1. Atoms and the Periodic Table

2. Matter Matter is everything around you that has mass.
Anything you can see, touch, taste, or smell is matter!
Air
Desks
People
Soil
Plants
What is it that makes up matter?!

3. Matter What is matter made of? Is it all the same?
Democritus (460 B.C B.C.) was a Greek philosopher believed the universe was mostly empty space and tiny bits of stuff.
He didn’t know what the stuff was but he knew it must be REALLY small!
So small it could not be broken into anything smaller

4. The Chalk Conundrum!
If you break a piece of chalk in half…is it still chalk?
When is it no longer chalk?

5. Can you make matter?
Democritus never explained where matter came from or where it could go
People just guessed that matter could change into different types of matter

6. Matter cannot be created or destroyed!
Can you make matter?
Matter cannot be created or destroyed!
If a space shuttle leaves Earth with astronauts and food and water and air weighing 10,000 lbs. it will return weighing 10,000 lbs.

7. Matter Atom – small particle that makes up matter
Atom in Greek means “cannot be divided”

8. Parts of an Atom Protons – positive charged particle
Atoms are made of only 3 different things
Protons – positive charged particle
Neutrons – particle with no charge
Electrons – negatively charged particle
Nucleus – center of the atom made up of protons and neutrons
Protons and neutrons are found in the nucleus or center of the atom
Electrons are found outside the nucleus

9. Parts of an Atom
Electrons are so small as it is we hypothesize that they aren’t made up of anything smaller
Protons and neutrons however…
Quarks – smaller particles that compose protons and neutrons of an atom
6 unique quarks have been discovered
It took almost 450 scientists several years to discover the 6th quark!

10. How big are Atoms?
SMALL! Really, really, really, really, small…

12. The Atomic Model So what exactly does an atom look like?!
Scientists have developed models over the years to explain how atoms work…

14. Gold Foil Experiment
Rutherford was one of the first to propose that atoms had a dense nucleus
Gold foil experiment
Particles were fired at a piece of gold foil
Most went straight through
Some were deflected

16. Electron Cloud Model
By 1926, scientists had developed the electron cloud model of the atom
Electrons do not follow fixed orbits
Instead they occur frequently in certain areas around the nucleus at any given time

17. What is in an Atom?

18. Bohr Model Orbital – each ring of electrons in an atom
The Bohr model represents an atom by using rings drawn around the nucleus with dots to represent electrons
Orbital – each ring of electrons in an atom
The 1st orbital can only hold 2 electrons!
The following orbitals can only hold a maximum of 8 electrons

19. Atoms
Element – a known substance that cannot be broken down into another substance
Made of only one kind of atom
Sulphur (S)
Potassium (K)
Aluminum (Al)
Chlorine (Cl)

20. Periodic Table
Periodic Table – a chart that organizes elements by the number of protons they have in the nucleus
Elements are listed by their chemical symbols
Aluminum = Al
Calcium = Ca
Gold = Au
Oxygen = O
Hydrogen = H
Carbon = C

22. How to Read a Periodic Table
Dimitri Mendeleev, a Russian Chemist, developed the first periodic table
Mendeleev based his table on the mass of the atoms
“I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.”
A British chemist later improved upon the periodic table by rearranging the elements based on their atomic number (the number of protons).

23. Atomic Number
Atomic number – the number of protons found in a single atom of the element
The periodic table is arranged based on these numbers

24. Atomic Mass
If you were asked how tall you were, would you answer in kilometers?
NO! You would use an appropriate unit! (cm, or m)
Scientists had to develop an appropriate unit for the mass of atoms since they were so tiny!
Atomic mass unit (amu) – unit of measure used for atomic particles
Atomic mass – the mass of an atom of the element

25. Atomic Mass How do we calculate the atomic mass?
1 proton is equal to almost exactly 1 amu
1 neutron is equal to almost exactly 1 amu
Electrons are so tiny they make little difference

26. How Many Neutrons?
The number of protons in an atom is equal to the element’s atomic number
The number of electrons in a neutral atom are equal to the number of protons
1 positive and 1 negative equals 0!
Often, the number of neutrons is equal to the number of protons but NOT ALWAYS!

27. How Many Neutrons? Krypton Has an atomic number of 36
Number of protons?
Number of electrons?
Number of neutrons?
Round the atomic mass to the nearest whole number
83.80  84
84 – 36 protons = 48 36 36

28. Reading a Periodic Table
All the rows read from LEFT to RIGHT
Each row is called a period
The period an element is in tells you how many electron orbitals are present
Elements in the top period have 1 orbital
Elements in the 3 period have 3 orbitals

29. Reading a Periodic Table
The vertical columns of the periodic table are called groups
Elements found in the same group have the same number of electrons in their outer orbital
Valence Electrons – the electron in the outermost ring of an atom
Elements in group 1 have 1 electron in their outer shell
Elements in group 4 have 4 electrons in their outer shell
The middle “transition elements” don’t follow this rule!
We’ll talk about them later on…

30. Try it! Nitrogen Atomic number? Number of protons? 7
Number of electrons?
Number of neutrons?
Atomic mass?
Number of valence electrons? 7 7 7 7 14 7

31. Isotopes Not all atoms of an element have the same number of neutrons!
Isotope – an atom of an element that has a different number of neutrons
Still have the same number of electrons and protons
Still the same element
Only difference is the mass!

32. Isotope
Isotopes of elements are indicated by their mass number
The average atomic mass of an element is the weighted-average mass of all isotopes
4 of 5 atoms of B have 6 neutrons
1 of the 5 have 5 neutrons
4 5 (11 amu) (10 amu) = 10.8

33. Isotopes
We indicate isotopes by writing the mass alongside the element
Boron – 11, Boron – 10
Carbon – 12, Carbon – 13, Carbon – 14

34. Isotopes and Radioactivity
Radioactive means that an atom is emitting a particle
As these atoms emit particles the element or isotope will change will change

35. Radioactive Isotopes Radioactive atoms have half-lives
We can use radioactive isotopes to determine the age of things
Radioactive atoms have half-lives
Half-life – the amount of time it takes half the mass of the atoms to decay
Carbon – 14 decays to Nitrogen – 14
1 half-life = 5,730 years
A bone is discovered which has 25 percent of the carbon-14 found in the bones of other living animals. How old is the bone?

36. Chemical Bonds C, O, Cl, H, N, Na
We’ve learned a few chemical symbols
C, O, Cl, H, N, Na
What about things like water and salt?

37. Compounds Ex. H2O, NaCl, SiO2
Chemical Compound – atoms that are chemically combined in a specific ratio
Ex. H2O, NaCl, SiO2

38. Salt = Sodium and Chloride (NaCl)
Compounds
When compounds are formed, the elements take on new properties
Sodium (Na) is a soft but reactant metal
Chlorine (Cl) is a yellow-green toxic gas
But combined…they make SALT!
Salt = Sodium and Chloride (NaCl) + =

39. Compounds Why do atoms form compounds? Stability!
Atoms will combine if they are more stable together than apart
Atoms want to have 8 valence electrons to be “happy”
(or 2 in He)

40. Noble Gases
If we look at a Lewis dot diagram of the noble gases we can see they have a complete outer energy level (shell)

41. Hydrogen and Helium
Hydrogen and helium are found in period 1 of the periodic table
He contains 2 electrons in its first and only shell and it is stable
H contains only 1 electron so it is not stable
H is more stable when part of a compound
This is why H is commonly found as part of so many chemical compounds

42. Chemical Bonds So how do elements fill their outer shell?
They must gain or lose an electron!
Elements that do not have a full outer shell will need to add or lose electrons to reach a stable level
Metals usually give up an electron
Nonmetals will usually take an electron

43. Ions If an atom gains or loses electrons it becomes an ion
Ion – a charged atom due to the gain or loss of electrons

44. The Ionic Bond
Ionic Bond – force of attraction between oppositely charged ions
Positive (+) and negative (-) ions are attracted to each other like magnets!
The result of this bond is a neutral compound!
The charges cancel each other out

45. The Ionic Bond What if there is more than 1 electron involved?!
In NaCl
Na has 1 valance electron
Cl has 8 valance electrons
1 atom of Na can form an ionic bond with 1 atom of Cl
What if there is more than 1 electron involved?!

46. The Ionic Bond
How would Mg and Cl form an ionic bond?

47. The Ionic Bond Not all molecules involve only 2 atoms!
Mg and Cl bond to form MgCl2

48. The Ionic Bond The result of an ionic bond is a neutral compound
The sum of the charges on the ions is ZERO
Usually occur between a metal and a nonmetal
Electrons are TAKEN by the atom with a stronger pull!

49. Electronegativity

51. The Covalent Bonds
Some atoms of nonmetals are less likely to gain or lose electrons
Take a look at C in group 4
Gain 4 electrons or lose 4 electrons to have a stable 8!
That’d take a lot of energy!

52. The Covalent Bond
Each time an atom loses and electron, the remain electrons are pulled in tighter
It is more stable for these atoms to SHARE electrons!
Covalent bond – bond formed between atoms when electrons are shared

53. Single and Multiple Bonds
Single Bond
2 electrons (1 pair) are shared
Usually 1 electron from one atom and 1 from the other
Multiple Bonds
Bonds containing more than 1 pair of electrons
Double and triple N2

54. Ionic vs. Covalent Ionic Bonds Covalent Bonds Electrons taken
Electrons shared

55. Unequal Sharing
Electrons aren’t always shared equally in a covalent bond
Electronegativity – the amount of attraction an atom has for its electrons
This causes electrons to be pulled to one side of a molecule

56. Electronegativity

57. Polar or Nonpolar
Due to unequal sharing, molecules can have slight charges!
Electrons are pulled toward one side causing a slight negative charge
Can only happen with uneven molecules

58. Polar vs. Nonpolar Polar Molecules Nonpolar Molecules
Molecule with slight positive and negative ends
Still neutral charge overall
Nonpolar Molecules
Electrons are equally shared across the molecule
Do not have charges ends

60. Water Water is considered by many to be the “universal solvent”
Water is a polar molecule
Try to draw one molecule of water from memory…

61. Water

62. Hydrogen bonding
When a H (a very small atom) is bonded to a larger more electronegative atom hydrogen bonding can occur
Hydrogen bond – the strong force of attraction between two polar molecules containing a hydrogen atom.
Holds heat
Great solvent
Ice floats

63. Chemical Reactions
Everything to the left of the arrow are called the reactants
Everything found on the right of the arrow are the products
In chemistry we say the arrow “yields” the reactants

64. Chemical Reactions Remember, energy cannot be created nor destroyed?
Neither can matter! (elements!)
Within any chemical reaction, the equation must be balanced

65. Balanced Reactions
Sometimes in order to keep a reaction balanced we need to indicate the number of molecules by placing a number in from of it

66. Chemical Reactions H2 + O2 2H2O
How about the reaction of hydrogen and oxygen to form water?
HINT: Hydrogen and oxygen are both gases and are found in pairs
H2 and O2 H2 + O2
2H2O

67. The Mole A mole is a certain number of items Mole = 6.02 x 1023
Dozen = 12
Baker’s dozen = 13
Million = 1,000,000
Mole = 6.02 x 1023

68. Oxidation States
The numbers with positive and negative signs found on the periodic table are oxidation numbers
The oxidation number is the most common number of electrons that must be transferred to meet the octet rule of 8 valence electrons
+ is given away
- is taken

69. Oxidation States
Occasionally elements may have more than one oxidation state
Elements with multiple oxidation states will be indicated by a romon numeral
Copper (I) 1+
Copper (II) 2+
Iron (II) 2+
Iron (III) 3+