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Dalton’s Atomic Theory (1808)
1. All matter is made of indivisible and indestructible atoms.
2. All atoms of the same element are identical in their physical and chemical properties.
3. Atoms of different elements have different properties.
4. Atoms of different elements combine in simple whole-number ratios to form compounds.
5. Atoms cannot be subdivided, created, or destroyed when they are combined, separated, or rearranged in chemical reactions.
The Atom
the smallest unit of an element that retains that elements properties
Made of protons, neutrons, and electrons Can you see inside an atom?
How did they know it contains protons, neutrons and electrons?
Cathode Ray Tube
When connected to electric current the remaining the gas forms a BEAM OF LIGHT.
The beam always started at the NEGATIVE electrode and flowed to the POSITIVE electrode.
The electrode is named by what type of particle it attracts Cathode: Negative (-) Anode: Positive (+)
Cathode Ray Conclusions
1. The beam was attracted to a POSITIVE magnet.
2. The beam must be made of NEGATIVE particles.
Radioactivity
Becquerel discovered RADIATION
uranium would expose photographic plates in the dark
The properties of an element changed as it gave off radiation
Curie Discovered radium and polonium
The radioactive emissions of alpha, beta and gamma rays were identified.
Ernest Rutherford’s Gold Foil ExperimentSet up Gold Foil with a detection sheet around it.
Set up radioactive source emitting alpha particles.
ALPHA PARTICLES shot at gold foil.
MOST particles went through the gold foil
SOME particles BOUNCED back
alpha particles shot through the gold foilbouncing back – like hitting the target
going through – missing the target
Gold Foil Conclusions
1. The atom is made up of mostly EMPTY SPACE
2. The center of the atom contains a POSITIVE CHARGE
3. Rutherford called this positive bundle of matter the NUCLEUS
Goldstein and Wien - 1886
Used a cathode ray tube Discovered collection of positively
charged particles
**DISCOVERED THE PROTON!!
Chadwick’s Experiment - 1932
Found that alpha particles shot at beryllium made a beam form
The beam had the same mass of a proton but was electrically neutral
**DISCOVERED THE NEUTRON!!
Niels Bohr – 1913
Developed a new diagram of the atom Electrons can only be at certain energies Electrons must gain a specific amount of
energy to move to a higher level, called a quantum
**DISCOVERED ENERGY LEVELS!!
Bohr Models
Energy Level(n)
# of Electrons
1
2
3
P+
no
n=3n=2n=1
Nucleus = correct number of protons & neutrons
Element Symbols
Rule 1 First letter is capitalizedH Hydrogen C Carbon O Oxygen
Rule 2 Second letter is lower caseCl Chlorine He Helium Ne Neon
Rule 3 Some are Latin namesNa Sodium (natrium) Fe Iron (ferrum)
Rule 4 Some elements are named for places, scientists,
greek gods…Eu Europium Am Americium
Hyphen Notation
The mass number is written with a hyphen after the name of the element.
Element – Mass#Uranium – 235Calcium – 40
Nuclear Symbol
The superscript indicates the mass number and the subscript indicates the atomic number.
C12
6
XAZ
Mass Number
Atomic NumberElement Symbol
ALL ATOMS ARE ELECTRICALLY NEUTRAL
Must have same number of protons and
electrons
Atomic Number: number of protons
NUMBER OF PROTONS NEVER CHANGES!
Every atom of an element has the same
number of protons which makes the element
unique
Examples
Lithium: atomic number of 3How many protons?
Hydrogen: atomic number of 1How many protons?If you add another proton, does it become positive?
6.94
3
Atomic Number
Li
Mass Number
Protons + NeutronsThis is not the actual mass of the atomMasses on the periodic table are NOT
whole numbers
Examples: Silicon 14 protons 14 neutrons
Mass Number = ______
Fluorine 9 protons ____ neutronsMass number = 19
ELEMENT SYMBOL ATOMIC NUMBER PROTONS NEUTRONS ELECTRONS MASS
NUMBER
Nitrogen 15
Cu 35
38 88
12 12
30 26
Hydrogen – 1 Hydrogen
Hydrogen – 2 Deuterium
Hydrogen – 3 Tritium
Hydrogen has 3 isotopes:
1 p 0 n 1 p 1 n 1 p 2 n
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
Do You Understand Isotopes?
ION : an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive chargewhen an atom loses an electron
anion – ion with a negative chargewhen an atom gains an electron
Na 11 protons11 electrons Na+ 11 protons
10 electrons
Cl 17 protons17 electrons Cl-
17 protons18 electrons
13 protons, 10 (13 – 3) electrons
34 protons, 36 (34 + 2) electrons
How many protons and electrons are in Al2713 ?3+
How many protons and electrons are in Se7834
2- ?
Do You Understand Ions?
Summary
Particle ProtonsNeutron
sElectro
ns
Atom Same Same Same
Isotope SameDIFFERE
NTSame
Ion Same SameDIFFERE
NT
NEVER CHANGES!!
!
Atomic Mass Unit
Carbon is the standard for all masses on the periodic table.
Carbon: 6 p and 6 n = 12 amu
Periodic table lists weighted average atomic masses of elements (like a GPA calculation)
Relative Atomic Mass