1. 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

2. 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

3. Atoms What is an atom? Atomic Structure
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

4. Nucleus Electron Cloud
Made up of closely packed neutrons and protons. + charge
Electron Cloud
Surrounds nucleus, made up of electrons. Why are electrons attracted to atom

5. 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

6. 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

7. 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, 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

9. 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

10. 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

11. 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

12. 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

13. Types of bonds Ionic bond Covalent bond Polar covalent 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

14. 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

15. Homogeneous Having same composition and properties throughout
Solution- 2 or more substances uniformly dispersed throughout mixture is a solution
Ex. Sea water

16. 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

17. 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
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
contains two s.f.
contains three s.f.

18. 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
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.

19. 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 to three s.f.= 64.8
75.52 to three s.f.= 75.5
to two decimal places= 9.08
to a whole number= 1346
to three s.f.=
to two s.f.=
Scientific Notation with significant figures