CHAPTER 4: Section 1

Arrangement of Electrons in

Atoms

In Rutherford’s model of the atom one of the major problems was

that it did not explain how negative electrons fill the space

surrounding the nucleus.

Visible light is a kind of electromagnetic radiation, which is

a form of energy that exhibits wavelike behavior as it travels

through space.

The electromagnetic spectrum is all of the forms of electromagnetic radiation.

Visible light is only a small part of the electromagnetic spectrum. Its

wavelength is from 400 nm to 700 nm.

The frequency and wavelength are mathematically related to each other.

c

In the equation c is the speed of light which is equal to 3 x 10 8 m/s

Wavelength ( ) is the distance between corresponding points on adjacent

waves.

Frequency is (v) and is defined as the number of waves that pass a given

point in a specific time.

Frequency is measured in waves/second. One wave/second is called a hertz (Hz).

EX: Determine the frequency of light with a wavelength of 4.257 x 10-9 m.

c

c

Rearrange to

3.0 x 10 8 m/s

4.257 x 10 -9 m

7.0 x 10 16 Hz

The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal. Which creates an electric current.

Light as particles

German physicist, Max Planck, was studying theemission of light by hot objects.

Planck suggested that the objects emit energy in small specific amounts called quanta. A quantum is the minimum quantity of energy that can be lost or gained by an atom.

Planck produced the following relationship:

E=(h) (v)

E= to the energy in joules, of a quantum of radiation.

v= to the frequency of the radiation emitted

h is the fundamental physical constant now known as Planck’s constant;

h= 6.626 x 10-34 j*s

A photon is a particle of electromagnetic radiation having a zero rest mass and carrying a quantum

of energy.

The dual wave-particle nature of light depends on the experiment that observes it, light behaves

like a wave or like a particle.

When a current is passed through a gas at a low pressure, the potential energy of some of the gas atoms increases. 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 called an excited state.

The Bohr model of the hydrogen atom depicts a hydrogen nucleus with a single electron circling the

nucleus at a specific radius called an orbit. The electron exists in only one of only a finite number

of allowed orbits.

1 p0 n

E

Section 4.2

The main energy level is the level of increasing energy, specified by the quantum number n, at which atomic

orbitals can exist.

Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals.

The principal quantum number is the number used to specify the main energy level of an atom.

The principal quantum number is symbolized by n. The values of n are positive integers only: 1,2,3, and so on.

The electron shells are all of the orbitals within the same main energy level.

The total number of orbitals per main energy level is equal to n2. The number of electrons allowed per main energy

level is equal to 2n2.

The angular momentum quantum number indicates an orbital’s shape. And is symbolized by l.

A sublevel or subshell, consists of the orbitals within a given main energy level that share the same value of l.

The magnetic quantum number, symbolized by m, indicates the orientation of an orbital around the nucleus.

The Spin Quantum number has only two possible values (+ ½, - ½ ) which indicates

the two fundamental spin states of an electron in an orbital.

Section 4.3

The arrangement of electrons in an atom is known as the atom’s electron configuration.

Rules for Electron Configuration

Aufbau Principle is an electron occupies the lowest energy orbital that can receive it.

Pauli exclusion principle is that no two electrons in the same atom can have the same set of four quantum

numbers.

Hund’s Rule is 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 spins

Orbital Notation

Unoccupied orbital is represented by a line ____

1s

An orbital containing one electron is represented as __↑__

1s

An orbital containing two electrons is represented as ↑↓

1s

Showing the electrons paired with opposite spins.

Ex: H ↑ He ↑↓

1s 1s

• The hydrogen configuration is represented by 1s1. The superscript indicates that one electron is present in hydrogen’s 1s orbital.

• The helium configuration is represented by 1s2. Here the superscript indicates that there are two electrons in helium’s 1s orbital.

• The three methods used to represent the arrangement of electrons are the

A) orbital notationB) electron-configuration notationC) noble-gas notation.

__↑

3s__________

The three methods used to represent the arrangement of electrons are:

Na

↑↑↑ ↑↑↑↑ ↑ ↑ ↑

1s 2s 2px 2py 2pz

A) orbital notationB) electron-configuration notation

1s 2 2s 2 2p6

C) noble-gas notation

[Ne] 3s1 3 1s

• An octet of electrons corresponds to filled s and p orbitals in an atom’s highest main energy level. Noble gas (except helium) contain octets.

Increasing energy

n = 1 1s

n = 2

3s

3pn = 3

2s

2p

3d

n = 4

4s

4p

4d

n = 5

5s

5p