1. Physical Science Chapter 6
Chemical Bonds

2. Bonding
Chapter 6 is about different types of atomic bonding
Forces of attraction is the key to this bonding
The physical properties of elements is key to the different types of bonds

3. Bonding

4. Draw the electron configuration of the elements neon
and sodium

5. What do you notice about the Valence electrons and the energy level of each element?

6. Stable Electron Configurations
When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react

7. Elements without complete sets of valence electrons tend to react
Ionic Bonds
Elements without complete sets of valence electrons tend to react
They react to try to achieve the stability of a full energy level…like the noble gases

8. Transfer of Electrons
Look at the electron dot diagrams for sodium and chlorine
What do you think these elements will want to do?

9. Atomic Chemical Reaction
When sodium and chlorine react: An electron is transferred from each sodium atom to a chlorine atom. Now each atom is more stable

10. When an atom gains or loses an electron, the protons and electrons are no longer equal and the atom is not neutral. An atom with a positive or negative charge is an ion

11. Notice the positive and negative charge on the new sodium and chlorine atoms

12. Charge
An ion with a negative charge is an anion.
Chlorine in NaCl is an anion…Cl-
It is negative because it has one more electron than protons, thus a charge of 1-
Anions are written using a part of the elemental name and the suffix ide.
chloride

13. Our new sodium ion, because it lost an electron now has more protons than electrons, making it positive or 1+
Na+
Cations are named just using the elemental name, sodium

14. Chemical Bonds A chemical bond is what holds atoms or ions together
Ionic bonds are what holds cations and anions together
Ionic bond forms when electrons are transferred from one atom to another

15. Chemical Bonds

16. Ionization Energy
The amount of energy used to remove an electron from an atom is ionization energy
It varies form element to element
The lower the ionization energy, the easier it is to remove an electron

18. Which element would it be easier to take an electron from, Magnesium or Calcium?

19. Ionic Compounds Compounds that contain ionic bonds are ionic compounds
These can be represented by a chemical formula:
Notation that shows what elements a compound contains and the ratio of the atoms or ions of these elements in the compound: NaCl

20. We want to make a compound with magnesium and chloride
Practice
We want to make a compound with magnesium and chloride
What group is magnesium in?
What group is chlorine in?
Group 2A, so it has 2 valence electrons
Group7A, so it has 7 valence electrons
This is pictured on the next slide

21. How will we combine these elements?= +
Magnesium will not be stable unless it gives away both of its electrons, so it will want to combine with two chlorine atoms

22. How will we combine these elements?+ =
MgCl2
Magnesium will not be stable unless it gives away both of its electrons, so it will want to combine with two chlorine atoms

23. MgCl2 = The subscript 2 shows how many atoms of that element are present
If there is not a subscript, that implies that there is only one atom

24. Ratios are Easier
It is easier to see the number of atoms when you break a formula down into ratios
For example, H2O has a hydrogen to oxygen ratio of 2:1
Find the ratios of the following formulas:
Sodium Chloride, NaCl=
Magnesium Chloride, MgCl2=
Sodium Oxide, Na2O=

25. Crystal Lattices How are the ions in a grain of salt arranged?(162)
Attractions between opposing charges keeps the ions in a fixed, repeating position
Solids whose particles are arranged in lattice structure are called crystals

26. The shape of an ionic crystal depends on the arrangement of ions in its lattice
The arrangement of the ions depends on the ratio of ions (like the exercise you just did) and their relative sizes

27. Compare Compare figure 5a and 5b (pg 162)
Answer the following questions:
1. How are the sodium ions represented?
2. How are the Chloride ions represented?
3. What do you notice about the locations of the positive and negative ions?
4. What is the similarity between the diagram of NaCl and the photograph of NaCl?

28. Properties of Ionic Compounds
The properties of NaCl are typical of other ionic compounds:
High melting point (801 degrees Celsius)
As a solid they are poor electric conductors
As a liquid they are good electric conductors
They shatter when struck with a hammer

29. All of these properties of ionic compounds are explained by the strong attractions within a crystal lattice

30. For electric current to flow, charged particles must be able to flow from one location to another
Ions in a crystal lattice have a fixed position
When they melt, the lattice breaks apart and ions are free to flow
Melted sodium chloride is an excellent elctric conductor

31. Complete the section 1 assessment in your book and the questions in your workbook for this section

32. Covalent bonds

33. Covalent Bonds
Someone read Covalent Bonds, pg 165
Covalent Bond: a chemical bond in which two atoms share a pair of valence electrons

34. Example: Hydrogen has one valence electron
If it had one more it could reach the stability of a full orbital for its energy level
So it wants to share an electron with another atom that also only has one valence electron…
Hydrogen

35. These two hydrogen atoms that share a valence electron form a molecule
Molecule: a neutral group of atoms that are joined together by one or more covalent bonds

36. The molecule is neutral because it has two protons and two electrons
The attraction between the shared electrons and the protons in the individual nuclei holds the atoms together in a covalent bond

37. The chemical formula for this covalent bond/molecule is H2
The subscript 2 is for the 2 hydrogen atoms in the molecule

38. Diatomic molecules: Two atoms
Many nonmetals make diatomic molecules…why?

39. Halogens, for example, all have 7 valence electrons
If two of them share an electron they both achieve a stable electron configuration

41. Multiple covalent bonds
Atoms can share more than one electron
They can share pairs
If they share 2 pairs, it is called a double bond
If they share 3 pairs it is called a triple pair

44. Ionic and Covalent bonds

45. Polar Covalent Bonds
A covalent bond in which electrons are not shared equally is a polar covalent bond
In a molecule with the same element, the attraction is the same
In a molecule of a compound, this may not be the case

46. Some atoms may have a greater attraction than others and thus the electrons spend more time near that atom in the bond than the other

47. Because they are sharing electrons, neither atom becomes + or – like ionic bonds.
However, they can become partially + or – when the electrons are shared unequally
If so, they are assigned the symbol delta – or delta +, depending on which one gains or loses the electrons most

48. Polar and Nonpolar Molecules

49. Polar and Nonpolar Molecules
*Recall that a molecule is a neutral group of atoms that are joined together by one or more covalent bonds*
A molecule that has only two atoms that share a covalent bond, the molecule will be polar
A molecule that has more more than two atoms that share a covalent bond, the molecule may not be polar

50. The type of atom in a molecule and its shape determine whether a molecule is polar or nonpolar

51. Nonpolar example Carbon dioxide CO2 Oxygen has a stronger attraction
for electrons
Therefore it is a polar molecule
Because the molecule is linear,
However, the equal pull cancels
Out the polarity and the
Molecule is nonpolar

52. Polar Example
Water, H2O
Oxygen has a stronger attraction to electrons than hydrogen, making this a polar molecule
Because the shape is bent, the polar bonds do not cancel out
This is a polar molecule

53. Attraction Between Molecules
Attractions between Molecular compounds are not as strong as ionic or covalent bonds
Attractions between polar molecules are stronger than attractions between nonpolar molecules

54. These strengths and weaknesses explain a lot about elements and their behavior
Water and methane are very similar in mass, but methane boils at C and water boils at 100 C

55. Methane is nonpolar and water is polar
These attractions increase the energy required for materials to boil/break the bonds

56. Activity Create a comparison chart
Compare the different bonds we have discussed
1. ionic bonds
2. covalent bonds
3. polar bonds
4. nonpolar bonds
Include how the electrons behave, types of elements involved in the bond, strength of the bond, etc.

57. When you finish
Complete the section 2 assessment
Complete the section 2 questions in your work book
Due tomorrow
Quiz tomorrow

58. 6.3: Naming Compounds and Writing Formulas/Ionic Formulas
Ionic formulas involve the transfer of electrons from one atom to another Many of our examples will include a metal giving away their electrons to a non metal

59. Both elements in the transaction now become atoms, specifically the element that lost electron(s) becomes a cation with a positive charge. The name of this ion remains the same
The element that gained electron(s) becomes a anion with a negative charge. The name of this ion is changed to the element name with the new suffix ide

60. Binary Ionic Compounds
Bi=two
Binary ionic compounds include only two elements: one cation and one anion
Ex: NaCl,
The order is always cation,anion

61. Common Anions

62. Metal Cations
Alkali metals, alkaline earth metals, and aluminum form ions with charges equal to their group number
Potassium ion= K+
Calcium ion= Ca2+
Aluminum ion= Al3+

63. Transition Metals
Many transition metals form more than one type of ion.
Look at the Table of metal cations on pg 172
There are several elements that can form more than one type of ion.
The Roman Numeral after the element name indicates the charge of the ion

64. So looking at the elements and their notation, how would you write the formula for the compound that makes red copper?
copper one oxide

65. Copper one= copper (I)= Cu1+
Oxide = O2-
Because it takes 2 of the copper with only one + charge to balance the -2 charge of the Oxide, we would write the formula:
Cu2O

66. Polyatomic Ions
Polyatomic ion: a covalently bonded group of atoms that has a positive or negative charge and acts as a unit.
Ammonium is an example (pg 172)
Many are anions

67. Writing Formulas for Ionic Compounds
1. Symbol for the Cation
2. Symbol for the anion
3. Use subscripts to show the ratio of the ions in the compound
4. All ionic compounds are neutral, so their charges must add up to zero

68. Discuss a scientific observation you made this weekend.

69. So how would we write the formula for this sodium sulfide?
Book example
Suppose an atom that gains two electrons, such as sulfur, reacts with an atom that loses one electron, such as sodium. There must be two sodium ions (Na+) for each sulfide ion (S2-)
So how would we write the formula for this sodium sulfide?
Na2S

70. Na2S
The -2 charge on one sulfide ion is balanced by the 1+ charges on two sodium ions.

71. Do the math skills and then math practice on page 174

72. Molecular Compounds
The name and formula of a molecular compound describe the type and number of atoms in a molecule of a compound

73. Naming molecular compounds
1. More metallic elements are first in the name
2. the name of the second element is changed to end in ide, like carbon dioxide

74. What would the name for N2O4 be?
Greek Prefixes
What would the name for N2O4 be?
NO2?
Dinitrogen tetraoxide
Mononitrogen dioxide/nitrogen dioxide

75. Writing Molecular Formulas
1. Write the symbols for the elements in the order they appear in the name
2. The prefixes indicate the number of atoms
3. If there is no prefix there is only one atom

76. What is the formula for diphosphorus tetraflouride?
How to
What is the formula for diphosphorus tetraflouride?
P2F4

77. Section review Complete the section review on page 175, 1-10
Complete questions in work book for 6.3

78. On your own Read section 6.4 Read the section “Science in History.”
Choose the milestones you find most interesting.
Write two paragraphs about the discovery, why you find it interesting/important, and how it applies to the subject you are learning about (metal alloys/metallic bonds/metallic characteristics)

79. Properties of metals are related to bonds within the metal
Structure of Metals
Properties of metals are related to bonds within the metal

80. Metallic bonds
The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and the surrounding valence electrons

82. The more valence electrons that can be contributed the stronger the bond will be
Melting points:
Sodium=97.8 C
Tungsten=3410 C

83. The mobility within a metal explains its properties
Malleability
Conduction

84. Alloy: a mixture of two or more elements, at least one is a metal
Alloys
Alloy: a mixture of two or more elements, at least one is a metal

85. Copper/Steel Alloys
Bronze: copper and tin
Brass: copper and zinc
Steel: iron and carbon

86. Bellwork
Tell whether the following are ionic bonds, or covalent bonds?
Write the name of the covalent formulas
Nacl
MgCl2
N2O4
P2F4