1. Did you practice your conversions today?

3. Classifications of Matter
Pure Substances:
Matter that has a fixed or definite composition
Elements
Composed of only one type of atom
Compounds
Composed of multiple types of atom
Ex. Water (H2O)
Always same proportion of hydrogen to oxygen
Chemical process can break compounds down into simpler substances

5. Example: NaCl

6. Mixtures
Almost everything exists as a mixture (clean air, water, etc.)
Heterogeneous Mixture:
One or more visible boundaries; not uniform
Example: milk
Homogeneous Mixture:
No visible boundaries; individual atoms, ions or molecules mixed
Example: sugar water

7. Mixtures v. Compounds In what ways are mixtures not compounds?
Proportions of the components can vary
The individual properties of the components are observable
The components can be separated by physical means

8. Pure substance or mixture?
Salt water
Helium gas
Vegetable soup
Hydrogen peroxide (H2O2)
MIXTURE
PURE / ELEMENT
MIXTURE
PURE / COMPOUND
Are the mixtures homogeneous or heterogeneous?

9. Elements and Symbols Elements: Chemical symbols
primary substances from which all other things are built.
Cannot be broken down into simpler substances
Chemical symbols
Each element has its own symbol
One or two letter abbreviations
First letter always capital letter
Second letter always lowercase letter
Ex. cobalt = Co
nitrogen = N

10. Elements Elements ordered by atomic number “Periodic” trends
Periodic table by Mendeleev (1871)

11. Reading the Periodic Table
Period: horizontal row Group: vertical column
Alkali Metals
soft, shiny metals; good electrical/thermal conductors
react vigorously with water
Alkaline earth metals:
shiny metals, less reactive than alkali metals
Halogens:
strongly reactive (i.e. Cl2, Br2)
Noble Gases:
unreactive

12. Metals, Nonmetals, and Metalloids
Left side of zigzag “staircase”
Shiny solids (Hg is a liquid!)
Ductile and malleable
Good electrical/thermal conductors
Nonmetals:
Dull
Poor electrical/thermal conductors
Lower melting points and densities
Metalloids:
B, Si, Ge, As, Sb, Te, Po, At

13. The Atom
Atom: smallest particle of an element that retains the characteristics of that element.
Dalton’s Atomic Theory (1808)
All matter is made up of tiny particles called atoms
All atoms of a given element are:
Similar to one another
Different from atoms of other elements
Compounds are combinations of atoms of two or more different elements. A particular compound always:
Is made up of same kinds of atoms
Has the same number of each kind of atom
Chemical reaction: rearrangement, separation or combination of atoms

14. Structure of an Atom
Rutherford gold foil experiment

15. Atoms and Subatomic Particles
Diameter of one atom: 0.1 – 0.5 nm
(Carbon atom: 0.15 nm)

16. Atomic Number and Mass Number
= # of protons in atom
Atoms are electrically neutral
# protons = # electrons
Mass Number
= # of protons + # of neutrons

17. Isotopes Mg Isotopes: Atomic Symbol
atoms of the same element that have different numbers of neutrons
Atomic Symbol 24
Mass # Mg 12
Atomic #

18. Isotopes of Carbon
12C : 6 protons + 6 neutrons 13C : 6 protons + 7 neutrons 14C : 6 protons + 8 neutrons
98.89 %
1.11 %
<0.01 %
All have nearly identical chemical behavior

19. Atomic Mass
Atomic Mass: weighted average of masses of all the naturally occurring isotopes of that element
Example: chlorine
Contribution to
average Cl atom
Mass (amu)
x Abundance (%) =
35Cl
34.97 x =
26.50 amu +
8.954 amu
37Cl
36.97 x =
Atomic mass of Cl
35.45 amu

20. Electromagnetic Spectrum
All waves in the EM spectrum travel at the same speed. Speed of light: c = 3.00 x 108 m/s
Longer wavelength  smaller energy
Shorter wavelength  more energy

21. Properties of Waves Which wave has the longer wavelength?
Which wave has more energy?

22. Carbon atoms

23. Atomic Spectra When light passes through a prism, it is dispersed
Splits into specific colors
Each type of material will produce different wavelengths of light when heated.
These patterns are called atomic spectra

24. Atomic Spectra

25. Energy States Each atomic spectrum line is associated with an electron
changing energy
Electrons can only have certain
energy levels (quanta)
Energy levels:
Principal quantum numbers
Positive integers
Smaller numbers
closer to nucleus, lower energy
Bigger numbers
Further from nucleus, higher energy
Note: biggest “step”
from n=1 to n=2

26. Changes in Energy Levels
Ground state: lowest level
n = 1
Excited states: higher levels
n = 2, 3, 4,…
Energy absorbed: electron jumps up to higher E
Energy released: electron drops down to lower E
If a photon is emitted, light may be observed.
The color of the light emitted relates to the wavelength of the photon emitted

27. Energy Sublevels Each level consists of sublevels
The number of sublevels in each level equals the principal quantum number
n = 1  one sublevel
n = 2  two sublevels
n = 3  three sublevels
n = 4  four sublevels 1s
2s & 2p
3s & 3p & 3d
4s & 4p & 4d & 4f
Increasing energy of sublevels within an energy level:
s < p < d < f

28. Orbitals
There is no way to know exactly where an electron is in an atom
Orbitals describe the regions with the highest probability of finding an electron
Each type of orbital has a given shape:
s orbital
p orbitals

29. Orbitals d orbitals Each orbital can hold TWO electrons s orbitals:
p orbitals:
d orbitals:
2 e-
6 e-
10 e-

30. Orbital Energy Levels Pauli Exclusion Principle:
Any orbital can hold up to 2 electrons
Electrons want to sit in lowest energy level
Which is lower: 2s or 2p orbitals?
For a given n value:
Order of sublevel energy: s < p < d < f
Orbital Diagrams

31. Electron Configurations
Periodic Table tells us the number of e- in an atom
Electron Configuration:
tells us which orbitals electrons are in for a given atom
Example: Hydrogen
Atomic Number: 1
(How many electrons?) 1 1s
Orbital Diagram: 1
Electron Configuration: 1s

32. Electron Configurations
Example: Helium
Atomic Number: 2
(How many electrons?) 2 1s
Orbital Diagram: 2
Electron Configuration: 1s
Example: Lithium
Atomic Number: 3
(How many electrons?) 3 1s 2s
Orbital Diagram: 2 1
Electron Configuration: 1s 2s

33. Electron Configurations
Example: Boron
Atomic Number: 5
(How many electrons?) 5 2p 1s 2s
Orbital Diagram: 2 2 1
Electron Configuration: 1s 2s 2p

34. Electron Configurations
Example: Oxygen
Atomic Number: 8
(How many electrons?) 8 2p 1s 2s
Orbital Diagram: 2 2 4
Electron Configuration: 1s 2s 2p 2 4
Abbreviated Configuration:
[He] 2s 2p

35. Electron Configurations relate to the Periodic Table!
For s block elements: electron configuration should end with electrons in s orbitals
Ex. Na: 1s2 2s2 2p6 3s1
For p block elements: electron configurations should end with electrons in p orbitals
Ex. P: 1s2 2s2 2p6 3s2 3p3
For d block elements: electron configurations should end with electrons in d orbitals
Ex. Ni: 1s2 2s2 2p6 3s2 3p6 4s2 3d8
Note: 4s orbital comes before 3d orbital

36. Sublevel Order Exceptions in sublevel order:
Cr: 1s2 2s2 2p6 3s2 3p6 4s2 3d4
Cr: 1s2 2s2 2p6 3s2 3p6 4s1 3d5
Cu: 1s2 2s2 2p6 3s2 3p6 4s2 3d9
Cu: 1s2 2s2 2p6 3s2 3p6 4s1 3d10
Half-filled or totally filled orbitals are more stable

37. Periodic Trends Valence electrons: Electron-Dot Symbols
Outermost electrons (last e- in electron config.)
Responsible for chemical behavior
Elements in a group have same number of valence e-
Elements in a group have similar chemical properties
Electron-Dot Symbols
Boron (B): 1s2 2s2 2p1
How many valence electrons? 3 B

38. Periodic Trends Electron-Dot Symbols 1s2 2s2 2p6 3s2 3p1
Alumnium (Al):
1s2 2s2 2p6 3s2 3p1 Al
How many valence electrons? 3
Chlorine(Cl):
1s2 2s2 2p6 3s2 3p5 Cl
How many valence electrons? 7

39. Periodic Trend: Atomic Size
Atomic radius: distance from nucleus to outermost e-
Decreases across a period
Increases down a group
(stronger pull from nucleus)
(more energy levels)

40. Periodic Trend: Ionization Energy
Ionization: removing an e- from an atom
Increases across a period
Decreases down a group
(stronger pull from nucleus)
(further from nucleus)

41. A neutral atom has 7 protons and 7 neutrons:
-What is the mass number?
-How many electrons does this element have?
-What is the atomic number?
-What Element is this?
-Is the atomic size Larger or Smaller than Boron?
-Is the atomic size Larger or Smaller than Phosphorus?
-What is the electron configuration?
-How many valence electrons?
-Write the electron dot symbol for this atom 14 7 7
Nitrogen
Smaller
Smaller
1s2 2s2 2p3 3 N .. .