Atomic Structure & Electron Configuration

Ch.3

(3-1) Atomic Theory

• All matter is composed of indivisible particles called atoms

• Certain characteristics shared by all chemical cmpds

Law of Definite Proportions

• Any sample of a cmpd always has the same composition (by mass)– Ex: NaCl always 39% Na & 61% Cl

Law of Conservation of Mass

• Product mass = reactant mass– Ex: S + O2 SO2

sulfur oxygen sulfur dioxide

32.07 amu 32.00 amu 64.07 amu

Law of Multiple Proportions

• Mass ratio for combining 1 element w/ another are expressed in small whole #’s– Ex: NO2

NO

N2O

Dalton’s Atomic Theory

1. Matter is made of indivisible & indestructible atoms

2. Atoms of a given element are identical in their properties

3. Atoms of different elements differ in their properties

Dalton’s Atomic Theory

4. Atoms of different elements combine in simple whole-# ratios to form cmpds

5. Chemical rxns consist of the combination, separation, or rearrangement of atoms.

Modifications to Dalton’s Theory

• 2 principles no longer valid – subatomic particles– overlooked atoms combining w/ their own

type

Atomic Mass

• p+ + n0 (e- mass negligible)

• Units: atomic mass units (amu)

• Exactly 1/12 the mass of 1 carbon-12 atom

Atomic Mass to Kg

• 1 amu = 1.66 x 10-27 kg

• Mass of copper atom:

63.546 amu x 1.66 x 10-27 kg = 1.06 x 10-25 kg

1 amu

Mole

• (mol): amt of substance

• Avogadro’s constant: 6.02 x 1023 particles

1 mol

• 1 g/mol = 1 amu

Mass & Moles

• Mass of 1 mol of Fluorine atoms:

18.9984 amu x 1.66 x 10-27 kg x 1000 g

1 amu 1 kg

x 6.02 x 1023 = 18.9984 g/mol

1 mol

(3-2) Subatomic Particles

• Smaller particles that make up an atom

• 3 types

Particle Location Size Charge

Electron (e-)

Outside nucleus

0.000 549 amu

Negative

Proton

(p+)

Nucleus 1.007 amu

Positive

Neutron (n0)

Nucleus 1.009 amu

Neutral

Electrodes

• Anode: where e- enter a metal; + charge

• Cathode: where e- leave a metal; -charge

Cathode Ray Tube Experiment

• J.J. Thomson– e- had mass– e- had negative charge

Nucleus

• Central region of an atom containing p+ & n0

• Plum-pudding model: Thomson– e- embedded in positively charged ball of

matter

Gold Foil Experiment

• Ernest Rutherford

• Alpha particles: + charged particles– dense nucleus w/ lots of empty space

around it

Atomic Number

• # of p+ in the nucleus of an atom

• Mass #: total # of p+ & n0 in the nucleus

• 42He: mass # = 4, atomic # = 2

– 2 p+, 2 n0, 2 e-

Coulomb’s Law

• The closer 2 charges come together, the greater the force b/w them

• Opposites attract, likes repel

• Strong force: greater than repulsive force at close distance– p+ in nucleus

Isotopes

• Atoms of the same element w/ different #’s of n0

– Ex: Helium-3 (1n, 2p), Helium-4 (2n, 2p)

• Radioisotope: unstable atom that undergoes radioactive decay

(3-3) Electromagnetic Spectrum

• Total range of electromagnetic radiation– e- have properties of both particles &

waves

Wavelength

• λ: distance b/w 2 consecutive peaks or troughs– m

Frequency

• v : # of waves that pass a stationary pt. in 1 sec.– Hz

Speed of Light

• c = 3.0 x 108 m/s

• Speed of light = freq. x wavelength

c = v λ

– Ex: v = _c_ = 3.0 x 108 m/s

λ 7.6 x 10-7 m

= 3.9 x 1014 /s = 3.9 x 1014 Hz

Line-emission Spectrum

• Distinct lines of colored light produced by excited atoms of an element passing through a prism

Quantum Theory

• Tells exact E of the e-, but only the probability that the e- is in a particular region– Quantized

Quantum #’s

• Principal (n): 1-7, E level e- is located

• Shape: sublevel w/in E level

• Orientation: orbital w/in sublevel

• Spin: +1/2, -1/2

Bohr’s Atomic Model

• Describes e- in terms of their E states– Ground state: lowest E state– Excited state: higher E state than ground

Orbitals

• Regions of space where you can expect to find e- of specific E

• s (sphere), p (dumb-bell), d, f

The “1s” orbital is asphere,centeredaround the nucleus

The 2s electrons have a higher energy than the 1selectrons. Therefore, the 2selectrons are generally moredistant from the nucleus,making the 2s orbital largerthan the 1s orbital.

The three 2porbitals,2px, 2py, 2pz

x

y

z

so 3s electrons aregenerally foundfurther from thenucleus than 1s,2s, or 2p electrons

Pauli Exclusion Principle

• No more than 2 e- can occupy a single orbital & must have different spins

Electron Configuration

• Description of occupied e- orbitals in an atom

• s (1 orbital), p (3), d (5), f (7)

• F: 1s22s22p5

• Main E level, orbital, # of e-

s p

s

d

f

Orbital Diagrams

• Similar to e- config. but lines designate orbitals and arrows designate e-– __ __ __ __ __

1s 2s 2p

http://www.colorado.edu/physics/2000/applets/a2.html

Aufbau Principle

• Lowest & most stable E levels filled first– 4s before 3d

Hund’s Rule

• Orbitals are occupied by 1 e- before any pairing occurs

Noble Gas Configuration

• Electron Config.: S: 1s22s22p63s23p4

• Noble Gas Config.: S: [Ne]3s23p4

• Unless specified do not use noble gas configuration!!!!