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Earth Chemistry
• Objectives– Compare chemical properties and physical properties
of matter– Describe the basic structure of an atom– Compare atomic number, mass number, and atomic
mass– Describe arrangement of elements in periodic table– Define isotope, compound, molecule– Interpret chemical formulas– Describe how electrons form chemical bonds between
atoms– Explain the differences between compounds and
mixtures
Matter
• What is matter?• Physical Characteristics
– Density, color, hardness, freezing pt, boiling pt, ability to conduct electric current
• Chemical Characteristics– How a substance reacts w/ other substances
to produce different substances– Ex. Iron-oxygen=rust, helium reacts w/
nothing
Atoms
• What is an atom?– Smallest unit of an element that has chemical properties of
that element
– Can it be broken down any farther? How big is an atom?
• Atomic Structure
• What makes up the atomic structure?– Protons= + charge, nucleus, dense
– Neutrons= neutral charge, nucleus, dense
– Electrons= negative charge, electron cloud. Travel at high speeds as they orbit the nucleus. Do not travel in same plane
• Nucleus– Made up of closely
packed neutrons and protons. + charge
• Electron Cloud– Surrounds nucleus,
made up of electrons. Why are electrons attracted to atom
Elements
• Substance that cannot be broken down into anything simpler, stable.
• More than 90 elements occur naturally on Earth– Examples
• 2 dozen created in lab• 8 elements make up
98% of Earth’s crust
Atomic and Mass Number
• Atomic Number– Number of protons in nucleus of atom– # of protons equals the # of electrons
• Periodic table- system for classifying elements, arranged according to atomic #– Same column, similar arrangements of electrons in
atoms• Atomic Mass
– Sum of number of protons and neutrons in atom=mass number
– Measurement read in atomic mass unit (amu)• Isotopes
– Atom that has same # protons but differs in neutron # of other atoms of that element.
– Have slightly different properties
Arrangement of Periodic Table• Elements arranged in columns=groups• Atom’s chemical properties determined by # of
electrons in outer energy level– Outermost electrons found in energy levels=valence
electrons– First energy level can hold 2 electrons, all after that can
hold 8 electrons• Groups 1 and 2, same # of electrons as group #, 3-
12 have 2 or more, 13-18 same as group # -10 except for helium (only has 2)
• Metals– Alkali, alkaline-earth, transition, others
• Nonmetals– Halogens, Noble gases, others
• Semiconductors and Hydrogen• Welcome to Discovery Education Player
Sec 2-Combination of Atoms
• Compound-Substance made up of 2 or more elements joined by chemical bonds between atoms of their elements– Valence electrons are involved in chemical
bonding– Octet rule-atoms combine to form compounds
and molecules in order to obtain the stable electron configuration like noble gases
• Molecule-smallest unit of matter that can exist by itself and retain all of substance’s chemical properties
Chemical Formulas
• What is a chemical formula?– Combination of letters and numbers that
shows which elements make up compound– Also shows # of atoms of each element to
make up molecule of compound– Examples
Chemical Equations• Reaction of elements and
compounds that are described in formula– Reactants=left side of
arrow– Products=right hand side– Arrow means gives or
yields• Why use chemical
equations?– To show the types and
amounts of the products that could form from a reactant
– Atoms must be equal on each side
– How do you do this?– Coefficient multiples
subscript
Chemical Bonds
• Forces that hold together atoms in molecules, form because of the attraction between positive and negative charges– How do they form bonds?
• Share or transfer valence electrons from one atom to another
• Ions-Particle (atom or molecule) that carries a charge– Electrons are transferred, atoms have electrical
charge because of the unequal # of electrons and protons
– NaCl- Sodium(11 protons/11 electrons), Chlorine (17 protons/17electrons). Sodium gives up electron, now a positive charge. Chlorine gains electron now a negative charge
Types of bonds
• Ionic bond– Attractive force between oppositely charge ions that
result from transfer of electrons from one atom to another
• Covalent bond– Bond formed by attraction between atoms that share
electrons– + nucleus attracted to – electron. The force keeps
atoms joined– Ex. Water
• Polar covalent bond– Covalent bond in which the bonded atoms have
unequal attraction for shared electrons
Mixtures
• Combination of 2 or more substances that are not chemically combined, substances keep individual properties– Mixtures can be separated into parts by
physical means
• Heterogeneous– Mixtures in which 2 or more substances are
not uniformly distributed– Ex. Igneous rock=granite + quartz and
feldspar
• Homogeneous– Having same composition and properties
throughout– Solution- 2 or more substances uniformly
dispersed throughout mixture is a solution– Ex. Sea water
Significant Figures
• Significant figures-digits necessary to express the results of a measurement to the precision with which it was made– Ex. Reading a thermometer
• Precision-how often a particular measurement will repeat itself in series of measurements
• Accuracy-tells how close the measured value is to a known or standard accepted value of the same measurement– Measurements might show high degree of precision
but might not always reflect a high degree of accuracy or vice versus
• When making measurements, it is important to determine the # of significant digits for results to be meaningful
• Rules must be followed– All nonzero digits (digits from 1 to 9) are significant
• 254 contains three significant figures• 4.55 contains three significant figures• 129.454 contains six significant figures
– Zero digits that occur between nonzero digits are significant
• 202 contains three s.f.• 450.5 contains four s.f.
– Zeros at the beginning of a number are considered to be placeholders and are not significant
• 0.00078 contains two s.f.• 0.00205 contains three s.f.
• Zeros that occur at the end of a number that include an expressed decimal point are significant. Decimal pt is taken as an indication that the measurement is exact to the places indicated– 57500. contains five s.f.– 34.00 contains four s.f.
• Zeros that occur at the end of a number without an expressed decimal pt are not considered to be significant– 2000 contains one s.f.– 40620 contains four s.f.
Rounding Off Numbers
• When dealing with scientific figures, it is often necessary to round off numbers in order to keep the results of calculations significant– Ex. Round 64.82 to three s.f.= 64.8
– 75.52 to three s.f.= 75.5
– 9.08352 to two decimal places= 9.08
– 1345.54 to a whole number= 1346
– 7962400 to three s.f.= 7960000
– 0.000275 to two s.f.= 0.00028
• Scientific Notation with significant figures
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