Unit 1: Introduction to Moles, Molar Mass, Atomic Structure, and Periodic Trends

Flashcards covering Unit 1 topics including moles, molar mass, stoichiometry, empirical/molecular formulas, percent composition, atomic structure, isotopes, mass spectrometry, electron configuration, Coulomb's law, periodic trends, and photoelectron spectroscopy (PES).

What is a mole ($\text{mol}$) in chemistry, and what is Avogadro's number?

A mole is the fundamental unit used to quantify the amount of a substance. One mole contains exactly $6.022 \times 10^{23}$ particles, which is known as Avogadro's number.

How many atoms are present in $0.5\,\text{mole}$ of carbon?

$3.011 \times 10^{23}$ atoms

What is molar mass, and what are its standard units?

Molar mass is the mass of one mole of a substance, expressed in units of $g/mol$.

What is the molar mass of water ($H_2O$) given atomic masses $H = 1\,g/mol$ and $O = 16\,g/mol$?

$$18\,g/mol$$

What equation relates the number of moles ($n$), mass ($m$), and molar mass ($M$)?

$$n = \frac{m}{M}$$

How many moles are present in a $10\,g$ sample of Aluminum ($Al = 27\,g/mol$)?

$$0.37\,\text{mole}$$

How many grams are present in $3\,\text{moles}$ of $NaCl$ ($M = 58.45\,g/mol$)?

$$175.35\,g$$

Which subatomic particles reside in the atomic nucleus, and which orbit the nucleus?

Protons (positive charge) and neutrons (no charge) reside in the nucleus at the center, while electrons (negative charge) orbit the nucleus.

How does an atom become a negatively or positively charged ion?

An atom becomes negatively charged when it gains electrons, and positively charged when it loses electrons.

On a standard periodic table key entry, what information do the number at the top and the number at the bottom represent?

The top number is the atomic number ($Z$, number of protons) and the bottom number is the average atomic mass ($A$).

What are isotopes?

Isotopes are atoms of the same element that have the same number of protons (same atomic number) but a different number of neutrons (different mass number). They share identical chemical properties but differ in physical properties.

What is mass spectrometry (MS) used for, and what specific ratio does it measure?

Mass spectrometry is a technique used to determine the mass of atoms or molecules and identify isotopes by measuring the mass-to-charge ratio ($m/z$) of ions.

Based on this mass spectrum showing isotope peaks at $m/z = 10$ and $m/z = 11$, which element is represented?

Boron ($B$), because the weighted average atomic mass is approximately $10.8\,g/mol$.

Which element's mass spectrum is represented by these peak abundances between $m/z = 92$ and $m/z = 100$?

Molybdenum ($Mo$)

What is an empirical formula?

The simplest whole-number ratio of atoms of each element in a compound.

What is the relationship between the molecular formula and the empirical formula of a compound?

$\text{Molecular Formula} = (\text{Empirical Formula})_n$, where $n = \frac{\text{molar mass of molecular formula}}{\text{molar mass of empirical formula}}$.

If Caffeine has an empirical formula of $C_4H_5N_2O$ and its molecular molar mass is $194\,g/mol$, what is its molecular formula?

$$C_8H_{10}N_4O_2$$

What is the formula for calculating the percent composition by mass of an element in a compound?

$$\% \text{ by mass of an element} = \frac{\text{mass of that element in 1 mole of compound}}{\text{molar mass of the compound}} \times 100$$

What is the percent by mass of nitrogen in $NH_4NO_3$ ($M = 80\,g/mol$)?

$$35\%$$

What is the maximum electron capacity for each of the $s$, $p$, $d$, and $f$ subshells?

$s \rightarrow 2\text{ electrons}$, $p \rightarrow 6\text{ electrons}$, $d \rightarrow 10\text{ electrons}$, $f \rightarrow 14\text{ electrons}$.

Following the Aufbau filling order shown in this chart, what is the full electron configuration of Sulfur (atomic number $16$)?

$$1s^2 2s^2 2p^6 3s^2 3p^4$$

When forming transition-metal cations, from which energy level are electrons removed first?

Electrons are removed from the orbital with the highest principal energy level first (for example, $4s$ electrons are removed before $3d$ electrons).

What is Coulomb's Law formula, and what relationship does it describe between charged particles?

$F = \frac{k(q_1)(q_2)}{r^2}$. It states that electrostatic force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

How do atomic radius, first ionization energy, and electronegativity change across a period (left to right)?

Across a period, atomic radius decreases, while first ionization energy and electronegativity increase.

What is the difference between valence electrons and core electrons, and why are valence electrons easier to remove?

Valence electrons are in the outermost shell, while core electrons are in inner shells. Due to Coulomb's Law, greater distance from the nucleus reduces attractive force, making valence electrons easier to remove than core electrons.

In Photoelectron Spectroscopy (PES), what do the height and position of each peak represent?

The height of a peak represents the number of electrons in that subshell, and the position of a peak represents the binding energy (ionization energy) of those electrons.

In this Photoelectron Spectrum (PES) of Silicon, which subshell corresponds to the tallest peak at energy $10.3\,\text{MJ/mol}$?

The $2p^6$ subshell (containing 6 electrons).