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Chemistry 101 : Chap. 2Chemistry 101 : Chap. 2
Atoms, Molecules and Ions
(1) Atomic Theory of Matter
(2) The discovery of Atomic Structure
(3) The Modern View of Atomic Structure
(4) Atomic Weight
(5) Periodic Table
(6) Molecules and Molecular Compounds
(7) Ions and Ionic Compounds
(8) Naming Inorganic Compounds
The Atomic Theory of MatterThe Atomic Theory of Matter
The history of development of atomic theory of matter begins in ancient Greece. However, modern atomic theory has it’s origin in a burst of scientific discovery between 1870 and 1930.
Democritus (460 ~ 370 BC)
Democritus proposed atomic theory of matter.
He and other Greek philosophers believed that material world must be made up of hard and tiny indivisible particles that they called atomos, which are in constant motion.
The Atomic Theory of MatterThe Atomic Theory of Matter
Aristotle (384 ~ 322 BC)
Aristotle proposed 4 element theory of matter.
Earth
Water
Fire
Air
hot dry
wet cold
The school of thought laid out by Socrates, Plato and Aristotle dominated the western philosophy for 2000 years and the atomic theory of matter was completely buried.
The Atomic Theory of MatterThe Atomic Theory of Matter
John Dalton (1766 ~ 1844)
Dalton proposed that all matter is made up of atoms and stated that elements are the simplest form of matter.
Dalton’s Atomic Theory(1)Each element is composed of atoms
(2)All atoms of a given element are identical,
but they are different from the atoms of
all other elements
(3) Atoms are neither created nor destroyed
in chemical reactions.
(4) Compounds are formed from chemical
combination of two or more atoms.
The Atomic Theory of MatterThe Atomic Theory of Matter
What can Dalton’s theory explain? (1) Law of constant composition
In a given compound, the relative numbers and kinds of atoms
are constant. [postulate 4]
(2) Law of conservation of mass
The total masses of material present before and after a chemical
reaction are identical [postulate 3]
(3) Law of multiple proportions
If elements A & B combine to form more than one compound, the
masses of B which can combine with a given mass of A are in
the ratios of small whole numbers
12g C + 16g O CO or 12g C + 32g O CO2 16g : 32g = 1:2
The Discovery of Atomic StructureThe Discovery of Atomic Structure
After Dalton’s atomic theory, not much of progress had been made andno one had direct evidence for the existence of atom. Then, things startedto change in late 1800s…
William Crooks (1832 ~ 1919): Cathode-ray tube (CRT) [1879]
A high voltage between two electrodes in a partiallyevacuated tube generates electrical discharge(cathode ray)
The Discovery of Atomic StructureThe Discovery of Atomic Structure
J. J. Thomson (1856 ~ 1940) : Discovery of electron [1897]
(1)Rays are the same regardless of the
identity of the cathode material
(2) Conduct quantitative analysis of the
effect of electric and magnetic field
determine the charge to mass ratio
charge/mass = 1.76 108 C/g
He discovered that cathode raysare negatively charged particles, whichhe originally called ``corpuscles’’ . He won a Nobel prize in physics [1906].
The Discovery of Atomic StructureThe Discovery of Atomic Structure
Robert Millikan (1868 ~ 1953) : Determine the charge of electron [1907]
Millikan’s oil-drop experiment
Measured charge = 1.60 10-19 C
Electron mass = charge/[charge/mass]
= 9.10 10-28 g
The machine on the right hand side isthe original apparatus Millikan usedto perform his oil-drop experiment.He won a Nobel prize in physics [1923].
The Discovery of Atomic StructureThe Discovery of Atomic Structure
Ernest Rutherford (1871~1937): Discovery of nucleus [1911]
Rutherford’s -particle [4He2+]scattering experiment
He directed his graduate student Hans Geiger and undergraduate studentErnest Marsden to carry out -paticleexperiment. He won a Nobel prize in chemistry [1908].
The Discovery of Atomic StructureThe Discovery of Atomic Structure
Radioactivity: Generation of - particles
- ray: particles with +2 charge - ray: particles with 1 charge
- ray: high energy radiation with no charge
The Discovery of Atomic StructureThe Discovery of Atomic Structure
From the scattering experiment….
(1) Most -particles simply pass through the gold foil.
(2) Small amount of scattering was observed at large
angles.
Rutherford postulated that..
(1) Most of the total volume of an atom is empty space. (2) Most of the mass of an atom and all of its positive charge reside in a very small region, called nucleus.
Rutherford also found the existence of protons inside of nucleus [1919].Another particle in nucleus, neutron, was found by James Chadwick in 1932.
Early Models of an Atom Early Models of an Atom
J. J. Thomson’s model “plum-pudding model”
Rutherford’s model
+
Rutherford's Model:
Electrons are negatively charged, but atoms as a whole are neutral.
Modern View of Atomic Structure Modern View of Atomic Structure
The list of subatomic particles has grown considerably since the discovery of electrons, but only the electron, proton and neutron have a bearing on chemical behavior.
A convenient unit (non-SI) to describe the dimensions of atoms and molecules is Angstrom (Å). 1 Å = 1 10-10 m = 100 pm
Modern View of Atomic Structure Modern View of Atomic Structure
Properties of subatomic particles
Particle Charge (C) Mass (g) Mass (amu)
Proton +1.60 10-19 (+1) 1.6727 10-24 1.0073
Neutron 0 ( 0) 1.6750 10-24 1.0087
Electron 1.60 10-19 (1) 9.1097 10-28 5.486 10-4
Every atom has an equal number of protons and electrons so that it hasno electrical charge
Atomic Mass Unit (amu)
1 amu = 1/12 of the mass of carbon (12C) atom
= 1.66054 10-24 (g)
Modern View of Atomic StructureModern View of Atomic Structure
The characteristics of each atom are determined by the numbers ofproton, neutron and electrons.
Atomic Number: The number of protons in the nucleus of an atom. Mass Number: The total number of protons plus neutrons in the atom Isotopes : Atoms with identical atomic numbers but different mass
numbers such as C-14 and C-12.
Hydrogen:1 proton
Helium:2 protons
2 neutrons
Lithium:3 protons
4 neutrons
Beryllium:4 protons
5 neutrons
Modern View of Atomic StructureModern View of Atomic Structure
Same information : An element is defined by the number of protons
Atomic WeightAtomic Weight
Atomic Mass Unit (amu) = 1.66054 10-24 g
12C = 12 amu (exact), 1H = 1.0078 amu, 16O = 15.9949 amu
Average Atomic Masses : Weighted average of all the isotopes of an element found in nature.
Example : Naturally occurring carbon is composed of 98.93% 12C and 1.07 % 13C. What is the average mass of carbon?
mass of C-12 mass of C-13fractional abundance ofC-12
(0.9893)(12 amu) + (0.0107)(13.00335) = 12.01 amu
This is the massof carbon atom shown in theperiodic table
Atomic WeightAtomic Weight
Example: Boron has two naturally occurring isotopes: 10B (10.01 amu)
and 11B (11.01 amu). If the average atomic weight of Boron
is 10.81, what are the fractional abundances of the two isotopes?
Periodic TablePeriodic Table
If the elements are arranged in order of increasing atomic number, their chemical properties are found to show a repeating, or periodic, pattern.
group
period
Elements having similar properties are placed in vertical columns
Periodic TablePeriodic Table
Alkalimetal
Alkaline earthmetal
Halogen
raregas
= H2, N2, O2, F2, Cl2, Br2, I2
Transition metals
Molecules and Molecular Compounds
Molecules and Molecular Compounds
Chemical Compounds
Molecular Ionic
(1) Molecular compounds are composed of more than
one type of atom
H2O, NH3, CH3OH, O2
(2) Most molecular substances contain only non-metallic atoms O2, H2O, H2O2, CO, CO2, CH4
Molecules and Molecular Compounds
Molecules and Molecular Compounds
Chemical Formulars
(1) Molecular Formulas : Indicate the actual numbers and types
of atoms in a molecule Ex. C2H4O2
(2) Empirical Formulas : Indicate the relative number of atoms of
each type in a molecule Ex. CH2O
(3) Structural Formulas : H O
H – C – C – O – H
H
Molecules and Molecular Compounds
Molecules and Molecular Compounds
Picturing Molecular Compounds (Ex. Methane)
Structural Formula
Ball-and-stick model
Perspective drawing
Space-filling model
Ions and Ionic CompoundsIons and Ionic Compounds
Ion : Atoms can readily gain or loose electrons and become ions.
Cation: An ion with a positive charge Anion: An ion with a negative charge
Na+ Cl
Ions and Ionic CompoundsIons and Ionic Compounds
Metals tend to form Cations
Nonmetals tend to form Anions
Alkali Metals
Alkaline Earth Metals
Noble Gases
Halogens
I A II A
III A IV A VA VI A VIIA
VIII A
Which elements form cations and which form anions?
Ions and Ionic CompoundsIons and Ionic Compounds
How many electrons each element can gain or loose?
Each element tends to have the same number of electrons as noble gases (rare gases).
Ions and Ionic CompoundsIons and Ionic Compounds
Example: Determine the number of electrons, protons and neutrons in each of the following ions
16O2-
40Ca2+
58Fe3+
80Br
No. of Protons No. of Neutrons No. of Electrons
Ions and Ionic CompoundsIons and Ionic Compounds
Ionic Compounds : Cations (metals) and anions (non-metal) combine to form ionic compounds
NaCl
Alternating positive and negativecharges
Ions and Ionic CompoundsIons and Ionic Compounds
Ionic compounds :
(1) Ionic compounds are generally combination of metals and nonmetals
NOTE: Molecular compounds are generally composed of nonmetals only (H2O , CH3OH , CH3CH2Cl , …)
(2) Ionic compounds are represented by empirical formulas
use simplest whole-number ratio of cations and anions
NOTE: There is no discrete (or isolated) molecule of NaCl
(3) Ionic compounds are always neutral. Therefore, the total positive charge equals the total negative charge
Mg2+ and N3- form Mg3N2 : 3(+2) + 2(3) = 0
Ions and Ionic CompoundsIons and Ionic Compounds
Example : Find the empirical formula for the ionic compound made of given cation and anion
Na, O =>
Al, O =>
Ca, O =>
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
Names of ionic compounds consist of the cation name followed by the anion name
CaCl2 = calcium + chloride calcium chloride
Names of Positive Ions (cations) :
(1) Cations formed from metal atoms have the same name
as the metal.
Na+ sodium ion, Zn+ zinc ion, Al3+ aluminum ion
NOTE: Ions formed from a single atom are called monatomic ions
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
(2) If a metal can form different cations, the positive charge
is indicated by a Roman numerical in parenthesis following
the name of the metal
Fe2+ iron (II) ion Cu+ copper (I) ion
Fe3+ iron (III) ion Cu2+ copper (II) ion
These ions are usually transition metals
NOTE: Metals that form only one cation group 1A Na+, K+, Rb+
group 2A Mg2+, Ca2+, Sr2+, Ba2+
and Al3+ (group 3A), Ag+ (group 1B), Zn2+ (group 2B)
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
(3) Cations formed from nonmetal atoms have names that
end in -ium
NH4+ ammonium ion H3O+ hydronium ion
NOTE: These ions are examples of polyatomic ions
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
Names of Negative Ions (anion) :
(1) The names of monatomic anions are formed by replacing
the ending of the name of the element with –ide.
H- hydrogen hydride ion, O2- oxygen oxide ion,
NOTE: polyatomic anions with common names ending with –ide OH- hydroxide ion, CN- cyanide ion
(2) Polyatomic anions containing oxygen (oxyanions)
a) ending with –ate : reserved for the most common oxyanion
NO3- nitrate ion, SO4
2- sulfate ion
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
b) ending with –ite : used for oxyanion with the same charge,
but one fewer O atom than those ending with –ate.
NO2- nitrite ion, SO3
2- sulfite ion
c) If a series of oxyanions extends to more than two members,
use prefix per- (one more) or hypo- (one fewer)
ClO4- perchlorate ion (one more than –ate)
ClO3- chlorate ion
ClO2- chlorite ion
ClO- hypochlorite ion (one fewer than -ite)
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
NOTE: Oxyanions with the maximum number of oxygens
(i) Charges increase from right to left.
(ii) Second row elements (C, N) have maximum 3 oxygen atoms
and third row elements (P, S, Cl) have maximum 4 oxygen
atoms (row # + 1).
(iii) All names end with –ate except for ClO4-
(3) Anions derived by adding H+ to an oxyanion are named by
adding as a prefix the word hydrogen or dihydrogen.
CO32- : carbonate ion HCO3
- : hydrogen carbonate ion
PO43- : phosphate ion H2PO4
- : dihydrogen phosphate ion
Naming Ions and Ionic CompoundsNaming Ions and Ionic Compounds
Halogen (7A)
Names of Binary Molecular Compounds
Names of Binary Molecular Compounds
(1) The name of the element farther to the left in the periodic table
appear first. (NOTE: Oxygen is always written last except when combined with fluorine.)
(2) If both elements are in the same group, the one having the higher
atomic number is named first
(3) The name of the second element is given an –ide ending
(4) Greek prefixes are used to indicate the number of atoms of each element (1 mono-, 2 di-, 3 tri-, 4 tetra-, 5 penta-, 6 hexa- )
Cl2O : dichloro monoxide NF3 : nitrogen trifluoride
N2O4 : dinitrogen tetroxide P4S10 : tetraphosphorous decasulfide
Naming Compounds : ExamplesNaming Compounds : Examples
Before you try to name a compound :
(1) Is the compound ionic or molecular?
(2) For ionic compounds, find the name of each ion.
For molecular compounds, find the number of each atom.
BF3 :
NiO :
KMnO4 :
SO
Naming Compounds : ExamplesNaming Compounds : Examples
Write down the chemical formulas for the following compounds
(1) Sodium Nitride, Q: Is this ionic or molecular?
Q: Is anion monatomic or polyatomic ion?
(2) Diphosphorus pentoxide,
Naming Compounds : ExamplesNaming Compounds : Examples
(1) NaClO :
(2) Fe2(CO3)3 :
(3) SF6 :
(4) aluminium hydroxide :
(5) ammonium sulfate :
(6) NaH2PO4 :