Unit 5 Electrons in Atoms Chemistry I Mr. Patel SWHS

Topic Outline Continue Learning Major Ions Atomic Models (5.1) Electron Configurations (5.2) Light and Quantum Mechanics (5.3) Lewis Dot Structures (7.1)

Atomic Models Democritus’s Model Thomson’s Plum Pudding Model Rutherford’s Model – Electrons travel in orbit around nucleus – Could NOT explain chemical properties of elements – Need a model for electrons

Bohr Model Niels Bohr – electrons is found in a specific orbit around nucleus Each orbit has a specific energy = energy level The further away from the nucleus, the higher the energy

Bohr Model

An electron can move between levels – Can not be between levels – Think of a ladder An electron must gain or lose energy to change levels A quantum of energy – energy to move to another level

Bohr Model More energy between levels when closer to nucleus Less energy between levels when farther Energy levels get closer together

Bohr Model Ground state – lowest energy state for an electron Excited state – any higher energy state

Electron Excitation &feature=relmfu

Bohr Model Each ring on a Bohr Model is labeled as “n” n must be a whole number – n=1, n=2, n=3, etc. (period number) Each ring (n) can hold a specific number of electrons – n=1  2 electrons – n=2  8 electrons – n=3  18 electrons – n=4  32 electrons

Drawing Bohr (Rutherford) Diagrams Q&feature=relmfu

Ex: Draw the Bohr Diagram for Hydrogen.

Ex: Draw the Bohr Diagram for Neon.

Ex: Draw the PEL Diagram for Bromine.

Bohr Model Correct: Electrons have energy levels and can move Incorrect: Electrons move in orbits Matter has a Wave-Particle Duality

Dual Nature of Electrons Electrons as Particles Photoelectric Effect Electrons as Waves Young's Double Slit Experiment

Modern Theory Rutherford and Bohr based models on behavior of large objects Small objects behave differently – quantum mechanics Schrödinger Equation solutions  quantum mechanical model of the atom

Schrödinger Equation

The Cat – A Thought Experiment Schrodinger Cat 1 Schrodinger Cat 2

Quantum Mechanical Model Determines the allowed energies of the electrons The probability of where an electron is – electrons housed in electron clouds

Atomic Orbitals Region in space where there is a high probability of finding an electron Principal quantum number (n) – energy level – think of the ring labels of the Bohr model Each energy level can be made up of sublevels – orbitals of similar energy but different shapes

1. s orbital Shape: sphere

2. p orbital Shape: Dumbbell

3. d orbital Shape: clover (mostly)

4. f orbital Shape: multiple clover

Atomic Orbitals

Electron Configurations Electrons found in orbitals Electron configuration – ways in which various electrons are arranged in orbitals 4 orbitals: s (2 electrons), p (6 electrons) d (10 electrons), f (14 electrons)

Three Rules to find Elec. Config 1.Aufbau Principle – Electrons occupy orbitals of lower energy first – For same n, low to high energy: s, p, d, f

Three Rules to find Elec. Config 2.Pauli Exclusion Principle – Each atomic orbital can have at most 2 electron – Each electron in an orbital must have opposite spins – 2 spins: spin up or spin down – How we draw: 1 electron in s orbital: ____ 2 electrons in s orbital: ____ – We use arrow with “half head”

Three Rules to find Elec. Config 3.Hund’s Rule – Electrons occupy orbitals to maximize spin – For same n, place electrons spin up first then pair them with spin down – 1 electron in p orbital ____ ____ ____ – 2 electrons in p orbital ____ ____ ____ – 3 electrons in p orbital ____ ____ ____ – 4 electrons in p orbital ____ ____ ____ – 5 electrons in p orbital ____ ____ ____ – 6 electrons in p orbital ____ ____ ____

Orbital Blocks on PT s-block: Groups 1A and 2A (exception: He) p-block: Groups 3A-8A (exception: He) d-block: transition metals f-block: inner transition metals Remember, the period number is n = principal energy level

Orbital Blocks on PT

How to write electron configuration Ex: What is the electron configuration for O? O = oxygen, atomic number 8 = 8 electrons Draw spaces: ____ ____ ____ ____ ____ 1s 2s 2p Fill spaces according to rules: ____ ____ ____ ____ ____ 1s 2s 2p Write: 1s 2 2s 2 2p 4

How to write electron configuration Ex: What is the electron configuration for C? C = carbon, atomic number 6 = 6 electrons Draw spaces: ____ ____ ____ ____ ____ 1s 2s 2p Fill spaces according to rules: ____ ____ ____ ____ ____ 1s 2s 2p Write: 1s 2 2s 2 2p 2

3 ways to write electron configurations 1.Using boxes and arrows ____ ____ ____ ____ ____ 1s 2s 2p 2.Long EC: Cl: 1s 2 2s 2 2p 6 3s 2 3p 5 3.Short EC: Cl: [Ne] 3s 2 3p 5 – Put last noble gas in brackets and write electrons from there

Writing EC This is much easier than it looks. Simply, start at hydrogen and walk to the desired element counting all the elements you pass

Ex. Write EC (all three ways) for Boron.

Ex. Write EC (all three ways) for Mg.

Ex. Write EC (all three ways) for V.

Ex. Write EC (long and short) for Fr.