3.11 quizzzzzzz Flashcards
lewis dot structure rules
- count up total # of valence electrons for all atoms
- arrange atoms (least electronegative atom is usually central atom, which is usually written first in chemical formula)
- draw single bonds between central atom(s) + terminal atoms
- distribute remaining electrons so each atom has a complete octet (except for H, Li, Be, and B)
- create double or triple bonds if needed
- verify that all valence electrons have been accounted for
- don’t bind oxygen to oxygen unless absolutely necessary (O2, O3, etc)
- CNOPS form double bonds (CN forms triple bonds)
- don’t leave lone pairs on carbon
- no closed loops or cyclic structures
- all electrons must be paired
- halogens (group 17) are most often terminal in a lewis structure
- hydrogen must be terminal
- make molecules as symmetrical as possible
- if given an option, put lone pairs on the more electronegative atom
How does reactivity change according to the periodic table and why?
- it increases going down a group of metals because there’s an increasing atomic radius (AR) and decreasing effective nuclear charge (Zeff)
- it decreases going down a group of nonmetals because there’s an increasing atomic radius (AR) and increasing shielding effect (SE)
- it decreases moving L-R across a period
define shielding effect
a decrease in attractive force from then + nucleus on the - valence electrons due to the presence of the inner core electrons
the inner core electrons shield/block the attraction from the nucleus (-/- repulsion)
How does shielding effect change according to the periodic table and why?
it increases going down groups (vertically) because there’s more energy levels which increases the shielding
- it stays constant going across
define effective nuclear charge (Zeff)
- magnitude of net attractive forces from + nucleus felt by the - valence electrons after taking into account any electron shielding
How does effective nuclear charge change according to the periodic table and why?
- it decreases going down groups because there’s more energy levels to separate the nucleus from the valence electrons
- it increases going left to right across a period
define electronegativity
tendency for an element to attract electrons within a bond
uses Pauling scale
how does electronegativity change going across periods and groups and why?
it increases going left to right across periods because electrons are more attracted to the nucleus due to increased nuclear charge
it decreases going down a group since electrons are less attracted to the + nucleus as the number of energy levels increases
define atomic radius
a radius of an atom is found by measuring the distance between the nuclei of two touching atoms and then halving that distance
dependent on number of occupied electron levels (n), shielding effect (SE), and effective nuclear charge (Zeff)
how does atomic radius change going across a periodic table and why
it decreases going left to right across a period because the number of occupied energy levels are the same but the number of the protons increase, which increases the effective nuclear charge (Zeff)
(the energy levels are more attracted to the nucleus and are “pulled in tighter”
it increases moving down a group because there’s an increasing number of occupied energy levels, increasing shielding effect (SE) and decreasing effective nuclear charge (Zeff)
define ionization energy
the energy required to remove an electron from a neutral atom in the gas phase
uses kJ/mol
how does ionization energy change with the periodic table and why
- the larger the effective nuclear charge (Zeff) on the electron, the more energy it takes to remove it
- the farther the most probable distance the electron is from the nucleus, the less energy it takes to remove it
- therefore, it increases going left to right across a period, as the effective nuclear charge increases
- it decreases going down a group, as the valence electrons are farther from the nucleus
What trends (other than shielding effect [se] are somewhat directly related to each other?
decreases going down a group, increases going left to right across periods
- effective nuclear charge (Zeff), electronegativity (EN), and ionization energy (IE)
increases going down a group, decreases going left to right across periods
- atomic radius (AR)
- ionic radius (IR)
increases going down a group
- shielding effect (SE)
how is ionic radius different for cations and anions
- cations are smaller than their neutral counterpart because as electrons are lost, often there is a loss of an energy level (decreased # of electrons and distance results in greater attraction)
- there will be less electron repulsions and therefore greater attraction to the nucleus
- same # of protons holding in fewer electrons results in increased effective nuclear charge (Zeff)
- anions are always bigger than their neutral counterpart because more electron repulsions results in less attractive forces between the nucleus and energy levels
-same # of protons holding in more electrons results in decreaased effective nuclear charge (Zeff)
metallic character
- assesses how much an element is like a metal
- decreases going L-R across periodic table because electrons are more tightly held
- increases going down groups because there are more energy levels, causing lower ionization energy
how does solubility change with the periodic table
- decreases going down a group
how does density change with the periodic tacble
increases going down a group
describe VSEPR theory
stands for valence shell electron pair repulsion theory
- used to predict the 3d shapes of molecules
- shape of the molecule is determined by repulsions between the electrons present in the valence shell
- electron pairs in the valence shell of the central atom repel each other and align themselves to minimize this repulsion
- lone electron pairs (lp) take up more space around the central atom than a bonding electron pair (bp) since a lone pair is attracted to 1 nucleus but a bonding pair is attracted to 2 nuclei
- minimizing repulsions between electrons maximizes the molecule’s stability
what are the angles for the different tetrahedral thingys
tetrahedral tetrahedral: 109.5 degrees
trigonal pyramidal: 107 degrees
bent/angular: 104.5 degreesh
how does polarity change for the different mgs of molecules
- linear: nonpolar
- trigonal planar: nonpolar (3 terminal atoms)
- trigonal planar bent: polar (2 terminal atoms, 1 lone pair)
- tetrahedral: nonpolar, 109.5 degrees (4 terminal atoms)
- tetrahedral trigonal pyramidal: polar, 107 degrees (3 terminal atoms, 1 lone pair)
- tetrahedral bent: polar, 104.5 degrees (2 terminal atoms, 2 lone pairs(
