Download Chapter 4 Chem classnotes

Arrangement of Electrons in
Atoms
Chapter 4
Pages 96 - 122
The Development of a New
Atomic Model
Rutherford’s model did not explain how electrons are distributed
in space surrounding the positive nucleus. Bohr discovered the
hydrogen-atom spectrum which lead him to propose a new
atomic model. In the new model, electrons circle the nucleus
only in allowed paths called orbits.
Electromagnetic radiation is a form of energy that exhibits
wavelike behavior as it travels through space. What is the
electromagnetic spectrum?
Some examples of electromagnetic radiation are:
Visible (or white) light
Ultraviolet (UV) light
X-ray
Infrared (IR)
Gamma (γ) ray
Radio waves
The Development of a New
Atomic Model
All forms of electromagnetic radiation move at a constant speed:
c (speed of light) = 3.00 X 108 m/s (meters per second)
The Development of a New
Atomic Model
_________ is the distance between corresponding points on
adjacent waves.
_________ is the number of waves that pass a given point in a
specific time, usually 1 second.
Units of measurement for wavelength can be _________,
_________ or ________ and measures distance.
Frequency is expressed in waves/second and one wave/second is
called a ________.
Frequency and wavelength are wave properties of
electromagnetic radiation. But EM radiation (light) also behaves
as particles.
The Development of a New
Atomic Model
Wavelength (λ), frequency (ν) and the speed of light (c ) are
mathematically related as such: c = λν meaning that wavelength and
frequency are inversely proportional to one another.
The Development of a New
Atomic Model
A quantum of energy is the minimum quantity of energy that can
be lost or gained by an atom. Energy and frequency are related
according to the following equation:
E = hν where h is called “Planck’s constant” named
after German physicist Max Planck. h = 6.626 X 10-34Js
A photon is a particle of EM radiation that has zero mass and carries
a quantum of energy.
The lowest energy state of an atom is its ground state.
A state in which an atom has a higher potential energy than it has in
its ground state is an excited state.
The Development of a New
Atomic Model
Whenever a hydrogen atom (or any atom) falls to a ground state
from an excited state, it emits a photon of radiation. This
process is called emission. Energy must be added to an atom in
order to move an electron from a lower energy state to a higher
one – this process is called absorption.
The Quantum Model of the
Atom
The Heisenberg uncertainty principle states that it is impossible to
determine simultaneously both the position and velocity of an
electron or any other particle.
Quantum theory describes mathematically the wave properties of
electrons and other very small particles.
An orbital is a three dimensional region around a nucleus that
indicates the probable location of an electron.
Quantum numbers specify the properties of atomic orbitals and the
properties of electrons in orbitals.
principal quantum number, n
l
angular momentum,
The Quantum Model of the
Atom
The Quantum Model of the
Atom
Electron Configurations
The quantum model of the atom improves on the Bohr model
because it describes the arrangements of electrons in atoms
other than hydrogen.
The arrangement of electrons in an atom is known as the atom’s
________ ______________.
The Aufbau principle states that an electron occupies the lowestenergy orbital that can receive it. (shows the order in which
electrons occupy orbitals)
The Pauli exclusion principle states that for two electrons to
occupy the same orbital, they must have opposite spin states.
Hund’s rule states that orbitals of equal energy are each occupied
by one electron before any orbital is occupied by a second
electron, and all electrons in singly occupied orbitals must have
the same spin state.
Electron Configurations
Youtube.electronconfiguration.tutorial.com
https://youtu.be/K-jNgq16jEY
Electron Configurations
PRACTICE: The electron configuration of nitrogen is 1s22s22p2.
How many electrons are present in an N atom? How many
protons? Write the orbital notation for nitrogen.
The electron configuration of fluorine is 1s22s22p5. How many of
its p orbitals are filled?
Electron Configurations
To simplify sodium’s notation, the symbol for neon, enclosed in
square brackets, is used to represent the complete neon
configuration: [Ne]3s1. This is called noble-gas notation.
How many electron-containing orbitals are in an atom of iodine?
27
How many of these orbitals are filled?
26
How many unpaired electrons are there in an atom of iodine?
1
Write the noble gas notation for tin, Sn.
[Kr]5s24d105p2
How many unpaired electrons are there in an atom of tin?
2
Electron Configurations
Write the complete electron configuration notation for a rubidium
atom.
1s22s22p63s23p64s23d104p65s1
Write the noble-gas notation for a rubidium atom.
[Kr]5s1
Identify the element having the following electron configuration:
1s22s22p63s23p3
Phosphorus, P
Identify the element having the following electron configuration:
[Ar]4s1:
Potassium, K