bonding and chemical interactions

Question 1

why can elements past period 3 break the octet rule

Answer 1

expand into the d orbital

• However, some of the third-period elements (Si, P, S, and Cl) have been observed to bond to more than four other atoms, and thus need to involve more than the four pairs of electrons available in an s2p6 octet. This is possible because for n=3, the d sublevel exists, and it has five d orbitals.
• Size is also an important consideration: The larger the central atom, the larger the number of electrons which can surround it.

Question 2

which elements have incomplete octets

Answer 2

H (2), He (2), Lit (2), beryllium (4) and boron (6)

Question 3

boron

Answer 3

6

Question 4

beryllium

Answer 4

4

Question 5

ionic bonding

Answer 5

one or more electrons from an atom with low ionization energy ( energy needed to remove an electron = metal) are transferred to an atom with high electron affinity ( higher= wants more- def = the amount of energy released when atom gains an electron - exothermic) this is usually a nonmetal. Once one steals the others electron(s) - it becomes an anion and is attracted to the cation - this is the bond ( electrostatic attraction)

Question 6

covalent

Answer 6

shared between 2 atoms

• typically 2 nonmetals that have simular electronegativity
• polarity depends on the difference between the two’s electronegativity

Question 7

if both electrons are given by one of the atoms in the colvealent bond it is called a

Answer 7

coordinate colvalent

Question 8

BP of ionic compounds

Answer 8

high - bc of the strength of the electrostatic force

Question 9

other characteristics of ionic compounds

Answer 9

good conductors, disolve in water and other polar solvents, sold state form a crystalline lattice

Question 10

bonding force of colvalent bonds

Answer 10

the electrons (both in the shared pair) feel an attraction to the two positive nuclei of the bonded atoms

Question 11

to remember if nonmetals lose or gain electrons: Nonmetals …..

Answer 11

Nonmetals gain electons to become aNions and Negative

Question 12

when an ionic bond forms

Answer 12

generally extremely exothermic (energy released)

• even if some energy input is needed (electron affinity- always endothermic) - the amount of energy given off when a salt lattice is HUGE - making in exothermic

Question 13

properties of covalent compounds

Answer 13

they become there own lil molecules that have weak intermolecular reactions so they are poor conductors, low boiling point sand melting points- don’t break into constituent ions

Question 14

bond order

Answer 14

number of shared electron pairs between two electrons

• single = 1 bond order
• double = bond order of 2

Question 15

bond length

Answer 15

shorter with increasing bonds

Question 16

bond strength

Answer 16

strongest with most bonds ( triple)

Question 17

dipole moment

Answer 17

p= qd ( q is mag of charge and d is displacement seperating the 2 charges)

Question 18

lewis base

Answer 18

any compound that will donate 2 electrons to form a coordinate covalent bond

• b’s and d’s ( a Base will Donate 2 electrons)

Question 19

formal charge

Answer 19

the difference in the valence electrons given in a lewis diagram (when its in a colavent compund) and the actual amount of valence electrons in the neutral atom ( when its not in a covalent compound)

formal charge= V normal - Nonbonding - 1/2 bonded

or

= V normla - dots (nonbonded=2) - sticks (one)

” what’s the difference in the electrons given in the lewis structure and the actual valence electrons that the atom normally has–> if its +1–> this means it has one less electron than what it normally does”

Question 20

backbone of lewis

Answer 20

H is always on the end
halogens are normally on the end
the next least electroneg is in the center

Question 21

steps for lewis diagram

Answer 21

• construct the backbone
• tally total valence electrons
• draw single bonds between all atoms present
• complete the octets of the terminal atoms ( remember H has only 2)
• place any extra on the central atom
• and if the central atom is not full octet- add double or triple bonds

Question 22

resoance structures

Answer 22

its possible to draw coumpounds that have the same atom arrangment bu that differ in the placemnt of the electrons - these are resoanace structures
- actualy distribution is hybrid

Question 23

formal charges for assessing stability

Answer 23

• if formal charges are present- the one with 2 opposite charges closest together is more stable
• negative charge on themost electronegative atom is best
• smallest number of fc’s

Question 24

VSEPR theory

Answer 24

geometrical shape (nonbonded pairs want to be as far apart as possible) this is the basis of all the shapes

Question 25

SF6

Answer 25

octahedral

Question 26

PCl5

Answer 26

trigonal bipyramidal

Question 27

NH3

Answer 27

• trigonal pyramidal

- not trigonal planar ( like BH3- which has only 6), bc there is alone paor which repels the 3 other bonds

Question 28

difference between electronic geometry and molecular geometry

Answer 28

electronic- all electrons (bonded and nonbonded)
molecular- only the bonded pairs ( for this one only needs to consider the cordinate number ( the number of atoms bonded to the central atom)

Question 29

H2O, CH4 and NH3 electronic geometry

Answer 29

all the same = tetrahedral - bc in electronic geo you treat all electrons ( whether bond or no, they same)

Question 30

H2O, CH4 and NH3 molecular geometry

Answer 30

molecular geometry depends only on the bonded pairs

• so H2O= bent
• NH3- trigonal pyramidal
• CH4- tetrahedral

Question 31

the important take away about electronic geometry vs molecular ( bc MCAT mostly concerned with molecular)

Answer 31

the electronic tells us the ideal bond angle - but keep in mind that even though H2O ad CH4 both have the tetrahedral molecular formula–> bc in water there are 2 nonbonded electrons- this creates more push, so the bond angle is less than the ideal

Question 32

atoms involved in H-bonds

Answer 32

pick up the FON

Question 33

london dispersion forces get bigger when

Answer 33

the size of the atom increases