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
Chemical Symbol- One capital letter or one
capital letter plus one or two small letters
› Carbon: C, Argon: Ar, Oxygen: O, all on the periodic table!

Atom- smallest piece of matter that has the
properties of the element- represented by
chemical symbol
› Composed on protons, neutrons, and electrons
› Protons and Neutrons exist in the center of an atom-
the nucleus.
› Protons are positive.
› Neutrons have no charge.
› Electrons are negative and surround the nucleus
Even protons, and neutrons are made up
of smaller particles- quarks
 Quarks- smallest particles- make up
protons, neutrons, and electrons- 6 types

› up, down, top, bottom, strange and charm

To study quarks- accelerate charged
particles to high speeds and cause them
to collide with protons, breaking the
proton

http://en.wikipedia.org/wiki/Particle_accelerator
A proton is made up of 2 up quarks and
1 down quark = charge of +1
 a neutron contains 1 up quark and 2
down quarks, yielding a net charge of 0
 All you’ve learned about atomic
structure is just a model
 Model- help you visualize or understand
something too large or small to see all at
once


http://www.teachersdomain.org/resources/phy03/sci/phys/matter/atoms/index.html
Democritus- first to propose that atoms
exist
 Dalton’s model- atom was a sphere
 Thomson’s model- plum pudding modelpositive sphere with negative charges
embedded

› Problems: electrons are actually around the
nucleus, not inside of it

Rutherford- all mass of an atom was in
the center- the nucleus- discovered by
gold foil experiment
› Electrons surround nucleus and travel in
orbits like planets around the sun
› Problem: did not distinguish protons &
neutrons and electrons do not actually
move in the way he thought
›
http://www.chemsoc.org/timeline/pages/1911.html

http://www.shsu.edu/%7Echm_tgc/soun
ds/pushmovies/l2ruther.gif - source of
animation

Bohr-electrons travel in a fixed orbit around
the nucleus
› Problem: electrons are actually in regions or
clouds around the nucleus

Difference between Bohr and Rutherford:
› Rutherford said electrons travel in orbits like
planets- problem- electrons also emit energy
and should spiral closer to the nucleus
› Bohr- only certain orbits are possible – they gain
and lose energy as they move from one orbital
to another
 Distiguished between protons and neutron while
Rutherford did not

Electron Cloud Model- nucleus with
protons and neutrons in the center
› Electrons in clouds around the nucleus- very
large area compared to the nucleus
› Electrons move too fast to find exact
location at any one time
› Atoms are mostly empty space!
http://www.teachersdomain.org/resource/p
hy03.sci.phys.matter.atoms/

Nucleus- contains most of the mass of an atom
› Protons & Neutrons contains most of an atom’s mass
› Electrons- 1/2000th of the mass of a proton

Grams are not used to measure mass of atoms
because atoms are too small
› Amu is used instead
› Amu = atomic mass unit

Mass of proton = mass of neutron = 1amu
Amu – 1/12th the mass of a carbon-12
atom, which contains 6 protons and 6
neutrons
 Protons- determine the identity of an
atom

› Every atom has a different # of protons
Atomic number- tells us the number of
protons
 Mass number- total number of protons &
neutrons
 # of neutrons = mass # - atomic #

Electrons- determine physical and
chemical properties of atoms
 Charges of atoms- indicates # of
electrons gained or lost
 Cation- ion with a positive charge- lost
electrons
 Anion- ion with a negative chargegained electrons



Isotope- Atoms of the same element with different
numbers of neutrons
To indicate the identity of an isotope, write the
element name – mass #
› Carbon-12 Carbon-14

Average atomic mass- a weighted average of the
masses of the isotopes of an element
› Average atomic mass = (% x mass) + (% x mass) + (% x
mass)….
› Reason it is an average- there are several isotopes for each
element
mass number 13 exact weight
12
12.0000
percent
abundance
98.90
13
13.003355
1.10
To calculate the average atomic weight, each exact atomic
weight is multiplied by its percent abundance (expressed as
a decimal). Then, add the results together and round off to
an appropriate number of significant figures.
This is the solution for carbon:
(12.000000) (0.9890) + (13.003355) (0.0110) = 12.011
C has an average atomic mass of 12.011
amu.
 This is closer to 12 than to 13, which
means most isotopes must be carbon-12.
 This matches our known data, which say
that 98.90% of carbon atoms are C-12.

Periodic- Repeated in a pattern
 Elements are ordered by:

› increasing atomic number
› changes in physical & chemical properties

Mendeleev- Ordered elements by
atomic mass
› Left blank places in his table to line up
elements according to their properties
› Elements were later discovered and fit into
the places he left blank

Moseley- organized elements by
atomic number rather than atomic
mass
› Same arrangement as today
Groups/Families- vertical columns of
the periodic table
 Rows of Periodic Table- periods
 Electrons

›
›
›
›
Around the nucleus in an electron cloud
Energy levels dictate location of electrons
Closer to nucleus = less energy
Fill energy levels from inner to outer levels
Electrons in outer shell – determine
chemical properties of elements
 Complete outer shell- needs 8 electrons
to be stable
 Energy levels and # of electrons in each:

›
›
›
›
Level 1
Level 2
Level 3
Level 4
Holds 2
Holds 8
Holds 18
Holds 32

Sublevel

s

p

d

f
# e in sublevel
Shape
2
sphere
6
dumbbell
10
double dumbbell
14
complex

http://library.thinkquest.org/3659/structur
es/shapes.html
Level 1
 Level 2
 Level 3
 Level 4

s
s&p
s, p, d
s,p,d,f
 Valence

2 electrons
2 + 6 = 8 electrons
2 + 6 + 10 = 18 e2 + 6 + 10 + 14 = 32 e-
Electrons
Group 1A – 8A have 1-8 valence
electrons

Electron dot diagram (or Lewis dot
diagram) - A symbol of an element
surrounded by dots to represent
electrons in the outer energy level
› First 2 electrons go together
› Next electrons go one on each side, then
start to double up
http://www.ausetute.com.au/lewisstr.h
tml
 Properties of elements in the same
group- similar due to same # of
valence electrons
 Alkali metals- group 1A- very reactive
metals
 Alkaline metals- group 2 A- less
reactive than alkali


Halogens- group 7A
› Likely to react with Alkali metals- group 1A

Noble Gases- group 8A- not reactivedon’t form compounds

Hydrogen and Helium
› Combine to form elements with larger
atomic numbers – can only occur through
nuclear reactions
› http://www.teachersdomain.org/resources/
phy03/sci/phys/matter/origin/index.html
› http://www.teachersdomain.org/resources/l
sps07/sci/phys/matter/stability/index.html
› http://www.teachersdomain.org/resources/
ess05/sci/ess/eiu/fusion/index.html

Metals- good conductors of heat & electricity.
› All but one (Hg) are solid at room temperature.
› Lustrous- reflect light
› Malleable- can be hammered or rolled into sheets,
› Ductile- can be drawn into wires
Metals- have 1-3 valence electrons, so they lose
electrons to become stable- they become cations
 Metallic bonding- positively charged metallic ions
are surrounded by a cloud of electrons.

› Outer electrons are not held tightly and can move
among the ions- allows conduction of electricity
http://www.eng.auburn.edu/~w
fgale/intro_metals/section1.ht
m





Alkali- Group 1 A very reactive because they have
1 valence electron
Alkaline earth- Group 2A- fairly reactive- have 2
valence electrons
Transition elements- Groups 3-12 or 1B-8B, metals,
often form colored compounds
Lanthanides are elements after lanthanum and
many are used to produce colors on our TV screens
Actinides- follow actinium. All are radioactive and
unstable, so they are difficult to research

Elements beyond Uranium are
radioactive› As # of protons increases, the repulsive force
within the nucleus also increases- forces the
atom to break apart.
› (Radioactive substances are substances in
which the nucleus breaks down and gives off
particles and energy )

Nonmetals- gases or brittle solids at room
temperature.
› not malleable or ductile.
› do not conduct heat or electricity well
› not shiny
Nonmetals don’t conduct electricity
because- electrons are strongly
attracted to the nucleus
 Gain electrons to form anions
 Can form either covalent or ionic bonds

› Covalent- shared electrons
› Ionic- gain and loss of electrons

Diatomic- molecule that consists of two atoms of the
same element covalently bonded
› Includes (memorize these!!)
 H2 Cl2 F2 N2 O2 Br2 I2

Hydrogen is diatomic because it is very reactive.
› Bonding makes it more stable

Halogens- nonmetals from group 7A or 17.
› very reactive.
7 valence electrons
› form reactive diatomic molecules with distinctive colors
›

Noble gases- stable due to full outer energy levels.
› don’t make compounds naturally

Metalloid- can form ionic or covalent
bonds.
› properties of both metals and nonmetals

Semiconductor- element that conducts
electric current under certain conditionslike Silicon (Si is a metalloid)

Allotrope- same element with different
forms and different properties
› Example: Diamond and graphite
Both are made of carbon.
 Diamond- clear, hard

› each C atom bonded to four other C atoms
forming a giant crystal.

Graphite- black powder with hexagonal
layers of C atoms.
› Each C is bonded to 3 other C.
› Layers can slide past each other, so graphite is
a good lubricant.