homework read pages 360 – 364 372 – 375 379 & 380
TRANSCRIPT
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