Chem 20-1: Chapter 3 - Bonding

Edward Frankland

* first stated that each element had a fixed bonding capacity

Friedrich Kekulé

* expanded on franklins ideas and showed bonds between atoms as dashes (known as the structural formula)

Jacob van't Hoff + Joseph le Bel

* extended the formula to 3 dimensions (3D)
* the revised the existing theory in order to explain the ability of certain substances to change light as it passes through a sample of a substance (optical ability)

Richard Abegg

* bonding capacity is related to atoms electron structure
* stability of noble gases (inert) was due to the number of electrons in the atom
* also stated that due to electron structure, halogens are likely to gain and e- to become stable and alkali mental will lose and e- to become stable

Gilbert Lewis

* credited with the idea of valence and stable electron numbers for atoms
* stated that atoms could become stable by sharing or transferring electrons
* electrons can only be shared is atoms remain close together - this’d results in an attractive force known as a covalent bond

valence level

only electrons in the ___________ _____ of an atom can be shared or transferred

ionic bond

the attraction between positive and negative ions resulting in the transfer of one or more electrons

covalent bond

the simultaneous attraction of the nuclei of 2 atoms for the valence electrons that they shared between them

Quantum Model

* electrons are describes in terms of their energy content and by the probability of affecting other electrons in the region of space around the nucleus
* electrons exist as a cloud of probability

Linus Pauling

* his work (quantum mechanics) explains why certain electron arrangements are stable and why electrons stay in particular orbits and do not crash into the nucleus
* also explained that electron sharing must cover a complete range from equal attraction to total transfer

the energy theory

states that electrons in lower levels are held so strongly by the positively charged nucleus that during a reaction they remain essentially unchanged, which allows for the highest energy level, the valence level, to be able to move more freely to share and transfer electrons (shielding)

shielding

* the outmost electrons are repelled by the inner electrons, so the nucleus’ effective charge on the outer electrons is decreased
* hence the nucleus has less grip on the valence electrons, allowing them to move more freely

orbital

* region of space around the atom’s nucleus where an electron may exist
* 3D space that defines where an electron may be

valence

in bonding we are only concerned about _______ orbitals

valence orbital

the volumes of space that can be occupied by an electron or pairs of electrons in an atoms highest energy level

bonding electron

an atom with a valence orbital occupied by a single electron that could share that electron with another atom

lone pair

2 electrons occupying the same orbital are called a lone pair

valence electrons

* in a chemical reaction it is the _______ __________ that determine the chemical properties for ionic and molecular substance
* the only electrons available for the formation of a chemical bond

chemical bonding

* an electrostatic attraction between atoms
* allows individual atoms to obtain full valence energy levels, causing the atoms to become stable

Friedrich Kukule

invented the structural formula

Gilbert Lewis

invented the lewis dot formula

2,8,8,18

How many electrons can fit in each orbital? (_,_,_,__)

two

how many electrons fit in the first energy level?

hydrogen

* which element is an exception to most chemical rules
* has only one energy level
* smallest reactive atom with the simplest structure

4 each

how many orbitals can fit in the second and third energy levels?

8 each

how many electrons can fit in the second and third energy levels?

yes

can an orbital be empty?

spread out

electrons _____ ___ to occupy and empty valence orbitals before forming lone pairs.

lone pairs

electrons spread out to occupy and empty valence orbitals before forming ____ _____.

group 18 - noble gases

lack of reactivity indicates that the structures with 8 electrons in their valence levels very stable, in which group do these atoms occur?

octet rule

the idea that a maximum of 8 electrons (4 pairs) can occupy orbitals in the valence level of an atom

C, N, O and F

which elements always obey the rules when bonding?

lewis symbol

* created by Gilbert Lewis
* simple model of the arrangement of electrons in atoms
* explains and predicts empirical formulas

lewis symbol

the _____ ______ is useful to help describe how atoms bond

steps to draw the Lewis Symbol

1. write the element symbol to represent the nucleus ad any filled energy levels
2. add a dot to represent each valence electron
3. start by placing valence electrons into each of the four orbitals (top, right, bottom, left)

factors that affect electronegativity

1. the father away from here nucleus that the electrons are, the weaker their attraction to the nucleus
2. inner electrons (closer to the nucleus) shield valence electrons from the attraction of the + nucleus
3. the greater the number of protons in the nucleus, the greater the attraction for electrons must be

electronegativity

* a value assigned to any atom describing how well it attracts electrons shared in a covalent bond with another atom
* used to describe the relative ability of an atom to attract a pair of bonding electrons in its valence level

electrons

when two atoms collide, the atom with the greater electronegativity pulls the other atoms ________ towards it

Linus Pauling

electronegativity is usually assigned on a scale developed by

fluorine (F)

which element has the highest electronegativity

Cerium (Cs)

which non-mental element has the lowest electronegativity

low, high

one average, metals tend to have a ______ electronegativity and non-metals have a relatively ____ electronegativity

high, low

metals tend to have ____ melting and boiling points, and non-metals tend to have relatively ___ melting and boiling points

Activity Series

* ability to react with water and acids
* used to determine the products of single replacement reactions

Ionization energy

energy required to remove an electron

Electron Affinity

energy required to gain an electron

trend of electron affinity and ionization

the trend tends to go up and to the right

trend of atomic radii

trend tends to go down and to the left

covalent bonding

* if both electronegativities are relatively high, neither atom will “win” and the bonding of electrons will be shared between the two atoms
* simultaneous attraction of 2 nuclei for the shared pair of bonding electrons
* normally 2 non-metal atoms

ionic bonding

* if electronegativties are widely different, that atom with the greater attraction for electrons (electronegativity) may succeed in removing electrons from the valence level of another atom
* creates ions

crystal lattice

* ions in ionic compounds always pack together to arrange themselves in a regular repeating 3D pattern

metallic bonding

* if both electroegtaivties of colliding atoms have relatively low electronegativity, the atoms can share electrons without a reaction taking place
* valence electrons are not held very strongly and the atoms have vacant valence orbitals
* do not organize their atoms in specific arrangements
* resulting substance is flexible, maleable and ductile

diatomic molecules

Nitrogen - N2(g)

Oxygen - O2(g)

Hydrogen - H2(g)

Florine - F2(g)

Chlorine - Cl2(g)

Iodine - I2(g)

Bromine - Br2(g)

diatomic molecules

atoms in natural occur naturally as pairs

polyatomic molecules

Phosphorus - P4(g)

Sulfur - S8(g)

octet rule

each atoms must be surrounded by and octet (8) electrons

double bond

attraction between atoms in a molecule due to the sharing of two pairs of electrons in a covalent bond

triple bond

an attraction between atoms in a molecule due to sharing of three pairs of electrons in a covalent bond

molecular compounds

* cannot be represented by the simplest ration formula as ionic compounds can be
* to distinguish these compounds, it is necessary to represent them with molecular formulas

bonding capacity

* max number of single covalent bonds that an atom can form
* determined by the number for bonding electrons an atom has

coordinate covalent bond

* a covalent bond in which one of the atoms donates both electrons
* this concept is useful in explaining the structure of many molecules and polyatomic ions

empirical formula

* shows the simplest whole number ratio of atoms in the compound
* rarely useful for molecular compounds

molecular formula

* show the actual number of atoms that are covalently bonded to make up each molecule
* often has the atom symbols written in a sequence that helps you determine which atoms are bonded to which

lewis formula

* aka lewis diagram/electron dot diagram
* uses symbols to show electrons sharing in covalent bonds, electron transfer in ionic bonds and the formation of stable valence octet of electrons in molecule

structural formula

* aka structural diagram
* shows which atoms are bonded and the types of covalent bonds between atoms

stereochemical formula

* a structural formula drawn to try to represent the the 3D molecular shape
* this style of representation often becomes too complete complex to be practical

central atom

atom which all other atoms are bonded

peripheral atoms

other atoms that are bonded to the central atom

vsepr theory

* aka nyhlom-gillespie theory
* based on the electrical repulsion of bonded and unbounded electron pairs in a molecule
* pairs of electrons in valence shell stay as far apart as possible because of repel of like charges

valence shell electron pair repulsion

what does vsepr stand for?

valence bond theory

* created by linus pauling in 1930’s
* explained many atoms orientations in molecules and ions
* worked with gilbert lewis
* used x-ray of crystals to determine chemical structures

stereochemistry

study of the 3D spatial configuration of molecules and how this affects their reactions

central

vsepr diagrams are found by counting the number of bonded and lone pairs around _______ atoms

according to vsepr:

* only valence electrons of central atoms are important for molecular shape
* valence electrons are paired in a molecule or polyatomic ion
* bonded pairs of electrons and lone pairs of electrons are treated about equal
* valence electrons repel each other
* the molecular shape is determined by the position of the electron pairs when they are a maximum distance apart

repel

all pairs of valence electrons _____ each other equally and try to get as far from each other as possible

process for predicting vsepr shape

1. draw lewis formula
2. count # of boned orbitals and lone pairs
3. refer to the table of stereochemical formulas \*you should have memorized

electronegativity

* a periodic property of atoms
* attraction of electrons of one atom to the nucleus of another

non polar covalent bond

* occurs when 2 or more atoms have equal electronnegativity

polar covalent bond

occurs when electronegativities of 2 or more atoms are unequal

increases

increasing the electronegative forced, _______ the polarity

transfer

a very high different in electronegativity can cause a __________ of electrons resulting in a ionic bond

closer

due to an unequal charge of polar molecules, electrons spend more time ______ to the more electronegative atoms nucleus

δ-

partial negative charge when in a polar compound

δ+

partial positive change when in a polar compound

linear

has to bonded electron pairs and no lone pairs

trigonal planar

has 3 boned pairs and no lone pairs

tetrahedral

has 4 bonded pairs and no lone pairs

trigonal pyramidal

has three bonded pairs and one lone pair

angular (bent)

has 2 bonded pairs and 2 lone pairs

linear

has one bonded pair and 3 lone pairs

charged

molecules are made of ________ particles (+&-)

polar molecule

* molecule in which the negative (electron) charge is not distributed symmetrically among the atoms making up the molecule
* partial positive and negative charges on either sides of the molecule

non-polar molecule

molecule that has a symmetrical electrical charge/distribution

no

does a polar bond mean a molecule is automatically polar?

use stereochemical shape and electronegativity

how do we predict polarity?

bond dipole

* charge celebration that occur when electronegativity difference of two bonded atoms shifts the shared electrons making one end slightly + and one end slightly -

how to predict polarity

step 1: draw lewis diagram'

step 2: use VSEPR rules to determine shape around central atom

step 3: use electronegativities to determine podiatry of each bond

step 4: add the bone dipole vectors to determine wether the final product is polar or non-polar

polar

polar substances are solvable in _____ solvents

non-polar

non-polar compounds are soluble in ________ solvents

the resulting mixture will become homogeneous

how can you determine if two molecules are both polar