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• RECOGNIZE PERIODIC TRENDS OF
ELEMENTS, INLCUDING THE NUMBER OF
VALENCE ELECTRONS, ATOMIC SIZE AND
REACTIVITY.
• CATEGORIZE ELEMENTS AS METALS,
NONMETALS, METALLOIDS AND NOBLE
GASES.
• DIFFERENTIATE BETWEEN FAMILIES AND
PERIODS.
• USE ATOMIC NUMBER AND MASS NUMBER
AND MASS NUMBER TO IDENTIFY
ISOTOPES.
COS 1.0, 1.1, 1.2, 1.3
WHAT YOU’LL LEARN
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State the charge, mass, & location of each part of an atom
according to the modern model of the atom.
Relate the organization of the periodic table to the
arrangement of electrons within an atom.
Identify isotopes of common elements.
Determine how many protons, neutrons, & electrons an
atom has, given its symbol, atomic number, & mass
number.
Locate alkali metals, alkaline earth metals, & transition
metals in the periodic table.
Locate semiconductors, halogens, & noble gases in the
periodic table.
ATOMIC STRUCTURE
WHAT ARE ATOMS?
• smallest part of an element that
still has element’s properties.
• building blocks of molecules
WHAT’S IN AN ATOM?
NUCLEUS
• center of each atom
• small & dense
• has positive electric charge
PROTONS
• subatomic particle that has positive charge
• found in nucleus
NEUTRONS
• subatomic particle that has no charge
• no overall charge
• equal number of protons and electrons
whose charges exactly cancel
ELECTRONS
• subatomic particles with negative charges.
• located in a cloud (orbit) moving around
outside nucleus
QUARKS
• particles of matter that make up protons and
neutrons
MODELS OF THE ATOM
DEMOCRITUS
Greek philosopher
developed theory around 400 B.C.
proposed that atoms make up all
substances
Atom — “unable to be divided”
JOHN DALTON
Developed atomic theory in 1808
first atomic theory with a scientific basis
model was simple sphere
thought the atom could not be split
Atoms of same element exactly alike
J.J. Thomson (1897)
Discovered negatively charged particles
atom was divisible!
Particles discovered are electrons
Atom consists of positively charged
material with negative charges spread
evenly throughout
Rutherford (1908)
Gold Foil Experiment
Positive particles shot at gold foil
occasionally bounced back!
Proposed dense, positively
charged center called the
nucleus
NIELS BOHR
theory developed in 1913
suggested that electrons in an atom move in set
paths around the nucleus much like planets orbit sun
It is impossible to determine an electrons:
exact location
speed
direction
Best scientists can do is:
calculate chance of finding an electron in a certain
place within an atom
ENERGY LEVELS
• path of a given electron's orbit
around a nucleus, marked by
a constant distance from the
nucleus
• Closer to nucleus, lower
energy level of electrons
• Further from nucleus, more
energy electrons have
• Number of filled energy levels
an atom has depends on
number of electrons
ORBITAL
• region in an atom where there is a high
probability of finding electrons
VALENCE ELECTRONS
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found in outermost shell of an atom
determines atom’s chemical properties
participate in chemical bonding
Every atom has between one and eight
THE PERIODIC TABLE
ORGANIZATION OF THE
PERIODIC TABLE
• Groups similar elements together
• organization makes it easier to predict
properties of an element based on
where it is in periodic table
• Elements are listed in order of number
of protons
PERIODIC LAW
• states that when elements are arranged this way,
similarities in their properties will occur in a
regular pattern
• helps determine electron arrangement
PERIODS
• Horizontal rows
• number of protons & electrons increases as
you move from left to right
FAMILY/GROUP
• vertical column of elements
• Atoms of elements in same group have
same number of valence electrons
• elements have similar properties
IONS
• an atom or group of atoms that has lost or
gained one electron and has a negative or
positive charge
HOW THE STRUCTURES OF
ATOMS DIFFER
ATOMIC NUMBER (Z)
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number of protons in the nucleus
MASS NUMBER (A)
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number of protons plus the number of
neutrons in nucleus
ATOMIC RADIUS

is size of atom
GROUPS
 radius increases as one proceeds down any group of
periodic table
WHY?
 adding layers of electrons
PERIODS
 radius decreases as one proceeds across any row of
periodic table
WHY?
 increasing number of protons in nucleus as you go
across the period pulls electrons in more tightly.
ISOTOPE
has same number of protons as other
atoms of same element do but has a
different number of neutrons.
 Some are more common than others.
 If you know the atomic number and
mass number of an atom, you can
calculate the number of neutrons it has.
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Example
Chlorine 35 has a mass number of 35.
Has an atomic number of 17.
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Mass number (A):
35
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Atomic number (Z):
–17
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Number of neutrons:
18
ATOMIC MASS UNIT (amu)
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Mass of an atom or molecule that is
exactly 1/12th the mass of a carbon
atom with mass number 12
AVERAGE ATOMIC MASS
• weighted average of masses of all naturallyoccurring isotopes of an element
(mass # )(# of atoms)  (mass # )(# of atoms)
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total # of atoms
AVERAGE ATOMIC MASS
EXAMPLE
 About 8 out of 10 chlorine atoms are chlorine35. Two out of 10 are chlorine-37.
Avg.
(35 u)(8 atoms)  (37 u)(2 atoms)
 35.4 u
Atomic 
10 atoms
Mass
FAMILIES OF ELEMENTS
HOW ARE ELEMENTS CLASSIFIED?
 By similar physical & chemical
properties.
ALKALI METALS
group 1
 shiny
 malleable
 ductile
 React violently w/ water
 Very reactive b/c it has only one
valence electron
 Has +1 charge
 Not found in nature as elements
 Found only in compounds
 Ex: salt (NaCl)
Lithium
 used to treat bipolar disorder
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ALKALI EARTH METALS
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Group 2
two valence electrons
+2 charge
shiny
malleable
ductile
Form compounds in stone & human body
Calcium (Ca):
• Shells of sea animals, coral reefs
(limestone), skeletal structure humans …
Magnesium (Mg)
• Air plane construction
• Activates enzymes that speed up processes
in humans
• brilliant white color in fireworks
Medicines
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milk of magnesia
Epsom salt
TRANSITION METALS
• groups 3-12
• most familiar
• found in elemental state
Iron
• most abundant metal
• used in steel
Aluminum
• making containers, automotive parts,
cookware…
MERCURY
• only metal at room temperature
• used in thermostats, thermometers,
batteries …
NONMETALS
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Some elements found in groups 13-16 & all elements in
groups 17-18
except hydrogen
usually gases or brittle solids at room temperature
poor conductor of heat & electricity
may be solids, liquids, or gases at room temperature.
HALOGENS
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Group 17
very reactive in elemental state
Chlorine
• greenish yellow gas
• Kills bacteria
• Elemental chlorine is very poisonous
• obtained from seawater
Fluorine
• Poisonous yellow gas
• used in toothpaste
Bromine
• Dark red liquid
• only nonmetal liquid at room temperature
• obtained from seawater
Iodine
• shiny, purple-gray solid
• Used as disinfectant
• obtained from seawater
NOBLE GASES
• group 18
• Exist only as single atoms instead
of molecules
• Unreactive b/c orbitals are full of
electrons
Neon
• Signs
Helium
• Less dense than air
• Gives lift to blimps & balloons
Argon/Krypton
• Used in light bulbs
SEMICONDUCTORS
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elements that can conduct electricity
under certain conditions
Aka metalloids:
Composed of only six elements
Boron, silicon, germanium, arsenic,
antimony & tellurium
Boron
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Extremely hard
Added to steel to increase hardness &
strength at high temperatures.
Antimony
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Used as fire retardants
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Makes up 28% of earths crust
Sand most common compound
Used in electronics
Silicon