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