chemical bonding#

1. WEEK 3
CHEMICAL BONDING

2. What is Ion
• Ion is an electrically charged atom or group of
atoms.
• Cation is a positively charged ion
• Anion is a negatively charged ion.
• Ionization energy is the energy required to
remove one electron from a single atom in a
gaseous state.
• Electron affinity is the energy released on adding
an electron to a single atom in the gaseous state.

3. • Ionization energy
The ease with which an atom loses an electron
to form a positively charged cation. Eg, Alkali
metal
• Electron Affinity
The ease with which an atom gains an electron
to form a negatively charged anion. Eg, Halogen

4. Types of Chemical Bonds
1. Ionic Bonds – Gain/Lose electrons
2. Metallic Bonds – “sea of electron”
3. Covalent Bonds – “sharing”

5. Why do atoms form bonds?
• Chemical bonds allow atoms to exist at lower
energy states that are more stable.
– Na and Cl – two very reactive and dangerous
substances,…
» Together they make salt (NaCl)

6. Chemical Bonding
• Whether atoms will interact depends almost
entirely on;
1. The arrangement of their outer energy level
electrons (valence electrons)
2. Strength of attractive force between protons and
electrons.

7. Outer Energy Level Electrons
• Valence electrons
– Goal : get 8 valenve electrons
– Octet Rule (Rule of eight)
– Makes atoms more stable
• Only s and p sublevel electrons will be valence
electrons
– Core electrons – those in the lower energy levels.

8. What are Electron Dot Diagrams?
(Lewis Dot Diagrams)
• A way of keeping track of valence electrons.
• How to write them;
– Write symbol
– Determine number of valence electrons
– Put one dot for each valence electron
– Don’t pair up until they have to

9. Electron (Lewis) Dot Diagrams
Valence Electrons
• Electrons in the highest unfilled energy level
(these are the electrons that make chemical
bonds)
• Example
Lithium (Li)
1s22s1
What is the highest energy level
that has electrons?
How many valence electrons does
lithium have?
2
1

10. 3 ways to determine valence
electrons
1. Given a Bohr model, count the electrons in
the outer energy level
2. Given an Electron Configuration, count the
electrons in the highest energy level.
3. Use the periodic table

11. 1. Given a Bohr model, count the
electron in the outer energy level
• How many electrons
are in carbon’s
outer energy level?
• What does the
electron dot
diagram look like?
4

12. 2. Given an electron configuration, count
the electrons in the highest energy level
• Carbon’s electron
configuration is:
1s22s22p2
• What is the highest
ENERGY LEVEL in
carbon?
2
• How many electrons
are in carbon’s
highest energy level?
• What does the
electron dot diagram
look like?
2 + 2=4

13. 3. Use the periodic table
Example : what column is carbon in?
• Use the following table to determine how many
valence electrons that column has.
Column 1 2 13 14 15 16 17 18
Valence
Electrons
1 2 3 4 5 6 7 8

14. 1
2
3 4 5 6 10987 11 12
13 14 15 16 17
18
1
2
3 4 5 6 7
8
Valence Electron
Column

15. Write the electron dot diagram for
the following:
• Arsenic
• Iodine
• Silicon
• Sulfur

16. Chemical bonding
• Whether atoms will interact depends almost
entirely on;
1. The arrangement of their outer energy level
electrons
• Octet Rule
2. Strength of attractive force between protons
and electrons.

17. Attractive Force – Protons & Electrons
• Electronegativity – the tendency of an atom to
attract electrons
– Helps determine the type of bond formed
between atoms.
• Ionic, polar covalent, nonpolar covalent

19. Pair- Share
• Arrange the following from the least to
greatest in electronegativity:
Sr, S, F, Fr

20. Types of Chemical Bonds
1. Ionic Bonds – Gain/Lose electrons
2. Metallic Bonds – “sea of electron”
3. Covalent Bonds – “sharing”

21. Ionic Bonds
• Electrons are transferred between atoms.
• Metal and NonMetal
– One atom gains electrons
– Other atom loses electrons
• Each atom becomes an ion.

22. Ionic Bonds
Note : for elements in ionic compounds, show the charges on the
electron dot diagrams

23. Why are ionic Bonds so strong?
• Anions and cations are held together by
opposite charges.
– Electrostatic attraction
– Occurs between
all the ions

25. Properties of Ionic Compounds
• Solid crystal at room temperature
– Crystal Lattice
– Ions are strongly bonded.
• High melting points
• Soluble in water
• Conducts electricity
– When melted or dissolved
– Electrolyte-compounds that conduct electricity

26. Practice
• Ionic compound consisting of Aluminum &
Sulfur
1. Write the formula;
Alluminium Sulfite
2. Draw the Lewis dot structure of the
compound.

27. Types of Chemical Bonds
1. Ionic Bonds – Gain/Lose electrons
2. Metallic Bonds – “sea of elcetron”
3. Covalent Bonds – “sharing”

28. Metallic Bonds
• Metal – Metal compound
• Metals hold onto their valence electron very
weakly
• Positive ions surrounded by a sea of electrons.

29. Properties of Metals
• Solid at room temperature
• Conduct electricity
• Malleable – can be hammered into a shape
(Bendable)
• Ductile – drawn into wires

30. • What is the different between an ionic bond
and metallic bond?
• What is the different in properties between
ionic compounds and metallic compounds?

31. IONIC BONDS METALLIC BONDS
• Solid crystal at room
temperature:
- Crystal Lattice
• Conducts electricity
- When melted or
dissolved
• Brittle
• High melting points
• Soluble in Water
• Solid at room
temperature
• Conducts electricity
• Malleable
• Ductile

32. Types of Chemical Bonds
1. Ionic Bonds – Gain/Lose electrons
2. Metallic Bonds – “sea of electron”
3. Covalent Bonds – “sharing”

33. Covalent Bonds
• Electrons are shared between atoms
– Atoms that do not lose electrons easily usually
form covalent bonds
• The attraction between both nuclei and he
shared electrons hold the atoms together in a
covalent bond

35. Covalent bonding
• Fluorine has seven valence electrons
• A second atom also has seven
• By sharing electrons
• Both end with full orbitals

36. Properties of Covalent Bonds
• Gases, Liquid or solids.
• Low melting points
• Poor electrical conductors
• Not soluble in water, but soluble in nonpolar
liquids.

37. Electron Dot Diagram for covalent
compounds
• First let’s review how to do electron dot
diagrams for ionic compounds:
– H2O
– CO2

38. Steps for Electron Dot Diagrams (Lewis
structure) for Covalent Compounds
1. Count the number of valence electrons
2. Write the symbols and place a bond between
each.
– A single bond requires 2 share electron
3. Place a total of 8 electrons around each
atom.
4. If come up short, then try putting a double or
triple bond between the atoms.
Draw the electron dot diagram for : Br2,NF3,CO2

39. Octet Rule – double & Triple Bonds
• Some atoms share more than one pair of
electrons
• Double bond – two pairs
of electrons are shared by
the bonding atoms
– Ex : CO2
• Triple bond – three pair of
electrons are shared
– Ex : N2

40. Carbon dioxide
• The only solution is to share more
• Requires two double bonds
• Each atom gets to count all
the atoms in the bond
8 valence electrons
8 valence electrons

41. Shared Electron/Bond Shortcut
• Can use a line to indicate a bond
– Not for one pair electrons
• Each line is 2 valence electrons
• Called a structural formula

42. Shared Electron / Bond Shortcut

43. Coordinate Covalent Bond
• When one atom donates both electrons in a
covalent bond.
• Carbon monoxide (CO)

44. Coordinate Covalent Bonds
• When one atom donates both electrons in a
covalent bond
• Carbon monoxide (CO)
• SO4
-2

45. Resonance
• Resonant structure : when more than one
electron dot structure is possible
– Ex : sulfur trioxide – SO3
– In a resonant structure, the molecule is said to
exist in a hybrid state between the two.
• Bond strength is greater than a single bond, but less
than a double bond

46. Octet Rule Exceptions
• Molecules with an odd number of electron
(NO)
• Elements without octets (BF3 and BeF2)
• Elements with more than an
octet (SF6)

47. BOND
2 or more atoms chemically combined

48. HOW IS BOND FORMED
Attraction between positive nucleus of 1 atom
to negative electrons of another (covalent bond
sharing) or attraction between positive and
negative ions (ionic bonds)

49. WHY ATOMS BOND
To fill outermost s&p sublevels (location of
valance electron)

51. PROCESS OF BOND
Get 8 electrons to fill them completely because
you need 8 electrons to follow the octet rule
because the elements wish to be like noble
gases

52. COVALENT BONDS
Electrons between atoms and nuclei between 2
or more non-metal atoms sharing of valence
electrons leads to proper positioning

53. IONIC BOND
between metal and non-metal, transfer of
valence electrons which causes attraction
between cation and anion

54. CRYSTAL LATTICE
where cations and anions attract to one
another/basic structural unit of ionic
compounds

55. WHY IS 8 MOST STABLE
because when bonds are formed, energy from
chemical potential account is released and when
it decreases, they become more stable

56. ELECTRONEGATIVITY DIFFERENCE
compares electronegativity between 2 atoms

57. ELECTRONEGATIVITY
Measure of how strong an atom in a molecule
can attract electrons in a chemical bond

59. MOST ELECTRONEGATIVE
F, O, Cl, N because non-metals like to gain
electrons and more reactive as you go up a
group

60. THE GREATER THE DIFFERENCE IN
ELECTRONEGATIVITY
the more the electrons will be attracted to the
element with the greater electronegativity

61. WHAT HAPPENS DURING METALLIC
BONDING
metals conduct electricity as solid, mobile
valance electrons(charge that can move and
conduct) --> empty overlapping orbitals
especially in transition

62. METALLIC BONDING
attraction between delocalized electrons and
metals atoms

63. COVALENT BONDS VARY IN STRENGTH
metallic strongest --> ionic --> covalent weakest