Post on 30-Jun-2020
Elements and Compounds
Elements combine together to make an almost limitless number of compounds.
The properties of the compound are totally different
from the constituent elements.
Compounds ≠ Mixtures
Hydrogen gas b.p. -253º
Oxygen gas b.p. -183º
Water b.p. 100º
Hydrogen peroxide b.p. 150º
Hydrogen and Oxygen gases can mix in any ratio.
Hydrogen and Oxygen atoms
present in fixed ratios
Chemical Bonds
Compounds are made of atoms held together by bonds.
Chemical bonds are forces of attraction between atoms.
The bonding attraction comes from attractions between protons and electrons.
Bond TypesTwo general types of bonding between atoms found in
compounds, ionic and covalent.
Ionic bonds result when electrons have been transferred
between atoms, resulting in oppositely charged ions that
attract each other.
Generally found when metal atoms bond to nonmetal atoms
Covalent bonds result when two atoms share some
of their electrons.
Generally found when nonmetal atoms bond
together
Formation of an Ionic Compound
}Na0
Cl0
⤸Neutral Atoms Undergo
Electron Transfer
Na+Cl-
Charged Ions
An Orderly Aggregate Called an Ionic Crystal
repulsive forces
attractive force
attractive force
Formation of an Covalent Compound Involves Competing Forces
nucleus
electron cloud
The total energy of the atoms is a combination of the attractive and repulsive forces
Ener
gy
Internuclear distance
74 pm
Chemical Formulas Describe Compounds
A compound is a distinct substance that is composed of atoms of two or more elements.
We describe the compound by describing the number and type of each atom in the simplest unit of the compound.
Each element is represented by its letter symbol.
The number of atoms of each element is written to the right of the element as a subscript.
Polyatomic ions are placed in parentheses.
(if more than one is present)
Types of Formulas: Empirical FormulaAn empirical formula gives the relative number of atoms of each element in a compound.
It does not describe how many atoms, the order of attachment, or the shape.
For example:
1) The empirical formula for the ionic compound fluorspar is CaCl2. This means that there is 1 Ca2+ ion for every 2 Cl− ions in the compound.
2) The empirical formula for the molecular compound oxalic acid is CHO2. This means that there is 1 C atom and 1 H atom for every 2 O atoms in the molecule.
Types of Formulas: Molecular Formula
A molecular formula gives the actual number of atoms of each element in a molecule of a compound.
It does not describe the order of attachment, or the shape.
The empirical formula for the molecular compound oxalic acid is CHO2.
The actual molecular formula is C2H2O4
Types of Formulas: Structural Formula
A structural formula uses lines to represent covalent bonds and shows how atoms in a molecule are connected or bonded to each other.
Structural Formulas of Oxalic Acid
O C
O
C
O
O HH
Practice — Find the empirical formula for each of the following
The ionic compound that has two aluminum ions for every three oxide ions
arabinose, C5H10O5
pyrimidine
ethylene glycol
C
C
N
C
N
C
H
HH
H
Al2O3
CH2O
C2H2N
CH3O
}
C4H4N2
C2H6O2
ElementsMOST ELEMENTS
Single atoms are the constituent particles. The atoms may be physically attracted to each other, but
are not chemically bonded together.
A FEW ELEMENTS Molecules are the constituent particles.
The molecules are made of two or more atoms chemically bonded together by covalent bonds.
Compounds
SOME COMPOUNDS Composed of ions arranged in a 3-dimensional pattern
These are called ionic compounds.
OTHER COMPOUNDS Composed of individual molecule units
Each molecule contains atoms of different elements chemically attached by covalent bonds
These are called molecular compounds.
Propane – contains individual C3H8
molecules
Table salt – contains an array of Na+ ions
and Cl- ions
Molecular vs. Ionic Compounds
Classify Each of the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or
Ionic Compound
Aluminum, AlAluminum chloride, AlCl3Chlorine, Cl2Acetone, C3H6OCarbon monoxide, COCobalt, Co
atomic elementionic compound
molecular elementmolecular compound
molecular compoundatomic element
A compound must have no total charge, therefore we must balance the numbers of cations and
anions in a compound to get ø charge.
Practice — What are the formulas for compounds made from the following ions?
Potassium ion with a nitride ion
Calcium ion with a bromide ion
Aluminum ion with a sulfide ion
K3N
CaBr2
Al2S3
K+ with N3−
Ca2+ with Br−
Al3+ with S2−
calcium bromide
aluminum sulfide
potassium nitride
Li Be B C N O F
Na Mg Al Si P S Cl
K Ca Ga Ge As Se Br
Rb Sr In Sn Sb Te I
He
Ne
Ar
Kr
Xe
H
IA
IIA IIIA IVA VA VIA VIIA
VIIIA(1)
(2) (13)
(18)
(17)(14) (15) (16)1
2
3
4
5
Periodic Table-Main Groups Only
Li Be B C N O F
Na Mg Al Si P S Cl
K Ca Ga Ge As Se Br
Rb Sr In Sn Sb Te I
He
Ne
Ar
Kr
Xe
H
Gain electrons
IA
IIA IIIA IVA VA VIA VIIA
VIIIA(1)
(2) (13)
(18)
(17)(14) (15) (16)
Lose electrons
1
2
3
4
5
B C N O F
Al Si P S Cl
Ga Ge As Se Br
In Sn Sb Te I
He
Ne
Ar
Kr
Xe
H
Gain electrons Lose electrons
H
Li Be B C N
Na Mg Al Si P
K Ca Ga Ge As
Rb Sr In Sn Sb
1
2
3
4
5
Cs Ba
1
2
3
4
5
6
C N3- O2- F-
Si P3- S2- Cl-
Ge As3- Se2- Br-
Sn Sb Te2- I-
He
Ne
Ar
Kr
Xe
H-
H+
Li+ Be2+ B C N
Na+ Mg2+ Al3+ Si P
K+ Ca2+ Ga3+ Ge As
Rb+ Sr2+ In3+ Sn Sb
1
2
3
4
5
Cs+ Ba2+
1
2
3
4
5
6
IA IIA IIIAVA VIA VIIA VIIIA
A compound must have no total charge. Therefore we must balance the numbers of cations
and anions in a compound to get zero charge.
Writing Formulas for Ionic Compounds
Remember !!!!
Metal atoms lose electrons to form cations.
Nonmetal atoms gain electrons to form anions.
The number of electrons lost or gained can be predicted from the elements position on the Periodic
Table.
Why is a particular number of electrons lost or gained ?
Na Cl nucleus
core electronsvalence electrons
Na+ Cl-
Na + Cl -Na Cl + +
Determining the Number of Valence Electrons in an Atom
The column number on the Periodic Table will tell you how many valence electrons a main group atom has.
Lewis Dot Structures of Atoms
We represent the valence electrons of main-group elements as dots surrounding the symbol for the element.
H
Li Be B C N O F Ne
He
Na Mg Al Si P S Cl Ar
B C N
P
IA
IIA IIIA
IVA VA VIA VIIA
VIIIA
The column number on the Periodic Table will tell you how many valence electrons a main group atom has.
Cl
CaCl2
Formation of Calcium Chloride
Ca
Cl
Ca 2+
Cl - Cl -
20p 20e
20p 18e
17p 17e 17p
18e
17p 17e
17p 18e
Stable Electron Arrangementsand Ion Charge
Metals form cations by losing electrons to get the same number of valence as the previous noble gas.
Nonmetals form anions by gaining electrons to get the same number of valence electrons as the next noble gas.
A noble gas electron configuration with eight valence electrons appears to be particularly stable.
Octet RuleWhen atoms bond, they tend to gain, lose, or share
electrons to result in eight valence electrons
ExceptionsH, Li, Be, B attain an electron configuration like He
He = two valence electrons (a duet) Li loses its one valence electron H may share or gain one electron
It commonly loses its one electron to become H+ Be loses two electrons to become Be2+
It commonly shares its two electrons in covalent bonds, resulting in four valence electrons
B loses three electrons to become B3+
It commonly shares its three electrons in covalent bonds, resulting in six valence electrons
Expanded octets for elements in Period 3 or below
Na +Na
O
Cl - NaCl
Cl
CaCl2
Ca
Ca 2+
Cl
Cl - Cl -
Na
Cl
Na
O 2-Na +Na +
Na2O
Dot structures can illustrate the process.
sodium chloride
calcium chloride
sodium oxide
What type of compound is it ?
Ionic Compound Covalent (Nonionic) Compound
Acid
Cation with fixed charge
Cation with variable charge
Binary Contains polyatomic ion Binary Contains
polyatomic ion
Binary Acid
Oxy Acid
Aluminum, AlChlorine, Cl2 Aluminum chloride, AlCl3Iron (II) chloride, FeCl2Sodium Phosphate, Na3PO4Tin (IV) Chloride SnCl4Carbon monoxide, COCarbon dioxide, CO2Hydrochloric Acid, HClPerchloric Acid, HClO4
atomic element
ionic compoundmolecular element
molecular compound
ionic compoundionic compound
ionic compound
molecular compoundbinary acidoxy acid
What type of compound is it ?Practice:
Naming Metal Cations
Some metals form cations having only one possible charge
IA , IIA , Al , Ag , Zn , Sc IA+, IIA2+, Al3+, Ag1+, Zn2+, Sc3+
name of cation = name of metal
Naming Metal Cations
Most metals can form cations with more than one possible charge.
The charge must be determine from the charge on the anion.
name of cation = name of metal with Roman numeral charge in parentheses
IVA VA VIA VIIA
H -
hydride
C4-
carbideN3-
nitrideO2-
oxideF -
fluoride
Si4-
silicideP3-
phosphideS2-
sulfideCl -
chloride
As3-
arsenideSe2-
SelenideBr -
bromide
Te2-
TellurideI -
iodide
Naming Monatomic Nonmetal AnionsDetermine the charge from position on the Periodic Table.
To name anion, change ending on the element name to –ide.
C22-
Si?-
As?-
XX
X
Naming Binary Ionic Compounds for Metals with Invariant Charge
1. Name the metal cation first, name nonmetal anion second
2. Cation name is the metal name
3. Nonmetal anion named by changing the ending on the nonmetal name to -ide
name of cation(metal)
base name of anion (nonmetal) “ide”+ +
1. KCl
2. MgBr2
3. Al2S3
potassium chloride
magnesium bromide
aluminum sulfide
name of cation(metal)
base name of anion (nonmetal) “ide”+ +
Name the following compounds
Naming Binary Ionic Compounds for Metals with Variable Charge
1. Name metal cation first, name nonmetal anion second
2. The metal cation name is the metal name followed by a Roman numeral in parentheses to indicate its charge determine charge from anion charge.
3. Nonmetal anion named by changing the ending on the nonmetal name to -ide
name of cation(metal)
base name of anion (nonmetal) “ide”+( )+ +charge of cation (metal) in
roman numerals
Determine a charge from the formula of a specific compound.
The sum of all the charges must be zero.
Example: The charge on iron (Fe) in FeCl3 must be 3+ in order for the compound to be charge neutral with
the three Cl- anions.
name of cation(metal)
base name of anion (nonmetal) “ide”+( )+ +charge of cation (metal) in
roman numerals
Name the following compounds
1. CuF2 2. TiCl4 3. PbBr2
4. CrO3
5. Fe3N2
6. Fe2S3
Charge on Cation?Cu= 2+
Ti = 4+
Pb = 2+
Cr = 6+Fe = 2+Fe= 3+
copper (II) fluoride
titanium (IV) chloride
lead (II) bromide
chromium (VI) oxideiron (II) nitrideiron (III) sulfide
Na +Na
Cl - NaCl
ClFeCl2
Fe
Fe 2+
Cl
Cl - Cl -
Cl
Fe 3+FeCl3
Using dot structures can illustrate the formation of binary ionic compounds.
sodium chloride
iron (II) chloride
iron (III) chloride
ClFe
Cl
Cl
Cl -
Cl -Cl -
O
FeOFe
Fe 2+
Na
Na
O 2-Na +Na +
Na2O
Using dot structures can illustrate the formation of binary ionic compounds.
sodium oxide
iron (II) oxide
iron (III) oxide
O O 2-
Fe Fe
O O O
Fe 3+
Fe 3+
O 2-
O 2-O 2- Fe2O3
Compounds Containing Polyatomic Ions
Polyatomic ions are ions that contain more than one atom.
Often identified by parentheses around ion in formula
Name and charge of polyatomic ion do not change
An ionic compound is always named by naming the cation first and then the anion.
+3 +4 +5 +6 +7
BO33-
borateCO32-
carbonateNO3-
nitrate
SiO32-
silicatePO43-
phosphateSO42-
sulfateClO3-
chorate
AsO43-
arsenateSeO42-
selenateBrO3-
bromate
TeO42-
tellurateIO3-
iodate
Periodic Pattern of Polyatomic Ions-“ate” groups
“formal charge” on central atom
Name the Following Compounds
1. Na2SO4
2. Fe(NO3)3
3. NH4Cl
4. Ca(C2H3O2)2
5. Cu(NO3)2
sodium sulfate
iron (III)nitrate
ammonium chloridecalcium acetate
copper(II) nitrate
SO42-, sulfate; NO3 -, nitrate;
NH4 +, ammonium; (C2H3O2) -, acetate
Writing formula for ionic compounds containing polyatomic ions
Aluminum sulfate
Iron (III) phosphate
Chromium (II) hydrogen carbonate
Al2(SO4)3
FePO4
Cr(HCO3)2
SO42-, sulfate; PO4 3-, phosphate;
(HCO3) -, hydrogen carbonate
Hydrates
Hydrates are ionic compounds containing a specific number of waters for
each formula unit.
In formula, attached waters indicated
CoCl2·6H2O or CoCl2(H2O)6
In name attached waters indicated by prefix+hydrate
after name of ionic compound:
CoCl2·6H2O cobalt(II) chloride hexahydrate
CaSO4·½H2O calcium sulfate hemihydrate
Writing Names of Binary Molecular Compounds of Two Nonmetals
1. Write name of first element in formulaa) element furthest left and down on the Periodic Table b) use the full name of the element
2. Write name the second element in the formula with an -ide suffix, as if it were an anion; however, remember these compounds do not contain ions!
3. Use a prefix in front of each name to indicate the number of atoms (Never use the prefix mono- on the first element)
BF3
NO2
PCl5
I2F7
Formulas --------------> Names
boron trifluoride
nitrogen dioxide
phosphorous pentafluoride
diiodine heptafluoride
prefix prefix “ide”name of first element
name of second element+ + + +
Name -------------> Formula
dinitrogen pentoxide
dinitrogen tetroxide
sulfur hexafluoride
diarsenic trisulfide
N2O5
N2O4
SF6
As2S3
prefix prefix “ide”name of first element
name of second element+ + + +
Acids
Acids are molecular compounds that form H+ when dissolved in water.
(aq) is often written after the formula
Sour taste
Dissolve many metals such as Zn, Fe, Mg; but not Au, Ag, Pt
Formula generally starts with H e.g., HCl, H2SO4
Naming Binary Acids
HCl HF HI
hydrochloric acid
base name of nonmetal“hydro” “ic” acid+ + +
hydrofluoric acidhydroiodic acid
Naming OxyacidsName the polyatomic anion !!!!!
If polyatomic ion name ends in –ate,
base name of oxyanion
“ic” acid
If polyatomic ion name ends in –ite,
base name of oxyanion
“ous” acid
+ +
+ +
Oxyanion formula Oxyanion name Acid Formula Acid Name
NO2 ⊖ nitrite H+ HNO2 nitrous
NO3 ⊖ nitrate H+ HNO3 nitric
SO3 2⊖ sulfite 2H+ H2SO3 sulfurous
SO4 2⊖ sulfate 2H+ H2SO4 sulfuric
ClO2 ⊖ chlorite H+ HClO2 chlorous
ClO3 ⊖ chlorate H+ HClO3 chloric
C2H3O2 ⊖ acetate H+ HC2H3O2 acetic
CO3 2⊖ carbonate 2H+ H2CO3 carbonic
Names of Common Oxyacids and Their Oxyanions
H2SO4 sulfuric acidH2SO3 sulfurous acid
HClO hypochlorous acidHClO2 chlorous acidHClO3 chloric acidHClO4 perchloric acid
“-ate” = “-ic” ; “-ite” = “-ous”
Naming Oxyacids
Formula ----------> Name
H2S
HClO3
HNO2
hydrosulfuric acid
chloric acid
nitrous acid
ClO3-, chlorate; NO2-, nitrite