Exam 1- Units 1&2
Terms in this set (90)
What is chemistry?
The study of the properties of materials and the changes that materials undergo.
Measurements associated with numbers.
Equation for Celsius to Kelvin?
Add 273.15 the the celsius temperature.
How to convert from fahrenheit to celsius?
How to convert from celsius to fahrenheit?
Is a form of matter that has definite composition and distinct properties.
Substances can either be ___? (2)
A substance composed of 2 or more elements chemically united in fixed proportions.
*A compound cannot be separated by any physical process.
A physical combination of 2 or more substances.
*2 types: Homogeneous and heterogeneous
A collection of measurements accumulated throughout English history with no systematic correlation.
Composed of a set of units that are related to each other decimally.
*By powers of 10
Base SI Units?
Mass- Kilogram- kg
Time- Seconds- s
Temperature- Kelvin- K
Amount of Mass- Mole- mol
*Often expressed as (g/cm^3) or (g/mL)
*Since the volume of a liquid can change with temperature, densities are often specified at a given temperature.
Rules for Significant Figures?
1. All non-zero numbers are significant.
2. Zeros between non-zero numbers are significant.
3. Zeros to the right of numbers and to the right of decimals are significant.
4. Zeros to the right of the decimal point but to the left of nonzero numbers are not significant.
Particles with the same charge repel one another?
True; particles with opposite charges attract each other.
3 Subatomic Particles?
1. Protons (+)
2. Neutrons (=)
3. Electrons (-)
Have equal amounts of protons and electrons.
Have unequal balance of protons and electrons.
Atoms with identical atomic numbers (same number of protons), but different mass (different number of neutrons).
Conversion from inches to miles. (Pic)
Prefixes with SI Units. (Pic)
Prefixes with SI Units. (Pic 2)
Convert 15.2 kg to mg? Pic
Temperature Equations (Pic)
Convert units (i.e. length, mass, volume, temperature) between unit systems.
Convert units (i.e. length, mass, volume, temperature) between unit systems.
Convert units (i.e. length, mass, volume, temperature) between unit systems.
Example: Cubic length
A pound of coffee beans yields 50 cups of coffee (4 cups = 1 qt.) How many milliliters of coffee can be obtained from 1 g of coffee beans?
1. define what unit (or information) is given
2. determine what unit is desired (end up with)
3. identify conversion factors necessary
4. set up problem and check unit cancellation
Example: What is the volume in liters occupied by 1.00 gram of air, given that the density of air is 0.00129 g/mL?
Scientific notation (exponential notation) represents very large or very small numbers as powers of ten.
To convert a number greater than 1 to scientific notation?
The original decimal point is moved n places to the left, and the resulting number is multiplied by 10^n.
To convert a number less than 1 to scientific notation?
the original decimal point is moved n places to the right, and the resulting number is multiplied by 10^-n.
There are two types of numbers:?
Exact and Inexact
Measured quantities are always an inexact number?
True: Measured quantities, which are always inexact, are reported in such a way that the last digit is uncertain.
*Different measuring devices have different uncertainties and degrees of accuracy.
Significant Figure Rules for Addition and Subtraction:?
The answer of a calculation based on measurements cannot have greater significance than any of the measurements that produced the answer.
The least certain measurement (fewest decimal places) limits the certainty of the calculated answer.
*Line up the decimal points and report the answer based upon the fewest decimal places.
Significant Figure Rules for Multiplication and Division:?
The calculated answer can be no more precise than the least precise number from which the answer is derived.
The least precise number is the one with the fewest sig figs.
Rules for Rounding Off Numbers?
1. When the leftmost number removed is less than 5, the preceding number is left unchanged.
Ex: Round 45.2624 to four significant digits: 45.26
2. When the leftmost digit removed is 5 or greater, the
preceding number is increased by 1.
Ex: Round 3.75 to two significant figures: 3.8
Study of Chemistry (Pic with few terms)
(460 - 370 BC) thought that the world must be made up of tiny particles called atomos.
(1642 - 1727) furthered this idea with regard to gases, believing atoms to be invisible particles in air.
linked the idea of elements and the reaction to form new substances with the idea of atoms in the period 1803 - 1807.
John Dalton's atomic theory involved four postulates, summarized into three points in the text:
1. Each element is composed of extremely small particles called atoms. All atoms of an element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.
2. Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
(The law of constant composition or law of definite proportions states that the elemental composition (the number and types of atoms) of a pure compound is constant.)
Ex: water (H2O) molecules will always be composed of two hydrogen atoms and one oxygen atom.
3. Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.
(The law of conservation of mass (law of conservation of matter) states that matter is neither created nor destroyed in a chemical reaction.)
Each element is composed of one or more type(s) of atom(s).
False; Each element is composed of only one type of atom.
Law of Multiple Proportions.
If two elements (such as the carbon and oxygen shown) combine to form more than one compound, the mass of carbon that can combine with a given mass of oxygen is in the ratio of small whole numbers.
Cathode ray tubes
A high voltage, passed through a partially evacuated glass tube, produced radiation (called cathode rays).
Glass tubes, in which founded the discovery of the subatomic particles.
*Experiments showed that cathode rays are deflected by electric or magnetic fields, suggesting that the particles within the tube were negative.
J. J. Thompson
Constructed a cathode-ray tube with a fluorescent screen at one end in order to quantitatively measure effects of electric and magnetic fields.
Devised experiments to calculate the mass of an electron by first determining an experimental value for the charge (1.6- x 10^-19 C).
Millikan was able to determine the mass of an electron (after having determined the charge):
In 1910, Ernest Rutherford performed an experiment to examine the angles at which alpha particles (positively charged particles) were deflected as they passed through a piece of thin gold foil.
Most alpha particles passed directly through without being deflected.
A small amount were slightly deflected.
Most surprisingly, some particles scattered back in the direction from which they came (major deflection noted).
Ernest Rutherford's experiment disproved Thompson's "plum pudding" model.
Additional subatomic particles in the nucleus of an atom were subsequently identified.
Classifications of Matter: Elements & Chemical Symbol
Elements: Elements are characterized and identified by unique physical and chemical properties.
Chemical symbol: a symbol assigned to an element based on the name of the element, consisting of one capital letter or a capital letter followed by a lowercase letter.
• The names of elements, thus their chemical symbols, are derived from Latin, English, Greek, German, etc. names.
• Elements have also been named in honor of scientists, or the geographic location where they were discovered.
*Knowing the chemical symbols allows scientists to use "shorthand" notation.
Know Name and Symbol.
Nonmetals tend to lose electrons, and metals tend to gain them?
In general, metals tend to lose electrons and nonmetals tend to gain electrons.
What subatomic particles reside in the nucleus of the atom?
Protons and neutrons.
*The area surrounding the nucleus is a diffuse region of negative charge where the electrons reside.
The sum of the protons plus the neutrons of an atom is called the mass number.
One or two letter designation representing the atom.
The number of protons in the atom (often omitted).
The sum of the protons and neutrons.
Charge of the Particle
Indicates whether an atom is neutral, positively or negatively charged.
Isotopes of an element have identical chemical properties?
True; Isotopes of an element have identical chemical properties.
Modern view of atomic structure examples.
What did Julius Lothar Meyer & Dmitri Mendeleev do?
Independently devised classification schemes of the elements based upon increasing atomic mass.
The periodic table is arranged in order of increasing atomic number, and can be further classified by..?
Group or family: vertical (up and down) column of elements that have similar chemical properties.
Period: horizontal (side to side) row in the periodic table.
There are three main categories on the periodic table, what are they?
1. Metals - elements that tend to lose electrons during chemical change, forming positive ions.
2. Nonmetals - substances whose atoms tend to gain electrons during chemical change, forming negative ions.
3. Metalloids (semimetals) - have properties intermediate between metals and nonmetals.
*Metalloids form a narrow diagonal band between metals and nonmetals (Al is an exception - classified as a metal).
*The properties of metalloids fall between those of metals and nonmetals.
Properties of Metals? (5)
1. High thermal conductivity
2. High electrical conductivity
3. Malleability (able to be hammered or pressed permanently out of shape without breaking or cracking.)
4. Ductility (ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling.)
5. Has a metallic luster
*Nonmetals may occur as brittle, powdery solids or gases.
*Nonmetals are generally located on the right side of the periodic table.
a pure substance that cannot be chemically
converted into a simpler substance.
A pure substance composed of two or more
elements united chemically in definite proportions.
Compounds are formed when atoms of an element interact (react) to form new substances.
Molecules are chemical combinations of two or more atoms.
How are molecules held together?
by the sharing of electrons (covalent bonds).
The assignment of a correct and unambiguous name to each and every chemical compound.
Breakdown flow chart of Compound.
Writing formulas from names of binary ionic compounds:?
Common polyatomic ions?
indicates one more oxygen atom than the oxyanion ending in -ate.
indicates one oxygen atom fewer than the oxyanion ending in -ite.
Atomic Mass Unit
Atoms have very small masses - the atomic mass unit is used instead of describing mass in grams.
Atomic mass unit (amu): A unit based on the value of exactly 12 amu for the mass of the 12C isotope (6 protons and 6 neutrons in the nucleus).
*The average atomic mass of each element (expressed in atomic mass units) is known as its atomic mass or atomic weight.
How to calculate Atomic Mass Unit to find atomic mass of an element?
To calculate :
1. Multiply the decimal fraction of the natural abundance of each isotope by its mass (which is roughly equal to its mass number)
2. Add the results of these multiplications together.
(decimal fraction x mass of isotope #1)
+ (decimal fraction x mass of isotope #2)
+ (decimal fraction x mass of isotope #3)...
= the atomic mass (atomic weight) of the element.
*The amu is impractical (too tiny) for laboratory use.
In order to use large quantities of atoms or molecules and weigh out the amount of a substance needed, we can shift our thinking to the gram.
Masses on the periodic table are relative masses:
The mass of a single oxygen atom is 16 times the mass of a single hydrogen atom.
If we think of the masses of the elements on the periodic table as relative, we may express units in grams instead of amu.
The average atomic mass of an element is shown on the periodic table?
True; The average atomic mass of an element is shown on the periodic table.
*What about molecules? Ionic substances?
Formula weight (FW): the sum of the atomic masses of each atom in its chemical formula.
By using the atomic weights from the periodic table and the chemical formula, the formula weight may be calculated
The term molecular weight (MW) or molecular mass is used for the sum of the weights of atoms present in molecules?
True; The term molecular weight (MW) or molecular mass is used for the sum of the weights of atoms present in molecules.
Ionic substances exist as three-dimensional arrays of ions rather than as molecules (more in Unit 7).
The chemical formula of an ionic substance is called a formula unit.
One formula unit for NaCl is one Na+ and one Cl- ion.
The formula weight of NaCl is the mass of one formula unit.
Chemists use the mole (abbreviated mol) to relate the amount of a substance to the mass in "real world" quantities.
The amount of substance that contains the same number of particles as there are atoms in 12 grams of 12C.
How to calculate for mol?
The mass in grams of one mole (mass in g/ 1 mol) of a substance.
The molar mass of a compound is always numerically equal to its formula weight.
Molar mass is calculated for both elements and compounds.
Elements: directly from periodic table.
Compounds: sum number and type of atoms as for calculation of formula weight.
Conversion factors may be developed to convert between the number of atoms (or molecules), mass (grams), and moles.
*(Pic) Take Zn for example; Zn:
NOTES ON MOLES
Note that there are several items to consider when solving conversions between particles (atoms or molecules), mass, and/or moles:
1. What unit are you given (grams? # of atoms? # of molecules? # of moles? grams of element within a compound)?
2. What unit do you want to end up with grams? # of atoms? # of molecules? # of moles? grams of element within a compound)?
3. What conversion factor(s) do you need to complete the calculation?
• arrange conversion factors to cancel out units before performing any calculations - use dimensional analysis.
The percentage by mass contributed by
each element in a sample.
If the chemical formula of a substance is known, the percentage composition may be calculated by: (Pic)
Simplest ratio (whole number) of the types of atoms present in a compound.
Cr2O3: 2 atoms of Cr, 3 atoms of oxygen.
H2O: 2 atoms of hydrogen, one atom of oxygen.
Describes actual numbers of atoms of each element in a molecule.
Some molecular formulas are also empirical formulas (H2O ) and some are not... (Pic)
Commonly used to experimentally determine the empirical formula for compounds containing predominantly carbon and hydrogen.
The # of moles of C and H in the original sample may be determined by the mass of CO2 and H2O produced.
Law of conservation of matter?
Matter cannot be either gained or lost in a chemical reaction.
The total mass of products must equal the total mass of the reactants.
*Atoms are neither created nor destroyed in chemical reactions.
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