1. Unit 1: Atomic Structure & Electron Configuration

2. I. Theories and Models
Scientific Model – A pattern, plan, representation or description designed to show the structure or workings of an object, system or concept.

3. A. Greeks
400 B.C.
Democritus
particle theory- matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained and would be indivisible.
called nature’s basic particle atomos-indivisible
no experimental evidence to support theory

4. B. John Dalton 1808 English school teacher
Established first atomic theory:
Matter is composed of atoms.
Atoms of a given element are identical to each other, but different from other elements.
Atoms cannot be divided nor destroyed.
Atoms of different elements combine in simple whole-number ratios to form compounds.
In chemical reactions, atoms are combined, separated or rearranged.
Model: tiny, hard, solid sphere

5. C. JJ Thomson 1897 cathode ray tube experiment
given credit for discovering electrons, resulting in the electrical nature of an atom
Plum pudding model – sea of positive charges with negative charges embedded evenly throughout.

6. Ernest Rutherford
1911
Gold Foil (Alpha Scattering) Experiment

7. Conclusions: Model: atom is mostly empty space
most of mass of atom is in the nucleus
nucleus is positively charged
Model:

8. E. Niels Bohr 1913 Rutherford’s student
electrons arranged in energy levels (orbits) around the nucleus due to variation in energies of electrons
higher energy electrons are farther from nucleus
Planetary Model:

9. F. Quantum Model 1924-current Collaboration of many scientists
Better than Bohr’s model because it describes the arrangement of e- in atoms other than H
Based on the probability (95% of time) of finding and e- or an e- pair in a 3D region around the nucleus known as an orbital
Model (on board)

10. II. General Structure of Atom
nucleus
e- cloud
center of atom
p+ & n0 located here
positive charge
most of mass of atom, tiny volume
very dense
surrounds nucleus
e- located here
negative charge
most of volume of atom, negligible mass
low density

11. III. Quantification of the Atom
A. Atomic Number - the number of p+ in nucleus
All atoms of the same element have the same atomic number.
Periodic table is arranged by increasing atomic number.
if atom is electrically neutral, then the
#p+ = #e-

12. B. Mass Number - the total number of p+ & n0 in nucleus of an atom.
Round the atomic weight to a whole number
n0 = mass number - atomic number

13. C. Ions – atoms of an element with the same number of p+ that have gained or lost e-, therefore having a – or + charge
atoms form ions in order to be more stable like the noble gases
anion – ion with negative charge (gained e-)
non-metal elements tend to form anions (ex. S2-)
change the end of the element name to –ide (sulfide ion)
cation – ion with a positive charge (lost e-)
metal elements & H tend to form cations (ex. Sr2+)
Roman numerals may be used in the name of some metal ions that can lose various numbers of e- (ex. Tin (IV) ion)

14. D. Isotopes – atoms of an element having the same number of p+, but a different number of n0, resulting in a different mass number.
Two ways to represent isotope symbols:
or C-14
Write mass # after the element name:
carbon-14
mass #
mass #
atomic #

15. Isotopes of Hydrogen Hydrogen-1 (protium) 1 Hydrogen-2 (deuterium) 2
Name
Symbol e- n0 p+
Mass #
Atomic #
Hydrogen-1 (protium) 1
Hydrogen-2 (deuterium) 2
Hydrogen-3 (tritium) 3

16. E. Average Atomic Mass – weighted average of all natural isotopes of an element expressed in amu* (atomic mass units).
based on % abundance of isotopes
steps for calculating:
change % to decimal
multiply decimal and mass number
add all results
place amu unit with answer
*amu=1/12 mass of C-12 isotope

17. IV. Electromagnetic Radiation
A. Properties
1. Form of energy which requires no substrate to travel through.

18. 2. Exhibits properties of a sine wave
amplitude
wavelength (λ)
crest
trough
line of origin

19. a. wavelength = distance between consecutive
a. wavelength = distance between consecutive crests (Greek letter lambda = λ)
b. frequency = # wave cycles passing a given point over time (seconds); (Greek letter nu = ν )
*measured in Hertz (Hz)= 1/s, s-1, or per second
c. all types of ER travel in a vacuum at the speed of light (c) = 3.00 x 108 m/s

20. 3. light equation
c=λν
* λ & ν are inversely (indirectly) proportional (as one increases, the other decreases)

21. *energy equation: E=hνλ ν
*energy & ν are directly related (as one increases/decreases, so does the other
*energy equation: E=hν
h= Plank’s constant = 6.63 x J·s

22. V. Emission/Absorption Spectra
*The e- is the only SAP that absorbs/emits energy.
A. Absorption Spectrum –when an e- absorbs energy, it moves from the ground state (most stable arrangement of e-) to an excited state (which is not stable)
B. Emission Spectrum - when an e- emits energy, it falls from the excited state back to ground state, releasing energy in the form of electromagnetic radiation, which may be visible
*unique to each atom

23. VI. Electron Configuration
A. Describes the arrangement of e- in an atom
1. each main energy level is divided into sublevels
2. each sublevel is made up of orbitals, each of which can hold up to 2 e-
*chart

24. Sublevel
# of orbitals
shape s 1 p 3 d 5 f 7

25. 3. due to main energy levels getting closer
3. due to main energy levels getting closer together, sublevels overlap

26. 4. Aufbau principle – states that e- fill
4. Aufbau principle – states that e- fill orbitals of lower energy sublevels first
5. Abbreviated Configurations – use the preceding noble gas symbol (in brackets) to represent the filled inner core of e-. Then write the remaining configuration for the atom.

27. 6. Orbital Configurations- arrangement of e- within sublevels
2 rules determine arrangement:
a. Hund’s Rule – each orbital within a sublevel receives 1 e- before it gets 2
* orbitals in the same energy sublevel are degenerate (of equal energy)
b. Pauli Exclusion Principle – no 2 e- in an orbital can have the same spin.
= clockwise spin = counterclockwise spin
*exceptions