1. Atoms and Bonding
Chapter 5

2. The Structure of Atoms
Atom: the smallest part of an element or of matter, can not be broken down any further
Atoms of the same element are alike

3. The Structure of an Atom
Atoms have an inner region and an outer one
Inner Region: called the nucleus which contains:
1. Protons: positive charge, make up ½
the mass of an atom
2. Neutrons: neutral charge, make up
most of other ½ of atom’s mass
The main way one atom’s nucleus differs from another’s is in the number of protons they contain.

4. Nucleus of an atom

5. The Structure of an Atom
The Outer Region (mostly empty space and contains:
Electrons:
have a negative charge
contribute little to the mass
are much smaller than protons or neutrons

6. The structure of an atom

7. Atoms and the Periodic Table
Much information about atoms is found on the periodic table
Atomic Number
Equals the number of protons or electrons
Located above element symbol
Used to identify elements because the # of
protons NEVER changes without changing
the identity of the element

8. Atoms and the Periodic Table
2. Atomic Mass
Equals the number of protons + neutrons
Located beneath element’s symbol
The # of electrons is always the same as
the # of protons if an element is neutral.
The number of neutrons if found by:
Atomic Mass – Atomic # = neutrons

9. Atoms and the Periodic Table
Most of the time like charges repel each other and opposite charges attract, thus
you would expect protons to repel each
other.
However, protons and neutrons are tightly packed in the nucleus and held together by “the strong nuclear force”.

10. Atoms and the Periodic Table

11. Isotopes
For a particular type of atom, its nucleus always has the same number of protons.
The number of neutrons can vary.
Isotope: an atom of the same element that has the same number of protons but a different number of neutrons

12. Isotopes
Isotopes of Carbon

13. Isotopes Isotope Name # Protons # Neutrons Carbon 12 6 Carbon 13 78

14. Isotopes To find the number of neutrons an isotope has:
Isotope # - protons = neutrons
Carbon Isotope # 14
protons
Neutrons

15. Valence Electrons and Bonding
Two things are responsible for the physical and chemical properties of an element:
The # of electrons in the electron clouds
The arrangement of electrons in the clouds
The different positions of electrons in an atom are called energy levels.

16. Valence Electrons

17. Valence Electrons and Bonding
Each energy level can hold a specific number of electrons:
1st level = up to 2 electrons
2nd level = up to 8 electrons
3rd level = up to 18 electrons
4th level = up to 32 electrons

18. Valence Electrons and Bonding
The outermost energy level is called the Valence and the number of electrons in it will determine how the element bonds with other elements.
To find the number of electrons in the valence, look at the numbers beneath the family or group number. This number will have an A or B beside it. The number tells the number of valence electrons

19. Valence Electrons

20. Electron Configuration
The number of neutrons in a neutral atom increases as you move from left to right across the periodic table
In order to be stable, an atom must have a full valence.
If the atom has only 1 energy level, that energy level must have 2 electrons.
Any levels over 1 must have 8 electrons to be full.

21. Electron Configuration
The only elements that are stable as neutral atoms are the elements in group 18, the Noble Gases.
All of the Noble Gases have 8 electrons in their valence.
The only neutral element that is stable with 2 electrons is Helium.

22. Electron Configuration

23. Electron Configuration
How many valence electrons do the following elements have? Are any of them stable?
Hydrogen Arsenic Neon
Titanium Zinc Sulfur

24. Electron Configuration
If there are from 1 to 7 valence electrons, the element is reactive.
An element with 8 valence electrons is usually not reactive because it is stable as it is.

26. Electron Dot Diagrams
The electrons in the valence determine most of the chemical properties of an atom.
Scientist use a model called an electron dot diagram to show the valence electrons.

27. Electron Dot diagrams

28. Electron Dot Diagrams
An electron dot diagram consists of the symbol of an element surrounded by the number of electrons in the valence (NEVER MORE THAN 8 Electrons)

29. Electron Dot diagrams

30. Electron Dot Diagrams
The symbol has an imaginary box and each side of the box holds a pair of electrons.
Each side must be filled with a single electron before you can go back and put a pair.

31. Electron Dot Diagrams
Start at the top, then move to the right, bottom, and left.
Once each side is filled with a single electron first, then start back at the top again, if you have more than 4 electrons.
Again, move top, right, bottom and left to make the pairs.

32. Electron Dot Diagram Steps
Write the symbol for the element.
Look up the number of valence electrons on the periodic table. Recall that the valence electrons are the number under the family group number (have letters A or B beside them)

33. Electron Dot Diagrams
Start at the top and put one electron per side, moving to the right, then bottom, then left and back to the top.
Once each side has one electron, start back at the top, filling each side with another electron.

34. Electron dot diagrams
Dot diagram for Oxygen

35. Electron Dot Diagrams
Phosphorous

36. Electron Dot Diagrams
Cargon

37. PRACTICE On your paper, draw dot diagrams for the following elements:
Hydrogen Fluorine
Nitrogen Neon
Beryllium Aluminum
Sulfur Nitrogen

38. Electron Dot Diagrams

39. Chemical Bonding

40. Atoms and Bonding
Elements with 8 valence electrons are stable and do not usually combine with other elements.
Elements with less than 8 valence electron usually do combine with other elements in an effort to become stable

42. Bonding
A chemical bond is a force of attraction that holds two atoms together as a result of rearrangement of electrons between them.
Atoms can bond in two ways:
They can loose or gain electrons
They can share electrons

44. Ionic Bonding
Ion: An atom or group of atoms that has an electric charge.
If an atom loses an electron, it becomes a positively charged ion because it now has more protons (+) than electrons (-).

45. Ionic Bonding
If an atom gains an electron, it becomes negatively (-) charged because it now has more electrons (-) than protons (+)

46. IONS

47. Ionic Bonding
If an atom has 1,2 or 3 valence electrons, it will lose these in order to become stable. The atom will have a (+) charge.
If an atom has 5, 6 or 7 valence electrons, it will gain 3, 2 or 1 electron in order to become more stable and will have a negative (-) charge.

48. Ionic Bonding

50. Ionic Bonding
The bond formed between two elements that lose or gain electrons is called an IONIC BOND.
It forms because of the attract between positive and negative ions.
It is a bond between a metal and a non-metal

53. Ionic Bonding
When two or more elements are chemical combined in an ionic bond, they form a COMPOUND.

54. Ionic Bonding
The Compound, Salt

55. Ionic Bonding
Ionic bonding can be shown by Lewis Dot Diagrams. Follow the directions for drawing dot diagrams and use arrows to show how electrons are transferred.

56. Ionic Bonding
Formulas for the compound are written by writing the symbol for the metal first, followed by a superscript with a (+) charge equal to the number of electrons lost.
Then write the symbol for the non-metal followed by a superscript with the (-) charge equal to the number of electrons gained.

57. Ionic Bonding

58. Examples See Teacher Examples for the following on the board:
Sodium + Chloride
Magnesium + Oxygen
Lithium + Fluorine
Magnesium + Chlorine

59. Covalent Bonding
The chemical bond formed when two atoms share electrons is called a COVALENT BOND.
By sharing electrons, each atom has a stable set of eight.

61. Covalent Bonding
The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.

62. Covalent Bonding
If one pair of electrons is shared, a single covalent bond is formed.

63. Single Covalent Bond

64. Double Covalent Bond
If two pairs of electrons are shared, a double covalent bond is formed.

66. Triple Covalent Bond
If three pairs of electrons are formed, a triple covalent bond is formed.

67. Covalent Bonding
When atoms join by covalent bonding, a molecule is formed.
The molecule is neutral because no electrons are gained or lost.
Recall that in ionic bonding, a compound is formed.

68. Molecule of Water

69. Lewis Dot diagrams for Covalent Bonds
Write the symbols for each element.
Create a Lewis dot structure for each.
NOTE: Use dots for one element and
x’s for the other element so you can tell which electrons belong to which element.

70. Covalent Bonding

71. Covalent Bonding
Bond all unpaired electrons with unpaired electrons until ALL atoms have octets. These are usually placed in the middle between the two symbols. If needed, more element can be added until each one is stable.
Octet: full valence (8 electrons)

72. Covalent Bonding

73. Covalent Bonding 4. Paired Electrons can not bond.
5. Shared electron pairs count for both
atoms when determining if valence is
full.

74. Covalent Bonding
Draw circles to show the sharing of electrons. Use one circle for each pair.
If desired, you can draw lines to show a shared pair.

75. Covalent Bonding

76. Covalent Bonding
7. Write the chemical formula for the molecule. Since there is no gain or loss of electrons, the elements in the molecule do not have a charge as they do in ionic bonds.

77. Covalent Bonding See teacher examples on the board for the following:
Chlorine + Chlorine
Hydrogen + Chlorine
Oxygen + Oxygen
Hydrogen + Oxygen

78. Metallic Bonding
Metallic Bonds form when two metals share pooled electrons.
Pooled electrons hold atoms together so that they do not break when drawn into a thin wire (ductile) or hammered into sheets (malleable).
Metallic bonds help metals conduct electricity better.

79. Metals with metallic bonding

80. Metallic Bonding

81. Polar Bonds
Some atoms attract electrons more strongly than others, which causes unequal sharing of them
A covalent bond in which electrons are shared unequally is called a polar bond.

82. Polar Bonds
The atom with the stronger pull is slightly negative (-) while the one with the weaker pull is slightly positive (+).

83. Polar Bond

84. Non-polar Bond
A covalent bond in which electrons are shared equally is called a non-polar bond.

85. Chemical Shorthand Symbols are used to represent atoms and compounds.
Elements are represented by 1, 2 or 3
letter symbols.
Compounds are described using element symbols and numbers
Example: H2O

86. Chemical Shorthand In the formula H2O, the small 2 after the
H is called the subscript. It indicates the number of atoms of hydrogen present in the molecule.
???? In the element, C6H12O6 how many elements. . .
of carbon? of Hydrogen? of oxygen?

87. Chemical Shorthand A chemical formula is a combination of
chemical symbols and numbers.
It tells which elements are present and how many atoms of each element there are
If there is no subscript, it means there is only one atom of that element present.

88. Chemical Shorthand WaterH2O MethaneCH4 BenzeneC6H6 SulfurS8
GlucoseC6H12O6