Unit 3 - Atomic

Who discovered the atom and what did they find?

Dalton - atoms are indivisible (empty) spheres

Who discovered the electron and what did they find?

Thompson - an atom is a positive sphere with negatively charged particles (“plum pudding” )

What is a cathode ray tube?

current passes through oppositely charged metal plates → beam was bent toward the positive plate

Who discovered the nucleus and what did they find?

Rutherford - nucleus of the atom is small, dense, and positively charged

What was the gold foil experiment?

alpha particles were shot at a thin sheet of gold foil → most went through (empty space), some bounced back, some deflected due to repulsion (++)

Who discovered the neutron?

Chadwick

What is the order of discoveries?

Dalton (atom) → Thompson (e-) → Rutherford (nucleus)→ Chadwick (neutron)

What does the atomic number represent?

the number of protons

What is atomic mass?

the weighted average of all the naturally occurring isotopes of an element

What is an isotope?

atoms of an element that have the same number of protons but different number of neutrons (therefore different mass)

Do isotopes of an element have the same chemical behaviors?

yes, they react the same way

What is mass spectrometry used for?

to identify the isotopes of an element and its relative abundances

How does a mass spectrometer work (processes)?

(1) a sample of an element is placed

(2) atoms are bombarded with electrons in order to knock off an electron to create ions

(3) atoms are heated to gas phase

(4) ions are accelerated through a magnetic field

(5) atoms deflect based on mass and charge and are detected by a computer

Why is it necessary to have the mass spectrometer under a vacuum?

gas particles behave best under low pressure and it ensures that there are is nothing else other than the sample of atoms

What is the relationship between the mass of an atom and its deflection?

less mass = more deflection

more mass = less deflection

How does fragmentation occur during mass spectrometry?

since the electrons are colliding with the atoms at high energy, some atoms may break into smaller pieces

How is it possible to sometimes have more lines on a spectrometer graph?

when fragmentation occurs, some fragments may be detected by the computer, resulting in a line on the graph

Do second ionizations occur often; why?

no → more energy required = less often

What is the relationship between the charge of an atom (ion) and its deflection?

greater (+) charge = more deflection

Do electromagnetic waves (light) travel at the same speed?

yes, their speed is the constant c

What is the relationship between wavelength, frequency, and energy?

short wavelength = ↑ frequency , ↑ energy

long wavelength = ↓ frequency , ↓ energy

What is the order of electromagnetic radiation?

(high) gamma → X-ray → UV → visible → infrared → microwave → radio waves (low)

What was Planck’s explanation?

energy is emitted or absorbed in units called quanta

What is a quantum?

a distinct amount of energy (plural → quanta)

What is Planck’s constant?

h

How do electrons become excited?

when atoms are exposed to a specific amount of energy, they absorb it and move to a higher PEL (not all e- absorb the same amount of quanta)

What is the stability of an atom when an electron is excited?

excited atoms are very unstable and therefore return to ground state by releasing energy

How is an atomic spectrum produced?

when excited electrons release energy and return to the ground state

What are atomic spectrums significant?

they serve as the fingerprint of the element, helping identify elements

What was Bohr’s explanation for the movement of electrons?

he believed that electrons orbit the nucleus in circular paths (FALSE!)

Why did Bohr’s explanation not work for other elements?

there are sublevels within each PEL, making it hard to exactly locate an electron with elements with more than one electron

What are the paschen series?

when an electron moves from a high PEL to PEL #3 (emits infrared light)

What are the balmer series?

when an electron moves from a higher PEL move PEL #2 (emits visible light)

What are the lyman series?

when an electron moves from a higher PEL to ground state (emits UV light)

What is the atom economy equation?

AE = mass of desired products / mass of reactants

What is ionization energy?

the amount of energy required to remove an electron

What is first ionization energy?

the amount of energy required to remove the outermost, loosely bound electron

What is the relationship between energy and frequency?

they are directly proportional

(high frequency = high energy)

How is ionization energy measured?

in the gas phase using electron spectroscopy

How does photoelectron spectroscopy work (process)?

high energy photos (UV or X-ray) are applied to a sample in order to remove electrons

What do the peaks on a PES graph represent?

• each peak represents electrons in a sublevel

• peak w/ low binding energy = valence e-

• peak w/ high binding energy = core electrons

How do the binding energies of valence and core electrons compare?

valence electrons require less energy than core electrons to be removed

When talking about electrons, why is Coulomb’s law significant?

as the distance between charges decrease, the force of attraction decreases

(distance between nucleus and electron)

What is the shielding effect?

electrons that are furthest away from the nucleus are “shielded” by inner core electrons 

(therefore, they are less attracted to the nucleus + easier to remove)

What are orbitals?

a space where an electron is likely to be found

(IT’S A REGION; NOT OBJECT)

How many electrons does each orbital hold?

2 e-

Describe the s orbital

• sphere shape

• comes in a group of 1

Describe the p orbital

• dumbbell shape

• comes in a group of 3

Describe the d orbital

• varies in shape

• comes in a group of 5

Describe the f orbital

• varies in shape

• comes in a group of 7

What are the other three orbitals?

g, h, i

What is the equation that relates KE(photon), IE, and KE(electron)?

KE(photon) = IE + KE(electron)

What will happen if an electron is given the exact amount of IE?

it will be ejected, but will not have KE

What will happen if an electron is given more than the amount of IE required?

it will be ejected and will have KE

What are the four types of quantum numbers?

(1) principal

(2) angular

(3) magnetic

(4) electron spin

Describe the principal quantum number

• symbol: n

• represents PEL #

• values: 1 → 7

Describe the angular quantum number

• symbol: l

• represents the orbital (s, p, d, f)

• values: 0 → n-1

Describe the magnetic quantum number

• symbol: m_l

• represents the orientation of the sublevel

• values: -l → l

Describe the electron spin quantum number

• symbol: m_s

• represents the direction of electron spin

• values: + ½ or - ½