Atomic Structure
Atom: the smallest particle of an element that
retains the chemical identity of that element
Nucleus: very small, very dense, positively charged
center of the atom containing
Atomic Number = # of protons
(p+)
determines atoms
identity
For neutral
atoms: # p+ = e-
(electrons)
Bohr models
p+
& n in nucleus
e- in
energy levels around nucleus
3 energy levels
-1st has up to 2e-
-2nd has up to 8e-
-3rd has up to 8e-
Lewis Dot Structures
Valence
electrons are represented as dots around the element symbol
Xs and Ox can
also be used
Matter:
anything that has mass and volume
Atomic Structure
Ions: charged particle that is formed when an atom
or group of atoms loses or gains electrons
Charge
of ion = # of p+ - # e-
Ex: An atom of calcium (Atomic # 20) loses 2 e-
Charge
of ion = 20 18 = +2 => Ca 2+
Isotopes: atoms that have the same number of protons
but different number of neutrons
Most elements
exist in nature as a mixture of isotopes
Isotopes have
essentially identical chemical properties, but have different masses
Identify
isotopes by mass number
Mass
number = # of protons + # of neutrons
Example:
Aluminum-27
Average Atomic Mass
Average Atomic Mass: The weighted average of the masses of the
isotopes of an element
Relative Abundance: The
fraction of each isotope that occurs in nature
Relative
Abundance = % Abundance/100
To find Average atomic mass:
Multiply the
mass of each isotope by its relative abundance
Add the
values for each isotope together
Average Atomic Mass Example
The % abundance
of two isotopes of carbon are listed below.
Calculate the average atomic mass of carbon.
Isotope %
Abundance
Carbon-12 98.89
Carbon-13 1.11
Average
Atomic Mass =.9889(12) + .0111(13)
=
11.8668 + 0.1443 = 12.011
Democritus
400 B.C. Greek
philosopher
Coined the term
atomos which means, Indivisible.
Atoms are hard,
solid particles, made of the same material but are of different shapes and
sizes.
Dalton
Dalton: combined several ideas
J.J. Thomson
1897 English
Chemist.
Atoms are made
of even smaller particles.
Plum pudding
model (Chocolate Chip Cookie Dough Model)
Positively
charged material through which negative particles are scattered.
Atoms are
neutral, therefore, there must be + particles too, but Thomson never found them.
Rutherford Gold Foil Experiment
A beam of + particles (alpha particles)
shot through a thin sheet of gold foil.
Most particles passed straight
through. (Most of atom is empty space.)
A few were deflected. (Positive
core-similar charges repel each other.)
Very few bounced off. (Solid core is very
small.)
Rutherfords Gold Foil Experiment
Neils Bohr
1913 Danish Scientist
Planetary model.
Electrons are held in place by the
attraction between them and the + charged nucleus.
Each electron occupies a specific energy
level and orbit the nucleus like planets circling the sun.
Wave Model
Electrons are waves not discreet particles
moving in discreet orbits.
The probable location of an electron
depends on how much energy it has.
Electrons seem to be everywhere at once,
like the moving blades of a fan.
Electron Cloud Model
Positively charged protons and neutral
neutrons are held together with a huge amount of energy forming the nucleus of
the atom.
Negatively charged electrons move rapidly
around the outside of the nucleus forming clouds of negative charge.
Most of the mass of the atom is in the
nucleus.
Also known as: Quantum Model.
History of the Atom Cont.
Law
of Conservation of Matter:
Lavoisier
The father of Chemistry
Matter, like
energy, is neither created nor destroyed in any process.
In every
chemical reaction, there is an equal quantity of matter before and after
Law
of Constant Composition:
(Joseph
Proust) a given compound always
contains the same elements in the same proportions by mass
Updating the Atomic Theory
Atoms are not
indivisible but are made up of even smaller particles
Atoms can be
changed from one element to another, but not through chemical reactions
Atoms of the
same element are not always exactly alike
Quantum Theory
Planks
Theory: The amount of energy an object
emits or absorbs is restricted to pieces of particular size, each piece = 1
quanta
Energy
= Planks Constant * frequency
E = h n
Dual Nature of
Radiant Energy: Light acts like waves
(when it travels through space) but it also acts like a particle (when it
interacts with other particles)
Line Spectra
Samples of all elements emit light when they are vaporized in an
intense flame or when electricity is passed through them. When the light is broken down by a prism,
only a few colors of light are seen.
Electron absorbs energy gets excited
jumps up an energy level
Electron drops down to ground state and releases energy in form of
light
Energy emitted = difference in energy between ground state and
excited state
Atomic Orbitals
Atomic Orbital
a region around the nucleus where an elecron is likely to be found.
Orbitals have characteristic sizes and
shapes
s orbitals = spheres
P orbitals = dumbells
As energy level
increases, the size of the orbital and the distance from the nucleus increases.
Electrons will remain as close to nucleus
as possible and will only pair up if there are no unpaired slots left in the
lowest energy sublevel.
Energy Levels, Sublevels, & Orbitals
Electron Configurations
Describes where
electrons are found and what energy they possess in the ground state (lowest
possible energy)
Fill
orbitals according to:
Aufbau
Principle: e-s are added one
at a time to the lowest energy orbital available
Pauli Exclusion
Principle: each orbital holds at most 2
electrons and these electrons must have opposite spin (up or down ―)
Hunds Rule: e-s
occupy orbitals so that a maximum number of unpaired e-s results
Quarks
Quarks
are simpler particles that make up protons and neutrons
Never directly
observed
Their existence
helps explains what happens during nuclear reactions
Types of
Quarks: Up, Down, Beauty, Truth,
Charmed, and Strangeness
Each quark has a
charged assigned to it
Proton = 2 ups +
1 down
2(2/3)
+ 1(-1/3) = +1
Neutron = 2
downs + 1 up
=
2(-1/3) + 1(2/3) = 0