CHEMISTRY Chemical Bonds
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What is the Octet Rule?
- Atoms with 8 valence elecrons are stable (unreactive)
- *Atoms without this stable octet react so they end up with 8 valence electrons
What are chemical reactions?
- Rearrangements of atoms as they form stable octets and go toward lower energy states
- *Old bonds break, new bonds form
When do bond formations occur?
- When atoms or molecules collide
- *Involves valence electrons (D sublevel electrons in transition metals may also be involved
- *Is exothermic
What kind of reaction is breaking bonds?
- *Must replace energy given off when bond was formed
When is a reaction exothermic?
If the energy given off by forming new bonds is greater than the energy needed to break old bonds
When is a reaction endothermic?
If the energy needed to break old bonds is greater than the energy given off by forming new bonds
What is activation energy?
- The energy needed to get a reaction started
- *Used to break old bonds
- *Continuous for endothermic reactions, not continuous for exothermic
What is a chemical bond?
- A force of attraction between atoms due to opposite charges
- *Electrons may be transferred or shared
What is an ion?
An atom with the wrong number of electrons
What is a cation?
An atom losing electrons that is positively charged
What is an anion?
An atom gaining electrons that is negatively charged
What is an ionic bond?
- A force of attraction due to the transfer of one or more valence electrons from one atom to another
- *Atoms attract due to opposite charges
What is the resulting compound of ionic bonds?
An ionic compound
An ionic compound is _______ (charge)
Arranged in regular repeating patterns called ______ which are not molecules
Have _____ bonds, causing them to be _____ at room temperature and to have high _____ point
Separate into _____ (dissociate) when dissolved in water
Aqueous solutions conduct ______
They are _____
- strong, brittle, melting
What is a covalent bond?
- A force of attraction due to sharing one or more pairs of valence electrons, with each atom contributing one electron in a pair
- *The electron pair jumps back and forth between atoms
- *Causes temporary charges that result in attraction
- *Makes covalent compounds
- *Can havedouble and triple bonds that are stronger than single bonds
Covalent compounds are also called _____ compounds
Has a _______ charge
Do not ______
Have weak intermolecular forces, causing them to be _____ at room temperature
Have ___ melting points
- gases or liquids
What is the rearrangement of orbitals in a valence shell into equal energy orbitals?
- *Allows a larger number of equal energy covalent bonds
- *Carbon is an example
What are large covalently bonded structures?
- Network solids
- *The number of bonds gives these a great strenght and very high melting point
- *Example: diamond
What is a molecule?
Two or more atoms Covalently bonded
What is a compound?
Two or more different atomschemically bonded
Molecule or Compound?
- Molecule and compound
- Not a molecule, but a compound
- A molecule, not a compound
What are two atoms of the same element covalently bonded?
What are the seven diatomic elements?
- H, N, O, F, Cl, Br, I
- *Written H2, N2 etc.
What are metallic bonds?
- A force of attraction caused by sharing loosely held valence electrons among many metal ions
- *This results in the special properties of luster, conductivity, malleability and ductility
- *Usually between like atoms in a piece of the element
- *Form alloys, not compounds
- *Mixtures show individual metallic properties
What is a bond formed between a metal and a nonmetal?
What is a bond formed between two nonmetals?
What is a bond formed between two metals?
What are the:
Phases at room temperature
Conductivity when melted
Conductivity of water solution
of ionic versus covalent compounds?
- Crystalline solid ....... Solid, liquid or gas
- High ....................... Low
- Yes .........................No
What is the measure of an atom's attraction for electrons in a covalent bond?
- *Scale from 0 to 4
What is the most electronegative element?
Flourine, because it only needs to gain one electron and it is the smallest. Not Hydrogen because it only has one proton pulling on it.
What is the least electronegative element?
Electronegativity ______ from left to right on the periodic table
- *This is due to the increase in the number of protons and smaller atomic size
Electronegativity __ as you move down a group on the periodic table
- *This is due to teh increase in atomic size and shielding effect of electrons between the nucleus and valence shell
If the difference in electronegativity is greater than 2.0, the bond is _____
If it is less that 2.0, it is ______
What is a bond that has perfect sharing?
- Pure covalent bond
- *Occurs when difference in electronegativity equals 0
- *Diatomic elements have pure covalent bonds
What is a covalent bond in which the difference in electronegativity is greater than 0.4
- A polar covalent bond
- *Has a positive and negative end
- *Negative end has the higher electronegativity
- *The greater the difference in electronegativity, the stronger the polarity
When is there a nonpolar covalent bond?
- When the difference in electronegativity is less than or equal to 0.4
- *Unequal sharing so little that polaritiy is not significant
What are molecules with polar bonds and a geometry that allows poles to occur?
- Polar molecules
- *Also called dipoles
- *Polarity affects physical properties
What are some properites affected by polarity?
- Phase at room temperature
- Melting point/Boiling point (Polar have high BP/MP)
- Viscosity (Polar are more viscous)
- Density (Polar are more dense)
- Solubility (Polar solvents dissolve polar solutes)
What kind of bond has shared electrons that come from one atom
- Coordinate covalent bonds
- *Occurs in some polyatomic ions
What are models showing bonding and nonbonding electrons in molecules?
- Lewis structures
- *Primarily for covalent molecules
- *Doesn't show molecular geometry
What are the bonding rules for the families?
- H and Halogens - 1
- O Family - 2
- N Family - 3
- C Family - 4
- B - 3
What is resonance?
- When molecules have more than one correct lewis structure
- *Electrons shift between these arrangements
What is the difference between the number of electrons each atom has in the lewis structure and its valence electrons?
- Formal Charges
- *Always occurs in ions
- *Atoms with more electrons are negative, with more protons are positive
What are the bonding rules for ions?
- H and Halogens - 1
- O family - 1, 2, or 3
- N family - 2, 3, or 4
- C family - 4
- B - 4
What is VSEPR?
- Valence shell electron -pair repulsion
- *Method of predictiong molecular shape
What does A, X and E stand for?
- A - central atom
- X - atom bonded to a
- E - lone pairs
What is the VSEPR notation for, predicted shape, and bond angles for:
2 atoms bonded to a
3 atoms bonded to a
4 atoms bonded to a
3 atoms bonded to a and 1 lone pair
2 atoms bonded to a and 2 lone pairs
- AX2, linear, 180
- AX3, trigonal planar, 120
- AX4, tetrahedral, 109.5
- AX3E, trigonal pyramidal, 107
- AX2E2, bent, 104.5
Lone pairs ______ more than bonded electrons
- *This affects tetrahedral shapes AX3E and AX2E2*Actual angles known only by experiment
Polar bonds ______ polar molecule
Strongly affected by _____
After determing shape, look for _____
____ reduces polarity
Lone pairs are _____ sites
- do not equal
- positive and negative sites
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