HC Unit 4 - Electrons in Atoms Review

Recall that in Rutherford's model,

the atom's mass is concentrated in the nucleus and electrons move around it (it doesn't explain how the electrons were arranged around the nucleus or why negatively charged electrons aren't pulled into the positively charged nucleus)

In the early 1900's, scientists observed certain elements

emitted visible light when heated in a flame.

Analysis of the emitted light revealed that an element's chemical behavior

is related to the arrangement of the electrons in its atoms

Scientists discovered that certain elements gave up specific types of

visible light when excited (heated)
- colors were associated with element families

Visible light is a type of ___________________, a form of energy that exhibits wave-like behavior as it travels through space.

electromagnetic radiation

Wavelength

the shortest distance between equivalent points on a continuous wave
- Greek symbol lambda - λ
- Units - nm, m, cm

Wavelength symbol

λ

Frequency

the number of waves that pass a given point per second
- Greek symbol nu - ν
- Units - Hertz (Hz), cycles/sec, sec^-1 = (1/sec)

amplitude

the wave's height from the origin to a crest

The speed of light (3.00 x 108 m/s) is

the product of its wavelength and frequency

Every wave travels at

the speed of light, no matter the wavelength or frequency

lower frequency =

longer wavelength

higher frequency =

shorter wavelength

Equation for Electromagnetic Radiation

c = λ ν
c = speed of light 3.0 x 108 m/sec or 3.0 x 1010 cm/sec
λ = wavelength (lambda)
ν = frequency (nu) (hertz)

Review handwritten notes, examples, and periodic table

ok

Sunlight contains a

continuous range of wavelengths and frequencies

A prism separates sunlight into

a continuous spectrum of colors

electromagnetic spectrum

includes all forms of electromagnetic radiation

order of electromagnetic spectrum

radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays (Ron Made It Very Ultra Xtra Good)

The wave model of light cannot explain all of light's characteristics. Some examples include:

-Why heated objects emit only certain frequencies of light at a given temperature.
-Why do some metals emit electrons when light of a specific frequency shines on them?

Planck's study led him to a startling conclusion:

Matter can gain or lose energy only in small, specific amounts called quanta

quantum

the minimum amount of energy that can be gained or lost by an atom

Energy of a Quantum equation

E = hv

Planck's constant

6.626 x 10^-34 J*s

Photoelectric effect

when electrons are emitted from a metal's surface when light of a certain frequency shines on it

Energy below the threshold

has no effect

The excited atoms return to their stable state by

emitting light to release energy

atomic emission spectrum

(of an element) the set of frequencies of the electromagnetic waves emitted by the atoms of the element

Electrons that are in an excited state

lose their energy to return to a ground state

The energy is lost by

the emission of a photon of light, only certain transitions occur

Each element has a unique pattern

for its emission spectra, like a "fingerprint"

Albert Einstein proposed in 1905 that

light has a dual nature.

A beam of light has

wavelike and particle-like properties.

photon

a particle of electromagnetic radiation with no mass that carries a quantum (certain amount) of energy

The lowest allowable energy state of an atom is called its

ground state (where an electron is normally found)

When an atom gains energy, it is in an

excited state

In an excited state, an atom...

It jumps to a new energy level (ring around the nucleus). It is unstable here so it will eventually go back to the ground state, emitting a photon or light when it does so.

Bohr atom

Electrons are arranged in circular paths, with fixed energy levels, and need a specific amount of energy to move an electron to another energy level

Bohr's Model of the Atom

-Each orbit was given a number, called the quantum number.
-Hydrogen's single electron is in the n = 1 orbit in the ground state.
-When energy is added, the electron moves to the n = 2 orbit.

Quantum mechanical model (where we are today)

A mathematical based model of the atom.
-Electron can only have certain energy values (a quantum of energy)
-We talk about the probability of locating an electron at a position around the atom.

We can predict a three-dimensional region around the nucleus called the

atomic orbital

Principal quantum number (n)

indicates the relative size and energy of atomic orbitals

n specifies the atom's major energy levels, called the

principal energy levels

The higher the principal quantum number

the farther from the nucleus an electron is found.

Energy sublevels

are contained within the principal energy levels;
each sublevel (s p d f) has some number of atomic orbitals

s Sublevel

-One S orbital
-Spherical
-Holds 2 electrons
-Must have opposite spin

p Sublevels

-3 p orbitals (each holds 2 electrons)
-Three orientations (dumbbell shaped)
-Px, Py, and Pz
-6 electrons total

d Sublevel

-5 types of d orbitals
-10 electrons total
-Clover leaf shaped
-dxy dxz dyz dx2-y2 dz2

f Sublevel

-14 electrons total
-Complex

The arrangement of electrons in the atom is called the

electron configuration (ground-state)

aufbau principle

states that each electron occupies the lowest energy orbital available (Start with the 1s orbital , then move to 2s, then 2p, etc. - follow the Aufbau diagram)

Pauli exclusion principle

states that a maximum of two electrons can occupy a single orbital, but only if the electrons have opposite spins.

Hund's rule

states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same energy level orbitals.

Valence electrons

electrons in the atom's outermost orbitals - those associated with the atom's highest principal energy level (these are the electrons that are furthest from the nucleus)

The electron configurations for certain transition elements, like ________ and ________, do not follow the aufbau diagram due to increased stability of half-filled and filled sets of s and d orbitals.

chromium; copper

The aufbau diagram can be used to write correct ground-state electron configurations for all elements up to and including

Vanadium, atomic number 23.

Correct configuration for chromium (Cr)

1s2 2s2 2p6 3s2 3p6 4s13 d5

Correct configuration for copper (Cu)

1s2 2s2 2p6 3s2 3p6 4s13 d10