1. Agriculture Chemistry
Atomic Structure
Agriculture Chemistry

2. Defining the Atom
The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”)
He believed that atoms were indivisible and indestructible
His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy

3. Dalton’s Atomic Theory (experiment based!)
All elements are composed of tiny indivisible particles called atoms
Atoms of the same element are identical. Atoms of any one element are different from those of any other element.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds
In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.
John Dalton
(1766 – 1844)
Pictured atom as sphere with no internal structure

4. Sizing up the Atom
Elements are able to be subdivided into smaller and smaller particles – these are the atoms, and they still have properties of that element
If you could line up 100,000,000 copper atoms in a single file, they would be approximately 1 cm long
Despite their small size, individual atoms are observable with instruments such as scanning tunneling (electron) microscopes
Not all atoms are created equal!

5. Structure of the Nuclear Atom
One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles:
Electrons, protons, and neutrons are examples of these fundamental particles

6. Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron

7. Conclusions from the Study of the Electron:
Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons.
Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons
Electrons have so little mass that atoms must contain other particles that account for most of the mass

9. Conclusions from the Study of the Electron:
Eugene Goldstein in 1886 observed what is now called the “proton” - particles with a positive charge, and a relative mass of 1 (or 1840 times that of an electron)
1932 – James Chadwick confirmed the existence of the “neutron” – a particle with no charge, but a mass nearly equal to a proton

10. The Rutherford Atomic Model
Based on his experimental evidence:
The atom is mostly empty space
All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”
The nucleus is composed of protons and neutrons (they make the nucleus!)
The electrons distributed around the nucleus, and occupy most of the volume
His model was called a “nuclear model”

11. Rutheford’s Gold Foil Experiment

12. Review!

13. Distinguishing among atoms
-Elements are different because they contain different numbers of protons. Atomic Number- # protons in atom. This identifies the element. Remember, atoms are neutral, so # positive particles (protons) must equal negative particle (electrons) Therefore, # protons = # electrons Mass Number- # protons + # neutrons. How to Find: # Electrons: Atomic # # Protons: Atomic # # Neutrons: Mass # - Atomic #

14. Practice
Carbon
Sodium
Nitrogen

15. Practice Finding # protons, neutrons, electrons Fabulous Foldable!!
Include definitions and an example for the following terms:
Proton
Neutron
Electron
Nucleus
Mass Number

16. Distinguishing Among Atoms

17. Isotopes
Isotopes- Atoms that have the same number of protons but different number of neutrons.
They also have different atomic masses/mass numbers
However, isotopes are chemically alike because they have identical numbers of protons and electrons (which are the particles responsible for chemical behavior)

18. Atomic Mass
In nature, most elements occur as a mixture of two or more isotopes.
Each isotope has a fixed mass and natural abundance (the percentage that isotope is found in nature)
Atomic mass- weighted average mass of atoms in a naturally occurring sample of the element. This reflects the mass and the relative abundance of the isotopes as they occur in nature.
Atomic mass is expressed in amu or atomic mass units
1 atomic mass unit = × kilograms

19. Calculating Average Atomic Mass
CHLORINE: atomic mass = on p. table
Chlorine-35 accounts for 75% naturally occurring atoms (75% natural abundance) with mass of 34.9
Chlorine-37 accounts for 25% naturally occurring atoms (25% natural abundance) with a mass of 36.9
(.75 x 34.9) + (.25 x 36.9) = 35.4

20. Calculating Atomic Mass for Carbon
Carbon has 2 stable isotopes:
Carbon-12 with a natural abundance of 98.89% and mass of 12.00amu
Carbon-13 with a natural abundance of 1.11% and mass of amu
Mass of C on p. table: 12.01am
Calculate Atomic Mass of Carbon:
(12.000amu x .9889) + (13.003amu x .0111) = 12.01amu

21. Practice Check answer on periodic table Mass # = 63.55
The element copper has naturally occurring isotopes Copper 63 and Copper 65. The relative abundances and atomic masses are 69.2% for mass = amu, and 30.8% for mass = amu.
Calculate average atomic mass for copper.
Check answer on periodic table
Mass # = 63.55

22. Practice Check answer on periodic table!
Calculate the atomic mass of bromine. The two isotopes of bromine have atomic masses and relative abundances of amu (50.69%) and amu (49.31%)
Check answer on periodic table!
Br = 79.90

23. Average Atomic Mass Stations!
You will start at one of the three stations around the room.
Write down the question on a piece of paper, then solve!
Show all your work
When you’re done, go back to your desk and study your notes in preparation of the review game!

24. Review!

25. The smallest particle of an element that retains the properties of that element is a(n)
A. atom
B. electron
C. proton
D. neutron

26. The subatomic particles of an atom are
A. Protons and neutrons
B. Protons and electrons
C. Electrons and Neutrons
D. Protons, neutrons, and electrons

27. What two particles are in the nucleus?
A. protons and electrons
B. neutrons and electrons
C. protons and neutrons

28. What is the charge of an electron?
A. Negative
B. Positive
C. Neutral

29. What was Rutheford’s model of the atom?
A. A dense sphere with no charge
B. A tiny sphere with negative charged particles throughout
C. A dense nucleus center with orbiting electrons

30. Dalton thought the atom was a
A. tiny, dense sphere with no charge
B. A tiny sphere with negatively charged particles throughout
C. A positively centered nucleus with negative electrons orbiting around it

31. J.J. Thompson discovered the electron with the use of the
A. Gold Foil experiment
B. Cathode Ray Tube
C. an electron microscope

32. All atoms are
A. positively charged, the number of protons exceeding the number of electrons
B. negatively charged, with the number of electrons exceeding the number of protons
C. neutral, with the number of protons equaling the number of electrons
D. neutral, with the number of protons equaling he number of electrons, which is equal to the number of neutrons.

33. A theory is A. proposed explanation for an observation
B. well tested explanation for a broad set of observations
C. summary of the results of many observations
D. procedure used to test a proposed explanation.

34. Which of the following is NOT a physical property
A. mass
B. color
C. Ability to rust
D. melting point

35. When a substance forms a vapor, what physical state was it before?
A. gas
B. liquid
C. solid
D. liquid or solid

36. What state of matter has no definite shape or volume?
A. solid
B. Liquid
C. Gas
D. Both a and c

37. Which state has a definite volume but no definite shape?
A. gas
B. Solid
C. Liquid
D. both a and c

38. Which state of matter has both a definite shape and definite volume?
A. solid
B. Liquid
C. Gas
D. both a and c

39. What is another word for a homogeneous solution?
A. Solutions
B. Homozygous mixture
C. Mixture
D. Compound

40. Which of the following is an example of a homogeneous mixture?
A. Oil and water
B. Rubbing alcohol
C. Italian salad dressing
D. Raw milk

41. Which is true for compounds?
A. They can be physically separated
B. They have compounds that vary
C. They are substances (aka pure substances)
D. They have similar properties to elements.

42. Which of the following is a chemical property?
A. hardness
B. Color
C. melting point
D. ability to react with oxygen

43. When metal rusts, it is evidence of a
A. Physical change
B. Chemical change
C. homogeneous solution
D. heterogeneous solution

44. What is the difference between a mixture and a substance (aka pure substance)
A. substance are compounds, mixtures are not
B. Mixtures are groups of elements and compounds arent
C. Sample of the same substance have different properties
D. Mixtures can be physically separated, while compounds can’t.

45. Quick Review In scientific method:
Another word for independent variable is manipulated variable.
Another word for dependent variable is responding variable

46. The variable that is observed during an experiment is called what type of variable?
A. independent
B. manipulated
C. control
D. responding

47. All of these are examples are physical changes EXCEPT:
A. bending
B. cutting
C. rusting
D. polishing

48. During a chemical reaction
A. matter is neither created nor destroyed
B. some matter is destroyed
C. some matter is created
D. some matter is destroyed, some is created

49. The number 2012 in scientific notation is
A x 10^3
B x 10^-3
C x 10^-3
D x 10^4

50. In the measurement 0.709ml, which digit is the least precise?
B. 0
C. 9
D. all numbers

51. In the measurement, .6745g, which number is the estimated digit?

52. When a measurement is close to the correct value, it has good
A. Precision
B. Accuracy
C. Usefulness
D. Reproducibility

53. The closeness of your measurement to those of your lab partners indicates
A. accuracy
B. precision
C. reproducibility
D. usefulness

54. How many significant figures are in 3008?
B. 4
C. 1
D. 5

55. How many sig figs are in ?
A. 2
B. 6
C. 5
D. 3

56. Round 1050 to two significant figures
A. 1.0 x 10^3