Chem Unit 2

Whose was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos

Democritus

What did Democritus believe?

1. Matter is composed of empty space through which atoms move

2. Atoms are sold, homogeneous indestructible, and indivisible

3. Different kinds of atoms have different sizes and shapes

4. The differing proportions of matter are due to the size, shape, and movement of atoms

5. Apparent changes in matter result from changes in groupings of atoms and not from changes in the atoms themselves

Who disagreed with Democritus?

Aristotle, because he didn't believe empty space could exist

What did many ancient scholars believe matter was composed of?

earth, water, air, and fire

Did ancient scholars believe matter could be endlessly divided?

Yes

Who revived the idea of the atom?

John Dalton in the early 1800s

What did John Dalton believe?

1. All matter is composed of extremely small particles called atoms

2. All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of a specific element are different from those of any other element.

3. Atoms cannot be created, divided into smaller particles, or destroyed

4. Different atoms combine in simple whole - number ratios to form compounds

5. In a chemical reaction, atoms are separated, combined, or rearranged

What do we now know, that prove some of the elements of Dalton's Theory false?

1. atoms can be split

2. elements can have atoms with different masses, isotopes

What instrument allows individual atoms to be seen?

The scanning tunneling microscope (STM)

What did J. J. Thomson do?

He discovered the first subatomic particle, the electron

Which experiment did J. J. Thomson perform

The cathode ray tube experiment

What are cathode rays?

A stream of particles carrying a negative charge (electrons)

Who determined the charge and mass of the electron?

Robert Millikan, using the oil drop experiment

What is the charge of an electron?

-1 (or 1.6x10^-19 coulombs)

What is the mass of a single electron?

9.10x10^-28 g

1 / 1840 the mass of a hydrogen atom

What information was known that led scientists to believe there was some sort of positive charge in an atom

Matter is neutral

What was J. J. Thomson's model of the atom?

Plum pudding model --\> the atom is a uniform positively charged sphere containing electrons

Which experiment did Ernest Rutherford do?

The gold foil experiment --\> he shot alpha particles at gold foil

What did Rutherford to expect to happen when he shot the alpha particles at gold foil?

He expected the paths of the alpha particles to be only slightly altered by a collision with an electron

( he expected this because if the plum pudding model was correct, the alpha particles would collide with the electrons and their course would be slightly altered )

What did Rutherford find instead?

Most of the alpha particles went through the gold foil, a few of them were deflected slightly, and a few bounced back, some at large angles

Why did this happen?

The alpha particles that went through didn't collide with the electrons or the nucleus

The ones that were slightly deflected were affected by the repulsive force between the nucleus and alpha particles (both positively charged)

The ones that bounced back at large angles hit the nucleus

What did Rutherford conclude?

1. that atoms are mostly empty space

2. Almost all of the atom's positive charge and almost all of its mass is contained in a dense region in the center of the atom called the nucleus

3. Electrons are held within the atom by their attraction to the positively charged nucleus

Who discovered the existence of neutrons?

James Chadwick

Who used x-ray spectroscopy to determine the atomic number of an element

Henry Moseley

Who created the planetary model of the atom?

Niels Bohr

What are the three fundamental subatomic particles in an atom?

proton (+), neutron (0), electron (-)

What are atomic mass units (amu) defined as?

1/12th the mass of a carbon - 12 atom

How heavy is a proton?

1 amu

How heavy is a neutron?

1 amu

How heavy is an electron (in amu)

0 amu

What are isotopes?

Atoms of the same element that have different masses

Where is most of the mass located in the atom?

nucleus

What is the atomic number of an atom?

the number of protons in an atom

What is the number of protons + number of neutrons

atomic mass

What are protons and neutrons composed of?

quarks

What is the ratio of electrons to protons in a neutral isotope?

There are the same amount of electrons as protons

Do Isotopes have the same chemical behavior?

Yes

How do you write in hyphen notation?

element - mass \#

Ex. Hydrogen - 2

How do you write in nuclear notation?

How do you calculate the average atomic mass of an element?

relative abundance of isotope 1 x mass of isotope 1 + relative abundance of isotope 2 x mass of isotope 2

How do you calculate the percent abundance of an isotope?

(M1)(x) + (M2)(1-x) \= M(avg)

M1 \= the mass of 1st isotope

x \= relative abundance

M2 \= the mass of the 2nd isotope

M(avg) \= the atomic mass of the element from the periodic table

What is a nuclear reaction?

A reaction that affects the nucleus of the atom

What is radioactive decay?

Spontaneous disintegration of a nucleus into a lighter and more stable nucleus accompanied by emission of particles, electromagnetic radiation, or both

What is nuclear radiation?

Particles of electromagnetic radiation emitted from the nucleus during radioactive decay

What is nuclear stability?

Some nuclei are unstable (radioactive) while other are stable (nonradioactive)

For most elements from hydrogen to lawrencium what is the ratio of mass number to atomic number

2 : 1 --\> mass \= twice the number of protons

Which elements are unstable, and under some type of radioactive decay?

Elements past Bismuth

Which element is the most stable?

iron

What is the symbol for alpha particles

What are alpha particles?

2 protons and 2 neutrons. Has the same mass as helium

What is the nuclear equation of Uranium - 238 going through alpha decay

238 / 92 U --\> 4 / 2 He + 234 / 90 Th

What is the symbol for a beta particle?

What is a beta particle?

A fast moving electron

What is a positron?

positively charged electron

What is the nuclear equation of Carbon - 14 going through beta decay?

14 / 6 C --\> 14 / 7 N + 0 / -1 B

What is the symbol of gamma rays?

What are gamma rays?

high energy electromagnetic waves emitted from a nucleus as it changes from an excited state to a ground state

What are the properties of gamma rays?

Short wavelength, high energy, high frequency radiation. they are neutral so are not deflected by electric fields, but do have the greatest penetrating ability

Who discovered nuclear radiation?

Henry Becquerel

What is the charge of alpha particles?

+2

What is the charge of beta particles?

-1 charge

What is the charge of gamma rays?

0

What is the penetrating ability of alpha particles?

Low, stopped by paper

What is the penetrating ability of beta particles?

Medium, stopped by heavy clothing

What is the penetrating ability of gamma rays?

High, stoped by lead

Can alpha and beta particles be deflected by electric fields?

Can gamma rays?

alpha and beta particles are charged, so they can be deflected, gamma rays are neutral and can't be deflected

What is half - life?

the time required for half the atoms of a radioactive nuclide to decay

What is the equation for calculating half-life?

mf \= mi / 2^n

mf \= final mass

mi \= initial mass

n \= number of half-lives

How does carbon dating work?

Carbon - 14 is used for radiocarbon dating. As plants use CO2 during photosynthesis they constantly store the naturally occurring amount of carbon - 14 in their tissues. As they age, the carbon - 14 decays into carbon - 12. Measuring the amounts of carbon - 14 and carbon - 12 enables people to determine the age of fossils, relics, etc.

What is nuclear fission?

The process where a heavy nucleus splits into more stable, lighter nuclei

What is a chain reaction?

A reaction in which the starting material that starts the reaction is also one of the products and can start another reaction

What are the uses of nuclear fission?

Nuclear power plants use heat from fission to produce electrical energy

What are the disadvantages of nuclear fission?

Disposal of radioactive nuclear waste is an environmental problem

What is nuclear fusion?

The process where light-mass nuclei combine to form a heavier, more stable nucleus

What are the uses of nuclear fusion?

hydrogen bomb. Also, potential long-term energy source for electrical generation but currently fusion reactions cannot be constructed because no known materials can withstand the temperatures of up to 10^8 K

What are the advantages of nuclear fusion?

Doesn't create radioactive nuclear waste