Structure & Properties of Ionic & Covalent Compounds Flashcards
What is an ionic bond?
Attractive force due to transfer of 1 or more electrons from one atom to another
What is a covalent bond?
Attractive force due to sharing of electrons between atoms
Ionic Bonding
- Electron lost by a metal
- Electron gained by by a nonmetal
- two ions formed: cation and anion (of opposite charge =attracted)
- opposite charged ions held together by electrostatic force
What is a crystal lattice?
Positive and negative ions arrange themselves in regular 3D repeating array to produce stable arrangement
Covalent Bonding
- Each atom attains noble gas configuration by sharing electrons
- Tend to form between atoms with similar tendencies to gain or lose electrons
- Polar and nonpolar covalent bonding
What are the diatomic elements?
Completely covalent bonds (totally equal sharing)
Example: Doctor BrINClHOF
Br2, I2, N2, Cl2, H2, O2, F2
What is polar covalent bonding?
Bonds made up of unequally shared electron pairs
Reference notes for symbols
What is electronegativity?
Measure of ability of atom to attract electrons in a chemical bond
- higher EN = greater ability to attract electrons than elements with low EN
What is bond polarity?
Difference in electronegativity
Bond is:
-Ionic Bond: 🔺EN>1.9
- Polar Covalent Bond: .5🔺EN
What does nomenclature mean? What are the two naming systems?
Assignment of correct & unambiguous name to each & every chemical compound
- ionic compound
- covalent compound
How do you write the formula for an ionic compound?
- Determine charge of each ion
- metals: charge = group #
- nonmetals: charge = group #-8
- cations and anions combine to give formula with net change of 0 - Name the cation followed by name of anion (change anion suffix to -ide)
What is the stock system?
If a cation of the element has several ions of different charges (i.e. transition metals) use a Roman numeral following metal name
- Roman numerals give charge of metal
What are common nomenclature system?
- use -ic to indicate higher of charges that ion might have
- use -ous to indicate lower of charges that ion might have
What are monatomic ions?
Ions consisting of a single charged atom
Ex: all alkali metals, all halogen metals, be, ca, al, ag, ba, mg, o, s, n, p
What are polyatomic ions?
Jons composed of 2 or more atoms bonded together with an overall positive or negative charge
How to write formulas of an ionic compound from its name?
- Determine charge of each ion
2. Write formula so resulting compound is neutral
How do you name covalent bonds?
- Write in order in which they appear in formula
- Greek prefix indicates # of each kind of atom:
- mono=1; di=2; tri=3; tetra=4; penta=5; hexa= 6; hepta=7; octa=8; nona=9; deca=10 - If only one atom of a particular element is present in a molecule, prefix mono- is usually omitted in first element
- Stem of name of last element is used with suffix -ide
- Final vowel in prefix is often dropped before vowel in stem name
What are the physical states of ionic and covalent compounds?
- ionic compound: usually solids at room temp
- covalent compound: usually solids, liquids, gases
What is melting point?
Temperature at which solid is converted into a liquid
What is boiling point?
Temperature at which a liquid is converted into a gas
What are the melting points of ionic and covalent compounds?
- ionic compounds have higher melting points and boiling points
- covalent compounds have lower melting points and boiling points
What are the structure of ionic and covalent compounds at solid state?
- ionic compounds are crystalline (organized)
- covalent compounds are crystalline (organized) or amorphous (unorganized)
What is the difference between covalent and ionic compounds electrical conductivity?
Electrolytes: ions present in solution allowing solution to conduct electricity
Nonelectrolytes: covalent solids usually do not dissociate and do not conduct electricity
How to draw a Lewis structure?
- Use chemical symbols for various elements to write skeletal structure of compound
- least electronegative atom will be placed in central position - Determine number of valence electrons associated with each atom in compound
- combine valence electrons to determine total # of valence electrons in compound - Connect central atom to each of surrounding atoms with single bonds
- Complete octets of all atoms bonded to central atom
- lone pair: electrons not involved in bonding - If not enough valence electrons to give central atom an octet, move lone pair electrons from terminal atoms to form new bond with central atom
- Recheck that all atoms have octet rule satisfied and total # of valence electrons used
What are single bonds, double bonds, and triple bonds?
- single bond: one pair of electrons are shared between 2 atoms
- double bond: 2 pairs of electrons are shared between 2 atoms
- triple bond: 3 pairs of electrons are shared between z atoms
What is bond energy?
Amount of energy required to break a bond holding 2 atoms together
Triple bond> double bonds>single bond
What is bond length?
Distance separating nucleI of 2 adjacent atoms
- single bond>double bond>triple bond
What is resonance?
Two or more Lewis structures contribute to real structure
What are the three exceptions to the octet rule?
- Incomplete octet: less than 8 electrons around an atom other H
- Odd electron: if there is an odd # of valence electrons, it is not possible to give every atom 8 electrons
- Expanded octet: an element in 3rd period or below may have 10 and 12 electrons around it
What is the VSEPR Theory?
Valence shell electron pair repulsion theory
- used to predict shape of molecules
- electrons arrange themselves as far away as possible to minimize electronic repulsion
How does a linear structure look like?
-bonded atoms:2
-non binding lone electron pairs:0
-bond angle:180°
-molecular geometry: linear
Ex: CO2
How does a trigonal planar structure look like?
Bonded Atoms: 3 Non bonding lone electron pairs: 0 Bond Angle: 120° Molecular Geometry: Trigonal planar Ex: SO3
How does a bent structure look like?
Bonded Atoms: 2 Non bonding lone electron pairs: 1 Bond Angle: < 120° Molécula Geometry: Bent Ex: SO2
How does a tetrahedral structure look like?
Bonded Atoms: 4 Non bonding lone electron pairs: 0 Bond Angle: 109.5° Molecular Geometry: tetrahedral Ex: CH4
How does a trigonal pyramidal structure look like?
Bonded Atoms: 3 Non bonding lone electron pairs: 1 Bond Angle: 107° Molecular Geometry: trigonal pyramidal Ex: NH3
How does a different bent structure look like?
Bonded Atoms: 2 Non bonding lone electron pairs: 2 Bond Angle: 104.5° Molecular Geometry: bent Ex: H2O
How do you determine molecular shape?
- Write Lewis structure
- Count number of bonded atoms & lone pairs around central atom
- If no lone pairs are present, geometry is:
- 2 bonded atoms: linear
- 3 bonded atoms: trigonal planar
- 4 bonded atoms: tetrahedral - If there are lone pairs, look at the arrangement of atoms & name geometry
How do you determine polarity?
- Write Lewis structure
- Draw geometry
- Use following symbol to denote polarity of each bond
Positive end of bond= less electronegative atom
Negative end of bond= more electronegative atom attracts electrons more strongly towards it
What are the guidelines for determining polarity?
- molecules that have no lone pair on central atom & all terminal atoms are same are non polar
- molecules with one lone pair on central atom are polar
- molecules with more than one pair on central atom usually polar
What are intramolecular forces and intermolecular forces?
-Intramolecular Forces: attractive forces within molecules
Ex: chemical bonds
-Intermolecular Forces: attractive forces between molecules
What is solubility?
Max amount of solute that dissolves in given amount of solvent at specific temperature
Polar molecules: most soluble in polar solvents
No polar molecules: most soluble in nonpolar solvents
What is hydrogen bonding?
Attractive forces, called hydrogen bonds pull ammonia into water distributing ammonia molecules throughout water, forming homogeneous solution
What factors influence boiling and melting points?
- Strength of attractive force holding substance in its current physical state
- Molecular mass
- larger molecules have higher m.p. and b.p. than smaller molecules - Polarity
- polar molecules have higher m.p. and b.p. than non polar molecules of similar molecular mass due to its strong attractive force
