Gen Chem 1: Lesson 1- Atomic Mass

Uranium has an atomic number of 92 and an atomic mass of 235. How many neutrons does Uranium contain? (A) 92 (B) 110 (C) 143 (D) 235

(C) 143 235 neutrons and protons - 92 protons = 143 neutrons

Which is a neutral atom? (A) Na+ (B) Br- (C) Cl (D) H-

(C) Cl Neutral atom = Number protons Equal to Number of electrons with No Overall charge

Deuterium and Hydrogen are related in that they are: (A) Isomers (B) Isotropes (C) Isotonic compounds (D) Isotopes

(D) Isotopes Isotopes are similar in atomic number but different in terms of their atomic mass due to differing numbers of neutrons.

A Fission reaction occurs when Uranium 235 absorbs a low energy neutron, briefly forming an excited state of U 236, which then Splits into Xenon 140, Stronium 94, and more neutrons. 235^U92 +1^n0 -> 236^U*92 -> 140^Xe54 + 94^Sr38 +1^n0 When balanced, how many neutrons are produced in the last reaction?

236 - (140+94) = 236 -234 =2 nucleons Because protons are balanced these 2 nucleons must be Neutrons

If you start with 4 mg of phosphorus 32, how much is left after 57.2 days? T1/2 = 14.3 days

57.2 days / 14.3 days Half life = 4 4 mg -> 2 -> 1 -> .5 -> .25mg or 4mg (1/2)(1/2)(1/2)(1/2) = .25 mg or 4 mg (1/2)^4 = 4(1/16) =.25 mg

What are applications of Energy Mass Equivalance?

A relationship between energy and mass exist, where Mass is just another form of energy E = mass x Speed of light^2 a) Gamma radiation b) lab conditions c) Sun is continuously producing electromagnetic radiation which is slowly decreasing the mass of the sun d) Mass defect

If nuclear charge and nucleons are conserved what type of decay is this? A) Alpha B) Beta C) Gamma

A) Alpha decay

What type of nuclear decay releases an alpha particle? ex: 238^U 92 -> 4^He 2 +234^Th 90

Alpha decay is the emission of an alpha particle which is a 4^He 2 Nucleus (2 Protons, 2 Neutrons, 0 electrons) - emission of an a-particle means that the atomic number of the daughter nucleus will be 2 less than that of the parent nucleus and the mass number will be 4 less. *Forms a New Element* A^X z -> A-4 ^ Y z-2 + 4^ a 2

How much is one atom of carbon 12?

Atomic mass is the average of* All the isotopes of an element* 1 atom of Carbon 12 = 12 amu 1 amu = 6.02 x 10^23 aka Avogadro's number -Atomic weight of carbon is 12.0 amu which means that the average carbon atom has a mass of 12.0 amu and 6.02 x 12^23 carbon atoms have a combined mass of 12.0 grams.

Element Q consists of 3 different isotopes A,B,C. Isotope A has an Atomic mass of 40 amu and accounts for 60% of naturally occuring Q. Isotope B has an atomic mass of 44 amu and accounts for 25% of Q. Finally isotope C has an atomic mass of 41 amu and accounts for 15% of Q. What is the atomic weight of element Q?

Atomic weight is the weighted average of the *naturally occurring isotopes* of that element .60(40amu) + .25(44amu) +.15(41amu) = 24.00 amu + 11.00 amu + 6.15 amu Atomic weight = 41.15 amu

which is not one of the 4 fundamental forces of nature? A) Gravitation B) Van Der Waals forces C) Weak nuclear force D) Electrostatic foces

B) Van der Waals forces is Not a fundamental force of nature 1. Strong Nuclear force 2. Weak Nuclear force 3. Electrostatic force 4. Gravitation

What type of nuclear decay ejects a electron from the nucleus? ex: 166 ^Pm 61 -> 146 ^Y 62 + 0^ B- -1

Beta decay ejects an electron aka Beta particle (e- or B-) from the nucleus (0^B- -1) *loss a neutron but gain a proton* (neutron -> proton) *Forms a new Element*

How much energy is needed to separate the subatomic particles that constitute a helium atom? Assume that the rest mass of the proton and electron is 1.00783 amu. The neutron is 1.00867 amu and that of Helium is 4.00260 amu?

Binding energy = energy needed to separate atom into subparticles Rest mass energy of the Helium + Binding energy = Rest mass energy of the Particles (Neutrons, Electrons, Protons) Helium = 2 protons, 2 neutrons, 2 electons 4.00260 amu - (2(1.00783) + 2(1.00783) + 2(1.00867) Binding energy = .0304 amu

What is the difference between isotopes of hydrogen?

Both have 1 proton in nucleus and 1 electron outside -Differ in Atomic Mass Protium- No neutron (mass # =1) Deuterium - Has neutron (Mass # =2) Tritium - has 2 neutrons ( Mass =3)

The actual mass of Helium is .03 amu less than its predicted mass (the mass expected based on the individual masses of its protons, neutrons and electrons). In the case of Helium, .03 amu is considered the A) Binding Energy B) Atomic Mass C) Atomic Mass difference D) Mass Defect

D) Mass defect Mass defect is the difference between the Calculated and True Mass - can be used to determine the Nuclear binding energy needed to break apart atoms

What type of nuclear decay capatures an electron and combines it with a proton to form a neutron? ex: 40^K19 + 0^e -1 -> 40 ^Ar 18 + 0^y0

Electron capture - takes an electron and combines with a proton to form a neutron and Gamma (y) radiation

When a large nucleus is split in half during an experiment at a nuclear physics lab, the result is usually two medium-sized nuclei. This is reaction is called A) Decay B) Fission C) Fusion D) Combustion

Fission = spliting of large nucleus into smaller nuclei

When small nuclei join together to form a Larger Nucleus this is called A) Fission B) Fussion C) Alpha decay D) Gamme Decay

Fusion = combination of small nuclei to from a larger nucleus

The sun's use of 4 hydrogen nuclei to make 1 helium nuclei is an example of what reaction A) Fission B) Conduction C) Fusion D) Alpha Decay

Fusion is the combination of smaller nuclei (4 hydrogens) to form a larger nucleus (1 Helium)

What type of nuclear decay releases energy but not a particle? ex: 99m^Tc 43 -> 0^y 0 + 99^Tc 43

Gamma decay releases energy -Gamma rays have No charge or Mass Excited state Nucleus emit gamma ray to return back to ground state *Same element*

The larger the number of protons in a nucleus the Less stable

Greater than 83 protons = Unstable nucleus -> High rate of radioactive decay

The half life of Carbon 11 is 20 minutes. If we begin with 100 grams of Carbon 11, how much do we have left over after 60 minutes?

Half life = time required for a certain amount of pure substance to fall to Half its amount 100 --(20 mins aka 1 half life) -> 50 g --(20 min aka 2nd half life)-> 25g --(20 min aka 3rd half life) -> 12.5 g 60 min = 3 half live = 12.5 g left over

Correctly match the following terms with their abbreviation: I. Mass number II. Atomic number III. Number of neutrons (A) A (B) M (C) N (D) Z

I. (A) II. (D) III. (C) Mass number- A Atomic number- Z Number of neutrons- N

Measurements of the atomic mass of a neutron and a proton yield these results Proton = 1.00728 amu Neutron = 1.00867 amu Helium contains 2 protons and 2 neutron, which should theoretically give a helium nucleus a mass of (2 x 1.00728) + (2 x 1.00867) = 4.03190 amu. However the True mass of the Helium nucleus is 4.00260 amu. What is the mass defect and binding energy of this nucleus? Note: C^2 = 932 (MeV/amu)

Mass defect = the difference between the Sum of the masses of Unbound nucleons forming a nucleus and the mass of the nucleus in the bound state Binding energy = radiation of energy via heat, light, or electromagnetic radiation due to the bonded system at a lower energy than the unbounded Mass Defect = Calculated - TRUE = 4.03190 - 4.00260 Mass = .02930 amu Energy = Mass x Speed of Light^2 E =mc^2 = (.02930 amu) x 932(MeV/amu) Energy = 27 MeV

How does the mass defect relate to the binding energy?

Mass defect is related to the binding energy such that there is a transformation of nuclear matter to energy with a resultant loss of matter. Nuclear Binding Energy = mass defect x speed of light ^2 E=mc^2

Why do you need to input energy to break apart atoms containing like charges?

Nuclear strong force enables liked charges to be bound together repelling electrostatic forces. Therefore Binding energy must be added to overcome Nuclear strong force to break nucleons. *Energy can become mass and mass can be energy* represented by E=mc^2

What type of nuclear decay is this. 7^Be 4 -> 7^Li 3 + 0^e 1

Positron Emission (0^e +1) - release of a positron without changing Atomic mass *Proton becomes a Neutron

The atomic number of Uranium is 92.the Mas number is 235. How many protons, neutrons, and electons in this atom of Uranium?

Protons = 92 Mass number = 235 A =Z +N 235 - 92 = 143 neutrons Neutral charge : Protons = Electrons Electrons = 92

Why does Half life vary inversely with the decay constant

Radioactivity increases (decay constant increases) and the amount of time it should take the atoms to decay should decrease t1/2 = ln(2) / decay constant

When is Strong nuclear force ideal

Strong Nuclear force is when protons and neutrons aka Nucleons come together to form the Nucleus - strong enough to combat repulsive electromagnetic force - Only short distances -Stronger than Weak nuclear force, Electrostatic forces, and gravity

A given unstable isotope has a decay constant of .1^-1. Find the half life of this isotope. If we begin with a 100 gram sample, find how much is leftover after 25 years?

t 1/2 = ln(2) / .1 y^-1 = 6.93 years N = (NInitial)e^(decay constant x time) N = (100 g) e^(-.1)(25yrs) N = 8.21 grams