Arrangement of Electrons in Arrangement of Electrons in AtomsAtoms

Chapter 4Chapter 4

Electromagnetic Spectrum

Photoelectric Effect

Quantization of Energy

Energy of a Photon

Absorption and Emission Spectra

Bohr Model of the Atom

Electron Cloud

Quantum Theory- describes mathematically the wave properties of electrons.

Definitions:

orbital: three-dimensional region around the nucleus that indicates the probable location of an electron. (Each can hold a maximum of 2 electrons.)

ground state: lowest energy state electrons in an atom have.

excited state: state in which electrons in an atom have a higher energy than ground state.

Quantum NumbersSpecify the properties of atomic orbitals and the properties of electrons in orbitals.

Symbol Description

Principal Quantum # n main energy level occupied by an electron

Angular momentum # l shape of orbital in a particular sublevel

Magnetic Quantum # m orientation of orbital around nucleus

Spin Quantum # s direction of spin of electron

Energy Levels and Sublevels- each principal energy level (n) has one or more sublevels.-the number of sublevels is the same as the principal quantum number

First Principal Energy Level (n=1) has 1 sublevel

Second Principal Energy Level (n=2) has 2 sublevels

Third Principal Energy Level (n=3) has 3 sublevels

Each electron in a given sublevel has the same energy

Sublevels continued…Sublevels are named using letters:

- the first sublevel is called s- the second sublevel is called p- the third sublevel is called d- the fourth sublevel is called f

and so on (g, h …..)

If n=1, how many sublevels are there and what are they called?

Answer: 1 sublevel called s

If n=2, how many sublevels are there and what are they called?

Answer: 2 sublevels called s and p

OrbitalsEach sublevel contains 1 or more orbitals

s - sublevel has 1 orbitalp - sublevel has 3 orbitalsd - sublevel has 5 orbitalsf - sublevel has 7 orbitals

Remember each orbital contains a maximum of 2 electrons.

The maximum number of electrons per sublevel:s → 2p → 6d → 10f → 14

More Orbitals Angular Momentum and Magnetic Quantum Numbers

Quantum Numbers and Orbitals

Shapes of s, p, and d Orbitals

Electrons in Energy Levels and Sublevels

Principal Sublevels # of orbitals # of electrons Total electrons Energy available in sublevel possible in for energy levelLevel sublevel (n) (n) (n2) (2n2)

2

2

3

4

ss

sp

p

d

1 1 2

8

18

32s

dp

f

1

313

51357

2

62

2

6

6

10

1014

Electron Configurations- shows the arrangement of electrons in an atom- there are 3 different ways to show electron configurations:

1. Orbital notation2. Electron-configuration

notation3. Noble gas notation- electrons are in the ground state unless otherwise noted.

-unfortunately, there is energy overlap beginning at n = 3.

- How can we predict the sublevel order if this occurs?

Aufbau Principle- electrons occupy the lowest energy levels first.

1s2s 2p3s 3p 3d4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f7s 7p 7d 7f

Hund’s Rule- Before a second electron can be placed in any orbital, all the orbitals of that sublevel must contain at least one electron.

Pauli Exclusion Principle- In order for two electrons to occupy the same orbital they must have opposite spin.- Relates to the Spin Quantum Number (s = +1/2 or -1/2)- Electrons spin clockwise or counterclockwise.

Orbital Notation

-When illustrating orbital notation for an element: 1. Boxes are used to represent orbitals

2. Each box is labeled with principal energy level and sublevel.

3. Arrows are used to represent electrons.

Examples

↑

Hydrogen

1s

Lithium

↑↓ ↑

1s 2s

Aluminum

↑↓↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑

1s 2s 2p 3s 3p

Electron Configuration Notation

-When writing electron configurations for an element: 1. Boxes are not used.

2. The principal energy level is written, followed by the sublevel.

3. The total number of electrons are superscripted on each sublevel.

Examples

Helium

1s2

Sodium

1s2 2s2 2p6 3s1

Bromine

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5

Noble Gas Notation

-Noble gas notation may be used for elements beginning with period 3:

1. Find the period the element in question is in. 2. Locate the closest noble gas (must have

fewer electrons than the element in question).

3. Write the symbol of the noble gas in brackets (This represents ‘x’ number of electrons).

4. Continue the notation with the principal energy level of the period the element is located in.

ExamplesChlorine

[Ne]3s2 3p5

Iron

[Ar]4s2 3d6

Iodine

[Kr]5s2 4d10 5p5

Noble-Gas Notation

Blocks of the Periodic Table- The periodic table can be used to predict the order in which electrons enter sublevels.

Valence Electrons- Electrons that are located in the highest principal energy level.- The maximum number of valence electrons and element can have is eight.- Usually valence electrons are found only in s and p sublevels.- Electrons that are not valence electrons are inner-shell electrons.

ExamplesChlorine

[Ne]3s2 3p5

Iron

[Ar]4s2 3d6

Bromine

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5