unit 2 molecular and ionic compound strucutre and properties

11th ap chemistry

ionic bonds

metal (cation) and nonmetal (anion) transfer electrons

covalent bonds

two nonmetal shares electrons

molecular compounds

- two or more nonmetals bonded together to form a compound
- bonds between atoms are nonpolar covalent or polar covalent

electronegativity

- metals: low
- nonmetals: high
- most: N, O, F

ionic bond polarity

big difference in electronegativity

polar bonds

different nonmetals

nonpolar bonds

same nonmetals and CH bonds

polarizable

easy to get a partial charge

properties of ionic solids

- high melting points
- very hard
- low volatility (doesn't evaporate)
- brittle
- repetitive pattern
- not malleable or ductile
- most are soluble in polar solvents
- conducts electricity only when dissolved in a polar solvent (higher concentrations of ions= higher conductivity)

properties of covalent compounds

- lower melting and boiling points
- soft and flexible
- does not conduct electricity, except for acids

crystalline solids

arranged in a repeating pattern

amorphous solids

random pattern

metallic solids

- sea of electrons
- delocalized electrons
- only solid to conduct electricity as a solid
- conducts heat
- malleable and ductile
- lack directional bonds (not rigid because electrons are free to move)

sea of electrons

nuclei and inner core electrons are localized and valence electrons are delocalized

delocalized

valence electrons are free to move around

solution

homogeneous mixture of two or more substances

solvent

substance that is MORE PLENTIFUL in a solution

solute

substance that is LESS PLENTIFUL in a solution

alloy

solid solution composed of two or more metals, or one or more metals and nonmetals

interstitial alloys

atoms with a small radius occupies the spaces between atoms with a larger radius (difference in atomic radius)
ex: steel- more rigid, less malleable, less ductile, and more dense than pure iron

substitutional allloys

- radii of the solute and solvent atoms are similar (same atomic radius)
- alloys remain malleable and ductile
- usually transitional metals because they're roughly the same size
ex: brass

melting point

- formula: product of charges/ distance between ionic centers (ionic radius)
- higher melting point= greater force of attraction= more energy needed to separate

product of charges

forget the signs and multiply the charges. MOST IMPORTANT

distance

look at the periodic table to find the ionic radius

bond energy

- only covalent bonds
- potential energy of valence electrons decreases as they approach the nucleus of another atom
- ↑BE= ↓PE

potential energy

- highest when particles are infinitely separated
- lowest when electron repulsions
- ← → increases PE

bond length

- only covalent bonds
- atomic radius
- shorter the bond, stronger the bond
- ↓BL= ↑BE= ↓PE

bond order

- only covalent bonds
- number of bonds between two atoms (single, double, triple)
- ↑BO= ↓BL= ↑BE= ↓PE

bonds

↑BO= ↓BL= ↑BE= ↓PE

lewis structures

- only for covalent compounds
- polyatomic ions get a bracket
- center: least electronegative atom. NEVER F & H
1. count valence electrons (mostly even)
2. complete octets
3. verify electrons equal up to VE

carbon in lewis structures

- always the center
- never put lone pairs

incomplete octets (exception to the octet rule)

boron has an octet of 6 and will always be the center

expanded octets (exception to the octet rule)

- atoms in period 3-7 can expand, not always
- noble gases are expanded
- never double bond an F
- only central atoms can expand

formal charge

- formula: valence electrons - electrons assigned
- 0, -1, +1 accepted
- single bond= 1 e⁻ assigned (because two atoms are sharing the two electrons so it gets split between the atoms)

resonance structure

- the double or triple bond alternates between all the bonds in the compound
- use the bond order formula to find the bond order

bond order formula

# of bonds between same terminals/ # of same terminal atoms

charge clouds

any type of bonds and lone pairs= 1

compounds with multiple central atoms

make a chain and treat it as one central atom for each

bond polarity

- more electronegative atom= negative charge
- longer vector= stronger bond
- symmetrical molecules with same terminal atoms are nonpolar because the dipoles cancel out

diatomic molecules

same valence electrons= same lewis structure= same VSPER