Atomic Structure and Electronic Configuration

Flashcards covering fundamental atomic structure, subatomic particle properties, isotopes, chemical formulas, quantum numbers, and electron configuration principles (Aufbau, Pauli exclusion, and Hund's rule) for CHM 101.

What is the definition of an atom?

The smallest unit of matter that retains the properties of an element, composed of three fundamental subatomic particles: protons, neutrons, and electrons.

What are the charges, approximate masses in atomic mass units, and locations of protons, neutrons, and electrons within an atom?

Proton ($p^+$): charge $+1$, mass $1.0073\,\text{amu}$, located inside the nucleus; Neutron ($n^0$): charge $0$, mass $1.0087\,\text{amu}$, located inside the nucleus; Electron ($e^-$): charge $-1$, mass $\sim 1/1836\,\text{amu}$, located outside the nucleus in energy levels or shells.

What is the equivalent mass of $1\,\text{amu}$ in grams, and how many electrons equal the mass of $1$ proton?

$1\,\text{amu} = 1.66 \times 10^{-24}\,\text{g}$, and the mass of $1\,\text{proton}$ equals $1{,}836\,\text{electrons}$.

How do the physical diameters of an atom and its nucleus compare according to atomic scale analogies?

An atom has a diameter of approximately $10^{-10}\,\text{m}$ and its nucleus has a diameter of approximately $10^{-15}\,\text{m}$. If an atom were expanded to the size of a football stadium, the nucleus would be the size of a single blueberry.

What is the atomic number ($Z$) of an element, and what does it equal in a neutral atom?

The atomic number ($Z$) is the number of protons present in an atom's nucleus. It determines the identity and periodic table position of the element. In a neutral atom, it also equals the number of electrons.

What is the mass number ($A$) of an atom, and how is it determined?

The mass number ($A$) is the total number of protons and neutrons in the nucleus. It is calculated by the formula: $\text{Mass Number }(A) = \text{Number of Protons }(Z) + \text{Number of Neutrons}$.

Why is only the first letter of a chemical symbol capitalized?

To avoid confusion between elemental symbols and chemical compounds, such as distinguishing cobalt ($\text{Co}$) from carbon monoxide ($\text{CO}$).

From which Latin words do the chemical symbols for gold ($\text{Au}$), iron ($\text{Fe}$), lead ($\text{Pb}$), and potassium ($\text{K}$) derive?

Gold ($\text{Au}$) derives from aurum (for Aurora, the goddess of dawn); iron ($\text{Fe}$) derives from ferrum; lead ($\text{Pb}$) derives from plumbum; and potassium ($\text{K}$) derives from kalium.

What is the fundamental difference between a molecular formula and a structural formula?

A molecular formula shows the actual number of atoms of each element in a molecule without showing structural layout, whereas a structural formula shows how the atoms are connected or bonded to each other.

In this diagram of methane, what four representations are depicted from (a) through (d)?

(a) Molecular formula, (b) structural formula, (c) ball-and-stick model, and (d) space-filling model.

What are the molecular formula and empirical formula of the acetic acid found in vinegar?

The molecular formula of acetic acid is $\text{C}_2\text{H}_4\text{O}_2$, and its empirical formula is $\text{CH}_2\text{O}$.

What are isotopes, and how do their chemical and physical properties compare?

Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons (same atomic number, different mass numbers). They have identical chemical properties, but differ in physical properties such as stability or radioactivity.

What formula defines the maximum electron capacity of a principal energy shell ($n$), and what are the capacities for shells $n = 1, 2, 3,$ and $4$?

The maximum capacity is given by $2n^2$: $K$ ($n=1$) holds $2$ electrons, $L$ ($n=2$) holds $8$ electrons, $M$ ($n=3$) holds $18$ electrons, and $N$ ($n=4$) holds $32$ electrons.

How many orbitals and maximum electrons are found in the $s$, $p$, $d$, and $f$ subshells?

Subshell $s$ ($l=0$): $1$ orbital, max $2$ electrons; subshell $p$ ($l=1$): $3$ orbitals, max $6$ electrons; subshell $d$ ($l=2$): $5$ orbitals, max $10$ electrons; subshell $f$ ($l=3$): $7$ orbitals, max $14$ electrons.

What are the four quantum numbers and what property does each describe?

Principal quantum number ($n$): defines energy level; Azimuthal quantum number ($l$): determines orbital shape; Magnetic quantum number ($m_l$): specifies spatial orientation; Spin quantum number ($m_s$): describes intrinsic angular momentum ($+1/2$ or $-1/2$).

What does the Aufbau principle dictate regarding electronic configurations?

Electrons first occupy orbitals of the lowest available energy and only enter higher energy orbitals once lower ones are completely filled ($n+l$ rule), following the sequence: $1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \dots$

What principle and electronic filling scheme are illustrated in this diagram?

The Aufbau principle, showing the order of subshell filling by increasing energy based on the diagonal rule.

What is the Pauli exclusion principle?

No two electrons in the same atom can have the same set of four quantum numbers; therefore, an orbital can hold a maximum of two electrons, and they must have opposite spins ($\uparrow$ and $\downarrow$).

Which electronic configuration rule explains why the middle pair of electron spins is correct while the top and bottom pairs are incorrect?

The Pauli exclusion principle, which dictates that two electrons occupying the same orbital must have opposite spins to minimize repulsion.

What does Hund's rule ('Bus Seat Rule') state about placing electrons in degenerate orbitals?

When electrons occupy orbitals of equal energy (degenerate orbitals), one electron enters each orbital singly with parallel spins before any orbital receives a second electron, minimizing electron repulsion.

Which orbital filling rule is demonstrated as being correctly applied in the top diagram and violated in the bottom diagram?

Hund's rule, which states that electrons must occupy degenerate orbitals singly before pairing up.

What is the full electronic configuration of calcium ($Z = 20$), and why does its last subshell fill at $4s$ rather than $3d$?

Calcium's electronic configuration is $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2$ (or $[\text{Ar}] 4s^2$). It fills the $4s$ subshell before $3d$ because the $4s$ orbital has lower energy than the $3d$ orbital.

How many neutrons are contained in an atom of $^{40}_{18}\text{Ar}$?

$22$ neutrons, calculated as: $\text{Mass Number } (40) - \text{Atomic Number } (18) = 22$.

If an atom has $11$ protons and $10$ electrons, what species is it and what is its net charge?

It is a cation with a $+1$ charge (specifically a sodium cation, $\text{Na}^+$).