Chemistry 121 Exam 1

Rules for Counting Significant figures

1.leading zeros are never significant figures 2. captive zeros are always significant figures trailing zeros are sometimes significant figures 3. exact numbers never limit the number of significant figures in a calculation

compound

A compound is a particle with more then one element present. Usually, we use different colored spheres to indicate different elements present in the compound. As long as the spheres are linked or overlapping, we consider them to be in a compound together.

Law of Definite Proportions:

A given compound always has the same ratio of atoms and elements.

Law of Multiple Proportions

Atoms of two elements can combine in more than one way, but must combine in whole number ratios

Which one of the following compounds is an ionic compound? a. sulfur dioxide NH4Cl chlorine gas phosphorus pentafluoride BrF2

B. a. sulfur dioxide SO2, molecular b. NH4Cl ionic c. chlorine gas Cl2, element, not a compound d. phosphorus pentafluoride PF5, molecular e. BrF2 molecular

Oxyanions can be written with what elements?

Br, I, Cl

Millikan's Oil Drop Experiment

By observing oil droplets hit by electrons and tuning a positively and negatively charged plate, Millikan was able to determine the charge/mass ratio of an electron. From this, we get that the charge on an electron is -1.

Rutherford's Gold Foil Experiment:

By observing what happened to alpha particles shot through a piece of gold foil, Rutherford determined that atoms had tiny, dense, positive nuclei but were mostly empty space.As a result of these experiments, and others, scientists learned the following: Protons: located in the nucleus with a charge of +1 and mass of ~1 amu, these define the identity of an element. Neutrons: located in the nucleus with a charge of 0 and a mass of ~1 amu, the neutrons keep the protons from repelling one another. Electrons: located outside the nucleus with a charge of -1 and a mass ~0.00055 amu, the electrons/proton count will control the charge on an atom

Thomson's Cathode Ray Experiment

By sending cathode rays (which turned out to be beams of electrons), through a tube, Thomson discovered that there were charged particles in atoms....in other words, he discovered electrons.

How to find density?

Density =mass /volume

Which one of the following is an example of a homogeneous mixture? a. Pure water b. NaCl c. Orange juice with pulp d. A balloon filled with helium e. Iced tea

E. Iced tea a. Pure water pure substance b. NaCl pure substance c. Orange juice with pulp heterogeneous mixture d. A balloon filled with helium pure substance e. Iced tea homogeneous mixture

Rules for Addition/Subtraction:

For addition and subtraction operations, we don't need to count significant figures. The answer should have the same amount of uncertainty as the number used to calculate it which has the greatest uncertainty.

Sold mixture (element or compound)

Identify

gas mixture (element or compound)

Identify

Law of Conservation of Mass:

Matter can be neither created nor destroyed.

What is matter?

Matter is the stuff the universe is made of. Matter has mass and takes up space. Most of the things we see and touch are matter. However, what we also want to know is how to represent that which we cannot see

Solid

Particles are very close together (dense) and typically cannot be compressed. particles are organized and typically have a rigid form particles are on the bottom of their container particles have very slow motion (something we cannot see in our model)

Rules of Multiplication/Division of sig figs

The number of sig. figs. the answer should have is the same as the least number of sig. figs. in the numbers used in the calculation

element

a particle with only one type of atom. Most elements would be represented by single spheres, but there are some which always exist in diatomic (two atom) form. These elements include H2, N2, O2, F2, Cl2, Br2, and I2.

Which one of the following has the smallest molar mass? a. zinc(II) oxide b. (NH4)3PO4 c. phosphorous pentafluoride d. BaC2O4 e. C14H22O

a. zinc(II) oxide ZnO: 81.39 g/mol

Which one of the following statements is false? a. Converting a liquid into a gas is an example of a physical change. b. In a gas, the molecules are typically closer together than they would be in a solid. c. When hydrogen gas reacts with oxygen gas to form water, a chemical change is | taking place. d. Mixing sugar into water is a physical change. e. Liquids are not rigid, but solids are rigid.

b. In a gas, the molecules are typically closer together than they would be in a solid.

Which one of the following statements is false about protons? a. Protons are found in the nucleus of an atom. b. Protons have about the same mass as electrons. c. Protons are positively charged. d. The number of protons determines the identity of an element. e. In the second period of the periodic table, the elements are listed in order of increasing number of protons.

b. Protons have about the same mass as electrons.

Pure Substances:

comprised of one type of particle (keep in mind that linked spheres can be considered one type of particle, just one representing multiple atoms)

Which one of the following was determined by Millikan's Oil Drop Experiment? a. Atoms contain negatively charged particles. b. Atoms contain a tiny, dense nucleus. c. The nucleus of an atom has a positive charge. d. The charge on an electron is -1.60 x 10-19 coulombs. e. The nucleus of an atom contains neutrons.

d. The charge on an electron is -1.60 x 10-19 coulombs

10. Which one of the following statements is false? a. Lithium is an alkali metal and its most common ion has a +1 charge. b. Chlorine is a halogen and its most common ion has a -1 charge. c. Hydrogen and nitrogen both exist as diatomic gases in their natural state. d. The most common ion of silicon will have a -3 charge. e. Neon will most likely not form an ion.

d. The most common ion of silicon will have a -3 charge.

The element Yttrium, Y, has a mass of 88.91 listed on the periodic table. Which one of the following statements is false? a. The mass of 88.91 amu is the weighted mass of all possible isotopes of yttrium. b. The most common isotope of yttrium is probably yttrium-89. c. All atoms of yttrium will have 39 protons. d. No single atom of yttrium will have a mass of 88.91 amu. e. The mass of the neutrons in all atoms of yttrium is 49.91 amu.

e. The mass of the neutrons in all atoms of yttrium is 49.91 amu.

Classification of matter

element, compound, mixture- (Heterogeneous- having visibly distinguishable parts) (Homogeneous- visibly distinguishable parts)

Atoms with non-zero charges are called?

ions.

chemical change

is one in which chemical bonds are made or broken between atoms. In other words, the identity and composition of the particle is changing

physical change

is one in which no chemical bonds are broken and we only rearrange particles. Think about a physical change as simply rearranging where the molecules are located.

When atoms have different numbers of neutrons, they are known as

isotopes

Gas:

particles are far apart (low density) and are easily compressible. particles are not organize and have no rigid form particles fill their entire container particles have lots of motion and are moving quickly

Liquid

particles aren't as close together (not as dense as a solid) but can only be compressed a tiny bit. particles are not organized and don't have a rigid form particles are on the bottom of their container and fill the bottom of the container particles have some motion, more than solids, but less than gases.