CHEM CHP 1

Scientific Notations

-For a number that is greater than or equal to 10, shift the decimal point to the left by n places until you obtain a number between 1 and 10 Multiply the result by 10n For example: 6792.5 is written in scientific notation as 6.7925 X 103 For a number that is less than 1, shift the decimal point to the right by n places until you obtain a number between 1 and 10 Multiply the result by 10-n For example: 0.047 is written in scientific notation as 4.7 X 10-2

1 centimeter (cm)

10 millimeters (mm)

1 kilogram (kg)

1000 grams (g)

Rutherford: The nucleus

Ernest Rutherford (1907) Scattered alpha particles off gold foil Most passed through without significant deflection A few scattered at large angles Conclusion: an atom's positive charge resides in a small, massive nucleus Later: positive charges = protons James Chadwick (1932): also neutral neutrons in the nucleus

RULES FOR ROUNDING OFF NUMBERS

If the fist digit you remove is less than 5, round down by dropping it and all following digits. Thus, 4.874563 becomes 4.87 when rounded to three significant figures. If the first digit you remove is 5 or greater, round up by adding 1 to the digit on the left. Thus, 4.56645 becomes 4.6 when rounded to two significant figures.

HOW TO DECIDE HOW MANY FIGURES TO KEEP AND HOW MANY TO IGNORE?

In carrying out a multiplication or division, the answer can't have more significant figures than either of the original numbers.Example: 1.25 (3 sig. fig.)m/10.20 (4 sig. fig.)s = 0.122 (3 sig. figures) In carrying out an addition or subtraction, the answer can't have more digits to the right of the decimal point than either of the original numbers.Example: 1.23 (ends two places past the decimal point) + 0.04136 (ends five places past the decimal point) = 1.27 (ends two places past the decimal point)

Discovery of the electron

J. J. Thomson (late 1800's) Discovered negatively charged electron Measured electron's charge-to-mass ratio Identified electron as a fundamental particle

How can the components of a mixture be separated?

Mixtures can be separated using differences in their physical properties.

If all the molecules of a body remained part of that body, would the body have any odor?

No, because there would be no molecules traveling to our nose.

How might you separate a mixture of sand and salt?

Two of the above answers are reasonable.

Controlled experiment

comparing two situations with all factors alike except one

Isotopes

refers to atoms of the same element that contain the same number of protons but different numbers of neutrons in the nucleus identified by mass number, which is the total number of protons and neutrons in the nucleus differ only in mass and not by electric charge; therefore, isotopes share many characteristics Total number of neutrons in isotope = mass number - atomic number

heterogeneous mixtures

the different components can be seen as individual substances.

Dependent Variable

the response to the change that is measured.

Atom

the smallest characteristic part of an element.

Dalton's Atomic Theory

1. All matter = indivisible atoms 2. An element is made up of identical atoms. 3. Different elements have atoms with different masses. 4. Chemical compounds are made of atoms in specific integer ratios. 5. Atoms are neither created nor destroyed in chemical reactions.

THE SCIENTIFIC METHOD

1. Observe some aspect of nature.2. Propose an explanation for something observed.3. Use the explanation to make predictions.4. Test the predictions with experiments or more observations.5. Modify the explanation as needed.6. Return to 3.

1 meter (m)

100 centimeters (cm)

1 kilometer (km)

1000 meters (m)

1 gram (g)

1000 milligrams (mg)

1 Liter (L)

1000 milliliter (mL)

If two protons and two neutrons are removed from the nucleus of an oxygen-16 atom, a nucleus of which element remains?

12 6 C

The nucleus of an electrically neutral iron atom contains 26 protons. How many electrons does this iron atom have?

26

If an atom has 43 electrons, 56 neutrons, and 43 protons, what is its approximate atomic mass?

99 amu

Mixtures can be separated into their components by taking advantage of differences in the chemical properties of the components. Why might this separation method be less convenient than taking advantage of differences in the physical properties of the components?

A chemical property involves a chemical change so that you no longer have what you had.

Mixture

A collection of two or more pure substances. Can be separated by physical means

Solution

A homogenous mixture consisting of ions or molecules

Pure substance

A material consisting of only one type of element or compound.

Concentration

A measure of the amount of solute dissolved in solution

What is the difference between a compound and a mixture?

A mixture can be physically separated into its components; a compound cannot be physically separated into its components.

Controlled Variable

A variable that is not changed

Distinguish between an atom and an element.

An element is made of only one type of atom.

elements

An element is made up of identical atoms.

Quantitative Observation

An observation that deals with a number or amount

Qualitative Observation

An observation that deals with characteristics that cannot be expressed in numbers.

Matter

Anything that has mass and takes up space

Why is it important to conserve fresh water?

As the human population grows, so does our need for fresh water. There is little fresh water available to us on our planet It is expensive to purify non potable water. ALL OF THE ABOVE

Ions

Atom gained or lost an electron Results in overall charge Gained electron = negative charge (Anion) Lost electron = positive charge (Cation)

Atomic weight

Atomic mass of an element, averaged over naturally occurring isotopes

Atoms

Atoms are not alike Each element has its own kind of atoms

What role does the atomic number play in the periodic table?

Atoms in the periodic table are ordered by increasing atomic number.

THE NATURE OF SCIENCE

Beginnings ~300 years ago Associated with Galileo and Newton Ancient natural philosophers - "thinking only" Additional component here - understanding based upon experimental evidence

density equation

D=m/v

Early model of the atom

Dalton - atoms indivisible Thomson's "Plum pudding" model Electrons embedded in blob of positively charged matter like "raisins in plum pudding"

Ancient Greeks

Democritus (460-362 BC) - indivisible particles called "atoms" Prevailing argument (Plato and Aristotle) - matter is continuously and infinitely divisible John Dalton (early 1800's) - reintroduced atomic theory to explain chemical reactions

Periodic table

Each element is represented by a "box" in the periodic table.

Saturated

Said of a solution in which no more solute will dissolve.

What holds atoms together?

The attractive forces between the unlike charges. The proton has a charge equal in magnitude but opposite in sign to that of an electron (1+). The electron has a charge of "1-". The electrons contribute so little to the atom's total mass. The electrons mass in an atom is usually disregarded.

What is the difference between a compound and a mixture?

The components of a mixture are not chemically bonded together.

Solvent

The major component of a solution

Solute

The minor components of a solution

What is the purpose of adding aluminum salts and a base to water during water treatment?

The two together gel and trap dirt and bacteria.

How does distillation separate the components of a mixture?

The volatile components in a mixture boil off first and are then condensed.

Why can't the elements of a compound be separated from one another by physical means?

Their atoms are too tightly bound to one another.

What do chicken noodle soup and garden soil have in common?

They are both examples of heterogeneous mixtures.

Why isn't distillation used commercially to purify water?

Water requires large amounts of energy to boil affordably.

SIGNIFICANT FIGURES

Zeros in the middle of a number are like any other digit; they are always significant. Thus, 5.807 cm has four significant figures. Zeros at the beginning of a number are not significant. Thus, 0.00654 has three significant figures. Zeros at the end of a number and after the decimal point are always significant. Thus, 76.870 m has five significant figures.

Classify the following as a homogeneous mixture, heterogeneous mixture, element, or compound: table salt.

a compound

The following image represents which kind of matter?

a compound

solid

a definite shape and volume.

liquid

a definite volume, but has no definite shape

Molecule

a group of atoms bound together as a unit

Classify the following as a homogeneous mixture, heterogeneous mixture, element, or compound: planet Earth.

a heterogenous mixture

Classify the following as a homogeneous mixture, heterogeneous mixture, element, or compound: blood.

a homogenous mixture

Classify the following as a homogeneous mixture, heterogeneous mixture, element, or compound: steel.

a homogenous mixture

The following image represents which kind of matter?

a mixture

What is at the center of every atom?

a nucleus

Hypothesis

a tentative explanation for some observation

Neutrons

accompany protons in the nucleus have about the same mass as protons but no charge, so are electrically neutral

Which of the following is a mixture?

air

Which of these is a scientific hypothesis (that could be proved wrong)?

an atom is the smallest bit of matter in a material

Electrons

are identical repel electrons of neighboring atoms have electrical repulsion that prevents atomic closeness

Isotopes are identified by their _______.

atomic mass number

Which of the following is a pure substance?

baking soda

Which has the greater density, a lake full of water or a cupful of lake water?

both have the same density

Protons

carry a positive charge—same quantity of charge as electrons are about 1800 times as massive as an electron have the same number of protons in the nucleus as electrons surrounding the nucleus of an electrically neutral atom

Many dry cereals are fortified with iron, which is added to the cereal in the form of small iron particles. How might these particles be separated from the cereal?

collect the iron filings with a magnet

A combination of two or more substances in which they no longer retain their chemical properties is called a(n

compound

A combination of two or more substances in which they no longer retain their chemical properties is called a(n)

compound

Impure materials

contain two or more elements or compounds

1 milliliter (mL)

cubic centimeter ( cm3 )

Suspension

different components in different phases.

Experimental group

differs from control group by one influencing factor

If we double the mass of an object without a change in volume, its density would be

double

Which contributes more to an atom's size?

electrons

Success in science is mainly linked to emphasis on

experiments

Control group

fixed set for comparison

Elements

fundamental substances from which all material things are made represented by chemical symbols. The first letter of the symbol is always capitalized; the second is always lower case. Examples are: Cu, Zn, H and Mg.

When a scientist is dishonest and reports false information, he or she

gets no second chance in the scientific community

If the volume of an object doubles with no change in mass, its density would be

half

Which is the oldest element?

hydrogen

Atomic number

is the number of protons in each element listed in the periodic table

The mass of a high speed train is 4.5××105 kgkg, and it is traveling forward at a velocity of 8.3××101 m/sm/s. Given that momentum equals mass times velocity, determine the values of mm and nn when the momentum of the train (in kg⋅m/skg⋅m/s) is written in scientific notation.

m,n = 3.7,7

Determine the values of mm and nn when the following average magnetic field strength of the Earth is written in scientific notation: 0.0000451 T

m,n = 4.51, -5

Determine the values of mm and nn when the following mass of the Earth is written in scientific notation: 5,970,000,000,000,000,000,000,000 kg

m,n = 5.97, 24

Determine the values of mm and nn when the following charge of a proton is written in scientific notation: 0.000000000000000000160 C

m,n =1.60, -19

Given that average speed is distance traveled divided by time, determine the values of mm and nn when the time it takes a beam of light to get from the Sun to the Earth (in ss) is written in scientific notation. Note: the speed of light is approximately 3.0×10^8 m/s.

m,n =5.0, 2

Compounds

made of two or more elements chemically combined

homogenous mixtures

mixtures that look the same throughout.

gas

neither definite volume nor definite shape.

How many types of atoms can you expect to find in a pure sample of any element?

one

A scientific hypothesis can be disproved with

one reproducible experiment.

Which contributes more to an atom's mass: electrons or protons?

protons

Experiment

recreation of an event or occurrence to test a hypothesis

Physical Properties

those properties of a substance that can be observed without changing the substance Examples are: • Color• Mass• Weight

Chemical properties

those properties of a substance that can only be studied by forming new substances. melting freezing

Molecular models

three-dimensional representations of molecules.

What is the purpose of treating water with chlorine gas or ozone during water purification?

to kill bacteria

What is the purpose of allowing water to cascade or bubble in a fountain during the purification process?

to mix air into the water and improve flavor to remove unpleasant smelling chemicals like sulfur to remove radioactive gases ALL OF THE ABOVE

Atomic mass

total mass of the atom(s) [protons, neutrons, and electrons] listed in periodic table as atomic mass unit

When a chocolate bar is cut in half, its density of each half is

unchanged.

Independent Variable

variable that is manipulated