unit 4 chem

energy, compounds and forces

energy diagram

a graph showing the changes in potential energy during a reaction. It starts with the reactants on the left and proceeds to the products on the right

Ea

activation energy; the amount of energy that is required to start the reaction. the difference in potential energy between the reactants and the top of the ‘curve’.

ΔH

enthalpy; the difference in potential energy between the products and reactants

transition state

the high energy stage between the reactants and the products. rearranging of atoms has started, but not completed yet. also referred to as the activated complex.

endothermic

* gets __colder__
* __reactants__ have __less potential energy__ compared to products
* energy was __absorbed__ during this reaction (this is why the products have more energy)
* ΔH will be __positive__
* thermal → potential energy

exothermic

* gets __warmer__
* __reactants__ have __more potential energy__ compared to products
* energy was __released__ during this reaction (this is why the products have more energy)
* ΔH will be __negative__
* potential → thermal energy

did this reaction absorb or release more energy?

absorb

what type of reaction does this graph represent?

endothermic

which of the letters a-f in the diagram represent the potential energy of the __products__?

E

which of the letters indicate the potential energy of the __transitional state__?

C

which letter indicates the potential energy of the __reactants__?

A

which letter indicates the __activation energy (Ea)__?

B

which letter indicates the __heat of reaction (Δ H)__?

F

did this reaction absorb or release more energy?

absorb

what type of reaction does this graph represent?

endothermic

what is the quantitative value for the potential energy of the __reactants__?

80 kJ

what is the quantitative value for the potential energy of the __products__?

160 kJ

what is the numerical value for the __activation energy (Ea)__?

Ea = (240 kJ - 80 kJ) = **160 kJ**

what is the numerical value for __heat of reaction (Δ H)__?

Δ H= 160 kJ - 80 kJ = **80 kJ**

what is the potential energy of the __transitional state__?

240 kJ

compound

2 or more elements that are chemically combined (not just mixed)

metal + metal

metallic compound

metal + nonmetal

ionic compound

nonmetal + nonmetal

molecular compound

ion formation

each element has one particular ion it nearly always forms, when it bonds in an ionic compound (except for transition metals, which had multiple preferred ionic states).

in general, the ion an element will form can be predicted by the _____.

octet rule

octet rule

when an element forms an ion, it will do so in whatever way allows it to have a full outer shell (8 valence electrons) the easiest

ionic compound

consists of positive and negative ions that are held together in a crystal lattice

crystal lattice

a rigid geometric pattern

the forming of ionic compounds

* Generally, any compound containing a metal and a nonmetal is an ionic compound.
* The compound forms when the metal atom gives an electron to the nonmetal atom. T
* The metal atom becomes a positive ion (cation) and the nonmetal atom becomes a negative ion (anion).

the net charge of an ionic compound should always be ____.

zero

chemical nomenclature

a set of rules that all chemists agree upon to allow us to consistently name compounds

steps to name ionic compounds

1. name the positive ion, then the negative ion
2. the name of the positive ion is the same as the name of the atom. Ex: Mg2+ is the “magnesium” ion
3. the name of the negative ion has the “ide” ending. Ex: Cl-1 is the “chloride” ion
4. if the positive ion is a transition metal, you must include the charge of the atom as a Roman numeral in parentheses. Ex: Cr+4 is the “chromium (IV)” ion

chemical formulas

tell how many of each atom (or ion) are in a compound. when writing chemical formulas, subscripts are used to note that the smallest whole number ratio of ions in a ionic compound. (the positive ion is always written first in the ionic compound.")

how to write formulas for ionic compounds

1. determine the charge of each ion
2. determine how many of each ion are in the compound. (cross the charges for a short cut)
3. write the positive ion, then the negative ion. don’t write their charges, but do use a subscript to tell how many there are

roman numerals

one: I

two: II

three: III

four: IV

five: V

six: VI

practice: when potassium and oxygen form a compound

* what ion does potassium form? symbol: K+ name: potassium
* what ion does oxygen form? symbol: O-2 name: oxide
* there are 2 potassium ions for every oxide ion
* name the compound: potassium oxide
* compound formula: K2O

practice: when calcium and sulfur form a compound

* what ion does calcium form? symbol: Ca+2 name: calcium
* what ion does sulfur form? symbol: S-2 name: sulfide
* there is a calcium ion for every sulfide ion
* name the compound: calcium sulfide
* compound formula: CaS

polyatomic ions

groups of atoms that have bonded together and that have an overall charge. ex: SO4^-2 means that in one sulfur ion, there is one sulfur atom and 4 oxygen atoms and their overall charge is -2.

molecular compounds

* formed by __two nonmetals__
* composed of discrete molecules
* since nonmetals “need” to gain electrons to become more stable, they can share electrons to form molecular compounds
* called covalent bonding
* these compounds may exist as solids, liquids, or gases at room temp
* usually have lower melting points than ionic compounds

molecular compounds nomenclature

1. name each element
2. use a prefix to indicate the number of each atom there are in a molecule
3. for the first element, if there is only one atom in each molecule, don’t use “mono”
4. change the ending of the last element to “ide”

prefix of molecular compounds

1 : mono

2 : di

3: tri

4: tetra

5 : penta

6 : hexa

SO3

sulfur trioxide

N2O5

dinitrogen pentoxide

when a metal and nonmetal bond, they form a ____

large crystal lattice

which one is a covalent compound?

Fe2O3

MgCl2

SeO

CaS

SeO

when cesium and phosphorous bond, there are

3 times as many Cesiums ions as Phosphorous ions

what is the right name for BaCl2

Barium Chloride

what is the right formula for Selenium Diflouride

SeF2

endothermic reaction make their environment ___

colder

which bonds are stronger in endothermic reactions?

reactant bonds

what represents activation energy in a reaction?

reactants → transitional state

a reaction was calculated to have absorbed +200 kJ/mol and released -600 kJ/mol. this reaction is…

exothermic

stronger bonds require….

high activation energy

which is stronger: ionic or covalent bonds?

ionic

intermolecular forces

forces of attraction between molecules

intramolecular forces

hold atoms together in a molecule

hydrogen bonds

attractive forces in which a hydrogen covalently bonded to a very electronegative atom causes attractions to other molecules

ionic bond

A chemical bond resulting from the attraction between oppositely charged ions.

covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule

polar bond

a covalent bond between atoms in which the electrons are shared unequally

polar molecule

a molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive

nonpolar bond

a covalent bond in which electrons are shared equally

nonpolar molecule

a molecule that does not have oppositely charged ends

Melting

change from a solid to a liquid

Freezing

\n The change of state from a liquid to a solid

Condensing

The change of state from a gas to a liquid

Vaporizing

the change from a liquid to a gas

Sublimation

A change directly from the solid to the gaseous state without becoming liquid

Deposition

\n a change directly from a gas to a solid

weakest intermolecular force

london forces

strongest intermolecular force

hydrogen bond

intermolecular forces between ALL polar molecules

dipole dipole forces

London forces are strongest for __________________ molecules

nonpolar

hydrogen bonds can form when H is bonded to __________

nitrogen, oxygen, or fluorine

Polar molecules will have ____________ boiling points than nonpolar molecules

higher

Nonpolar molecules will have __________ boiling points than polar molecules

lower

_________________ are the strongest of ALL forces

ionic bonds

Miscible

Describes two liquids that are soluble in each other

imiscible

liquids are not soluble in one another

lewis structure

simple models that show how atoms are connected in a molecule or polyatomic ion

\
* note: lewis structure do NOT show the shape of a molecule, just how atoms are connect
* each line represents 1 share pair of electrons

ionic bonds are stronger when

there are higher charges and the smaller the atoms

covalent bonds are stronger when

more electrons are shared

covalent network compound

crystal lattice w/covalent bonds ex: diamond

intermolecular force

a force of attraction between two molecules. these forces must be overcome during phase changes

dipole-dipole forces

the attraction between the partial positive end of one polar molecule, and the partial negative end of a different molecule

* molecule MUST be polar to have this force
* stronger when molecules are more polar (more uneven sharing it a big difference in electronegativity)
* extra polar bonds: F-H, O-H and N-H

london dispersion forces

an attraction between TEMPORARY dipoles, that form because of the random motion of electrons within molecules

* stronger when there are more TOTAL electrons (more polarizable)

covalent networks are the _____ type of compound to seperate

hardest

if there is the same electronegative difference between molecules, check ____

size

what does not affect lattice energy?

polarity

what is an example of an intramolecular force?

H-Cl

what property describes a strong bond?

high boiling point

what is an example of a non polar covalent compound?

CO2

T/F : non polar covalent bonds are stronger than ion-ion bonds

false

T/F: hydrogen bonds are stronger than London dispersion forces

true

what is the correct order of bond strength from strongest to weakest: ion-dipole, dispersion forces, H-bond

H-bond, ion-dipole, dispersion forces

what is a London dispersion force?

interaction between non polar molecules

what is an ion-dipole force?

interaction between an ion and polar molecule

what is an ion-ion force?

interaction between a cation and anion

what is hydrogen bonding?

interaction between polar molecules