Atomic Structure, Isotopes, Electron Configuration, and Ionisation Energy

Comprehensive practice flashcards covering subatomic particles, isotopic abundance, quantum shells, subshell capacities, orbital geometries, principles of electronic configuration, and ionisation energy trends.

Where is most of the mass of an atom located, and which elementary particles reside there?

Most of the mass of the atom is in the nucleus, which contains positively charged protons and uncharged neutrons.

How do beams of protons, electrons, and neutrons behave when passed through an electric field?

Beams of protons and electrons are deflected by electric fields, whereas neutrons are not deflected.

In the isotopic notation shown for Boron, what do the numbers $11$ and $5$ indicate?

The top number ($11$) is the nucleon number (mass number, $A$), and the bottom number ($5$) is the proton number (atomic number, $Z$).

How is the number of neutrons in an atom calculated from its nucleon number ($A$) and proton number ($Z$)?

The number of neutrons is found by subtracting the proton number from the nucleon number: $\text{Number of neutrons} = A - Z$.

How does the count of protons compare to electrons in a neutral atom, a positive ion, and a negative ion?

In a neutral atom, the number of electrons equals the number of protons. When there are more protons than electrons, a positive ion is formed; when there are more electrons than protons, a negatively charged ion is formed.

What is the definition of isotopes?

Isotopes are atoms of the same element with the same atomic number but different nucleon numbers; they only differ in the number of neutrons they contain.

Identify the three isotopes of hydrogen shown in the diagram and state the number of protons and neutrons in each.

Protium ($^1_1\text{H}$) has $1$ proton and $0$ neutrons; deuterium ($^2_1\text{H}$) has $1$ proton and $1$ neutron; tritium ($^3_1\text{H}$) has $1$ proton and $2$ neutrons.

What is meant by isotopic abundance?

Isotopic abundance is the percentage of atoms of a particular isotope that naturally occur in a sample of an element.

What mathematical expression is used to calculate relative atomic mass from isotopic abundances and masses?

$$\text{Relative atomic mass} = \frac{(m_1 \times \text{abundance}_1) + (m_2 \times \text{abundance}_2)}{100}$$

How are principal energy levels designated, and which shell is located closest to the nucleus?

Main energy levels (shells) are given principal quantum numbers $n = 1, 2, 3, 4$, with the lowest energy level ($n = 1$) being closest to the nucleus.

How many orbitals are found in the $s$, $p$, and $d$ subshells, and what is the maximum electron capacity of each subshell?

Subshells $s$, $p$, and $d$ contain $1$, $3$, and $5$ orbitals respectively, and can hold a maximum of $2$, $6$, and $10$ electrons respectively.

What is an atomic orbital, and how many electrons can occupy a single orbital?

An orbital is the region of space in which an electron is likely to be found; each orbital can hold a maximum of two electrons.

Based on the provided illustration, what are the characteristic shapes of $s$, $p$, $d$, and $f$ orbitals?

$s$ orbitals are spherical; $p$ orbitals have two lobes (dumbbell-shaped); $d$ orbitals typically feature four-lobed cloverleaf geometries (with one having a central ring); and $f$ orbitals possess complex multi-lobed structures.

What does the Pauli exclusion principle dictate regarding electrons sharing the same orbital?

An orbital can contain a maximum of $2$ electrons, and they must have opposite spins (be paired).

What is the Aufbau principle?

The Aufbau principle states that electrons are added to orbitals starting from those in the lowest energy level first.

What rule governs how electrons occupy degenerate orbitals within the same subshell according to Hund's rule?

Electrons fill orbitals of the same energy singly first with parallel spins, before they pair up.

What does it mean if two species are described as isoelectronic?

They share the exact same electronic configuration.

How does an element's electron configuration relate to its position (period and block) in the periodic table?

The period corresponds to the highest principal energy level ($n$), and the block ($s$, $p$, $d$, or $f$) is determined by the subshell where the last electron is placed.

What is the formal definition of the 1st ionisation energy of an element?

The 1st ionisation energy of an element is the energy needed to remove one electron from each atom in one mole of atoms of the element in the gaseous state (to form gaseous $1+$ ions).

What four factors govern the magnitude of an element's ionisation energy?

1. The distance of the electron from the nucleus; 2. The number of positive charges in the nucleus; 3. The degree of shielding of outer electrons by inner electron shells; 4. Spin-pair repulsion.

What is the general trend in first ionisation energy down a group, and why?

First ionisation energy decreases down a group because the distance between the nucleus and outer electrons increases and inner shell shielding increases, causing outer electrons to be less strongly attracted to the protons.

What is the general trend in first ionisation energy across a period from left to right, and why?

First ionisation energy increases across a period because the number of protons (positive nuclear charge) increases while shielding remains similar, pulling the electrons more tightly toward the nucleus.

Why does oxygen have a lower first ionisation energy than nitrogen, contrary to the general period trend?

Oxygen has a pair of electrons in one $2p$ orbital ($1s^2\,2s^2\,2p^4$) whereas nitrogen has three singly occupied $2p$ orbitals ($1s^2\,2s^2\,2p^3$); the spin-pair repulsion between paired electrons in oxygen makes it easier to remove one electron.