Download APC-Ch.2-Atoms, Molecules, and Ions

Atoms, Molecules, and Ions
Chapter 2
Unit 1 - Chemical Foundations
AP Chemistry
History of the Atom
Dalton’s Atomic Theory
All matter is composed of extremely small particles called
atoms.
Atoms of a given element are identical in size, mass, and
othe properties; atoms of different elements differ in size,
mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple wholenumber ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or
rearranged.
History of the Atom
Modern Atomic Theory vs. Dalton’s Atomic Theory
Atoms of an element have a Atoms of a given element
characteristic average mass are identical in size, mass,
which is unique to that
and other properties; atoms
element.
of different elements differ
in size, mass, and other
properties.
History of the Atom
Modern Atomic Theory vs. Dalton’s Atomic Theory
Atoms cannot be
Atoms cannot be
subdivided, created, or
subdivided, created, or
destroyed in ordinary
destroyed.
chemical reactions.
However, these changes
CAN occur in nuclear
reactions.
History of the Atom
Mass Spectroscopy
Clearly shows the flaws in Dalton’s theory.
Shows that atoms have isotopes of with different masses.
History of the Atom
Mass Spectroscopy
atoms or molecules are passed into a beam of high speed
electrons.
this knocks the electrons OFF the atoms or molecules
transforming them into cations.
apply an electric field
send the accelerated cations into a magnetic field so
this perturbation changes the path of the cation
the amount of deflection is proportional to the mass;
heavy cations deflect little
ions hit a detector plate where measurements can be made
Determining Isotopes
3
Isotopes
Determining Isotopes
Highest Peak = Highest
Abundant or Most
Prevalent isotope
Determining Isotopes
0.9221 × 27.97693 = 25.800
0.0479 × 28.97649 = 0.139
0.0309 × 29.97379 = 0.926
26.87 amu
Determining Isotopes
Mass Spectroscopy
Sample Problem A
Answer the following questions referring to the mass
spectroscopy graph below.
a.How many isotopes does the
element shown have?
b. Identify the element.
Determining Isotopes
Mass Spectroscopy
Sample Problem B
Answer the following questions referring to the mass
spectroscopy graph below (next slide).
a.Determine the element’s atomic mass.
b. Determine the element shown.
History of the Atom
J.J. Thomson
Conducted experiments that led to the discovery of the
electron
In 1897, Thomson used a cathode ray tube to deduce the
presence of a negatively charged particle.
Cathode ray tubes pass
electricity through a gas that is
contained at a very low pressure.
History of the Atom
Thomson’s Model of the Atom
Thomson believed that the electrons were like plums
embedded in a positively charge “pudding,” thus it was
called the “plum pudding” model.
History of the Atom
Robert Millikan
Discovered the mass of an electron in
1909.
Conducted the Oil Drop experiment
Mass of the electron is 9.109 x
-31
10
kg
History of the Atom
Conclusions from Studying the Electron
Cathode rays have identical properties regardless of the
element used to produce them. All elements must contain
identically charged electrons.
Atoms are neutral, so there must be positive particles in the
atom to balance the negative charge of the electrons.
Electrons have so little mass that atoms must contain
other particles that account for most of the mass.
History of the Atom
Rutherford’s Gold Foil Experiment
Alpha particles are helium nuclei
Particles were fired at a thin sheet of gold foil
Particle hits on the detecting screen (film) are recorded
History of the Atom
Rutherford’s Gold Foil Experiment
Findings...
Conclusions
Most of the particles passed
The nucleus is small.
right through.
The nucleus is dense
A few particles were
The nucleus is positively
deflected.
charged.
VERY FEW were greatly
deflected.
Atomic Structure
Atomic Particles
Particle
Charge
Mass
(kg)
Proton
+1
1.673 x 10-27
nucleus
Neutron
0
1.675 x 10-27
nucleus
Electron
-1
9.109 x
-31
10
Location
electron cloud
Atomic Structure
Quarks
Protons and neutrons are NOT
fundamental particles.
Protons are made of two “up”
quarks and one “down” quark.
Neutrons are made of one “up”
quark and two “down quarks.
Quarks are held together by
“gluons.”
Atomic Structure
Isotopes
Isotopes are atoms of the same element having different
masses due to varying numbers of neutrons.
Isotope
Protons
Electrons
Neutrons
Mass Number
hydrogen-1
1
1
0
1
hydrogen-2
1
1
1
2
hydrogen-3
1
1
2
3
Atomic Structure
Atomic Mass
Atomic mass is the average of all the naturally
occurring isotopes of that element.
Carbon’s atomic mass is 12.011.
Isotope
Carbon-12
carbon-13
carbon-14
Symbol
12
6
13
6
14
6
C
C
C
Composition of the
Nucleus
6 protons
6 neutrons
6 protons
7 neutrons
6 protons
8 neutrons
% in Nature
98.89%
1.11%
<0.01%
Atomic Structure
Atomic Mass
Sample Problem C
35Cl,
Naturally occurring chlorine is 75.78%
which
37
has an atomic mass of 34.969 amu, and 24.22% Cl,
which has an atomic mass of 36.966 amu. Calculate
the average mass of chlorine.
34.969 Cl × 0.7578 = 26.50
37
36.966 Cl × 0.2422 = 8.95
35.45
35
Atomic Structure
Atomic Number vs. Mass Number
Atomic number (Z) of an
element is the number of protons
in the nucleus of each atom of
that element.
Carbon = 6
Mass number is the number of
protons and neutrons in the
nucleus of an isotope.
Carbon = 12
+
0
Mass # = p + n
Molecules and Ions
Ions
Cation - a positive ion
2+
1+
Mg ; NH4
Anion - a negative ion
12Cl ; SO4
Ionic Bonding - force of attraction between oppositely
charged ions.
Ionic compounds form crystals, so their formulas are
written empirically (lowest whole number ratio of ions).
Naming Simple Compounds
Writing Ionic Compound Formulas
The charges have to add up to zero.
Get the charges of each piece.
Cation from the name or periodic table.
Anion from the periodic table or polyatomic ion list.
Balance the charges by adding subscripts.
Put polyatomic ions in paraenthesis if there is more than
one of them.
Naming Simple Compounds
Writing Ionic Compound Formulas
Write the formula for calcium chloride.
Calcium is
2+
Ca
Ca
+2
2
Chloride is
Cl
1Cl
−1
Ca Cl2
1. Write the ions involved.
2. We want to find the MAGIC NUMBER. It is the lowest number that
both charges can go into. Put in the middle and circle it.
3. Divide the MAGIC NUMBER by the charge of the ion. That number
becomes the element’s subscript.
Naming Simple Compounds
Writing Ionic Compound Formulas
Sample PRoblem D
Write the formula for the following compounds.
Barium nitrate
Ba(NO3 )2
Ammonium sulfate
(NH 4 )2 SO4
Iron (III) chloride
FeCl3
Aluminum sulfide
Al2 S3
Zinc hydroxide
Zn(OH )2
Naming Simple Compounds
Naming Ionic Compounds
Name the cation first, then the anion.
Monatomic cations - name of the element
2+
Ca - calcium ion
Monatomic anions - root + -ide
1Cl - chloride ion
Metals with multiple oxidation states
some metals form more than one cation
use Roman numerals in their name
Naming Simple Compounds
Naming Molecular Compounds
Compounds between two nonmetals
First element in the formula is names first
Second element is named as if it were an anion.
Use prefixes
only use the prefix “mono” on the second element
Naming Simple Compounds
Naming Compounds
Sample PRoblem E
Name the following compounds.
Na3 PO4
sodium phosphate
ZnSO4
zinc sulfate
Fe2 ( CO3 )3
iron (III) carbonate
N 2O
dinitrogen monoxide
SF4
sulfur tetrafluoride
Naming Simple Compounds
Naming Acids
Acids containing anions whose name ends in -ide
change -ide to -ic, then add hydro- to the anion name
Acids containing anions whose name ends in -ate
change -ate to -ic, then add the word “acid”
Acids containing anions whose name ends in -ite
change -ite to -ous, then add the word “acid”
Naming Simple Compounds
Naming Acids
Sample PRoblem F
Name the following acids.
HCN
hydrocyanic acid
HNO3
nitric acid
H 2 SO4
sulfuric acid
H 3 PO3
phosphorous acid