chemistry

what is the octet rule?
according to the octet rule atoms bond in order to become isoelectronic with a noble gas (usually 8 valence electrons)
what is it meant when we say that an atom or ion is isoelectronic with a noble gas?
an atom or ion is isoelectronic with a noble gas when it has the same number of electrons as a noble gas. all noble gases have 8 electrons in their outer energy level, except helium, which is full with 2 electrons.
in solid ionic compounds the ions are arranged in a rigid lattice. describe this lattice.
the rigid lattice in ionic solid is made up of oppositely charged ions packed tightly together, so that each negative ion is surrounded by positive ions and each positive ion is surrounded by negative ions.
why do ionic compounds have high melting points?
ionic compounds have high melting point because the ionic bonds holding the ions together in the lattice are very strong and a lot of energy (high temperature) is needed to break the lattice structure and allow the ions to move freely in the liquid state.
what happens to the lattice when an ionic compound is dissolved in water or melted?
when an ionic compound is dissolved in water or melted the lattice structure breaks and the ions are free to move.
why are ionic compounds good conductors of electricity only when they are dissolved in water or in their liquid state?
ionic compounds conduct when dissolved or melted because the ions are free to move and are therefore available to carry the electrical current.
explain why pure covalent compounds have a low melting point and low conductivity.
the intermolecular forces are very weak and doesn’t take a lot of energy to seperate the molecules.
what are the 7 diatomic elements?

Iodine, hydrogen, nitrogen, bromine, oxygen, chlorine and fluorine

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i have no bright or clever friends

what is a pure covalen bond?
in a pure covalent bond, two atoms with identical (same element) are nearly identical. electronegativies share electrons. electronegativity difference of less than 0.5 indicates a pure covalent bond.
how many electrons are shared in a double bond and ;triple bond?
four electrons are shared in a double bond and six electrons are shared in triple bond.
what is a polar covalent bond?
a polar covalent bond is a bond in which the electron pair is unequally shared between atoms that have electronic negativity difference between .5 and 1.7
describe how electrons can be shared unequally in a polar covalent bond.
electrons can be shared unequally in a polar covalent bond because the shared pair of electrons will spend more time near the atom with the higher electronicc negativity. making that end of the molecule , slightly negative.
what shape allows the electron pairs in a molecule to be the maximum distance from each other?
a pyramid with four equal faces (called a tetrahedron) allows the electron pairs in a molecule to be the maximum distance from each other.
what two factors determine whether a molecule to be polar? give an example of a polar molecule.

to be polar a molecule must have polar bonds and be asymmetrical.

water h2o ,

ammonia NH3

and hydrogen chloride HCl are all polar molecules.

Express;flourine as an ion
F
Express calcium as an ion
Ca2+
How do you determine whether or not an element has small or large radius.

The atomic size decreases going across a period. the atomic raidius increases from the top to the bottom of a group.

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If it is an ion with a positive charge then it will be bigger compared to the pure element. if it is an ion with a negative charge then it will be smaller, becase it would have;gained electrons.

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therefore less valence electrons the;bigger;the;radius.

write the ionic formula for compounds formed between the following ions

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  1. Na+ O2-
  2. Al3+Br

  1. Na2 O
  2. AlBr3

write names for the following ionic compounds

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  1. MgCl2
  2. K3P

  1. magnesium chloride
  2. Potassium phosphide

what are the polyatomic ions?

  1. (ClO3)-;;; Chlorate ion
  2. (NO3) nitrate ion
  3. (CO3)2- carbonate ion
  4. (PO4)3- Phosphate ion
  5. (SO4)2- Sulfate ion
  6. (NH4)+ Ammonium Ion
  7. (OH)hydroxide ion

define ion
an atom or group of atoms having an electrical charge because of a loss or gain of electrons.
how do compounds result?
compounds are the result of the formation of chemical bonds between 2 or more different elements
when do ionic bonds occur?
ionic bonds occur when atoms of one element lose valence elections and the atoms of another element gain valence electrons.
when do ionic compounds occur?

Ionic compounds occur between metals and non metals.

However,; atoms of nonmetals share valence electrons and form covalent compounds.

what happens in the formation of ionic bonds or covalent bonds.
atoms lose, gain, or share valence electrons to acquire an octet.
talk about naming and writing ionic formulas
in naming ionic compounds, the name of the positive ion is given first, followed by the name of the negative ion. ionic compounds containing two elements end with ide. except for Ag, Cd, Zn, transition metals form cations with 2 or more ionic charges. Then the charges of the cation is determined from the total negative charge in the formula and included as a Roman numeral following the name.
how would you write the name of compound containing a polyatomic ion.
most end with ite or ate
talk about covalent compounds

  • covalent bond – electrons are shared by atoms of 2 nonmetals (octet)
  • nonpolar covalent bond – electrons are shared equally
  • polar covalent bonds, electrons are unequally shared due to thier attraction to the more electronegative atom.
  • some covalent compounds double or triple bnds are needed to provide an octet.
  • the ending of the second nonmetal is changed to ide.

how do you use electronegativiy to determine the polarity of a bond?

  • EN is the ability of an atom to attract shared pairs of e-. The EN values of the metals are low, while nonmetals have high EN.
  • in polar covalent bonds, the atom w the lower EN is partially positive adn the atom with the higher EN is partially negative.
  • atoms that form ionic bonds have large differences in EN

Describe the attractive forces between ions, polar molecules and nonpolar molecules.

  • Ionic bonds consist of very strong attractivce forces between oppositely charged ions.
  • attractive forces in polar covalent bonds are weaker than ionic bondsand include dipole-dipole attractions and hydrogen bonds.
  • nonpolar covalent compounds form solids using temporary dipoles called dispersion forces.

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define dipole
the seperation of positive an negaive charges in a polar bond indicated by an arrow that is drawn from the more positive atom to the more negative atom.
define dipole-dipole attractions

attractive forces between opposiely charged ends of polar molecules

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a polar covalent bond that has a separation of charges is called a dipole

define disperson forces
weak dipole bonding that results from a momentary polarization of nonpolar molecules in a substance
define electronegativity
the relative ability of an element to attract electrons in a bond
what is a hydrogen bond
the attraction between a partially positive H atom and a strongly electronegative atom of F,O or N
what is a polar molecule
a molecule containig bond dipoles that do not cancel
in naming a compound when are roman numerals omitted?
roman numerasls are omitted when the metal has only one valence
what does the formula of an ionic compound indicate?

it indicates the number and kinds of ions that make up the ionic compound. the sum of the ionic charges in the formula is always zero

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note: that the ionic charges of the ions do not appear in the formula of the ionic compound.

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the cation is always written first followed by the anion

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how do you name metal ions and nonmetal ions?
the name of a metal ion is the same as its elemental name. the name of a nonmetalion is obtained by replacing the end of its elemental name with ide.
how do you name an ionic compound containing two elements?

  • the metal ion is named first follwed by the name of the nonmetal ion.
  • subscripts are never mentioned; they are understood as a result of the charge balance of the ions in a compound
  • ex. Mg2+Br=MgBr2

why do transition metals form two or more kinds of positive ions?

because they lose their outer electrons as well as electrons from a lower energy level.

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when a metal can form two or more ions, it is not possible to predict the ionic charge from the group number. we say that is has a variable valence.

How do you use a;naming system; to identify the particular cation in a compound?

to do this, a Roman numeral that matches the ionic charge is placed in parentheses afer the elemental name of the metal.

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zinc, cadmium and silver only form one ion.

how do you select the correct Roman numeral?

it depends upon the calculation of the ionic charge of the trasition metal in the formula.

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ex. Cu2S

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step 1: determine the charge of the cation from the anion. the nonmetal S in Group 6A forms the S2-, the charge of each Cu ion is 1+

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Metal:;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;Nonmetal

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Element: Copper;;;;;;;;;;;;;;;;;;;;;;;;;;;; Sulfur

Group: Transition;;;;;;;;;;;;;;;;;;;;;;;;;;;;6A

Ions: Cu ?;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; S2-

Charge balance: 2(1+);;;;;;;;;+;;;;;;;;;;(2-) = 0;

Ions: Cu+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; S2-

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step 2: name the cation by its element name, and use a roman numeral in parentheses for the charge

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copper(I)

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Step3: Name the anion by changing the last part of it’s element name to ide.

 

sulfide

 

Step 4: write the name of the cation first and the name of the anion second.

 

copper(I)sulfide

what is a polyatomic ion?

an ionic compound with 3 or more elements contais some type of polyatomic ion, which is a group of atoms that has an ionic charge. most polyatomic ions consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrgen bonded to oxygen atoms. these polyatomic ions have ionic charges 1-,2- or 3- because 1,2,3 electrons were gained by the atoms in the group to complete thier octets.

 

only one of the polyatomic ions is positively charged NH4+

How do you name polyatomic ions?

the names of most polyatomic ions end in ate.

 

 the ite ending is used for the names of related ions that have one less oxygen atom.

How do you write formulas for compounds containing polyatomic ions?

we follow the same rules of charge balance that we used for writing the formulas of simple ionic compounds. the total negative and positive charges must equal 0.

 

when more than one polyatomic ion is needed for charge balance, parentheses are used to enclose the formula of the ion. a subscript is written outside the closing parenthesis to indicate the number of polyatomic ions.

how do you name compounds containing polyatomic ions?

first write the positive ion, usually a metal, and then write th name of the polyatomic ion.

 

remember that other ionic compounds don’t use prefixes.

how do nonmetals achieve stability?

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atoms of nonmetals have high ionization energies ad do not lose electrons easily. thus, in covalent compounds, electrons are not transferred from one atom to another, but are shaed between atoms of nonmetals to achieve stability.
what happens when atoms share electrons?
they form molecules
define diatomic
elements that contain two like atoms
how do you name a covalent compound?
the first nonmetal is named by its elemental name; the second nonmetal is named with the ending changed to ide , subscripts indicating two or more atoms of an element are expressed as prefixes placed in front of each name.
what are the prefixes used in naming covalent compounds?

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

why do covalent compounds need prefixes?

because several different compounds can be formed from the same two nonmetals. for example, carbon; and oxygen can form two different compounds, carbon monoxide CO and carbon dioxide CO2

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– When vowels o and o

and

a and o

appear together, the first vowel is omitted as in corbon monoxide

Write a formula for the covalent compound diboron trioxide.

step 1: write the symbols in order of the elements in the names.

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B;;; O

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Step 2 : write prefixes as subscripts.

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B2O3

Why do nonmetals hav higher electronegativity than metals?
because they have a greater attraction for electrons than metals
why do small atoms have high electronegativity?
because the valence electrons they share are closer to their nuclei.
When does electronegativty increase

values increase from left to right across each period as well as from the bottom to the top of each group.

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there are no electronegativity values for the noble gases because they do not typically form bonds.

what are the ranges for predicting the types of bond between atoms.

under .5 nonpolar covalent bond

.5 to 1.7 polar covalent bond

1.7 and up is ionic bond

when electronegativity differences are from 0 to 0.4 the electrons are….
shared equally in a nonpolar covalent bond.
as electronegativity differences increases, from .4 to 1.8 the bond is…
polar covalent bond, this is when the it is increasing, the shared electrons are attracted more strongly to the more electronegative atom and the polarity of the bond increases.
differences in electronegativty of 1.8 or greater indicate a bond is?

ionic

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eventually the difference in electronegativy is great enough that electrons are transferred from one atom to another, which results in an ionic bond.

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what is VSEPR
it is the valence-shell electron-pair repulsion theory it indicates that electron groups will move as far apart as possible to reduce the repulsion between their negative charges.
a molecule with four electron pairs, but just 3 bonded atoms has a ___________; shape.
pyramidal
a molecule with four electron pairs, but just two bonded atoms, has a _________ shape.
bent
why are diatomic molecules nonpolar
because they contain one nonpolar covalent bond
what is a nonpolar molecule?
a molecule with 2 or more polar bonds can be a nonpolar mol if the polar bonds have a symmetrical arrangement in the molecule.
what is a polar molecule?
one end of the molecule is more negativly charged than another end. polarity in a molecule occurs when the polar bonds do not cancel each other.
what happens when the polar bonds or dipoles in a molecule cancel each other, the molecule is?
nonpolar
why do ionic compounds have high melting points?
large amounts of energy are needed to overcome the strong attractive forces between positive and negative ions.
talk about dipole-dipole attractions
for polar molecules , attractive forces called dipole-dipole attractions occur between the positive end of one molecule and the negative end of another.
talk about a hydrogen bond
when an hydrogen atom is attached to highly electronegative atoms of fluorine, oxygen, or nitrogen, there are strong dipole-dipole attractions between the polar molecules. hydrogen bond occurs between the partially positive hydrogen atom of one molecule and a lone pair of electrons on N, O, or F atoms in another molecule. hydrogen bonds are the strongest type of attractive forces between polar mols.
do nonpolar compounds form solids?

nonpolar compounds do form solids, but at low temperatures. very weak attractions called dispersion forces occur between nonpolar molecules.

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disstriubted symmetrically

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form liquids and solids

what are the melting points of substances related to?
related to the strength of the attractive forces within the compound. compounds w weak attractive forces such as dispersion forces have low melting points because only a small amt of energy is needed to seperate the molecules and form a liquid.
where are the highest melting points seen?
with ioic compounds that have very strong attractions between ions.
define physical change
we have seen that a change of state involves a change in the physical properties of substance. such a changes, called a physical change, alters the appearance of a substance, but not it’s formula
define chemical change
the reacting substances change into new substances that have different formulas and different properties.
compare chemical and physical changes

Chemical changes                     Physical changes

 

rusting nail                           melting ice

bleaching a stain                   boiling water   

burning a log                        sawing a log in half

tarnishing silver                    tearing paper

fermenting grapes                 breaking a glass

souring of milk                     pouring milk

what is a chemical reaction?

a chemical reaction alwasy involves chemical change as bonds between the atoms in the original substances are broken and new bonds are formed.

 

during a chemical change, new properties become visibly, which are clues that tell you a chemical reaction has taken place

what are types of visible evidence of a chemical reaction?

change in colour

 

formation of gas (|bubbles)

 

formation of a solid (precipiate)

 

heat (or a flame) produced by heat absorbed

what is a chemical equation?
a chemical equation tells us the materials we need and the products taht will form in a chemical reaction.

show a chemical equation for the following:

 

when you burn charcoal in a grill, the carbon in the charcoal combines with oxygen to form carbon dioxide.

Equation:     C(s) + O2(g) —-> CO2 (g)

                     Reactants                   Product

what does a delta sign mean (triangle)
indicates that heat was used to start the reaction
when would you use (aq) as an abbreviation in a chemical formula?
if a a substance is dissolved in water. it is an acqueous solution (aq)
can atoms be gained, lost or changed into other types of atoms during a chemical reaction?

NO,

 

every reaction must be showed as a balanced equation, which shows the same number of atoms for each element on both sides of the arrow.

how do you balance an equation?
to balance an equation you place whole numbers called coefficients in fron of some of the formulas.
can you change a subscript when trying to balance an equation?
NO
if an equation is balanced but with higher numbers than necessary, is that correct?
No , in an equation, the coefficients must be the lowest set of whole numbers that gives the same number of atoms of each element on both sides of the equation

write an equation for the following.

 

we can now balance the equation for the reaction of gas methane, CH4, and oxygen to produce carbon dioxide and water. this is the reaction that occurs in the flame of gas burner you use in the labratory and in the burners of a gas stove.

CH4(g) + O2 —-> CO2(g) + H2O (g)
what is a combination reaction?

in a combination reaction, two or more elements or compounds bond to form one product.

 

 for example, sulfur and oxygen combine to form the product sulfur dioxide.

 

S(s) + O2(g) —-> SO2(g)

 

what type of reaction is this:

 

the elements magnesium and oxygen combine to form a single product, magnesium oxide.

 

2Mg(s) + O2(g) —> 2MGO(s)

Combination Reaction
what is a decomposition reaction?

in a decomposition reaction, a reactant splits into two or more simpler products.

 

 for example when mercury(II)oxide is heated, the compound breaks apart into mercury atoms and oxygen.

   

           heated

2HgO(s) —-> 2Hg(l) + 02(g)

what is a replacement reaction?

in a replacement reaction, elements in a compound are replaced by other elements.

 

Replacement Reactions

 

what is a single replacement reaction

 

 

a reacting element switches places with an element in the other reacting compound.

 

A    +    BC  —–>   AC   + B

                   One element                  replaces                 another element

 

what is this an example of

 

Zn(s) + 2HCL(aq) ——> ZnCl2(aq) + H2(g)

single replacement

Replacement reaction

 

what is a double replacement reaction?

 

 

the positive ions in the reacting compounds switch places.

 

AB + CD    ———> AD + CB

                Two elements                   replace each other

Classify the following reactions as combination, decomposition, or single or double replacement:

  1. 2Fe2O3(s) + 3C(s) —-> 3CO2(g) + 4Fe(s)
  2. Fe2S3(s) —->2Fe(s) + 3S(s)
  3. 2AgNO3(aq) + MgCl(aq) —-> 2AgCl(s) + Mg(NO3)2 (aq)

  1. Single replacement reaction
  2. decomposition
  3. double replacement reaction

what happens in oxidation-reduction reaction (redox)
electrons are transferred from one substance to another. if one substance loses electrongs , another substance must gain electrongs
define oxidation
loss of electrons
define reduction
gain of electrons

Fill in the blank

 

in general, atoms of _____ lose electrons to form ___________ ions. whereas _____________ gain electrons to form _____________ ions. now we can say that metals are _______________ and ________________ are reduced.

in general, atoms of metals lose electrons to form positive ions. whereas nonmetals gain electrons to form negative ions. now we can say that metals are oxidized and nonmetals are reduced.

oxidation-reduction reactions

 

in photographic film, the following decomposition reaction occurs in the presence of light. what is oxidized and what is reduced?

        

          light

2AgBr(s)——–>Br2(g)

To determine oxidation and reduction, we need to look at ions and charges in the reactant. in AgBr, there is a silver ion

Ag+ with a 1+ charge and a bromide ion (Br) with a charge of 1-. we can write the reaction as follows:

 

2Ag+(aq) + 2Br(aq) ——>2Ag(s) + Br2(g)

 

now we can compare Ag+ with the product Ag atom. int his case, each Ag+ gained an electron, which is reduction.

 

2Ag+(aq) + 2e—–> 2Ag(s) reduction

 

then we compare the Br with the Br iin the product Br2. In this case, each Br lost an electron, which is oxidation.

 

2Br(aq) —–> Br2(g) + 2e  oxidation

in this reaction , bromide ion is oxidized and silive ion is reduced.

define balanced equation
the final form of a chemical equation that shows the same number of atoms of each element in teh reactants and products.
what is a polyatomic ion?

is a group of atoms

 

has an overall ionic charge

how do you name a polyatomic ion?
the positive ion first, followed by the name of the polyatomic ion
talk about nonpolar covalent bonds

  • occurs between nonmetals
  • is an equal or almost equal sharing of electrons
  • has almost no electronegativity difference 0.0 – 0.4

talk about a polar covalent bond

  • occurs between nonmetal atoms
  • is an unequal sharing of electrons
  • has a moderate electronegativity difference .5 to 1.7

talk about ionic bonds

  • occurs between metals and nonmetals
  • is a result of electron transfer
  • has a large electronegativity difference 1.8 or more

talk about melting points and attractive forces

  • ionic compounds requare large amounts of energy to break apart ionic bonds. thus, they have high melting points.
  • hydrogen bonds are the strongest type of dipole-dipole attractions. they require more energy to break than other dipole-dipole attractions.
  • dispersion factors are weak interactions and very little energy is needed to change state.