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STUDYING ATOMS
Ch. 4.1
True False Statement True False
Daltons atomic theory said all matter is made of atoms, which can
be divided
Thomson’s atomic model, showed that atoms are even smaller than
thought
Rutherford’s atomic model showed that the positive charge is contained
in the nucleus
Thomson’s model is also called the plum pudding model
Rutherford was the 1st to propose an atomic theory
Greek Atom- 2500 years ago Democritus- Greek philosopher
Atom from atomos – uncut, indivisible Different types of atoms with different
properties
Aristotle's Model :
Dalton’s Atomic Theory- 1800’s
Evidence Measured masses of
compounds Found that the ratio
of masses of the elements in a compound is always the same
Fixed composition!
Theory All elements are composed
of atoms All atoms of the same
element have the same mass, and atoms of different elements have different masses
Compounds contain atoms of more than 1 element
In a particular compound, atoms of different elements always combine in the same way
Dalton Summed Up:
All matter is made of individual particles, called atoms, which cannot be divided!
Thomson’s Experiment
Glass tube without air 1 side positive, 1 side negative Glowing beam appears in middle
Thomson’s Model of the Atom-1870’s
Evidence Negative charge
attracted to positive charge
1st evidence atoms are made of even smaller particles
Model Atom = neutral Negative and
positive evenly mixed
Called Plum Pudding after English dessert
Rutherford’s Experiment
Aimed alpha particles at gold screen Screen flash when struck by alpha
particle Traced path of alpha particles
Rutherford’s Atomic Theory-1900’s
Evidence Alpha particles- fast
moving positive charge
Positive is not evenly spread
Nucleus- dense, positively charged mass at atoms center
Theory All of an atoms
positive charge is concentrated in the nucleus
THE STRUCTURE OF AN ATOM
Ch. 4.2
True False Statement True False
Isotopes have the same atomic #, but different masses due to protons
The atomic # equals the # of protons in the element
The mass # is the sum of the protons and electrons
Protons and neutrons have almost identical masses
Protons, neutrons and electrons are subatomic particles of the atom
Subatomic Particles
Protons- Rutherford Positively charged particle found in the nucleus Same as atomic #
Electrons- Thomson Negatively charged particle found outside the
nucleus Atomic # - charge
Neutrons- Chadwick Neutral particle found in nucleus Mass almost exact to the proton Mass # - Atomic #
Comparing Subatomic ParticlesParticle Symbol Charge Relative
MassActual Mass
Electron e- 1- 1/1836 9.11 x 10-28
Proton p+ 1+ 1 1.674 x 10-24
Neutron n 0 1 1.674 x 10-24
Proton and neutrons= same ________
Atomic Number
Atoms of any given element always have the same # of p+
Every p+ is balanced by e- for a neutral charge
= # of e- in an atom of that element
= the # of p+ in an atom of that element
Because atoms are neutral!
Mass Number
= p+ + n
Ex: Al 13 p+ 14 n Mass # = 27
n = mass # - atomic #
Ex: Al Mass # = 27 Atomic # = 13 n= 27-13 14
Practice
Symbol Atomic #
Mass # Protons Electrons
Neutrons
Na 23 12
K
P
O
W
Isotopes
Every element does have the same # of protons and electrons
Neutrons can vary
Have the same atomic #, but different mass # due to neutrons
Practice
Symbol Atomic #
Mass # Protons Electrons
Neutrons
Be
Be+2 4 9 4 2 5
Cl
Cl-1
Na+3
MODERN ATOMIC THEORY
Ch. 4.3
True False Statement True False
Bohr’s model focused on electrons, and was adapted from Thomson
Electrons can jump energy levels by gaining or losing energy
Electron clouds are the likely areas in which you can find electrons
The higher the energy the fewer the atomic orbitals; the lower the
energy the higher # of orbitals
Electron configuration is based on lettering the periodic table- s, p d,
and e
Bohr’s Model
Partnered with Rutherford
Focused on electrons
Count the # of electrons, and place in orbit
Energy Levels
Energies that electrons can have
Electrons move levels when the atom gains or loses energy
Use with Bohr Models
Practice
B
Mg
Si
Ne
Electron Cloud Model
Improved Bohr Model
Visual model for most likely locations for electrons
Dense= electrons
Atomic Orbital's
Electron cloud = good approximation of how electrons behave in orbitals
Energy Level # of Orbitals Max # of Electrons
1 1 2
2 2 8
3 9 18
4 16 32
Electron Configuration
Arrangement of electrons in the orbitals Most stable = electrons in orbitals with
lowest energy Ground State= all electrons have lowest
energies
C= 1s22s22p2 Cr= 1s22s22p63s23p64s23d4
Practice
Li
Mg
K
Lewis Dot Structures
Count valance electrons (outer layer of electrons)
Place around element, no more than 8
Practice
P
Be
Ca
CO2
HCl
NaCl
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