chemistry final 1/6

formula unit : the chemical formula of an ionic compound

ionic compounds are made up of ions arranged in repeating patterns.

it represents the simplest ratio of ions involved. and overall charge is 0 , because the formula unit represents the entire crystal which is neutral.

monoatomic ion : one atom ion such as Br- and Mg2+ binary ionic compounds are composed of positively charged monoatomic ion and a negatively charged monoatomic ion.

oxidation number : also called oxidation state and is equal to the net charge of ions.

transition metals have more than 1 possible ionic charge.

the oxidation number of an element in an ionic compound = the number of electrons transferred from the atom to form the ion.

example : sodium donates 1 electron to chlorine to form sodium chloride. so the oxidation number of sodium is 1+ because one electron was transferred from the sodium atom to chlorine which makes chlorines oxidation number 1- .

Formulas for binary ionic compounds : the symbol of cation is always written first , followed by the symbol of anion and subscripts which are small numbers written to the lower right of the symbol which represents the number of ions & if no. subscript is written then its 1.

Example NaCl

polyatomic ions : ions made up of more than 1 atom they acts as an individual ion in a compound and its charge applies to the entire group of ions., the subscripts of polyatomic ions CANT be changed if u wanna add charge put parentheses.

study table

oxyanion : polyatomic ion composed of an element usually a nonmetal bonded to one or more oxygen atom. more than one oxyanion exists in nitrogen & sulfur

1- Name the cation followed by the anion. Remember that the cation is always written first in the formula.

2- For monatomic cations, use the element name.

3- For monatomic anions, use the root of the element name plus the suffix -ide.

roman numerals are only in transition metals.

if it has more than 1 oxidation number write roman numerals , in iron for examples.

covalent bond

lower energy , the more stable the atom is (inversely proportional )

covalent bond : the chemical bond that result from sharing valence electron.

molecule : when 2 or more atoms bond covalently. covalent bonds generally occur in elements close to each other in the periodic table. and it happens in nonmetallic elements.

diatomic molecules : hydrogen , nitrogen , oxygen , flourine , chlorine , bromine , iodine.

Repulsion occurs between nuclei and between electron cloud. if the 2 nuclei move closer the repulsion force increase.

hydrogen molecule is more stable than hydrogen atom

single covalent bonds :

lewis structure : they represent the arrangement of electrons in a molecule, A line or a pair of vertical dots between the symbols of elements represents a single covalent bond in a Lewis structure. H—H

lewis structure shows the lone pairs while structural formula doesn’t

Bond length & bond strength → inversely proportional

bond energy & bond length → inversely ‘‘ ‘‘

length : single>double>triple.

strength : single>double<triple

single bonds are easier to break.

sigma bonds : Single covalent bonds , sigma bond occurs when the pair of shared electrons is in an area centered between the two atoms. When two atoms share electrons, their valence atomic orbitals overlap end-to-end, concentrating the electrons in a bonding orbital between the two atoms. A bonding orbital is a localized region where bonding electrons will most likely be found.

when s overlaps with another s or a p orbital

H20 NH3 CH4 have sigma bonds.

double bond : 2 pairs of e- are between.

triple bond : 3 pairs of e- r shared. nitrogen have triple bond

pi bond : represented by the Greek letter pi (. ), forms when parallel orbitals overlap and share electrons. The shared electron pair of a pi bond occupies the space above and below the line that represents where the two atoms are joined together.

triple bond containts 1 sigma bond & 2 pi bonds.

bond dissociation energy : energy required to break covalent bonds. always +ve.

smaller bond length the more bond dissociation energy ( inversely) like when u wanna break apart really close friends its hard to break them .

bond length is the distance from a nucleus to the other nucleus.

endothermic reaction : greater amount of energy is needed to break the existing bonds than the one released while forming the new bond.

exothermic reactions : occurs when more energy is released during product bond formation than is required to break bonds in the reactants. (burning charcoal)

naming molecules

only for the 2nd element , the first element never uses mono only the 2nd one does.

name the following :

co_{2 : carbon dioxide.}

_{SO2 : sulfur dioxide}

acids : contains hydrogen and either another element which is called binary acid or hydrogen oxygen and another element which is also called an oxyacid

oxyacids : dont mix between them and oxyanions oxyanions r made up of polyatomic ions that have more than 1 oxygen atom

more oxygen : ___ic acid (1 oxygen)

less oxygen : ___ous acid (2 oxygen.)

solve :

h2so4 —>

h2so3 —>

h2so4 —→

the name of a molecular formula reveals its composition & its important in communicating the nature of the compound.

the formula of an acid for an acid can also be derived from the name

only binary acids start with hydro-

identify the formula for each :

silver chloride

di hydrogen mono oxide.

di sulfur deca flouride.

molecular structures :

structural formula : which uses letter symbols and bonds to show relative positions of atoms. You can predict the structural formula for many molecules by drawing the Lewis structure.

do the structural formula of NH3

co2

po4 *-3

Resonance : a condition that occurs when more than 1 valid lewis structure can be written for a molecule or ion.

they only differ in position of the electron pairs never the atoms position.

NO3 - , NO2 - , SO3 2- , CO3 2- , O3

EXCEPTIONS :

1 - ODD NO. OF VALANCE ELECTRONS . —> No2

2- FEW COMPOUNDS THAT FORM SUBOCTET —> Bh3

3- expanded octet : central atom contains more than 8. valance e. —> PCl5 or SF6

coordinate covalent bond : when one atom donates both of the electrons to be shared w an atom or an ion that needs 2 electrons to form octet.

a binary compound having only 1 sigma bond displays resonance : t or f

false , it doesn’t display resonance , resonance occurs when more than 1 lewis structure is available.

lesson 4

VSEPR model : Valence Shell Electron Pair Repulsion model, which is based on an arrangement that minimizes the repulsion of shared and unshared pairs of electrons around the central atom.

bond angle : caused by forces of repulsion and attraction it is the angle formed by 2 terminal atoms and the central atom

hybridization : when two things are combined and the result has characteristics of both. For example, during chemical bonding, if electrons come from 2 different atomic orbitals, such as a p or and they must rearrange or combine into a hybrid orbital with the same shape and energy level.

electronegativity & polarity :

electronegativity : indicates the relative ability of an element's atoms to attract electrons in a chemical bond.

Flourine has the greatest electronegativity

Francium has the least

xenon is a noble gas, it can sometimes form bonds with highly electronegative atoms such as flourine.

electronegativity trend : to the right : increase

down a group : decrease.

why aren’t noble gasses shown in the table ? because they generally don’t form compounds.

the scale of electronegativity allows chemists to evaluate the affinity of specific atoms in a compound for electrons. Electronegativity is a measure of the tendency of an atom to accept an electron. Excluding noble gases, electronegativity increases with increasing atomic number within a period and decreases with increasing atomic number within a group. so

electronegativity increase , the atomic number atomic number in a period increase .

but when electronegativity decrease , the atomic number within a group increases

As you move from left to right on the table, the number of electrons needed to complete the octet rule becomes less, thereby increasing an atom's affinity for electrons

what is affinity? when e- is added to a gaseous atom. (check)

A chemical bond between atoms of different elements is never completely ionic or covalent. Electrons in bonds between identical atoms have an electronegativity difference of zero-meaning that the electrons are equally shared between the two atoms. AKA non-polar covalent bond or pure covalent bond

polar covalent bond : different elements have different electronegativities , the electron pairs in a covalent bond between different atoms are not shared equally.

An electronegativity difference of 1.70 is considered 50 percent covalent and 50 percent ionic.

ionic increases if the electronegativity difference increases ( directly proportional)

polar covalent bonds form because not all atoms that share electrons attract them equally.

describe a polar covalent bond : When a polar bond forms, the shared electron pair or pairs are pulled toward one of the atoms. Thus, the electrons spend more time around that atom than the other atom. This results in partial charges.

The Greek letter delta (S) is used to represent a partial charge.

In a polar covalent bond, o represents a partial negative charge and 8* represents a partial positive charge.

The more-electronegative atom is at the partially negative end, while the less-electronegative atom is at the partially positive end.( dipole moment) which leads to uneven electron density

2 factors that affect polarity?

1- difference in electronegativity

2- molecular shape (symmetrical or unsym)

unsymmetrical = polar.

Differences in properties of atoms are a result of differences in both attractive and repulsive forces.These weak attraction forces are known as intermolecular forces, or van der Waals forces.

describe covalent network solids : composed of only atoms interconnected by a network of covalent bonds

example : quartz & diamond ,,, very strong, and solid looks like a web of carbon(diamond)

intermolecular forces : the forces that occur between molecules together and they are weak in covalent bonds .(ask abt it.)

intramolecular forces : orces that hold atoms together within a molecule.

• Much stronger than intermolecular forces.

The spatial arrangement of polar bonds in a molecule determines the overall polarity of a molecule.