Write the electron configurations for the following S 2- Ca Br O 2-
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Transcript of Write the electron configurations for the following S 2- Ca Br O 2-
Write the electron configurations for the following
• S2-
• Ca
• Br
• O2-
Draw Box diagrams for the following
• Co
• Al
• B
What did you discover in the periodic properties lab?
• What data can you use to support your claim?
• Alkali metals are more reactive than Alkaline earth metals
• As you go down the period things become more reactive.
• What patterns did you discover in the graphing activity?
• Atomic Size – Increases as you go down the periodic table– Decreases as you move from left to right
across the periodic table
• Ionization Energy – Decreases as you move down the periodic
table– Increases from left to right– Increases when an orbital is full
How does this relate to reactivity?
• Elements are more reactive as you move down the periodic table
• Relates to the amount of Electrons in an orbital.
• Atoms that only “need a few” electrons or can give away “a few” electrons to have a full orbital are more reactive.
What did you discover in the periodic properties lab?
• Which substance was the most volatile?
• Which substances had the lowest melting point
• Which substances conducted electricity?
• Which substances dissolved in water? Hexane?
The penny challenge…
• Why does water hold so many drops compared to hexane?
• Why does it bend toward charge?
• How does this relate to it being so unique?
• How are substances held together?
• Why are we able to live on the earth?
• Why is water so “unique”
• Why can bugs run across the water?
• Why do metals conduct electricity?
Chemical Bonds
Definition:The force that holds two atoms together.
Why does a bond form? So that an atom:
1. becomes more stable
2. takes on a noble gas configuration
To determine the type of bond
Electronegativity:
• measure of how strongly an atom attracts the electrons that are shared in a bond
• NaCl
• FeNO3
• KCl
• CsSO4
All these substances contain Ionic Bonds
What rules could you determine about ionic bonds from examining these compounds?
Types of Bonds
1. Ionic
The attraction between oppositely charged ions
• Atoms become ions by adding or losing electrons
• They form these charges to reach a noble gas configuration in their outer energy level
• Usually a Metal and a Non Metal
These compounds have covalent bonds. What rules could you
determine about covalent bonds?• CO2
• H2O
• CH4
• SiO2
2. Covalent Bonds
• A sharing of a pair of electrons between two atoms
• Individual atoms attain a noble gas configuration with the shared electrons in their outer energy level
Lewis Dot DrawingsShow the sharing or transfer of electrons
Also called “electron dot” drawings.
• Involve only valence electrons (those in the outermost energy level)
• Show the type of bond formed (either ionic or covalent)
• All atoms will satisfy the “octet” rule (except for hydrogen (duet rule) and metals)
Element valence electrons Lewis dot
N
O
F
C
Lewis dot drawings for1. Ionic bonds• Show electrons being transferred
• Include brackets and charges on ionsexamples:
• H and F• Na and Cl• Na and OH-
Lewis Structure for Covalent bonds
Technique: Place the atom with the largest number of unpaired electrons in the middle.
(Never put H in the middle of a molecule!!)
Determine how the electrons will be shared so that all atoms are stable (Octet Rule)
H2O
CH4
SCl2
Double and Triple BondsExample: HCNMake a table:
atomhave needH 1 2C 4 8N 5 8total 10 18
Difference: 18-10=8 divide by 2 = 4You need 4 bonds in this structure
Sharing 4 or 6 electrons (Double or Triple bonds allow this to happen)
• Examples
C3H6
SO2
Electron dot drawings for polyatomic ions
Always include brackets and charges, but have covalent bonds inside the ion
Count the number of valence electrons for each and the add or subtract and electron to make the correct charge
NH4+
OH-
SO42-
Draw NH4OH
Exceptions to the octet rule1. Metals
MgH2
BH3
2. Molecules with an odd number of electronsNO
NO2
3. Some Nonmetal atoms
because of their size, they can have more than an octet of electrons (due to the presence of empty “d” orbitals which can be used for bonding).
SF6
PCl5
DON’T FOCUS ON THESE BUT KNOW THEY OCCUR!
Note:
• Not all covalent bonds have equal sharing of electrons…
• There are electron hogs!!! Elements that hold on to the electrons more tightly than others
• You can determine if a bond is ionic,covalent and if there is an electron hogs, through looking at a characteristic property.
To determine the type of bond
Electronegativity:
• measure of how strongly an atom attracts the electrons that are shared in a bond
• The difference of electronegativity will determine the type of bond
What would you predict are the trends in electronegativity?
in families?in periods?
What family has the highest electronegativity?What family has the lowest electronegativity?What period has the highest electronegativity?What family has the highest electronegativity
Electronegativity
• Allows you to predict the nature of the bond between two atoms
• To determine where the electrons tend to spend the most time in the molecule
To determine the type of bond
• When the difference in electronegativity (ΔE.N.) is 2.0 or greater, the bond is ionic
Examples:NaClKF
Where are these atoms on the periodic table in relation to one another?
When the ΔE.N. is less than 2.0, the bond is covalent
Examples: H2O NO2
• This means the electrons spend more time around one of the elements giving it a partial charge
• Draw a picture of how you think the electrons would be distributed for each of these molecules.
When the electrons are shared equally
ex: H2 NCl3the bond is pure covalent and has no partial charge
Why do you think there would not be a partial charge on these bonds?
Which covalent bond do you think is stronger? H2 or N Cl
These bonds are called intramolecular forces
• Have various strengths– Ionic (STRONGEST)– Polar Covalent (NEXT STRONGEST)– Covalent (STRENGHTH DEPENDS ON
ELECTRONEGATIVITY DIFFERENCE)
Shapes of Molecules/Compounds
1. Determined by presence of electrons…
2. Electrons will repel each other
3. Ionic substances
don’t form molecules
Ions stack together, anions alternating with cations
The structure of Ionic solids
What types of shapes do you think molecules can have?
• Each balloon represents a bonded pair
• Non bonded pairs repel bonded electrons
Possible Shapes
• Linear Ex:
• Trigonal Planar
• Tetrahedral
• Triganol bipyramidal
• octahedral
2. Covalent compounds
The shape of the molecule is determined by the repulsion between the electrons that the atoms share
Example:
BH3
When it forms a molecule, the H atoms are 360/3= 120º apart
• A Lewis dot drawing cannot accurately show 3-dimensional shapes
VSEPR Theory
Valence Shell Electron Pair Repulsion
The shape of a molecule is determined by the repulsion between the electron of the bonded atoms
Molecules containing a central atom
• Lone pairs of electrons on a central atom influence shape
• They are more repulsive than bonded electrons because they flare (take up more space)
• Their influence must be taken into consideration when determining the shape of the molecule
Different shapes1. Molecules with only two atoms will
always be linear
2. Molecules with three atoms can have two different shapes
Example: BeCl2
H2O
This molecule is linear.
The H2O molecule is “bent” or “angular”
Effect of the lone pairs on shape or H2O
Molecules with four atoms Can have two shapes
Ex: NH3
BeF3
This one is trigonal pyramidal because of the lone pair of electrons
• This one is trigonal planar due to the absence of lone pairs on the central atom
Molecules with 5 atoms
If there are no lone pairs on the central atom:
Ex: CH4
This is called tetrahedral
Molecules with 6 atoms (and no lone pairs on the middle atom)
Ex.: PCl5
This is called trigonal bipyramidal
Molecules with 7 atoms and no lone pairs on the central atom
Ex.: SF6
This is called octahedral
• Predict the shapes of these molecules
• AlBr3
• PH3
• SO2
• CO2
Draw and predict shape:
CO32-
NO3-
SO3
Practice• Make electron dot drawings of the
following substances and predict the shape:
• CaCO3
Mg3(PO4)2
Trigonal bypyramidal
Polarity of water
The atom with the smallest E.N. has a partial positive charge on it
This is represented by the symbol δ+
The atom with the largest EN has a partial negative charge which is represented by the symbol
What type of bond is formed between
Na and F
Ca and N
C and I