completely with 11.9 g of Cl$_2$(g) to form NaCl(s)?

Accepted Answer

$19.6\ \mathrm{g}$

Question 3

Which statement best describes the law of definite proportions?

Accepted Answer

All samples of a given compound have the same proportion by mass of their constituent elements.

Question 4

A sample of water decomposes to give 3.0213 g of hydrogen and 23.9787 g of oxygen. What is the mass ratio of oxygen to hydrogen in this sample?

Accepted Answer

$\frac{23.9787}{3.0213} = 7.94$

Question 5

Which of the following is NOT a postulate of Dalton’s atomic theory?

Accepted Answer

Atoms can be divided into protons, neutrons, and electrons.

Question 6

Which subatomic particle has a mass of approximately $1.00727\ \mathrm{u}$ and a charge of $+1.60218 	imes 10^{-19}\ \mathrm{C}$?

Accepted Answer

Proton

Question 7

An atom of fluorine (F) gains one electron. What is the resulting ion called and what is its charge?

Accepted Answer

Anion, with a $-1$ charge

Question 8

Calculate the atomic mass of chlorine given the following isotope data: $^{35}$Cl (75.77%, 34.97 u) and $^{37}$Cl (24.23%, 36.97 u).

Accepted Answer

$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45\ \mathrm{u}$

Question 9

What is Avogadro’s number and what does it represent?

Accepted Answer

$6.022 	imes 10^{23}$, the number of units (atoms, molecules, etc.) in one mole of substance

Question 10

How many atoms are present in $2.00\ \mathrm{mol}$ of carbon?

Accepted Answer

$2.00 	imes 6.022 	imes 10^{23} = 1.2044 	imes 10^{24}$ atoms

Question 11

Which group in the periodic table contains elements that are very reactive and tend to lose one electron to form $+1$ ions?

Accepted Answer

Alkali metals (Group 1)

Question 12

Which of the following best describes a metalloid?

Accepted Answer

An element with properties intermediate between metals and nonmetals, often a semiconductor.

Question 13

A sample contains $3.00\ \mathrm{mol}$ of sodium atoms. What is the mass of sodium in the sample? (Atomic mass of Na = $22.99\ \mathrm{g/mol}$)

Accepted Answer

$3.00 	imes 22.99 = 68.97\ \mathrm{g}$

Question 14

Which of the following elements is a main-group element?

Accepted Answer

Magnesium (Mg)

Question 15

Which element is most likely to exist as a diatomic molecule and also form an anion with a $-1$ charge?

Accepted Answer

Chlorine (Cl)

Question 16

What is the charge and composition of a sodium cation (Na$^+$)?

Accepted Answer

11 protons, 10 electrons, $+1$ charge

Question 17

Which of the following statements about noble gases is correct?

Accepted Answer

They are very stable and unreactive gases.

Question 18

A mass spectrometer separates ions based on which property?

Accepted Answer

Mass-to-charge ratio ($\frac{m}{z}$)

Question 19

Which of the following is a correct statement about the nucleus of an atom?

Accepted Answer

It is very dense and contains protons and neutrons.

Atoms and Elements: Structure, Laws, and the Periodic Table

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