1. Atoms and Elements Goals:
Describe atomic structure and define atomic number and mass number.
Understand the nature of isotopes and calculate atomic weight from the isotopic masses and abundances.
Explain the concept of the mole and use molar mass in calculations.
Know the terminology of the periodic table.

2. The Atomic Structure Experimental basis
One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).
She discovered ___________, the spontaneous disintegration of some elements into smaller pieces.
- Rays emitted by polonium and radium – radioactive atoms disintegrate and emit rays: alpha (a), beta (b), gamma (g).
**Contradicted Dalton’s postulate: “atoms are indivisible”.

3. Experiment: Radiation
Three rays:

4. Experiment: Cathode-Ray Tubes
Electrons:
Same charge-to-mass ratio detected for different elements: electrons are present in all atoms.
Millikan (charge of the electron), Goldstein (positive ions).

5. Rutherford’s Gold Foil Experiment
Nucleus and the protons:
(+)
Chadwick (neutrons).

6. The Atomic Structure
J.J. Thomson and E. Rutherford (England ~1900) established a model of the atom – the basis of modern atomic theory.
Three subatomic particles:
Electrically positive protons
Mass = x g
Relative mass = atomic mass units (u)
Electrically neutral neutrons
Relative mass = u
Electrically negative electrons
Relative mass = u
Which particle is heavier, which particle is lighter?
____________ _______________

7. Atom Composition The atom is mostly empty space.
protons and neutrons in the nucleus.
the number of electrons is equal to the number of protons.
electrons in space around the nucleus.
extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

8. How big is an atom?
The radius of the typical atom is between 30 and 300 pm (3 x m to 3 x m). The radius of the nucleus is about pm.
If an atom were a macroscopic object, about the size of a football stadium, what would be the radius of the nucleus?
– __________________

9. What is Atomic Number?
Atomic number (Z) is the number of _____________ in the nucleus of an element. 13
Atomic number Al
Atom symbol
26.981
Atomic weight
All atoms of the same element have the same number of __________ in the nucleus.

10. What is Mass Number?
The mass number (A) is the number of ____________ plus the number of ____________ in the nucleus of an element.
C atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units (u)
1 u = x g
Mass Number (A) = # protons + # neutrons C 12 6 X A Z

11. What is the mass number of an iron atom with 30 neutrons?
The periodic table gives the atomic number for iron:
Why the periodic table gives a WEIGHT of = ? 26 Fe
Atomic number
Atom symbol
Atomic weight

12. Percent Abundance
50%/50% mixture
90%/10% mixture

13. What are isotopes? How do they affect atomic weight?
Because of the presence of atoms, the mass of a collection of atoms is an average of values.
Average mass = ATOMIC WEIGHT
Boron is 19.9% 10B and 80.1% 11B. That is, 11B is 80.1 percent abundant on earth.
What is the atomic weight of boron?
_________________

14. How many isotopes for H? 1H 1H 1H 1 proton and 0 neutrons, protium
1 proton and 1 neutron, deuterium 2 1H 3
1 proton and 2 neutrons, tritium
(radioactive) 1H

15. Students should become familiar with the
Gallium has two isotopes: 69Ga and 71Ga. How many protons and neutrons are in the nuclei of each of these isotopes? If the abundance of 69Ga is 60.1%, what is the abundance of 71Ga?
Students should become familiar with the
use of atomic number and mass number,
especially in isotopes calculations.

16. How are the masses of isotopes and their % abundances determined?
They are experimentally determined by using a ___________________________.
By changing the magnetic field, a beam of charged particles of different mass can be focused on the detector, and a spectrum of masses is observed.

17. Copper exists as two isotopes: 63Cu (62. 9298 u) and 65Cu (64. 9278 u)
Copper exists as two isotopes: 63Cu ( u) and 65Cu ( u). What is the approximate percentage of 63Cu in samples of this element?

18. Congratulations! You discovered a new element…
you name wyzzlebium (Wz). The average atomic mass of Wz was found to be amu and its atomic number is 120.
A) If the masses of the two isotopes of Wz are amu and amu, what is the relative abundance of each isotope?

19. Congratulations! You discover a new element…
B) What are the isotopic notations of the two isotopes? (e.g. W).
C) How many neutrons are in one atom of the more abundant isotope? A Z

20. What is Atomic Weight?
This tells us the mass of one atom of an element relative to one atom of another element.
OR — the mass of 1000 atoms of one element relative to 1000 atoms of another.
Example: an O atom is approximately times heavier than an C atom.
Define one element as the standard against which all others are measured
Standard = carbon

21. Counting atoms
In chemical reactions, how can we predict the amount of product given the mass of reactant?
Mg burns in air (O2) to produce white magnesium oxide, MgO.

22. The Periodic Table
Dmitri Mendeleev developed the modern periodic table. Argued that element properties are periodic functions of their atomic weights.
We now know that element properties are periodic functions of their __________ __________ (G. J. Moseley) . – Law of Chemical Periodicity
Students should become familiar with the organization of elements in the periodic table.

23. The Periodic Table
Family or
Group
Period

24. Elements Metals Metalloids (semimetals) Nonmetals
Solid (except for mercury)
Conduct electricity
Ductile (can be drawn into wires)
Malleable (can be rolled into sheets)
Alloys (solutions of one metal into another metal)
Metalloids (semimetals)
Physical characteristics of metals, but chemical characteristics of nonmetals.
Nonmetals
Do not conduct electricity (except from C – graphite)

25. Hydrogen Non-metal. Most abundant element in the universe.
Lightest element.

26. Group IA: Alkali Metals
React with water to give alkaline solutions.
Found in nature only combined in compounds.

28. Group IIA: Alkaline Earth Metals
React with water to give alkaline
solutions (except Be).
Found in nature only combined in compounds.

30. Group IIIA Cu Al All metals, but boron is a metalloid.
Al resists corrosion (in HNO3).
Cu Al
Gallium can be a liquid at room temp.
All metals, but boron is a metalloid.
Aluminum is the most abundant metal in the earth’s crust by mass (8.2%).

32. Group IVA Diamond Quartz, SiO2 C has large biological importance.
Nonmetal: C, Metalloids: Si, Ge, Metals: Sn, Pb.
All form analogous compounds such as their oxides: CO2, SiO2, GeO2, SnO2, PbO2.

33. What are allotropes? Characteristic of the chemistry of nonmetals.
Allotropes: _________________________ _______________________ each having its own properties.
C: graphite, diamond, buckminsterfullerene.

34. The periodic table

35. Practice Decide which represents more mass:
10 atoms of Fe or 10 atoms of K
b) 9 g of Na or 0.5 mol of Na

36. Group VA N2: makes up about ______ of earth’s atmosphere.
N and P have biological importance.
P has several allotropes.
Nonmetals: N2 and P, Metalloids: As and Sb, Metal: Bi.
Analogous oxides: N2O5, P2O5, As2O5.
White and red P

38. Group VIA O2: makes up ______of earth’s atmosphere.
S, Se, Te are the chalcogens (present in cupper ores).
O2 has an allotrope: O3 (ozone).
Nonmetals: O2, S and Se, Metalloids: Te, Metal: Po (radioactive).
Analogous oxides: SO2, SeO2, TeO2.

40. Group VIIA: Halogens
All nonmetals, named the halogens (salt forming, they react violently with metals of group IA.
All exist as diatomic molecules.
F2 and Cl2 are gases. Br2 is a liquid. I2 is a solid.

42. Group VIIIA: Noble Gases
All are gases.
The least reactive elements (called inert gases).
Helium is the second most abundant element in the universe. But non is abundant on earth or earth’s atmosphere (also called rare gases).

43. The Transition Elements
Lanthanides
Actinides

44. The Transition Elements
Most occur naturally in compounds. Ag, Au, and Pt are much less reactive and can be found in nature as pure elements.
Some are of biological importance: Fe, Zn, Cu, Co.

45. Essential Elements
Found in hemoglobin (Fe), vitamin B12 (Co).

46. Practice Element in the 2th period, group 3A
Alkali metal in the 4th period
Metalloid in group 6A
Noble gas in 3th period

47. Units for counting 1 dozen = 12 objects Eggs are measured by the dozen
1 ream = 500 objects
Paper is measured by the ream, 500 sheets

48. Counting atoms
Chemistry is a quantitative science—we need a “counting unit.”
MOLE
Definition: 1 MOLE is the amount of substance that contains as many particles (atoms, molecules) as there are in __________________.

49. How many Particles in one Mole?
Amedeo Avogadro ( ).
There is Avogadro’s number of particles in a mole of any substance.
x 1023
1 mole = x 1023 items

50. What is Molar Mass?
1 mol of 12C = g of C = x 1023 atoms of C
12.00 g of 12C is its MOLAR MASS
Taking into account all of the isotopes of C, the molar mass of C is g/mol.

51. One Mole Amounts

52. Summary
The atomic mass expressed in grams is the molar mass of an element. It is different for each element.
1 molar mass = atomic mass of an element in grams
One mole of any element contains Avogadro’s number of atoms.
1 mol of atoms = x 1023 atoms
You can use these relationships to make conversions between number of atoms, mass, and moles.

53. Mass Moles Conversion
It is essential to convert from moles to mass and from mass to moles.
grams
1 mol
Moles x
= grams
Grams x
= moles
1 mol
grams
molar mass
1/molar mass

54. What amount of Mg in moles is represented by 0.200 g? How many atoms?12
Atomic number Mg
Atom symbol
Atomic weight
Mg has a molar mass of g/mol.
Students should become familiar with calculations using molar mass and avogadro’s number.

55. Remember Go over all the contents of your textbook.
Practice with examples and with problems at the end of the chapter.
Practice with OWL tutor.
Practice with the quiz on CD of Chemistry Now.
Work on your assignment for Chapter 2.