Unit 9 chemistry

require energy if more energy on the reactant side

(endothermic)

In the following draw a arrow indicating direction of the bond dipole including which is negative and which is positive? N-C

+C----->N-

In the following draw a arrow indicating direction of the bond dipole including which is negative and which is positive? H-Cl

+H-----> Cl-

In the following draw a arrow indicating direction of the bond dipole including which is negative and which is positive? O-N

+N-----> O-

In the following draw a arrow indicating direction of the bond dipole including which is negative and which is positive? N-S

+S-----> N-

Each atom in the molecules of elements forming diatomic molecules is assigned an oxidation number of _______

0

The oxidation number for elemental sodium is ? The algebraic sum of the oxidation numbers of all atoms in the formula of a compound ______

0, 0

What does it mean to say that a bond is polar? Give two examples of molecules with polar bonds. Indicate in your examples the direction of polarity.

A bond is polar if the centers of positive and negative charge do not coincide at the same point. The bond has a negative end and positive end. Any molecule in which the atoms in the bonds are not identical will have polar bonds. ex: HCL, HF

Why does calcium have a higher melting point than potassium?

Calcium is a smaller ion with twice the charge of potassium therefore has a stronger attraction for its delocalized electrons.

In the following diatomic molecules, which end of the molecule is positive relative to the other end? chlorine monoflouride ClF

Cl

What IMF is HI?

Dipole dipole

The amount of energy released when one mole of chloride ions are produced from one mole of chlorine atoms is the _____________

Electron affinity

metallic bonding

Electrostatic attraction between a lattice of positive ions and delocalized electrons

Intramolecular bonding in HCN?

Electrostatic attractions between pairs of electrons and positively charged nuclei

In the polar covalent bond which atom will be negative relative to the other atom? Cl-F

F because greater negativity

In the following diatomic molecules, which end of the molecule is positive relative to the other end? Hydrogen flouride HF

H

Which is more polar bond? (H-Cl, H-F)

H-F because F has higher electronegativity compared to Cl

Rank (H2, HF, HCl ) in order from predicted highest to lowest

HF(highest due to hydrogen bond), HCl (middle due to dipole-dipole), H2(lowest due to london dispersion)

Nonmetals typically have _______ Electro negativity

High

What IMF is HF?

Hydrogen bond

In the following diatomic molecules, which end of the molecule is positive relative to the other end? iodine monochloride ICl

I

what are the two possible shapes of a molecule composed of 3 atoms?

Linear and bent

What IMF is Br2?

London dispersion

What IMF is Ne?

London dispersion

What IMF is P4?

London dispersion

What can make a molecule favored compared with the lone atoms?

Molecules have more stability so they are more favored.

dipole-dipole forces

Molecules that have permanent dipoles due to electronegativity differences between the atoms can attract each other like little magnets, with the partial positive end of one molecule near the partial negative of the other. Both molecules needs to be polar

What are the three very electronegative atoms:

N,O,F when bonded to H cause the H to be very partial positive. The small H can get close to the partial negative N,O,F creating a strong coulombic (+/-) attraction.

Symbol equation for formation of a sodium ion from a sodium atom?

Na -----> Na+1 + e-

Describe in general terms the structure of ionic solids such as NaCl. How are the ions packed in the crystal?

NaCl consists of an array of alternating positively and negatively charged ions; that is each positive ion has as its nearest neighbors a group of negative ions and each negative ion has a group of positive ions surrounding it. So the ions are packed as tightly as possible.

In comparison on the bond energies of hydrogen, nitrogen, oxygen, flourine, chlorine, bromine, iodine which is the most stable and the least stable?

Nitrogen most stable (highest bond energy) and triple bond , Iodine least stable (lowest bond energy)single bond

When one atom combines with another, both usually attain a stable, highest energy level and have a __________

Noble gas configuration

The concept of what is an attempt to make up for the deficiencies in Lewis structures.

Resonance

What is the process for calculating delta H for the formation of ionic bonds in a lattice?

SIBEL (sublimation, ionization, bond energy, electron affinity, lattice energy)

Explain how the properties of hydrogen bonds make it the ideal choice of inter molecular force to bind together the strands of double helix?

The H bonds between base pairs are weak enough to break during replication and then return

Hybridization chemistry

The combining of two or more orbitals of nearly the same energy into new orbitals of equal energy.

What general principles determine the molecular structure of a molecule?

The general molecular structure of a molecule is determined by how many electron pairs surround the central atom in the molecule, and by which of the those pairs are used for bonding to the other atoms of the molecule.

How can you use hydrogen bonding to explain why ice is less dense than water?

The hydrogen bonding in ice creates a six member ed rings of water molecules with a lot of empty space in the middle. This increased volume makes ice less dense than water.

hydrogen bonding

This Intermolecular forces is a special type of very strong dipole-dipole, about 10x stronger than most dipole attractions(however, it is still 1/10 as strong as ionic or covalent.) Two conditions are necessary for a hydrogen bond to form: 1) Both molecules must have an N,O,F. (2) One molecule must have an H covalently bonded to the N,OF

sigma bond

a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei

pi bond

a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms

The process of electron transfer is __________ exothermic

always

Negative ions are called

anions

polar bond

anytime there is a difference in electrongeativity between atoms

The molar masses for ethane (c2H6) and methanol (CH3OH) are nearly the same and yet the boiling points for the two are 184K and 338K respectively. Why?

because CH3OH is ahydrogen bond while C2H6 is dipole dipole thus CH3OH will have high boiling point

Suggest an explanation for the fact that, at room temperature, CO2 is agas while SiO2 is solid?

because CO2 is a weak dispersion force while SiO2 is a network covalent like a diamond

Why does H2O have a higher boiling point than H2S?

because H2O is a hydrogen bond while H2S has dipole dipole and since hydrogen bonds is a stronger force H2O would have a higher boiling point.

Why does I2 have a higher boiling point than Br2?

because I2's size is larger than Br2 (stronger london dispersion)

Why is HCl boiling point -85 degress and LiCl 1360 degress?

because LiCl is ionic while HCl is covalent

Why is SCl2 polar but CO2 nonpolar?

because SCl2 is bent while CO2 is linear

How does the size of an atom relate to the boiling point?

bigger the size higher the boiling point

The energy required to break chemical bonds to form neutral atoms is called the ___________

bond energy

It requires energy to ____________

break a bond

Positive ions are called

cations

What bond is Cl-Cl?

covalent

no different in electronegativity means

covalent bond

bonding in SiO2

each sillicon atoms forms four single covalent bonds to oxygen atoms.

release energy if more energy on the product side

exothermic (negative)

energy is released when a bond is ____________

formed

What type of IMF in H20?

hydrogen bond

what does the legnth of net dipole arrow represent?

if the difference in electronegativity is higher then the arrow will be longer compared to if the difference in electronegativity is smaller.

What bond is K-Cl?

ionic

large differences in electronegativity means

ionic

Electron transfer results in _________ bonding; electron sharing results in ___________ bonding.

ionic, covalent

The amount of energy required to remove one mole of electrons from one mole of gaseous sodium atoms is the ___________

ionization energy

What are bond energies?

is the measure of bond strength in a chemical bond

Why is diamond harder, with a higher melting point, than graphite?

it has C atoms at sp3 hybridized. into a tetrahedral network, giving diamond properties of hardness, colorless, and a nonconductor.

Why is graphite soft?

it has C atoms that are sp2 hybridized. The C atoms for six membered rings within layers of graphite. These layers are held together by weak dispersion forces. The structure is soft, black and conducts

Non metallic ions are __________ than their corresponding atom

larger

What type of IMF in CCl4?

london dispersion

Metals are characterized by ______ Electro negativity values

low

What is the type of IMF in Hg?

metallic

A neutral group of atoms held together by covalent bonds is called __.

molecule

polar molecule

molecule with an unequal distribution of charge, resulting in the molecule having a positive end and a negative partial end. the bond dipoles must add like vectors for there to be a net dipole. If all bond dipole point at opposite direction then they are non polar meaning they have o net dipole

In the polar covalent bond which atom will be negative relative to the other atom? Cl-Cl

neither of them will have a more negative relative to the other one because they have the same negativity

If the electronegativity of H is 2.20 and of Cl is 3.55, which type of bond is formed between H and Cl, when they form hydrogen chloride?

polar covalent

What bond is Br-Cl?

polar covalent

intermediate differences in electronegativity means

polar covalent

If a molecule can be "separated" into two halves, one + and one - then the molecule is said to be _________ and have a _____________ (or dipole _____________)

polar, net dipole, moment

A charged group of covalently bonded atoms is called __.

polyatomic ion

In combinations involving nonmetals, the oxidation number of the less electro negative element is ________

positive

chemical bond

result of attractions between opposite electrical charges

Dispersion (London Dispersion)

results from a momentary shift in electrons that creates instantaneous dipole. These weak forces of attraction occur in all molecules and even atoms. They can, however become quite strong if the size of the molecule increases.

Compare the length and strength of single, double, and triple bonds?

single: longest/weakest, Double, Triple: shortest, strongest

Metallic ions are __________ than their corresponding atoms.

smaller

What kinds of atoms tend to have larger electronegativities?

smaller atoms

The equivalent orbitals of C in methane (CH4) are called ________

sp3

all single bonds are _____

sp3

What are intermolecular forces?

the attraction between molecules and are responsible for many of the physical properties we observe: phase changes(melting, boiling point), surface tension, and viscosity. There forces are far weaker than ionic, covalent and metallic bonds.

How is the structure around a given atom related to repulsion between valence electrons pair on the atom?

the electron repulsion is responsible for the fact that different p orbitals will be filled separately before a second electron is put in the same orbital of course with the different spin.. arrangement that minimizes the repulsion, thus determining the molecule's geometry.

Which atoms have to follow the octet rule in a molecule?

the period 2 elements especially the nonmetals, C,N,O,F )

What is electronegativity?

the relative ability of an atom in a molecule to attract electrons to itself.

Why do atoms form bonds with eachother?

to be stable

The process of electron sharing is ___________ exothermic

usually

The electrons in the incomplete, highest energy level of an atom are called the ___________ electrons

valence

Explain what the "duet" and "octet" rules are and how they are used to describe the arrangement of electrons in a molecule?

when atoms form covalent bonds, they try to attain a valence electron configuration similar to that of the following noble gases element. When the element in the first few horizontal rows of a periodic table form covalent bonds, they attempt to achieve the configurations of the noble gases helium (duet) an neon and argon (octet)