Homework

Read pages 360 – 364372 – 375379 & 380

Electrons in The atom

Further developments in the models of the atom

Nature Of Light(background Info)

Visible light is a form of Electromagnetic radiationDef: form of energy that exhibits

wave and particle behavior while traveling through space

Wave Characteristics

1. wavelength (l) – distance between corresponding points on consecutive waves

2. frequency (f) – the number of waves that pass through a point in a given amt of time (Hz)

3. Amplitude - the maximum displacement from rest

4. Wave Speed

a. Speed = l fb. EM radiation travels at constant speed in a

vacuum: c = 3.0 x 108 m/s or 186,000 miles/s

c. Speed is constant for EM waves, therefore, frequency is inversely proportional to wavelength

Frequency vs wavelength

EM Spectrum

• consists of all electromagnetic radiation, arranged according to wavelengths

EM Waves and Energy

1. The energy carried by an EM wave can be determined using the following equation:

Energy = Planck’s constant x frequencyORE = h fwhere E = energy in Joulesh = 6.63 x 10 -34 J sf = frequency in Hz

2. Energy of the wave is directly proportional to the frequency of that light wave

Light from Elements

Bohr Model of the Atom

• The chemical behavior of atoms depends on the arrangement of their electrons

- Electrons orbit the nucleus in concentric circular paths

• He proposed that the reason the electrons ( negatively charged particles) do not fall into the nucleus (positively charged) is because electrons orbit the nucleus with specific fixed amounts of energy

Bohr Model of the Atom

-Each energy level is associated with a specific amt of energy (called Principle Energy Levels or PEL)-Further from nucleus, greater the energy of an electron-Max # electrons in a PEL = 2n2

Bohr Model (cont’d)Why do atoms give off light?

-animation

-Electrons occupy the lowest possible energy level (ground state)-If they absorb sufficient energy, they make a quantum leap to higher energy level (excited state)

Emission Spectra

Excited electrons are unstable and will fall to ground stateGive off a burst of energy called a quantum of energyA quantum of energy that falls in visible spectrum called Photon

Electron Configurations(Bohr Model)

Shows the arrangement of electrons in an atom

Each element on your Periodic Table has an electron configuration

Indicates the number of electrons in each energy level for that atom

Write the electron configuration for an atom of sodium, Na, on the line below.

 __________________________________ How many electrons occupy the 1st PEL ? _________ How many electrons occupy the 3rd PEL? _________  Write a possible electron configuration for an

exited atom of sodium. _______________________________

Quantum Mechanical Model of Atom

Modern model of the atom

What was so wrong with the Bohr model of the atom?

The Bad• could not predict

spectra for atoms with more than one electron

• Heisenberg Uncertainty Principle – the location of an electron cannot be known at any one point in time

The Good• accurately predicted emission spectra of hydrogen

How did it change?

• Electrons were found to have wave – like properties

• Scientists began to treat electrons as waves and particles at the same time, developing new ideas on what an atom “looks” like as a result of these properties

Quantum Mechanical ModelElectrons are found in areas of definite energy (PELs)Electrons do not travel in definite paths around nucleus

Where are the electrons?

•Electrons are located in areas of most probable location (orbitals)•Visualized as a cloudy like region around the nucleus

Orbitals

Electrons found in orbitals which are part of a sublevel of each energy level

Electron configurations

According to the Wave – Mechanical Model

Definition

• Shows the arrangement of electrons in the atom

Sublevels of PELS

1. within an energy level, orbitals with different shapes occupy different regions, known as sublevels

2. the # of the principal energy level will identify the possible number of sublevels

3. first 4 assigned are the s, p, d, and f

S - sublevel

a. s sublevels have the lowest energy

b. contains one orbitalc. each orbital can hold a

max of 2 e-

d. has spherical shape

P sublevels

a. contains 3 orbitals b. Max of 6 e-, along 3 axisc. has peanut shape

D Sublevel

a. contains 5 orbitals b. has double peanut

shape

F sublevel

a. contain 7 orbitalsb. Has most energy of all sublevels

Chart of PELs and sublevelsPEL Sublevel # orbitals # electrons

1

2

3

4

The Rules for Electron Configurations• Aufbau principle – an electron occupies the lowest

energy orbital that can receive it

Fill order:

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d 6f

7s 7p 7d 7f

The Aufbau principle helps us to determine the electron configuration of atoms.

• Write the electron configuration of an atom of Beryllium (Be)

1. Identify the number of electrons in the atom.

Ex) ________

2. Begin to place electrons in the sublevels, by writing the number of electrons that will fit in each sublevel for that atom.

Ex) _____________________

1s

2s 2p

3s 3p 3d

4s 4p 4d 4f

5s 5p 5d 5f

6s 6p 6d 6f

7s 7p 7d 7f

Subtract the number of electrons that have been placed in the sublevel from the total number of electrons in the atom (this will tell you how many electrons you have leftover). Continue placing electrons in sublevels, following the fill order, until you run out of electrons for that atom.

Ex) _____________________

Configurations and the Periodic Table

Orbital Notation

• graphically represents the arrangement of electrons in their energy levels & sublevels

• Hund’s rule : electrons occupying the same orbital must have opposite spins (we’ll show that with arrows), and electrons will fill one electron per orbital (with identical spin) in a sublevel before they double up.

Write the electron configuration for N.

1s22s22p3

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for Ne

1s22s22p6

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for O

1s22s22p4

2p ______ ______ ______

Increasing 2s ______Energy

1s ______

Write the electron configuration for Ti

1s22s22p63s23p64s23d2

3d ______ ______ ______ ______ ______

4s ______3p ______ ______ ______3s ______2p ______ ______ ______

2s ______

1s ______

Valence Electrons

Definition: electrons that occupy the outermost PEL of an atom

- Maximum number of valence electrons is 8

Reason: result of full s and p sublevels

- energy levels (clouds) begin to overlap from the 3rd to the 4th energy level

How many valence electrons are there in the following:

Sodium: ________ Argon: ________

Oxygen: ________ Magnesium: ______

Carbon: ________ Strontium: ______

Ions

Definition: Electrically charged atoms (unequal # of protons and electrons)- formed when atoms lose or gain electrons- in order to have a complete valence energy level (stable configuration)

- Possible charges are listed on the Periodic Table

Cations

Def: a positively charged ion

- Formed when atoms lose electrons

Ex) Sodium atom Sodium ion (Na+1)

Sodium ion configuration same as Neon

Anions

Def: negatively charged ions

- Formed when atoms gain electrons

Ex) Fluorine atom Fluoride ion (F-1)

Fluoride ion configuration same as Neon