1. Elements! Elements! Elements!
The Atom
Elements! Elements! Elements!

2. Objectives
Atomic Structure
The Atomic Theory and History
Atomic Math

3. Element Quizzes
In order to strengthen your familiarity with elements, you will be required to take element quizzes.

4. Element Wanted Poster
To demonstrate you knowledge of the concepts we will cover this six weeks. You will be expected to create a poster containing information about an element in the form of a WANTED poster.

5. Atomic Structure

6. Atomic Structure Atoms are the building blocks of matter.
Atoms make up elements – in fact everything is made of atoms!
There are 92 elements that occur naturally on Earth and about a dozen more that are man-made.
All the elements can be found on the Periodic Table of the Elements.
Atoms are mostly empty space.

7. There are two regions in the atom:
Nucleus
Most of the mass
Has a positive charge
Electron Cloud
Most of volume/space
Has a negative charge

8. Each region has specific subatomic particles
Nucleus
Protons p+
Have a positive charge
Mass = 1 amu
Discovered by E. Rutherford
Neutrons n0
Have a neutral or no charge
Discovered by J. Chadwick
Electron Cloud
Electrons e-
Have a negative charge
Mass = 0 amu
Discovered by J.J. Thomson

9. Let’s Check for Understanding
What are the two regions of the atom?
Which one is most of the mass of the atom?
Which one is most of the volume?
What are the subatomic particles and where are they found?

10. The Atomic Theory and History

11. Democritus and “atomos”
Democritus was an ancient Greek philosopher (he lived around 400 B.C.) who believed that matter could not be divided into smaller and smaller pieces forever and ever. He called the smallest pieces of matter “atomos” which means “indivisible” or “unbreakable.”

12. John Dalton
A nineteenth century scientist who also believed that matter was made up of atoms. He coined the term “atom” from the Greek word “atomos.”.

13. In this first modern atomic theory he stated:
1. Atoms are small, indivisible particles that are the building blocks of matter. (He viewed them as solid spheres.)
2. Atoms can be physically mixed together to form mixtures.
3. Atoms cannot be changed into another element through chemical reactions.

14. In this first modern atomic theory he stated:
4. Atoms can be combined or rearranged in whole number ratios to form compounds through chemical reactions.
5. All atoms of a particular element are exactly the same; atoms of different elements are different

15. Check for Understanding
What did Democritus believe?
Who expanded on Democritus’ beliefs and how?
Name the points of the Modern Atomic Theory.

16. Atomic Math

17. The Periodic Table of Elements
Let’s Review
From previous slides you have learned that all elements/atoms are listed on what?
The Periodic Table of Elements

18. H 1.008 Hydrogen 1 Atomic Number Element Symbol Atomic Mass
Element Name

19. H 1.008 Hydrogen 1 Atomic Number The whole number on the chart
Equivalent to the number of protons and electrons if there is no charge.

20. Atomic Mass
The decimal number on the chart.
Average number of different masses of naturally occurring isotopes of an element.
Units: may be in grams or atomic mass units (amu)
amu = defined as exactly 1/12th the mass of a carbon-12 atom 1 H
1.008
Hydrogen

21. 1 H
1.008
Hydrogen
Mass Number
The atomic mass rounded to the nearest whole number.
Equivalent to the number of protons plus the number of neutrons.

22. Atomic Math Overview # of p+ = Atomic Number
# of n = Mass Number - # of p0
# of e- (no charge) = # of p+

23. X Elemental Symbols A Z A- Mass Number Z- Atomic Number
X- Element Symbol X Z

24. Fe Try this one on your own 56 26 Element Protons Neutrons Iron
Electrons
Atomic #
Mass #
Charge 56 Fe 26 30 26 26 26 56

25. How many protons and neutrons are in one atom of 37Li?
How many protons and neutrons are in one atom of 74184W?
3 protons and 4 neutrons
74 protons and 110 neutrons

26. Isotopes

27. Isotopes
Atoms that have the same number of protons and electrons but different numbers of neutrons
Isotopes have different mass numbers because of the differing numbers of neutrons

28. Isotope names are the atom name and mass number hyphenated
Isotopes with practical uses:
carbon-14 ~ archaeological carbon dating
americium-241 ~ smoke alarms
cobalt-60 ~ treatment of cancer

29. Isotopes
In nature, most elements occurs as a mixture of two or more isotopes.
Each isotope of an element has a fixed mass and a natural percent abundance.
Example: Carbon has two isotopes. Both have 6 protons
carbon-12: six neutrons (C-12)
carbon-13: seven neutrons (C-13)

30. Isotopes & Atomic Mass
Atomic mass of an element is a weighted average of the masses of its isotopes.
You can calculate atomic mass based on relative abundance. You will need the :
mass of each isotope
natural percent abundance of each isotope

31. Calculating Atomic Mass
To calculate the atomic mass of an element:
Multiply the atomic mass of each isotope by its abundance expressed as a decimal
Add the results for all isotopes

32. Example
Magnesium occurs in nature in three isotopic forms: atomic mass
Mg-24 (78.70% abundance) amu
Mg-25 (10.13% abundance) amu
Mg-26 (11.17% abundance) amu
Calculate the atomic mass of magnesium for these data.

33. Calculation: For Mg-24: 23.985 amu x 0.7870 = 18.88 amu
atomic mass = amu

34. Ions

35. Ions Atoms are electrically neutral: # protons (+) = # electrons (-)
Atoms may lose or gain electrons when they react with atoms of other substances. They become electrically charged particles called ions.

36. Two Types of Ions Cations Anions Loss of electrons
Now has more protons than electrons
Anions
Gain of electrons
Now has more electrons than protons
*Denoted by charge in upper right of symbol.

37. X Atomic Math A Y Z A- Mass Number Z- Atomic Number Y- Charge
X- Element Symbol A Y X Z

38. Denoting Ion Charges Ion charges – the sign follows after the number
To calculate ion charges: # protons - #electrons
Example: An atom of lithium loses 2 electrons (lithium normally has 3 e-). It now is an ion with 2 more protons than electrons. (Ion charge: 3 protons – 1 electron = 2+) Overall, this lithium ion has a positive 2 charge. Write this using the elemental symbol:
Li2+
We can now add the atomic number and mass number to the symbol: 7
3Li2+

39. Atomic Math Breakdown # of p+ = Atomic Number
Cheat Chart
# of p+ = Atomic Number
# of n = Mass Number - # of p
# of e- (no charge) = # of p+
# of e- (w/ charge) = # of p+ - charge

40. Fe Atomic Math 56 3+ 26 Element Protons Neutrons Iron Electrons
Mass #
Charge 56 3+ Fe 26 30 26 23 26 56 +3

41. Practice Problems

42. Fe Try this one on your own 56 2+ 26 Element Protons Neutrons Iron
Electrons
Atomic #
Mass #
Charge 56 2+ Fe 26 30 26 24 26 56 +2

43. How many protons, neutrons, and electrons are in one atom of 37Li1+?
How many protons, neutrons, and electrons are in one atom of 74184W3+?
3 protons 4 neutrons 2 electrons
74 protons 110 neutrons 71 electrons

44. Make up your own problem for each format used.
Then give it to your neighbor or Ms. Adams to try