ELECTRONS IN ATOMS

The chemical properties of atoms, The chemical properties of atoms, ions, and molecules are related to ions, and molecules are related to the arrangement of the the arrangement of the ELECTRONS within them. ELECTRONS within them.

Over time, the atomic model has Over time, the atomic model has evolved regarding where electrons evolved regarding where electrons are located.are located.

Electrons in AtomsElectrons in Atoms

Atomic Theory / ElectronsAtomic Theory / Electrons Democritus and DaltonDemocritus and Dalton

Atom is indivisible—no electronsAtom is indivisible—no electrons

Thompson’s Model (Plum Pudding)Thompson’s Model (Plum Pudding) Described the atom as a ball of positive Described the atom as a ball of positive

charge containing randomly placed charge containing randomly placed electrons.electrons.

Rutherford’s ModelRutherford’s Model Electrons are still randomly placed, but Electrons are still randomly placed, but

now there’s a positive nucleus.now there’s a positive nucleus.

Max Planck’s Quantum Energy TheoryMax Planck’s Quantum Energy Theory Energy is always absorbed or emitted in Energy is always absorbed or emitted in

“packets” which he called quanta.“packets” which he called quanta. Photon= quantum of lightPhoton= quantum of light

1010thth grader = High school student grader = High school student

Bohr’s Model (Planetary)Bohr’s Model (Planetary) Bohr used the quantum energy theory and Bohr used the quantum energy theory and

proposed that electrons move in particular paths proposed that electrons move in particular paths with fixed energy in “orbits” around the nucleus.with fixed energy in “orbits” around the nucleus.

Atomic TheoryAtomic Theory The Next StepThe Next Step

In Bohr’s Model…In Bohr’s Model… Electrons cannot exist between energy levels, Electrons cannot exist between energy levels,

but they can move from one level to another.but they can move from one level to another. Think of a ladder, and the electrons can only jump Think of a ladder, and the electrons can only jump

from rung to rung. from rung to rung.

To move from one energy level to another one, To move from one energy level to another one, an electron must gain or lose just the right an electron must gain or lose just the right amount of energy.amount of energy. This amount of energy is called a quantum of This amount of energy is called a quantum of

energy.energy.

Atomic Theory / ElectronsAtomic Theory / Electrons

Bohr’s Model was only partly successful.Bohr’s Model was only partly successful.

Two other contributions led to a new Two other contributions led to a new atomic theory.atomic theory. Louis de BroglieLouis de Broglie illustrated that illustrated that

electrons have a dual nature with properties electrons have a dual nature with properties of both particles and waves.of both particles and waves.

HeisenbergHeisenberg’s Principle of Uncertainty ’s Principle of Uncertainty stated that it was impossible to know both stated that it was impossible to know both the momentum and the position of an the momentum and the position of an electron.electron.

Atomic Theory / ElectronsAtomic Theory / Electrons

Schrodinger’s Quantum Mechanical Schrodinger’s Quantum Mechanical Model is the atomic model in use today.Model is the atomic model in use today. It was able to explain many previously unexplainable It was able to explain many previously unexplainable

phenomena.phenomena.

Restricts energy of electrons to certain valuesRestricts energy of electrons to certain values Same as BohrSame as Bohr

Does NOT define an exact path around the nucleus Does NOT define an exact path around the nucleus Unlike BohrUnlike Bohr

Estimates the Estimates the probabilityprobability of finding an electron in a of finding an electron in a certain position (Heisenberg).certain position (Heisenberg).

Modern Atomic TheoryModern Atomic Theory

Quantum Numbers: Quantum Numbers: Where is the electron??Where is the electron?? In Schrodinger’s model, there are four In Schrodinger’s model, there are four

“quantum” numbers that tell us where an “quantum” numbers that tell us where an electron is likely to be located.electron is likely to be located. Principal (n), 1-7, gives the energy levelPrincipal (n), 1-7, gives the energy level Subshell (Subshell (ll), s-p-d-f, gives the shape of region), s-p-d-f, gives the shape of region Orbital (m), gives the orientation in space of Orbital (m), gives the orientation in space of

the shapesthe shapes Spin (s), clockwise or counterclockwiseSpin (s), clockwise or counterclockwise

No two electrons have the same 4 No two electrons have the same 4 quantum numbers.quantum numbers.

Principal Quantum Number (Principal Quantum Number (nn)) Designates the Designates the energy levelenergy level

Tells how far away from the nucleus an electron Tells how far away from the nucleus an electron is likely to be.is likely to be.

Assigned values in order of increasing energy: Assigned values in order of increasing energy: nn = 1, 2, 3, 4, 5, 6, or 7= 1, 2, 3, 4, 5, 6, or 7

Corresponds to the rows/period on the periodic Corresponds to the rows/period on the periodic table.table.

+

n = 1

Lower value of n means the electron is closer to nucleus and has less energy.

Principal Quantum Number (Principal Quantum Number (nn))

n = 2

n = 3

Within each principal energy level there are a Within each principal energy level there are a certain number of sublevelscertain number of sublevels Energy level 1 has 1 sublevel; energy level 2 has 2 Energy level 1 has 1 sublevel; energy level 2 has 2

sublevels; energy level 3 has 3 sublevels, etc.sublevels; energy level 3 has 3 sublevels, etc. These sublevels are called s, p, d, or f.These sublevels are called s, p, d, or f. Each sublevel has a unique shapeEach sublevel has a unique shape These shapes These shapes describe the region of spacedescribe the region of space

where the electron is likely to be locatedwhere the electron is likely to be located

Subshell (Subshell (ll), s-p-d-f (Shapes)), s-p-d-f (Shapes)

s p d

Principal Principal Energy Energy LevelLevel

Number Number of of

SubshellsSubshells

Type of Type of SubshellSubshell

n = 1n = 1 11 1s1s

n = 2 n = 2 22 2s, 2p2s, 2p

n = 3n = 3 33 3s, 3p, 3d3s, 3p, 3d

How many sublevels will principal energy level 4 have, and what shapes will they be?

Subshell, (Subshell, (ll), s-p-d-f), s-p-d-f

(The orbital names s, p, d, and f stand for names given to groups of lines in the spectra of the alkali metals. These line groups are called sharp, principal, diffuse, and fundamental—This is not important.)

Orbitals (m)Orbitals (m)

•Within each sublevel there are a certain number of orbitals.

•s sublevel—1 orbital

•p sublevel—3 orbitals

•d sublevel—5 orbitals

•f sublevel—7 orbitals

•Orbitals within each sublevel have similar shapes, but are oriented differently in space.

Each orbital can only hold 2 electrons.

s - orbitalss - orbitals

Spherical shapeSpherical shape

Hold a maximum Hold a maximum of 2 electronsof 2 electrons

First found in the First found in the 11stst energy level energy level

p-orbitalsp-orbitals Pear or dumbbell Pear or dumbbell

shapedshaped 3 different 3 different

orientationsorientations Each orientation Each orientation

holds a max of 2 e-holds a max of 2 e- The p sublevel as a The p sublevel as a

whole holds a whole holds a maximum of 6 emaximum of 6 e--

First found in the First found in the 22ndnd energy level energy level

d - orbitald - orbital 5 different 5 different

orientationsorientations Each holds 2 eEach holds 2 e--’s’s The sublevel as a The sublevel as a

whole holds a whole holds a maximum of 10 emaximum of 10 e--

First found in the First found in the 33rdrd energy level energy level

Do not appear until the 4th shell (energy level) and higher.

Maximum eMaximum e ֿֿs Alloweds Allowed

The maximum # of electrons that can The maximum # of electrons that can occupy a occupy a principal energy levelprincipal energy level is given by is given by

the formulathe formula 22nn².².

How many eHow many e ֿֿs are allowed in energy level 3?s are allowed in energy level 3?

18

Let’s ReviewLet’s Review

How many orbitals are in the following sublevels?How many orbitals are in the following sublevels?a.a. 3p3p

b.b. 2s2s

c.c. 4f4f

d.d. 4p4p

e.e. 3d3d

3

1

7

3

5

Electron Configuration:Electron Configuration:

In an atom, electrons are positioned around In an atom, electrons are positioned around the nucleus in the most stable arrangement the nucleus in the most stable arrangement possible.possible. This is the arrangement that has the lowest This is the arrangement that has the lowest

energy.energy.

There are 3 important rules to help us find There are 3 important rules to help us find the configuration of electrons in atoms.the configuration of electrons in atoms.

•How are the electrons in any given element arranged?

Aufbau’s PrincipleAufbau’s Principle

Electrons will occupy orbitals having the Electrons will occupy orbitals having the lowest energy FIRST and then in order of lowest energy FIRST and then in order of increasing energy. increasing energy.

The "The "Ground StateGround State" of an atom is when " of an atom is when every electron is in its every electron is in its lowestlowest energy energy orbital.orbital.

Pauli’s Exclusion PrinciplePauli’s Exclusion Principle

An orbital can be empty, have one An orbital can be empty, have one electron, or electron, or AT MOSTAT MOST have two have two electrons. electrons.

Electrons occupying the same Electrons occupying the same orbital must have opposite spins! orbital must have opposite spins!

One clockwise, and one counter One clockwise, and one counter clockwiseclockwise

Hund’s RuleHund’s Rule

When electrons occupy orbitals When electrons occupy orbitals of equal energy, one electron of equal energy, one electron enters each orbital until all the enters each orbital until all the orbitals contain one electron with orbitals contain one electron with parallel spins. parallel spins.

Chemistry Riddle

Q: What happens when electrons lose their energy?

A: They get Bohr’ed!