1. Dalton’s Atomic Theory
1. Elements are made of tiny particles called atoms.
2. All atoms of a given element are identical (not exactly; isotopes)
3. The atoms of a given element are different from those of any other element.
4. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.
5. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.

2. Laws of Chemical Combination
Law of Definite Proportions: Different samples of the same compound always contain its constituent elements in the same proportions by mass
This is also called the Law of Constant Composition
Suppose we analyze samples of water from different sources
We will find in each sample the same ratio by mass of hydrogen to oxygen.

3. So…
A 10.0 gram sample of water, H2O, is comprised of 8.9 grams oxygen and 1.1 grams hydrogen.
Thus, a gram sample of water, is comprised of 89.0 grams of oxygen and 11.0 grams of hydrogen.

4. Laws of Chemical Combination
Law of Multiple Proportions (or, Dalton’s Law): If two elements can combine to form more than one compound, then the masses of one element that combine with a fixed mass of the other element are in the ratios of small whole numbers
For instance, the atom carbon forms two stable compounds with the atom oxygen:
Carbon Monoxide (C1O1) and Carbon Dioxide (C1O2)
Neither C1.2O1.3 nor C1.2O2.2, respectively

5. Formulas of Compounds
Chemical Formula: An expression showing the chemical composition of a compound in terms of the symbols for the atoms of the elements involved.
Rules for Writing Formulas
1. Each atom present is represented by its element symbol.
2. Metals are written first, followed by non-metals.
3. The number of each type of atom is indicated by a subscript written to the right of the element symbol.
4. When only one atom of a given type is present, the subscript 1 is not written.

6. Formulas of Compounds
Write the formula for each of the following compounds:
(a) A molecule contains four phosphorous atoms and ten oxygen atoms.
(b) A compound contains one uranium atom and six fluorine atoms.
(c) A compound contains one aluminum atom and three chlorine atoms.

7. The Structure of the Atom
Atom: The basic unit of an element that can enter into chemical combination
They are made of even smaller particles called subatomic particles (Dalton was wrong!)
Electrons
Protons
Neutrons

8. Summary of the Structure of the Atom
Mass and Charge of Subatomic Particles
Particle Mass (grams) Charge Unit
Electron x
Proton x
Neutron x
Nucleus in center of atom – houses protons & neutrons
Electrons around nucleus in orbitals

9. Atomic Symbols
Atomic Number: The number of protons in the nucleus of an atom.
Mass Number: The total number of neutrons (variable) and protons present in the nucleus of an atom.

10. Atomic Symbols We use the symbol to represent the atom
X = the symbol of the element
A = the mass number
Z = the atomic number
How do we calculate the number of neutrons?
Mass Number =
Protons + Neutrons
Thus, neutrons = A - Z

11. Atomic Symbols: Practice
Give the atomic symbol for a species that houses 38 protons and 48 neutrons.
Give the atomic symbol for a species that houses 38 protons and 50 neutrons.
What is the difference?

12. Isotopes
Atoms having the same atomic number but different mass numbers; i.e., different number of neutrons.
The Periodic Table houses average mass numbers based on percent abundance of each isotope.

13. Isotopic abundance
% abundance = (# atoms of isotope/total # of atoms of all isotopes) x 100%
For ex: element X has two isotopes
X-20 and X-21
Out of every 100 atoms of X, 90 are X-20 and the rest (10) are X-21
So, X-20 has an abundance of (90/100) x 100% = 90%
And X-21 has an abundance of 10%

14. Atomic weight
Atomic weight = (% abundance isotope/100)(mass of isotope 1) + …
An average measurement
Shown on the periodic table
Measured in atomic mass units (amu)
But more commonly in molar mass or grams/mole
Will discuss anon

15. Practice: What’s the atomic weight?
B-10 = 19.91% abundance
amu = mass
B-11 = 80.09% abundance
amu = mass

16. Atomic mass unit Amu or u = 1/12th mass of C-12 = 1.661 x 10-24 g
(C-12= 12 amu)
Used for subatomic particles

17. The mole
Mole = amt that contains as many “things” as there are atoms of 12 g of C-12
1 mole = x 1023 particles
Molar mass (MM) = mass in grams per 1 mole of particles (g/mol)

18. Practice
How much does one atom of argon (Ar) weigh?

19. Practice
How many moles and atoms of Ar are in a 5.00 gram sample?

20. Your turn
How many grams of niobium (Nb) are there in a 2.00 mole sample?
How many atoms?

21. Introduction to the Periodic Table

22. What do the numbers mean?
Each cell houses:
Elemental symbol
Elemental name
Atomic number
Molar mass
Sundry information
Let’s take a look

23. Introduction to the Periodic Table
Elements symbolized
by either one capital letter
or two letters; first capital, second lower-case
Examples:
B = boron
Cl = chlorine
P = phosphorus
Na = Sodium
Symbols don’t always match up with English names
Because use Greek and Latin words

24. Introduction to the Periodic Table
Groups: The elements in a vertical column of the periodic table
“Old” School: Group-A and Group-B
Taller groups: A
Shorter groups: B
“New” School: Groups I - XVIII
Elements classified in groups based on valence electron configuration: similar chemical properties
Group names:
Alkali Metals: The Group 1A elements (LiFr)
Alkaline Earth Metals: The Group 2A elements (BeRa)
Halogens: The Group 7A elements (FAt)
Noble Gases: The Group 8A (HeRn)
Transition Metals: The Group-B elements

25. Introduction to the Periodic Table
Period: The elements in each horizontal row of the periodic table
There are 7 periods
Increase in atomic number going to the right
Two rows at bottom are:
Lanthanides or rare-earth metals
Actinides (contain transuranium metals)

26. Introduction to the Periodic Table
Elements can be divided into 3 categories:
Metals
Metalloids
Nonmetals
Step-ladder divides metals from nonmetals
Metalloids surround step-ladder
Periodic Table roughly 75% metals
Let’s label the Periodic Table handout!

27. Introduction to the Periodic Table: Metals
1. Efficient conduction of heat and electricity
2. Malleability (they can be hammered into thin sheets)
3. Ductility (they can be pulled into wires)
4. A lustrous (shiny) appearance

28. Introduction to the Periodic Table: Metalloids
Or semimetals, have properties that fall between those of metals and nonmetals

29. Introduction to the Periodic Table: Nonmetals
Usually poor conductors of heat and electricity
More varied physical properties than metals

30. Natural States of the Elements
All metals and metalloids are solid
Except mercury = quicksilver
Non-metals both solid and gaseous
Noble gases
H, O, N, F, Cl
Some nonmetals are diatomic
A molecule that consists of two similar atoms
All halogens
Oxygen, nitrogen, and hydrogen
One is liquid
Bromine

31. Natural States of the Elements
Allotropes: Two or more forms of the same element that differ significantly in chemical and physical properties.
Example
Phosphorus: red and white
Carbon: Diamond, Graphite, Buckyball