Module 5: Electrons and Light

electron configuration

the arrangement of electrons in the energy levels, sublevels and orbitals of atoms

Aufbau Principle

states that each electron occupies the lowest energy orbital available

Pauli Exclusion Principle

maximum of two electrons may occupy an atomic orbital, but only if they have opposite spins

Hund's Rule

every orbital in a sublevel must have an electron before any orbital gets two, and all electrons in singly occupied orbitals have the same spin.

electron cloud

a region around the nucleus of an atom where all electrons are likely to be found (most probable location)

orbitals

regions within electron cloud where electrons orbit the nucleus; can hold a maximum of 2 electrons

s sublevel

spherical orbitals; first to fill for any energy level; only has 1 orbital.

p sublevel

'dumb-bell' shaped orbitals along the x, y and z axis at 90° to each other; has 3 orbitals.

d orbitals

5 orbitals; third to fill for any energy level; first found in the third energy level

f orbitals

elements in the 2 rows below the main periodic table have electrons occupying these; has 7 orbitals

principal energy levels

correspond to:

- orbits in the Bohr model

-rows in the periodic table for the first 3 rows.

-leading number in the electron configuration

sublevels

correspond to

-what do the letter symbols stand for in the electron configuration (s, p, d, and f)

-splitting of the principal electrons levels because of electron repulsion

-columns in the periodic table

The number of electrons in a sublevel

what do the superscripts stand for?

Nitrogen electron configuration

1s²2s²2p³

valence electrons

electrons in the highest occupied energy level of an atom; available for bonding

# of orbitals in any s sublevel

1

# of orbitals in any p sublevel

3

# of orbitals in any d sublevel

5

# of orbitals in any f sublevel

7

How do you determine the # of valence electrons using the electron configuration?

by counting the # of s and p electrons in the highest energy level.

Why do we fill the 4s orbital before the 3d orbital? (ENH)

because the 4s is lower in energy than the 3d, so it is filled first.

violet

in the visible light spectrum, which color has the highest frequency?

red

in the visible light spectrum, which color has the lowest frequency?

it decreases

As the wavelength gets longer, what happens to the energy?

How many valence electrons does this atom have? 1s²2s²2p⁶3s²3p²

4

ionization energy

the energy to remove an electron from an atom

Bohr model of hydrogen

-fixed orbits

-moving between orbits requires an increase or decrease in potential energy

-energy is determined by coulombic attraction between electron and the nucleus

-explains the spectrum of hydrogen

Quantum model

- probability of electrons being in orbitals

- energy associated with orbitals is an ionization energy

-orbitals accommodate two electrons

-orbital fill from lowest energy level to highest

-electrons pair up when energy level is more than half full

absorption

light energy is used to move electron from a lower energy level to a high energy level. In the Bohr model, the electron moves away from the nucleus.

emission

energy is released when an electron moves closer to the nucleus

fluorescence

- atom absorbs energy of a higher energy such as UV and releases photons of lower energy such as visible light

phosphorescence

- a very slow form of fluorescence. Atom absorbs photons of high energy and very slowly releases photons of lower energy

Ground state

an electron configuration in which all the electrons are in the lowest possible energy levels

Excited state

electron configuration for an atom which has absorbed energy so that one or more electrons on in energy levels higher than the energy levels occupied in the ground state

Core electrons

electrons in filled energy levels

ion

an atom in which electrons have been added or removed so that the number of electrons does not equal the number of protons

determining the number of valence electrons using the periodic table

In the s and p blocks, count the number of periodic table squares from the left

s-block

columns 1 and 2 in the periodic table

p-block

rightmost 6 columns in the periodic table

photon

a packet of light energy

wavelength

related to the size of a photon

hundreds of nanometers for visible light

Why does the quantum model of helium have sublevels?

repulsion between the two electrons

What is spin?

- quantity included in the quantum model to explain magnetism

-two possible states (up and down)

-think of electrons as acting like extremely tiny magnets

How do you figure out the total number of electrons in a neutral atom?

-atomic number

-add the superscripts of the electron configuration

photoelectric effect

when light energy absorbed is greater than the ionization energy of the valence electrons

quantum model explains

- chemical properties (valance electrons)

- magnetism ( up and down spin)

- absorption and emission spectra of elements (energy levels and sublevels)

Chemiluminescence

occurs when a product of a chemical reaction absorbs energy produced by the chemical reaction and emits light