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COS 1.0, 1.1, 1.2, 1.3. 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. - PowerPoint PPT Presentation
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COS 1.0, 1.1, 1.2, 1.3
• 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.
WHAT YOU’LL LEARN• 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
DEMOCRITUSGreek philosopher developed theory around 400 B.C.proposed that atoms make up all substancesAtom — “unable to be divided”
JOHN DALTONDeveloped atomic theory in 1808first atomic theory with a scientific basismodel was simple spherethought the atom could not be splitAtoms of same element exactly alike
J.J. Thomson (1897)Discovered negatively charged particlesatom was divisible!
Particles discovered are electronsAtom consists of positively charged material with negative charges spread evenly throughout
Rutherford (1908)
Gold Foil ExperimentPositive particles shot at gold foil occasionally bounced back!Proposed dense, positively charged center called the nucleus
NIELS BOHRtheory developed in 1913suggested 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 locationspeed 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
• 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) number of protons in the nucleus
MASS NUMBER (A) 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.
ExampleChlorine 35 has a mass number of 35.
Has an atomic number of 17. Mass number (A): 35 Atomic number (Z): –17 Number of neutrons: 18
ATOMIC MASS UNIT (amu) 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 naturally-occurring isotopes of an element
atoms of # totalatoms) of )(## (massatoms) of )(## (mass
Avg.AtomicMass
AVERAGE ATOMIC MASS
EXAMPLE About 8 out of 10 chlorine atoms are chlorine-
35. Two out of 10 are chlorine-37.
atoms 10
atoms) u)(2 (37atoms) u)(8 (3535.4 u
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
ALKALI EARTH METALS• Group 2• two valence electrons• +2 charge• shiny• malleable• ductile• Form compounds in stone & human
bodyCalcium (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 fireworksMedicines• milk of magnesia • Epsom salt
TRANSITION METALS• groups 3-12• most familiar • found in elemental stateIron• most abundant metal• used in steelAluminum• making containers, automotive parts,
cookware…MERCURY• only metal at room temperature• used in thermostats, thermometers,
batteries …
NONMETALS 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 • Group 17• very reactive in elemental state•Chlorine• greenish yellow gas• Kills bacteria• Elemental chlorine is very poisonous• obtained from seawaterFluorine • Poisonous yellow gas• used in toothpasteBromine• Dark red liquid• only nonmetal liquid at room
temperature• obtained from seawaterIodine• 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 electronsNeon• SignsHelium• Less dense than air• Gives lift to blimps & balloonsArgon/Krypton• Used in light bulbs
SEMICONDUCTORS• elements that can conduct
electricity under certain conditions • Aka metalloids:• Composed of only six elements• Boron, silicon, germanium, arsenic,
antimony & telluriumBoron • Extremely hard• Added to steel to increase
hardness & strength at high temperatures.
Antimony • Used as fire retardantsSilicon• Makes up 28% of earths crust• Sand most common compound• Used in electronics