atomic theory
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Atomic Theory. In the Beginning. Atoms originally named by Democritus Believed the a substance could be divided over and over again only to a point If divided further it would not be that substance anymore His atoms were solid, _________________________. - PowerPoint PPT PresentationTRANSCRIPT
ATOMIC THEORY
IN THE BEGINNING
Atoms originally named by Democritus
Believed the a substance could be divided over and over again only to a point
If divided further it would not be that substance anymore
His atoms were solid, _________________________
LAVOISIER: LAW OF CONSERVATION OF MASS
Precisely measured masses of reactants and products of chemical rxns
Law of conservation of __________- mass is neither created or destroyed in chemical rxn Mass of reactants equals the mass of the
products
PROUST: LAW OF DEFINITE PROPORTIONS
All samples of a particular compound have the same _______________ Elements have the same proportion by mass in
each sample
DALTON: LAW OF MULTIPLE PROPORTIONS
If two or more compounds containing the same two elements are examined (for example: CO and CO2) Then the ratio of masses of the element that
changes in both compounds (in our example: O) is a small whole number
Law of Multiple Proportions (cont.)
Four different oxides of nitrogen can be formed by combining 28 g of nitrogen with: 16 g oxygen, forming Compound I 48 g oxygen, forming Compound II 64 g oxygen, forming Compound III 80 g oxygen, forming Compound IV
Compounds I–IV are N2O, N2O3, N2O4, N2O5
What is the ratio 16:48:64:80 expressed as small whole numbers?
JOHN DALTON
Proposed atomic theory in 1803 Four ideas
All matter is composed of indivisible particles called atoms.
All atoms of one element are alike in mass and other properties, but the atoms of one element are different that the atoms of other elements.
Compounds are formed when atoms of elements unite in fixed proportions.
No atoms are created, destroyed, or broken apart in chemical reactions. Atoms are just rearranged
His atom is also a solid, _____________________
Dalton’s Theory Satisfies Laws
Six fluorine atoms and four hydrogen atoms before reaction …
… six fluorine atoms and four hydrogen atoms after reaction.
Mass is conserved.
HF always has one H atom and one F atom; always
has the same proportions (1:19) by mass.
J.J. THOMSON AND CATHODE RAYS
Worked with cathode ray tubes (made by Sir William Crooke) in the late 1800’s
Found that all matter had negative particles (___________________)
Calculates _______________ ratio of e-
J.J. THOMSON’S MODEL Atoms have negative particles, but overall they are
neutral His atom has a positive sphere with negative
particles embedded (often called the _______________________)
Robert Millikan’s Oil Drop Experiment
Calculated the charge of an e-
Made it possible to calculate the mass of the e-
Charged droplet can move either up or down, depending on the charge
on the plates.
Radiation ionizes a droplet of oil.
Magnitude of charge on the plates lets us calculate the charge on the droplet.
RUTHERFORD’S EXPERIMENT
Often called the ____________ experiment Expected almost all particles to pass
straight through the gold Although many did, some particles were
reflected back
RUTHERFORD’S CONCLUSION
Atom must have positive particles (_______________) concentrated in the center
Center is called the ______________ Electrons gravitate around the nucleus A lot of _________________ between nucleus
and electrons
JAMES CHADWICK
Discovered neutrally charged particles (_________________)
Particle was also found in the ______________
NIELS BOHR
Refined Rutherford’s atom model Put the electrons in fixed _______ (like
planets orbiting around the sun) Electrons could temporarily get excited and
jump levels
MODERN ATOMIC MODEL
Electron behave like _________________________ Can’t be tied down to a orbit like a planet Instead scientist show where an electron is
likely to be a any one point in time Forms an electron __________
COMPARING THE PARTICLES
In the nucleus Protons
Charge= ________ Mass = ___________________
Neutrons Charge= ______ Mass= ______________________
Surrounding the nucleus Electron
Charge= ________ Mass= _______________________
ELEMENTS
Composed of only one type of _________ Identity is based on ___________ number Atomic number (___)- number of protons
found in that atom (ID number for elements) Elements are ordered in periodic table according
to this number Mass Number (___)- mass of atom in atomic
unit Really the mass of the __________________________ Electrons are so tiny that they don’t count
CALCULATING PNE (GROUND STATE)
# of protons= __________________
# of electrons= _________________
# of neutrons= _______________________________
ISOTOPES
Different forms of the same atom type Differ by number of ____________ (so therefore
differ by mass as well) Isotope names- element name – mass
number Lithium-6 Lithium-7 Lithium-8
Atoms that lose or gain ___________ form ions Ions have a charge
Cation- ion with a ____________ charge Anion- ion with a _____________ charge
IONS
Forms when atoms _________ electrons
CATIONS
Forms when atoms __________ electrons
ANION
Cations “Name of the element” ion For example, Ca+2 is calcium ion
Anions “Name of the element with ending changed to –
ide” ion
For example Cl
- is chloride ion
NAMING IONS
CALCULATING PNE (IONS)
# of protons= atomic number
# of electrons = atomic number – charge for cations Atomic number + charge for anions
# of neutrons= mass number – atomic number
ATOMIC MASSES ON THE PERIODIC TABLE
Atomic masses on periodic table are an average of all naturally occurring ___________ based on their abundance
Calculating Atomic Mass
Need Mass of each isotope Fractional abundance of each isotope (must
change to fraction if given as %) For each isotope
Multiple the mass and the fractional abundance Add all of the answers together to get the atomic
mass
Proposed period table (1869)
Arranged elements according to ________________
Grouped elements by similar properties
Left holes for undiscovered elements and predicted their properties
Elements are arranged by _____________________
Elements occur in rows (or _________)- 7 periods in all
Elements occur in columns (or ___________________) with similar chemical properties- 18 in all
______________ law- elements can be organized into patterns in the table based on chemical and physical properties
The two series actually belong in the table like this, but we put them at the bottom to save space
Metal Good conductor of
electricity Malleable Ductile Shiny
Nonmetal Poor conductor of heat
and electricity Often gas or dull, brittle
solid Metalloid
Properties in between the other two
Most occur as solids
Br and Hg can occur as a liquid
Other occur as gas
Many elements can exist in different forms naturally
Carbon Both graphite and diamond are carbon, the
atoms are just arranged differently
Element occurs naturally in pairs 7 elements
Hydrogen (H2) Nitrogen (N2) Oxygen (O2) Fluorine (F2) Chlorine (Cl2) Bromine (Br2) Iodine (I2)