Ch 4 Arrangement of Electrons in atoms

ELECTROMAGNETIC RADIATION subatomic particles (electron, photon, etc) have both PARTICLE and WAVE properties Light is electromagnetic radiation - crossed electric and magnetic waves: Properties : Wavelength,  (nm) Frequency,  (s -1, Hz) Amplitude, A constant speed. c 3.00 x 10 8 m.s -1

7.1

Properties of Waves Wavelength ( ) is the distance between identical points on successive waves. Amplitude is the vertical distance from the midline of a wave to the peak or trough. 7.1

Atomic Line Spectra Bohr’s greatest contribution to science was in building a simple model of the atom. It was based on understanding the SHARP LINE SPECTRA of excited atoms. Niels Bohr Niels Bohr ( ) (Nobel Prize, 1922)

Line Spectra of Excited Atoms Excited atoms emit light of only certain wavelengths The wavelengths of emitted light depend on the element. H Hg Ne

7.3

Uncertainty Principle Problem of defining nature of electrons in atoms solved by W. Heisenberg. It is impossible to describe the exact location of an electron. W. Heisenberg

b. the greatest number of electrons in an energy level is indicated by the equation - 2n 2 II.Quantum theory B.4 quantum numbers 1.principle quantum number a.energy level, n, 1,2,3,4,5 A. ground state – when electrons are in their lowest energy

2.energy sublevels and orbital a.energy states in an energy level, l b. the number of energy states = the energy level i.1 has 1, 2 has 2 ect ii.s p d f special people deserve fudge

3.orientation in space a.s - spherical b.p - dumbbell x,y, z c.d - 5 orientations d.f - 7

4.spin of electrons a.electrons spin - must have opposite spins in order to be in same orbital b.orbital - space occupied by a pair of electrons

(s orbitals) 7.6 1s

p Orbitals The three p orbitals lie 90 o apart in spaceThe three p orbitals lie 90 o apart in space

(d orbitals) 7.6

f Orbital

principal quantum number n n = 1, 2, 3, 4, …. n=1 n=2 n=3 7.6

Boundary surfaces for all orbitals of the n = 1, n = 2 and n = 3 shells 2 1 3d n= 3 There are n 2 orbitals in the n th SHELL

Electrons act as though they spin about an axis through their centers. Because there are two directions in which they can spin, the spin quantum number has 2 values The last quantum number is the spin quantum number

Orbital diagram Use lines to represent the orbital's and arrows to represent electrons H 1s

“Fill up” electrons in lowest energy orbitals (Aufbau principle) H 1 electronHe 2 electrons Li 3 electronsBe 4 electronsB 5 electronsC 6 electrons ?? 7.7

C 6 electrons The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule). N 7 electrons O 8 electrons F 9 electrons Ne 10 electrons 7.7

Paramagnetic unpaired electrons 2p Diamagnetic all electrons paired 2p 7.8

Electron configuration is how the electrons are distributed among the various atomic orbitals in an atom. 1s 1 principal quantum number n Sublevel (angular momentum) quantum number l number of electrons in the orbital or subshell 7.8

“Fill up” electrons in lowest energy orbitals (Aufbau principle) H 1 electron H 1s 1 He 2 electrons He 1s 2 Li 3 electrons Li 1s 2 2s 1 Be 4 electrons Be 1s 2 2s 2 B 5 electrons B 1s 2 2s 2 2p 1 C 6 electrons ?? 7.7

C 6 electrons The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund’s rule). C 1s 2 2s 2 2p 2 N 7 electrons N 1s 2 2s 2 2p 3 O 8 electrons O 1s 2 2s 2 2p 4 F 9 electrons F 1s 2 2s 2 2p 5 Ne 10 electrons Ne 1s 2 2s 2 2p 6 7.7

Noble gas notation Use the nearest noble gas that is behind the element and then add to it e.g write the noble gas notation for Na Ne is the nearest noble gas – its configuration is 1s 2 2s 2 2p 6 Therefore [Ne] indicates 1s 2 2s 2 2p 6 Na would be [Ne] 3s 1

What is the electron configuration and noble gas notation of Mg? Mg 12 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s 2 2s 2 2p 6 3s = 12 electrons 7.8 Abbreviated as [Ne]3s 2 [Ne] = 1s 2 2s 2 2p 6

What are the possible quantum numbers for the last (outermost) electron in Cl? Cl 17 electrons 1s < 2s < 2p < 3s < 3p < 4s 1s 2 2s 2 2p 6 3s 2 3p = 17 electrons Last electron added to 3p orbital n = 3 l=p

Try These! Write the shorthand (Noble gas notation) for: Cu W Au [Ar] 4s 2 3d 9 [Xe] 6s 2 4f 14 5d 4 [Xe] 6s 2 4f 14 5d 9

Electron dot diagrams Valence electrons – those electrons in the outer most energy Level (those with the highest number) Mg 12 1s 2 2s 2 2p 6 3s 2 Mg has 2 valence electrons Mg

Fe 26 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 Fe only has 2 valence electrons Fe

S 16 1s 2 2s 2 2p 6 3s 2 3p 4 S

Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei X A Z H 1 1 H (D) 2 1 H (T) 3 1 U U Mass Number Atomic Number Element Symbol 2.3

6 protons, 8 (14 - 6) neutrons, 6 electrons 6 protons, 5 (11 - 6) neutrons, 6 electrons Do You Understand Isotopes? 2.3 How many protons, neutrons, and electrons are in C 14 6 ? How many protons, neutrons, and electrons are in C 11 6 ? d.Canal rays - in 1886 Eugen Goldstein observed a cathode ray tube also generates a stream of positively charged particles

VI.Hund’s rule - electrons must be placed in each orbital before pairing them up VII.Valance electrons - those in the outer most energy level - gives elements its chemical properties VIII.orbital notation - lines IX.Electron configuration -1s 2 2s 2 2p 6 X.Nobel gas notation - {Ar} 4s 1 XI.Electron dot notation - only use the valance electron Odds and ends

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