Transcript Conservation of Mass

Conservation of
Mass
Mass is neither created nor destroyed in
chemical reactions.
3 levels of representation
2 HgO s   2 Hg l   O2 g 
Comprehension question
Law of Definite
Proportions
Different samples of a pure chemical
substance always contain the same
proportion of elements by mass.
Comprehension question
Dalton’s Atomic Theory
• Elements are made of tiny particles called atoms
• The atoms of each element have the same
unique mass
• Chemical reactions make new substances by
combining atoms in small whole-number ratios
• Chemical reactions leave the atoms themselves
unchanged. Only the groupings of atoms
changes.
Dalton’s atomic theory predicts. . .
Law of Multiple
Proportions
Elements can combine in different
ways to form different substances,
whose mass ratios are small wholenumber ratios of each other.
How many ratios are there in the law of multiple proportions?
Comprehension question
Electrons: Cathode-ray experiment
Electrons: oil drop experiment
Electric & Magnetic Fields
All electrically charged particles are surrounded by an e-field (a field of electrical
attraction/repulsion). This field is very analogous to the emanation of gravity from a
mass.
Other charged particles feel this emanation like mass feels gravity*—charge is
accelerated by it. The force depends only on the strength of the field (E) and the
strength of the charge (e)
A charged particle doesn’t interact at all with a magnetic field unless it is moving. In
that case, it is accelerated in a direction that depends upon the sign of the charge,
and rotated 90 degrees to the acceleration from an e-field. The force depends upon
the strength of the magnetic field (H) and the magnitude of the charge (e) and the
velocity of the particle (v).
Picture from: home.att.net/~numericana/arms/crt.gif
Crookes tube
From Reasons to Ratios
Deflection Controllers
• A. Strength of magnetic field (H)
• B. Charge magnitude of electric
unit (e)
• C. Mass of electric unit (m)
• D. Speed of electric unit (v)
Experiment:
Hev  Ee
E
v
H
Magnetic force
Electric force
He knows H and E! He “dialed them in” to
his experiment!
So he can calculate v (~0.2 c)
With knowledge of the velocity, he can solve deflection in the e-field just like a
gravity problem to give him an e/m ratio: 1*10^8 Coulombs/gram
Comprehension
Huge result!!! The race is on!
question
Oil drop
experiment
• Oil drops have extra
electrons
• Oil drops reach
constant velocity
• E-field turned on
(different behaviors)
• Voltages that stop
some from dropping
always multiple of
1.6*10^-19 Coulombs
Each individual electron must carry a charge of 1.6*10^-19 Coulombs, and
therefore a mass of 1.6*10^-27 kg.
Comprehension question
Gold foil experiment
• If atom is continuous and uniform, alpha
particles should show ~0° deflection
• 1 out of 100,000 did something different
Nuclear Model of the Atom
Subatomic Particles
Comprehension question
Describing
atoms
Stage One: Protons and Electrons
Describing
atoms
Stage Two: Neutrons
Isotopes
Comprehension questions
Describing
elements
Atomic Mass
mass of
isotope 1abundance of isotope 1 
Atomic mass of X 
mass of isotope 2abundance of isotope 2  
Actual masses,
NOT atomic numbers
You are calculating a
weighted average.
Percent abundances
(must sum to 100%)
The masses for these calculations are (generally) in amu, not grams.
Comprehension question
Classifying Matter
Particulate Drawings
In particulate drawings, atoms are represented by shapes and one focuses on the
organization of the shapes rather than what the individual shapes represent.
A fully classified particulate drawing has the phase, the state of purity, and the nature of
each molecule fully labelled.
# of atoms (mono/di/tri)
# of elements (homo/hetero)
gas phase, monatomic element
Gas
Liquid
Solid
Mixture (hetero/homo)
Element
Compound
heterogeneous mixture of two solid phases,
one a heteroatomic diatomic compound and
the other a heteroatomic triatomic compound
Chemical Equations
Chemical Bonding: Covalent
Electron sharing
Only bonding type that makes molecules
Generally between nonmetals
Chemical Representation
Space-filling model
Ball-and-stick model
Chemical Bonding: Ionic
ions
Giving and taking of electrons results in no molecules,
instead we talk about ionic substances (usually ionic
solids)
Generally between a
metal and non-metal
The ratios of positive ions (cations) to negative (ions) makes the total charge on the
ionic substance equal to zero.
Polyatomic Ions
Acids and Bases
A compound that dissolves in water and yields H+ ions is an acid.
A compound that dissolves in water and yields OH- ions in water is a base.
Naming Binary Compounds: Ionic
Naming Binary Compounds: Covalent
Learning from the name
The initial observation of the name should tell you whether the
compound is ionic or covalent. How does it do that?
•Numerical prefixes? Must be covalent (watch for polyatomic
ion
exceptions)
•Ends in –ite or –ate? Must be ionic
•Neither of those two conditions apply? Check metal vs. nonmetal of
leading element.
Once you’ve got the bonding type, try to produce the formula.
•For covalent, use the prefixes and be done.
•For ionic, figure out the two ions and then balance the charge.
For now, the first element in the formula is the first element in the name.
Learning from the formula
The initial observation of the formula should tell you whether the
compound is ionic or covalent. How does it do that?
•More than two elements? Must be ionic
•Metal bonded to nonmetal? Must be ionic
•Non-metal bonded to non-metal? Must be covalent
If its covalent, put in the numerical prefixes and you’re done. (Remember to avoid
“ao” or “oo” combinations.
If its ionic, determine the two ions involved and write cation then anion and you’re
done. (Remember that if the cation is a transition/post-transition metal, the ion is
named with the charge in roman numerals inside parentheses (usually).
For now, the first element in the formula is the first element in the name.