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The Modern Atomic Theory
1. All matter is composed of atoms.The atom is the smallest body
thatretains the unique identityof the element.
2. Atoms of one element cannot be converted into atoms of another
element in a chemical reaction.Elements can only be converted
into other elements in nuclear reactions.
3. All atoms of an element have the same number of protons and
electrons, which determines the chemical behavior of the element.
Isotopes of an element differ in the number of neutrons, and
thus in mass number. A sample of the element is treated asthough its atoms have anaveragemass.
4. Compounds are formed by the chemical combination of two or
more elements in specif ic ratios.
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ParticleMass
(g)Charge
(Coulombs)Charge(units)
Electron (e-) 9.1 x 10
-28 -1.6 x 10
-19 -1
Proton (p+) 1.67 x 10
-24+1.6 x 10
-19 +1
Neutron (n) 1.67 x 10-24
0 0
mass p = mass n = 1840 x mass e-
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Electron- Negatively chargeparticle.
Proton- Positively chargeparticle- The number of protonare equalto thenumber of electronif the atom is neutral.- Proton has opposite sign of an electron- Proton has greater mass than electron.
Neutron- Carries no chargeparticle.- It has almost the ame mass with proton.- The number of neutron is not directly
related to proton or electron.
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General Features of the Atom
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Atom ic number(Z) = number of protons in nucleus
Mass number(A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopesare atoms of the same element (X) with different numbersof neutrons in their nuclei
XA
Z
H11 H (D)
21 H (T)
31
U23592 U23892
Mass Number
Atomic NumberElement Symbol
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What are Isotopes?
Isotopes are the elements that have the sameatomic number but the different number of mass.
Hydrogen Deuterium Tritium
H11 H (D)
21 H (T)
31
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How many protons, neutrons, and electrons are in C146 ?
How many protons, neutrons, and electrons are in C116 ?
6 protons, 8 (14 - 6) neutrons, 6 electrons
6 protons, 5 (11 - 6) neutrons, 6 electrons
Both C are isotopes of carbon. They have the same number of protons
but differ in number of neutrons
Exercise:
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Sample Problem
Determining the Number of Subatomic
Particles in the Isotopes of an Element
PROBLEM:
Silicon(Si) is essential to the computer industry as a majorcomponent of semiconductor chips. It has three naturally occurring
isotopes: 28Si, 29Si, and 30Si. Determine the number of protons,
neutrons, and electrons in each silicon isotope.
PLAN:
We have to use the atomic number and atomic masses.
SOLUTION:
The atomic number of silicon is 14. Therefore
28Si has 14p+, 14e-and 14n0(28-14)
29
Si has 14p+, 14e
-and 15n
0
(29-14)
30Si has 14p+, 14e-and 16n0(30-14)
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The periodic table is a handy tool that correlates the properties of theelements in a systematic way and helps us to make predictions aboutchemical behavior.
Element are arranged by atomic number (shown above the elementsymbol) in horizontal rows called Periodsand vertical columns known as
groupsor families , according to similarities in their chemicals properties
The elements can be divided into three categories- metals, nonmetalsand metalloids
Element are often referred to collectively by their periodic table group
number(Group 1A, Group 2A, and so on).
However, for convenience, some elements groups have been givenspecial names
Group 1A: Alkali metalsGroup 2A: Alkaline earth metals
Group 7A: HalogensGroup 8A: Noble gases, or rare gases
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Period
G
roup
AlkaliMetal
NobleGas
Halogen
AlkaliEarth
Metal
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1. Metallic properties increase. Why?Metals want to lose electrons the farther the electron is from the nucleusthe easier it will be to lose the electron.
2. Radius increases. There is an additional energy level added to each
successive atom.3. Ionization energy decreases. It takes less energy to form an ion.
4. Electronegativity decreases. Electronegativity is the attraction an atomhas for an electron. If the outer shell (valence shell) is farther from the
nucleus there will not be as great attraction if it were closer.5. Oxidation states (charges) remains the samebecause they all have the
same number of electrons in the outer shell and will therefore behave thesame.
6. They all have similar properties.
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1. Metallic properties decrease. As you go from one element to the next thenumber of electrons in the outer shell (valence shell) willincrease. A metal wantsto lose electrons and a nonmetal wants to gain electrons. The more electronspresent in this outer shell the harder it is to lose them all.
2. Radius decreases. All the elements that are on the same periodwill have the same
number of energy levels. The number of protons in the nucleus increases makingthe nuclear charge stonger.It therefore pulls the electrons toward it making theradius smaller as you go from one element to the next.
3. Ionization energy increases. There are more electrons in the outer shell and it istherefore harder to remove them. The electrons are also closer to the nucleus so
there is a greater force holding them there.4. Electronegativity increases. These elements want to gain electrons to complete
their outer shell, so they have a greater force of attraction. Oxidation stateschange (+1, +2, +3, + - 4, -3 , -2, -1)). They all havea different number of electronsin the outer shell.
5. Properties are all different
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Metals, Metalloids, and Nonmetals
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Metals Left-hand side of the table Tendency to lose electrons Conduct heat and electricity Usually solid at room temperature Malleable - can be hammered into different shapes Ductile - can be drawn into wires Luster - they shine
Nonmetals Right-hand side of the table
Tendency to gain electrons Poor conductors of heat or electricity Not malleable or ductile (those that are solids tend to be brittle) Do not exhibit luster
Metalloids (or semimetals)
Mixture of metallic and nonmetallic properties Used for semiconductors
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1A (Group 1) - Alkali metals
They will all form ions with a +1 charge. They all have one selectron in their outer shell. These are very active metals andare seldom found free in nature. As a matter of fact theseelements are not found free in nature.
11A (Group 2)- alkaline earth metals
These are also very active elements, but not as active as thosein group 1. These group 2 elements have properties similar toeach other. They all have two s electrons in their outer shell andwill therefore produce a +2 ion.
111B 11B ( Group 3 12) - Transition elements
These metals are located in the center of the periodic table.They make up groups 3 through 12.
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A moleculeis an aggregate of two or more atoms in a
definite arrangement held together by chemical bonds
H2
H2
O NH3
CH4
A diatom ic mo leculecontains only two atoms
H2, N2, O2, Br2, HCl, CO
A polyatom ic m olecu lecontains more than two atoms
O3, H2O, NH3, CH4
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An ionis an atom, or group of atoms, that has a net
positive or negative charge.
cat ionion with a positive chargeIf a neutral atom losesone or more electrons
it becomes a cation.
anionion with a negative charge
If a neutral atom gainsone or more electronsit becomes an anion.
Na 11 protons11 electrons Na+ 11 protons10 electrons
Cl17 protons
17 electrons Cl-17 protons
18 electrons
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13 protons, 10 (133) electrons
34 protons, 36 (34 + 2) electrons
What are Ions?
How many protons and electrons are in Al2713 ?3+
How many protons and electrons are in Se78342- ?
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A monatom ic ioncontains only one atom
A polyatom ic ioncontains more than one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
OH-, CN-, NH4+, NO3
-
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NH4+
ammonium SO42-
sulfate
CO32-
carbonate SO32-
sulfite
HCO3- bicarbonate NO3- nitrate
ClO3- chlorate NO2
-nitrite
Cr2O72-
dichromate SCN-
thiocyanate
CrO42-
chromate OH- hydroxide
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Chemist use chemical formulas to express the composition in terms of chemical symbols
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A molecular formulashows the exact number of atoms of each
element in the smallest unit of a substance
An empir ical formu lashows the simplest whole-number ratio of
the atoms in a substance
H2OH2O
molecular empirical
C6H12O6 CH2O
O3 O
N2H4 NH2
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An i on ic compoundsconsist of a combination of cations
and an anions
the formula is always the same as the empirical formula
the sum of the charges on the cation(s) and anion(s) in each
formula unit must equal zero
The ionic compound NaCl
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Formula of Ionic Compounds
Al2O3
2 x +3 = +6 3 x -2 = -6
Al3+ O2-
CaBr2
1 x +2 = +2 2 x -1 = -2
Ca2+ Br-
Na2CO3
1 x +2 = +2 1 x -2 = -2
Na+ CO32-
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Ionic Compounds
often a metal + nonmetal
anion (nonmetal), add ide to element name
BaCl2 barium chloride
K2O potassium oxide
Mg(OH)2 magnesium hydroxide
KNO3 potassium nitrate
Example:
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Transition metal ionic compounds
indicate charge on metal with Roman numerals
FeCl2
2 Cl- -2 so Fe is +2 iron(II) chloride
FeCl3 3 Cl- -3 so Fe is +3 iron(III) chloride
Cr2S3 3 S-2-6 so Cr is +3 (6/2) chromium(III) sulfide
Molecular compounds nonmetals or nonmetals + metalloids
common names
H2O, NH3, CH4, C60
element further left in periodic table is 1st
element closest to bottom of group is 1st
if more than one compound can be formed from the sameelements, use prefixesto indicate number of each kind ofatom
last element ends in ide
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HI hydrogen iodide
NF3 nitrogen trifluoride
SO2 sulfur dioxide
N2Cl4 dinitrogen tetrachloride
NO2 nitrogen dioxide
N2O dinitrogen monoxide
Molecular ompounds
TOXIC
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Sample Problem Naming Binary Molecular Compounds
PROBLEM:
Name the following molecular compound:
PLAN:
(a)SiCI4
SOLUTION:
Use the periodic table to decide which element is the metal and
which the nonmetal. The metal (cation) is named first and weuse the -idesuffix on the nonmetal name root.
(b)iodine and cadmium
(c)strontium and fluorine (d)sulfur and cesium
(a)Silicon Tetrachloride
(b)cadmium iodide
(c)strontium fluoride
(d)cesium sulfide
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An acidcan be defined as a substance that yields
hydrogen ions (H+) when dissolved in water.
HClPure substance, hydrogen chloride
Dissolved in water (H+Cl-), hydrochloric acid
All acids begin with H.
Two types of acids:
Oxyacids
Non-oxyacids (axoanion)
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oxo id
An oxoacidis an acid that contains hydrogen,
oxygen, and another element (The central element).
Usually written with the H first, followed by the central
elementand thenO, as illustrated by the followingexample :
HNO3 nitric acid
H2CO3 carbonic acid
H2SO4 sulfuric acid
HCIO3 chloric acid
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Addition of one O atom to the -ic acid: the acid calledper-ic acid. Thus Adding an O atomto HCIO3 changeschloric acid to perchloric acid (HCIO4)
Removal of one O atom to the -ic acid: the acid called -ous acid. Thus Removal of one O atomto HNO3changes nitricacid to nitrous acid (HNO2)
Removal of two O atom to the -ic acid: the acid called hypo-ous acid. Thus when Removal of two O atomto HBrO3changes to hypobromous acid (HBrO)
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When all the H ions was removed from -ic acid, the anionsname ends with -ate.
Example:
Chloric acid (HCIO3 ) changes to carbonate (CIO3)
When all the H atoms from the -ous acid, the anions nameends with -ite.
Example:(HCIO2) changes to chlorite(CIO2 )
-
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Oxoacid names are similar to those of the oxoanions, except for two suffix
changes:
Anion -ate suffix becomes an -ic suffix in the acid. Anion -ite suffix
becomes an -ous suffix in the acid. The oxoanion prefixes hypo- and per- are retained.
Example :
Thus, BrO4- isperbromate, and HBrO4isperbromicacid; IO2-is iodite, andHIO2is iodousacid.
A basecan be defined as a substance that yields hydroxide ions (OH-) when
dissolved in water.
NaOH sodium hydroxide
KOH potassium hydroxide
Ba(OH)2 barium hydroxide
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