Question

Which element corresponds to each of the following electron configurations? (a) $1s^{2}2s^{2}2p^5$ (b) $1s^{2}2s^{2}2p^{6}3s^{2}3p^6$ (c) $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^5$ (d) $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^5$

Short answer

(a) Fluorine (F), (b) Argon (Ar), (c) Technetium (Tc), (d) Iodine (I)

Step-by-step solution

Analyzing Configuration (a)

The electron configuration is $1s^{2}2s^{2}2p^5$. Count the total number of electrons: $2+2+5=9$. The element with 9 electrons is fluorine (F).

Analyzing Configuration (b)

The electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^6$. Count the electrons: $2+2+6+2+6=18$. The element with 18 electrons is argon (Ar).

Analyzing Configuration (c)

The electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^5$. Count the electrons: $2+2+6+2+6+2+10+6+2+5=43$. The element with 43 electrons is technetium (Tc).

Analyzing Configuration (d)

The electron configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^5$. Count the electrons: $2+2+6+2+6+2+10+6+2+10+5=53$. The element with 53 electrons is iodine (I).

Key concepts

Atomic Structure

Atoms are the building blocks of matter and fundamentally determine the structure and behavior of everything around us. Understanding atomic structure is like having a key to unlock the secrets of chemistry. At the heart of an atom lies the nucleus, which is made up of protons and neutrons.

• Protons: Positively charged particles that define the element's identity.
• Neutrons: Neutral particles that add mass but do not affect the chemical properties.

Outside the nucleus, electrons race around in orbitals, creating electron clouds. These negatively charged particles define how an atom will chemically bond and react with others.
The arrangement of electrons within these orbitals is not random but structured according to specific energy levels.
The principal energy levels (shells) are represented by numbers (e.g., 1, 2, 3), and within each shell, electrons occupy subshells (s, p, d, f) according to the rules defined by quantum mechanics. This distribution of electrons into shells and subshells is what we call the electron configuration.

Periodic Table

The periodic table is a comprehensive map of all known elements, designed to reflect their atomic structures and properties. Each element on this table is like a card in a perfectly ordered deck, arranged by increasing atomic number, which is the number of protons in an atom's nucleus. The periodic table's rows, known as periods, and columns, known as groups, help us understand patterns in elemental behavior.

• Periods: Elements are ordered from left to right by increasing atomic number. Moving across a period, properties such as electronegativity and ionization energy generally increase.
• Groups: Vertical columns that gather elements with similar chemical and physical properties, often because they hold the same number of valence electrons (the electrons in the outermost shell).

Notably, trends within the periodic table allow us to predict chemical reactions and element properties by simply referring to an element's position. It's like understanding a language of chemistry, where placing your finger on the correct 'word' leads to understanding an element's 'meaning' or behavior.

Element Identification

Every element is unique, defined by its distinct atomic structure. Element identification often involves using the electron configuration to determine which element is present. To identify an element, count the total number of electrons in the electron configuration, as this number equals the atomic number or number of protons in a neutral atom.For example, take the electron configuration $1s^{2}2s^{2}2p^5$, which adds up to 9 electrons. This means the atom is fluorine, the element with 9 protons in the periodic table.

• Identifying elements via electron configuration is a straightforward process of matching the electron count to atomic numbers on the periodic table.
• This method not only allows for identification but also provides insight into chemical properties and potential reactivity as the electron configuration indicates the distribution of electrons available for bonding.

By mastering electron configurations, students gain the skill to recognize elements and predict chemical behaviors effectively, making chemistry a hands-on and interactive subject.