Atomic Structure and Electron Configuration

#Atoms: The Building Blocks of Matter ⚛️

Let's dive back into the world of atoms! Remember, they're incredibly tiny but incredibly important. Atoms are composed of three fundamental subatomic particles:

#Dalton's Atomic Theory

John Dalton's atomic theory lays the foundation for our understanding of atoms. Here are the key points:

1. Each element is made up of indivisible and indestructible atoms.
2. All atoms of a given element have identical properties.
3. Atoms combine in simple, whole-number ratios to form compounds.
4. Chemical reactions involve the rearrangement of atoms.

The structure of an atom: protons and neutrons in the nucleus, with electrons orbiting around it.

#Coulomb's Law

Coulomb's Law helps us understand the forces between charged particles, like those in an atom. The formula is:

$$F_e = k \frac{q_1q_2}{r^2}$$

Image Courtesy of APlusPhysics

#Breaking Down Coulomb's Law

• $F_e$ = Electric force between particles
• $k$ = Coulomb's constant
• $q_1$ and $q_2$ = Charges of the particles
• $r$ = Distance between the nuclei

#Understanding the Law

The strength of the force depends on:

1. Magnitude of charge: Greater charge = stronger attraction.
2. Distance: Closer particles = stronger attraction.

#The Atom: Electrons

Let's zoom in on electrons! Each element has a specific number of electrons, and how they're arranged is key to understanding chemical behavior.

#The Bohr Model

The Bohr model pictures electrons orbiting the nucleus in fixed, circular paths, like planets around the sun ☀️🪐. These orbits are at specific distances, each with a fixed energy level. The closer an electron is to the nucleus, the less energy it has.

#The Bohr Model of Sodium

Sodium (Na) has 11 electrons. Check out how they're arranged:

Image Courtesy of Wikimedia

• Electrons are arranged in shells or energy levels.
• Each energy level has a fixed energy.
• Valence electrons (outermost) have the highest energy.

#Electron Configuration

Electron configuration describes how electrons are arranged within an atom. It's similar to the Bohr model, but it also accounts for different subshells within each energy level.

#Deriving Electron Configuration

Electrons occupy different energy levels (shells) and subshells (s, p, d, f).

• s subshell holds up to 2 electrons
• p subshell holds up to 6 electrons
• d subshell holds up to 10 electrons
• f subshell holds up to 14 electrons

#Core and Valence Electrons

• Valence electrons: Located in the outermost s and p orbitals.
• Core electrons: Located in the inner d and f orbitals.

#Electron Subshells on the Periodic Table

The periodic table is your map to electron configurations!

Understanding electron configuration is crucial for predicting chemical properties and bonding behavior. This topic appears frequently in both MCQs and FRQs.

#Electron Configuration Rules

1. Aufbau Principle: Fill electrons in order of increasing sublevel energies (1s, 2s, 2p, 3s, 3p, etc.).
2. Pauli Exclusion Principle: No two electrons in the same suborbital can have the same spin (one clockwise, one counterclockwise).
3. Hund's Rule: Unpaired electrons fill each orbital within a subshell before pairing up.

#Writing Electron Configurations

Let's write the electron configuration for Boron (B, element 5):

1. Start at Hydrogen (1s) and follow the periodic table like reading a book.
2. Note the subshells you pass: 1s, 2s, and 2p.
3. Count the elements in each block: 1s² 2s² 2p¹
4. Boron's electron configuration: 1s²2s²2p¹

#The Noble Gas Shortcut

Use the preceding noble gas in brackets to shorten the configuration. For Boron: [He]2s²2p¹

#Orbital Diagrams

Electron configurations can also be represented using orbital diagrams:

Image Courtesy of Chegg

• Each arrow represents an electron.
• Aufbau principle: Electrons fill in order of increasing energy.
• Pauli exclusion principle: Arrows in the same subshell point in opposite directions.
• Hund's rule: Electrons fill each orbital singly before pairing up:

Image Courtesy of Chemistry 301

#Writing the Electron Configuration of Iron (Fe)

Let's tackle Iron (Fe, element 26), which includes the d block:

Iron's electron configuration: 1s²2s²2p⁶3s²3p⁶4s²3d⁶

Note that the 3d block is filled after the 4s block.

Noble gas shortcut: [Ar]4s²3d⁶

#Understanding Core and Valence Electrons

Let's determine the number of valence electrons in Arsenic (As) given its electron configuration:

• Identify the outermost shell (n=4).
• Count the electrons in the s and p orbitals of the outermost shell: 4s²4p³
• Total valence electrons: 2 + 3 = 5

#Final Exam Focus

• High-Priority Topics:
  • Dalton's Atomic Theory
  • Coulomb's Law (conceptual understanding)
  • Electron Configuration (writing and orbital diagrams)
  • Valence Electrons (identification and importance)
• Common Question Types:
  • Multiple Choice: Identifying subatomic particles, applying Coulomb's law, writing electron configurations, determining valence electrons.
  • Free Response: Explaining trends using Coulomb's law, writing full and abbreviated electron configurations, drawing orbital diagrams, explaining the role of valence electrons in bonding.
• Time Management Tips:
  • Start with questions you know well to build confidence.
  • Don't spend too much time on one question. Move on and come back if time allows.
  • Use the noble gas shortcut to save time on electron configuration questions.
• Common Pitfalls:
  • Forgetting the d block when writing electron configurations.
  • Mixing up the order of filling subshells.
  • Misinterpreting Hund's rule in orbital diagrams.

#Practice Questions

Practice Question

Multiple Choice Questions

1. Which of the following statements is NOT part of Dalton's Atomic Theory? (A) All atoms of a given element are identical. (B) Atoms are composed of protons, neutrons, and electrons. (C) Atoms combine in simple, whole-number ratios to form compounds. (D) Chemical reactions involve the rearrangement of atoms.

2. Which of the following represents the correct electron configuration for a neutral atom of chlorine (Cl)? (A) 1s²2s²2p⁶3s²3p⁴ (B) 1s²2s²2p⁶3s²3p⁵ (C) 1s²2s²2p⁶3s²3d⁵ (D) 1s²2s²2p⁶3s²3p⁶

3. According to Coulomb's Law, which of the following changes would result in the greatest increase in the attractive force between two oppositely charged particles? (A) Doubling the magnitude of both charges and doubling the distance between them. (B) Halving the magnitude of both charges and halving the distance between them. (C) Doubling the magnitude of one charge and halving the distance between them. (D) Halving the magnitude of one charge and doubling the distance between them.

Free Response Question

Consider the element Vanadium (V), which has an atomic number of 23. (a) Write the complete electron configuration for a neutral Vanadium atom. (b) Draw the orbital diagram for the valence electrons of Vanadium. (c) How many valence electrons does Vanadium have? (d) Explain, using Coulomb's Law, why the 4s electrons are removed before the 3d electrons when Vanadium is ionized.

Scoring Breakdown

(a) (1 point) 1s²2s²2p⁶3s²3p⁶4s²3d³ (b) (2 points) Correctly drawn 4s orbital with two paired electrons and 3d orbitals with three unpaired electrons. (c) (1 point) 5 valence electrons (d) (2 points) Explanation should include: * The 4s electrons are further from the nucleus than the 3d electrons. * The 4s electrons experience less attraction to the nucleus due to increased distance. * Therefore, 4s electrons are removed first because they are less tightly held.