1. Atoms and the Periodic Table

2. Atomic Theory Democritus (400 B.C.)
Proposed that matter was composed of tiny indivisible particles
Not based on experimental data
Greek: atomos

3. Atomic Theory Alchemy (next 2000 years)
Mixture of science and mysticism.
Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

4. Atomic Theory John Dalton (1807) British Schoolteacher
based his theory on others’ experimental data
Billiard Ball Model
atom is a uniform, solid sphere

5. Atomic Theory John Dalton Dalton’s Four Postulates
1. Elements are composed of small indivisible particles called atoms.
2. Atoms of the same element are identical. Atoms of different elements are different.
3. Atoms of different elements combine together in simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged, but not changed.

6. Atomic Theory J. J. Thomson (1903) Cathode Ray Tube Experiments
beam of negative particles
Discovered Electrons
negative particles within the atom
Plum-pudding Model

7. Atomic Theory J. J. Thomson (1903) Plum-pudding Model
positive sphere (pudding) with negative electrons (plums) dispersed throughout

8. Atomic Theory Ernest Rutherford (1911) Gold Foil Experiment
Discovered the nucleus
dense, positive charge in the center of the atom
Nuclear Model

9. Atomic Theory Ernest Rutherford (1911) Nuclear Model
dense, positive nucleus surrounded by negative electrons

10. Atomic Theory Niels Bohr (1913) Bright-Line Spectrum Energy Levels
tried to explain presence of specific colors in hydrogen’s spectrum
Energy Levels
electrons can only exist in specific energy states
Planetary Model

11. Atomic Theory Niels Bohr (1913) Bright-line spectrum Planetary Model
electrons move in circular orbits within specific energy levels

12. Atomic Theory Erwin Schrödinger (1926) Quantum mechanics
electrons can only exist in specified energy states
Electron cloud model
orbital: region around the nucleus where e- are likely to be found

13. Electron Cloud Model (orbital)
Atomic Theory
Erwin Schrödinger (1926)
Electron Cloud Model (orbital)
dots represent probability of finding an e- not actual electrons

14. Atomic Theory James Chadwick (1932) Discovered neutrons
neutral particles in the nucleus of an atom
Joliot-Curie Experiments
based his theory on their experimental evidence

15. revision of Rutherford’s Nuclear Model
Atomic Theory
James Chadwick (1932)
Neutron Model
revision of Rutherford’s Nuclear Model

16. Properties of Atoms An atom refresher
Matter is anything that takes up space and has mass.
All matter is made of atoms
Atoms are the building blocks of matter, sort of how bricks are the building blocks of houses.

17. Properties of Atoms An atom refresher An atom has three parts:
Proton = positive
Neutron = no charge
Electron = negative
The proton & neutron are found in the center of the atom, a place called the nucleus.
The electrons orbit the nucleus.
Picture from

18. Properties of Atoms What are elements?
Elements are the alphabet to the language of molecules.
To make molecules, you must have elements.
Elements are made of atoms. While the atoms may have different weights and organization, they are all built in the same way.

19. Properties of Atoms More about Elements..
Elements are the building blocks of all matter.
The periodic table is a list of all of the elements that can build matter. It’s a little like the alphabet of chemistry.
The periodic table tells us several things…

20. O Properties of Atoms Oxygen 8 16 Atomic Number:
Number of protons and it is also the number of electrons in an atom of an element. 8 O
Element’s Symbol: An abbreviation for the element.
Oxygen
Elements Name
Atomic Mass/Weight:
Number of protons + neutrons. 16

21. Properties of Atoms Atom Models
There are two models of the atoms we will be using in class.
Bohr Model
Lewis Dot Structure

22. Properties of Atoms Bohr Model-
The Bohr Model shows all of the particles in the atom.
In the center is circles. Each circle represents a single neutron or proton. Protons should have a plus or P written on them. Neutrons should be blank or have an N.
In a circle around the nucleus are the electrons. Electrons should have a minus sign or an e. + + -

23. Electrons have special rules….
Properties of Atoms
Electrons have special rules….
You can’t just shove all of the electrons into the first orbit of an electron.
Electrons live in something called shells or energy levels.
Only so many can be in any certain shell.

24. Properties of Atoms Nucleus 1st shell 2nd shell 3rd shell
Adapted from

25. Electrons have special rules….
Properties of Atoms
Electrons have special rules….
You can’t just shove all of the electrons into the first orbit of an electron.
Electrons live in something called shells or energy levels.
Only so many can be in any certain shell.
The electrons in the outer most shell of any element are called valance electrons.

26. So let’s try it…. Li Lithium Protons = 3 3 7 Neutrons = 4 (7-3=4) - +
Electrons = 3
2 in the 1st shell, 1 in the 2nd shell
Neutrons = 4
(7-3=4)

27. Find the PEN and Draw
Carbon P= E= N=

28. Find the PEN and Draw
Chlorine P= E= N=

29. Find the PEN and Draw
Magnesium P= E= N=

30. O Properties of Atoms Lewis Dot Structure+ -
The Lewis Dot Structure is a bit different from the Bohr model.
It only shows the element symbol and it’s outer most electron shell.
Hint: Look at the number of the group the atom is in. • O • • •
• •

31. Properties of Atoms How to… Write the symbol.
Start on the right hand side, working your way clockwise around the symbol.
Try Lithium

32. Properties of Atoms How to… Write the symbol.
Start on the right hand side, working your way clockwise around the symbol.
Try Nitrogen

33. Properties of Atoms How to… Write the symbol.
Start on the right hand side, working your way clockwise around the symbol.
Try Sodium

34. Properties of Atoms Atom Differ by number of protons
Same amount of protons and electrons, Electrically neutral
Neutrons found using periodic table, usually around the same

35. Properties of Atoms Ion Differ by number of electrons
Different amount of protons and electrons, atom with a charge
Positive ion protons > electrons
Negative ion protons < electrons

36. Properties of Atoms Isotope Differ by number of neutrons
Same amount of protons and electrons
Different number of neutrons, so has a different mass

37. Properties of Atoms

38. The Periodic Table of Elements
1869, Dmitri Mendeleev, a Russian chemist, set out to organize the 63 known elements.
He started by organizing the elements by their mass in ascending order.
When elements were arranged in order of their mass, he noticed that their physical properties repeated

39. The Periodic Table of Elements
To group elements by similar properties, Mendeleev had to arrange a few elements out of order by mass.
the periodic trends did not fit perfectly with the elements’ masses.
When atomic numbers became known, scientists organized the chart of elements using the number of protons in each element instead of the atomic mass.

40. The Periodic Table of Elements
The modern periodic table of elements is a valuable resource. Check out the wealth of information contained in the periodic table:

41. The Periodic Table of Elements
Element name and symbol
Atomic number (number of protons in each atom)
Average atomic mass

42. The Periodic Table of Elements
Physical Properties: metal, non-metal, or metalloid

43. The Periodic Table of Elements
Electronegativity – ability to attract electrons
Bigger the number, the greater the ability to attract electrons and bond to other atoms
Increases as you go left to right and move up

44. The Periodic Table of Elements
Ionization Energy – energy needed to release an electron
Think, opposite of electronegativity
Increases as you go left to right and up

45. The Periodic Table of Elements
Atomic Radius
Relates to number of energy levels = quantum number
Increases as you go down and to the left

46. The Periodic Table of Elements
Valence Electrons – outermost electrons
Elements in the same group have similar valence electrons

47. The Periodic Table of Elements
Oxidation Number – number of electrons the atom uses or receives
+ when atom loses electrons, - when atom gains electrons

48. The Periodic Table of Elements
Representative Elements
Columns 1-2 and 13-18
Follow trends and behave more predicatibly than other groups

49. The Periodic Table of Elements
Exception to the Rules
Hydrogen
Placed with metals even though it is a gas
Placed in 1st column to reflect the properties of its electrons