Atomic Structure

Question 1

What are isotopes?

Answer 1

isotopes are atoms of the same element that contain a different number of neutrons but the same number of protons with their nuclei.

Question 2

True of false? Isotopes react differently chemically.

Answer 2

False. Isotopes react the same way chemically and thus can be distinguished only by mass separation techniques ( such as mass spectroscopy).

Question 3

How does one monitor isotopes throughout the body?

Answer 3

Isotopes can be monitored either by the radioactive decay they emit or by nuclear magnetic resonance imaging (NMR spectroscopy).

Question 4

How does one obtain the average atomic mass?

Answer 4

The average atomic mass of an element is a weighted average of the masses of all isotopes for that element.

Question 5

Describe the Thompson experiment. What was the conclusion.

Answer 5

A beam of e- was generated traveling left to right. An electric field was applied ( + and - plate on opp. sides) perpendicular to the e- beam. The magnitude of deflection depends on the strength of the field ( charge on plates) and the mass of the e-. It was found that there are two types of charges ( + and -). Because the deflection arc was constant in magnitude as the plates switched, it was concluded e- have a fixed charge to mass ratio.

Question 6

True or false. Gamma rays bend in electric fields.

Answer 6

A gamma ray is a photon. Photons do not bend in electric fields.

Question 7

Describe how a mass spectrometer works.

Answer 7

An element/molecule is ionized; the particles pass through a double filter to ensure a uniform perpendicular beam of particles enters the magnetic field; the particle enters the B-field and gets deflected counterclockwise by the perpendicular B-force. The radius is obtained from the strike point against ta collision detector. By comparing the curvature for an ion to a standard, the mass of the unknown ion can be determined.

Question 8

As momentum (increases/decreases), the particle deflects less, so the radius curvature obtained from mass spec (increases/decreases).

Answer 8

As momentum increases ( either the mass of initial velocity), the particle deflects less, so the radius of the curvature to decrease.

Question 9

Name other applications of mass spec aside from ascertaining the charge to mass ratio.

Answer 9

Mass spec can also be used to determine isotopic abundance. In organic chemistry, mass spec is used to determine the molecular mass and fragmentation behavior to help elucidate the structure of an unknown compound.

Question 10

Describe the Millikan Oil Drop experiment.

Answer 10

An oil gains a charge by losing or engulfing an e- as it travels. The droplets fall through a hole in an upper capacitor plate into a region where a uniform electric field exists. Each oil droplet is impacted by gravity. If the particle is suspended, then then net force is zero and mg = -qE. We know g, electric field strength E, and the average mass of the oil drop. We can solve for q, the charge of the electron.

Question 11

Describe the Rutherford Experiment.

Answer 11

A thin strip of gold foil is struck with an incoming beam stream of alpha particles ( 2P + 2N). The particles that pass through and hit the zinc sulfide strip on the back result in luminescence. Shadowy spots suggest particles ricocheting off gold. This exp showed that atoms have a dense nuclei with nearly all of the atomic mass centrally concentrated.

Question 12

What does Heisenberg’s Uncertainly principal state?

Answer 12

The uncertainly principal quantifies the idea that it is not possible simultaneously to identify a particle’s position ( where something is) and velocity ( how fast + where’s it going).

Question 13

Describe the Bohr atomic model.

Answer 13

e- cannot move at all distances from the nucleus of the atom. Bohr claimed that the e- are restricted to moving in fixed orbits at fixed distances from the nucleus. Each of these orbits represents a certain quantity of energy; the further away from the nucleus the orbit is, the higher its energy level. When e- stay in these fixed orbits, the atom emits no radiation. But an e- can leap from its current orbit to an orbit with less energy, thereby releasing surplus energy in the form of radiation – a so-called light quantum.

Question 14

(More/Less) energy is required to carry out transitions when the e- is nearest to the nucleus.

Answer 14

More.

Question 15

Energy is (absorbed/released) when an e- is excited to another level.

Answer 15

Absorbed. This is referred to as excitation and absorption of energy.

Question 16

The energy required to excite an e- from a lower level (orbital) to a high level is often in UV to visible range of EM. So, the energy given off as the e- drops back down to the lower level is emitted as _____.

Answer 16

Light energy.

Question 17

The smaller the gap between energy levels, the (more/less) energy given off, and therefore the (shorter/longer) wavelength of light that is emitted.

Answer 17

Less energy is given off between smaller gaps. The wavelength of the light emitted would be longer.

Question 18

The energy of a photon and its wavelength of light are inversely related. Give the equation for this.

Answer 18

E = hv = hc/lambda; E = energy of photon; v = frequency; c is speed of the wave; lambda is wavelength

Question 19

The first shell of an e- is called the ____, and the outermost shell is called the _______.

Answer 19

Core shell and valence shell.

Question 20

Define Zeff.

Answer 20

The net charge exerted upon the valence e- is referred to as the effective nuclear charge . Z eff = nucleus charge plus core electron charge. Ex. Li = +3 nucleus and -2 e- . Zeff = +1

Question 21

The effective nuclear charge (increases/decreases) as the periodic table is traversed from left to right.

Answer 21

Increases. An additional proton has a greater effect on the effective nuclear charge than an additional valence e-.

Question 22

Relate spin pairing and magnetism.

Answer 22

A paramagnetic species ( aka radicals) is defined as an atom/ molecule with at least one unpaired e-. Because the e- is unpaired, the orbital is susceptible to b-fields. A diamagnetic species is defined as an atom/molecule with no unpaired e-. These are NOT susceptible to b-fields, as application of a b-field would cause the e- with diff spins to align with or against the field.

Question 23

If probability of finding an e- was plotted against d from nucleus, what would the graph look like?

Answer 23

The e- density map shows that e- are found most often near the nucleus.

Question 24

95% of the time, an e- can be found within the boundaries of a ___________.

Answer 24

Orbital.

Question 25

How many nodes does a p-orbital have?

Answer 25

A p-orbital has one node at the nucleus that is part of a nodal plane between the two nodes.

Question 26

When discussing orbitals, what does a node mean?

Answer 26

Absence of e- density at any point is referred to as a node.

Question 27

Name all the d orbitals and describe what they look like.

Answer 27

dxz, dxy, dyz, dx^2-dy^2, dz^2; they look like double barbells.

Question 28

Explain Pauli’s exclusion principle.

Answer 28

No two e- can have the same set of quantum numbers (n, l, ml, ms).

Question 29

Explain Hund’s rule.

Answer 29

e- completely fill lower energy levels before starting to fill higher energy levels. In a degenerate set of orbitals, e- singly occupy each orbital before a second e- pairs up with the same orbital.

Question 30

When dealing with transition metals, ionizing e- are not removed from the atom in reverse order. How are they removed?

Answer 30

the s-electrons are lost before the d- electrons. Outer shell e- are always removed first when forming cations.

Question 31

Which two columns on the periodic table are diamagnetic?

Answer 31

The alkaline earth metals and the nobel gases. COlum 2 and 8.

Question 32

What is the d-shell exception when writing out electronic configurations?

Answer 32

Half filled d-shell and filled d-shell stability results when a single e- is elevated from a lower energy level that is paired (usually the s-orbital) to yield even distribution of e- in the d-level.

Question 33

True or false. Elements in the same column of the periodic table have similar valence shells and electronic configurations, with the notable difference being the shell number.

Answer 33

True. Na is [Ne]3s^1 and K is [Ar]4s^1. These are s^1 metals and they have similar chemical behavior, given their common tendency to lose one e-.

Question 34

Describe an excited state electronic configuration.

Answer 34

When any e- absorbs E and moves to a higher energy level than it normally occupies in the ground state.

Question 35

There are four quantum numbers. Describe what they are.

Answer 35

n = the shell - the avg radius of the e- from the nucleus and E level; l = angular momentum - describes the oribital/shape of the e- cloud ( + value or 0); ml = magnetic - orientation of the orbital about a plane or axis ( -, + or 0); ms = spin - rotation of e- about its axis ( 1/2 or -1/2)

Question 36

How does one find “l” in quantum numbers?

Answer 36

Simple. l values increase from 0, 1, 2, 3, and so on. s = 0; p = 1; etc.

Question 37

True or false. The energy of the photon absorbed is equal to the energy of the photon emitted.

Answer 37

Somewhat true. In actuality, there is more than one singular energy level for the ground state and the excited state due to the coupling of electrical E levels and rotational E levels associated with the atom.

Question 38

Describe the VESPR theory.

Answer 38

Because negative charges repel one another, the molecular shape may distort slightly to minimize the repulsion due to e- in the valence shell. This is the Valence Shell electron pair repulsion (VESPR).

Question 39

True/False: an atom is mostly empty space.

Answer 39

True. The nucleus occupies only the tiniest fraction of an atom’s volume, which is mostly empty space.

Question 40

Describe what an ion is:

Answer 40

When a neutral atom gains or loses e-. it becomes charged and the resulting atom is called an ion.

Question 41

What force are protons and neutrons held together by?

Answer 41

The protons and neutrons in a nucleus are held together by a force called the “strong nuclear force”

Question 42

Unstable nuclei are said to be ____ and undergo a transformation to make them more stable.

Answer 42

They are said to be radioactive and alter the ratio of protons and neutrons or just by lowering their energy.

Question 43

Describe what occurs in alpha decay.

Answer 43

When a large nucleus wants to become more stable by reducing the number of protons and neutrons, it emits an alpha particle. This is equivalent to an He atom.

Question 44

Describe the energy of an emitted alpha particle.

Answer 44

Although alpha particles are emitted with high E from the parent nucleus, this energy is quickly lost as the particles travel through matter or air. These particles don’t travel far and can be stopped by outer layers of skin.

Question 45

Describe what occurs in beta- decay. Remember this one happens to be the most common.

Answer 45

When an unstable nucleus contains too many neutrons, it converts a neutron into a proton and an electron (aka a b particle) is ejected. The mass number remains the same and the atomic # increases by one.

Question 46

Describe what happens in beta+ decay.

Answer 46

When an unstable nucleus contains too few neutrons, it converts a proton into a neutron and a positron is ejected.

Question 47

Describe what electron capture is.

Answer 47

Another way for an unstable nucleus to increase its number of neutrons (aside from beta+) is to capture an e- from the closest e- shell and use it in a conversion of a proton into a neutron. Just like positron emission, the atomic # is reduced by 1 while the mass # remains the same.

Question 48

Which one is more dangerous, alpha or beta particles?

Answer 48

Beta particles are more dangerous since they are LESS massive. They therefore have more ENERGY and GREATER PENETRATING ability.

Question 49

Describe what gamma decay is.

Answer 49

A nucleus in an excited energy state, which is usually the case after it has undergone decay, can relax to its ground state by emitting an energy in the form of one or more photos of electromagnetic radiation. These are called gamma photons. There is no effect in the identity of the nucleus.

Question 50

Out of alpha, beta, and gamma decay, which is most dangerous?

Answer 50

Gamma photons or rays have neither mass or change and therefore can penetrate matter most effectively.

Question 51

Describe what half-life is and the equation associated with it.

Answer 51

The time it takes for half of some sample of the substance to decay.
N = No (1/2)^(T/t-half life)

Question 52

What is nuclear binding energy (Eb)? Which equations should we use to find it? *** Remember when nucleons bind together, some mass is converted to energy.

Answer 52

The E that was released when the individual nucleons (protons and neutrons) were bound together by the strong force. It’s also equal to the E required to break up the intact nucleus.
Δm = (total mass of separate nucleons) - (mass of nucleus)
Eb = (Δm)c^2

Question 53

What’s the equation for the energy of a photon?

Answer 53

E = hf = hc/λ; h = Planck’s constant - 6.63*10^-34;

Question 54

How do you find the energy of a particular energy level.

Answer 54

En = (-2.178 *10^-18J)/n^2; n = energy level

Use En with E = hc/λ to find the wavelength!

Question 55

Describe the quantum model.

Answer 55

The quantum model was developed to predict atomic spectra better. It is characterized by a unique address for each electron, consisting of four quantum numbers designating the shell, subshell, orbital, and spin.

Question 56

Describe the energy shell of the quantum model.

Answer 56

The energy shell (n) is analogous to the circular orbits in the Bohr model. An e- in a higher shell has a greater amount of E and a greater average distance from the nucleus.

Question 57

Describe the energy subshell level of the quantum model.

Answer 57

A subshell in an atom is composed of one or more orbitals, and is denoted by a letter (s,p,d, or f)

Question 58

Describe the orbital orientation of the quantum model.

Answer 58

Each subshell contains one or more orbitals of the same energy, aka degnerate orbitals. The s subshell contains one orientation and the p sublevel contains three (x, y, z). The d contains 5. F contains 7.

Question 59

Describe the electron spin of the quantum model.

Answer 59

Every e- has two possible spin state. Every orbital can accomodate a max of two e-, one spin up and one spin down.

Question 60

There are three major rules when it comes to representing an electron configuration in the quantum model. Describe what they are.

Answer 60

Electrons occupy the lowest E orbitals available (Aufbau). Electrons in the same subshell occupy available orbitals singly (Hunds Rule). There can be no more than two electrons in any given orbital (Pauli Exclusion)

Question 61

Describe diamagnetic atoms.

Answer 61

An atom that has all of its e- spin-paired is referred to as diamagnetic. They must contain an even # of e- and have all its occupied subshells filled. Since all e- are spin-paired, the magnetic fields they create cancel, so there’s no net B field. Such an atom will be repelled by an externally produced B field.

Question 62

If an atom’s electrons are not all spin-paired, it is said to be ______.

Answer 62

Paramagnetic atoms, which are attracted into externally produced magnetic fields.

Question 63

Writing out the e- configuration, tell us how the table of elements gives clues.

Answer 63

The period (row) gives us the shell (n), as long as we remember the d block rule: e- for an atom in the d block of period n go into the subshell (n-1)d. So subtract one from the period #. For the f block, subtract 2.

Question 64

There is one exception to e- configurations having to do with the d-subshell. Describe it.

Answer 64

Atomas can achieve a lower E state (higher degree of stability) by having a filled or half-filled, d subshell. This can be accomplished by promoting one of its 4s electrons to the d subshell. Or, a more stable E state can be obtained by promoting one of its s e- into the 3d subshell (half filled).

Question 65

How do we write the e- configurations of ions?

Answer 65

For atoms that gain e - (anions), we move to the right. For atoms that lose e- (cations), we move to the left. F- and Ne have the same electronic configuration. They are said to be isoelectronic.

Question 66

When an atom loses an e- it comes from which orbitals first?

Answer 66

E- that are removed from an atom always come from the value shell (the highest n level). So if an atom has a d shell, it would come from s first. Watch out for transition metals when naming their e- configuration. E- are taken from S FIRST.

Question 67

Describe families and their names.

Answer 67

Group 1 = akali; ns1
Group 2 = akaline earth; ns2
Group 7 = halogens; ns2np5
Group 8 = noble gases; ns2np6
d block = transition metals
f block = rare earth metals

Question 68

Elements that possess qualities of both metals and non-metals are called____.

Answer 68

Metalloids. B; Si; Ge; As; Sb; Te; Po