Chapter 24: Atomic & Molecular Structure Flashcards Preview

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Flashcards in Chapter 24: Atomic & Molecular Structure Deck (56):

Define Atom:

An atom is the basic building block of matter which represents the smaller unit of a chemical element


What is an atom composed of?

An atom is composed of protons, neutrons, and electrons


Describe the core vs. orbital of the atom

The core (nucleus) consists of protons and neutrons while the orbital consists of electrons


What are the 3 aspects of Dalton's Atomic Theory?

1. Elements are composed of small atoms which are identical in size, mass, and chemical properties

2. Compounds are composed of atoms of more than 1 element

3. Chemical reactions only involve separation, combination, or rearrangement of atoms; does not create/destroy atoms


What charge does a proton carry?

Protons have a positive charge


What does the number of protons equal?

The Atomic Number (Z)


What is the mass of a proton?

~ 1 unified atomic mass unit (AMU)


What charge does a neutron carry?

No charge


What is the mass of a neutron?

Slighter larger than a proton
- ~ 1 ASU


Describe an isotope

Isotopes of an element have the same number of protons but different number of neutrons


What charge does an electron carry?

A charge equal in magnitude but opposite in sign to a proton


What mass does an electron have?

1/1837 the mass of proton
- Very small


What is a valence electron?

The electron in the farthest orbital from the nucleus


How does distance determine valence electron strength?

Further = Weaker Force

Closer = Stronger Force


What does the atomic number indicate?

Number of electrons in a neutral atom


Describe a (+) vs. (-) charge

(+) = Loss of negatively charged electrons

(-) = Gain of negatively charged electrons


Determines the number of protons, neutrons, and electrons in a 58-Ni and a 60-Ni-2+ cation

- Atomic mass is 28 = 28 protons and electrons
- 58-28 = 30 neutrons

- Atomic mass = 28 protons
- 2+ means loss of 2 electrons; 28-2 = 26 electrons
- 58-26 = 32 neutrons


What does the atomic mass number equal?

Mass number (A) = Number of Protons + Number of Neutrons


What is the convention for both atomic and mass number?

A = Mass Number
Z = Atomic Number



What is molecular weight?

It is the weight in g/mole of an element


What is a mole?

A unit used to count particles
- Avogadro's Number = 6.02 x 10^32


What does Avogadro's Number represent?

How many atoms of carbon are in 12.0g of carbon-12


What does Avogadro's Number convert?

Converts amu and g


What is an isotope?

An element that has multiple species of atoms with the same number of protons but different number of neutrons


How do elements exist in nature?

Almost all elements exist as a collection of two or more isotopes, and they are usually present in the same proportions in any sample of a naturally occurring element


What is standard atomic weight?

Weighted average of all of the isotopes of an element`


Elements Q has isotopes A, B, and C - What is the atomic weight of element Q?
- Isotope A atomic mass is 40u accounting for 60%
- Isotope B atomic mass is 44u accounting for 44%
- Isotope C atomic mass is 41u accounting for 15%

(0.60)(40u) + (0.24)(44u) + ( 0.15)(41u) = 41.15u = 41.15 g/mol


What is Planck's Constant?

6.626 x 10^-34 J-s


What did Max Planck develop?

The first quantum theory - Proposing energy emitted as electromagnetic radiation from matter comes in discrete bundles called quanta


What is Bohrs Model?

E = - Ry/n^2


What did Bohr postulate? What does this allow?

1) That an electron can only exist in certain fixed energy states - the energy of an electron is quantized
2) It allows for generalizations of the characteristics of electrons
- Orbital radius: Smaller radius, lower energy states


At what level is the electron in its lowest state?

Ground state (n=1)


What is atomic emission spectra?

What is the formula to calculate the electromagnetic energy of these photons?

What is the formula according to Planck's quantum theory? What does this show?

Atoms that are excited to different energy levels eventually return to their ground state and emit a photon with a wavelength characteristic of the specific transmission is undergoes (line spectrum)

E = hc/lambda

E = hc/lambda = -Ry (1/ni ^2 - 1nf ^2) This shows the precise difference in energy between the higher-energy initial state and lower-energy final state


What is the Balmer series?

The group of H emission lines corresponding to transmissions from upper levels n > 2 to n = 2


What is the Lyman series?

The group corresponding to transitions between upper levels n > 1 to n = 1


What is atomic absorption spectra?

When an electron is excited to a higher energy level, it must absorb energy - the energy absorbed when an electron jumps from a low to a high energy orbital is characteristic of the transition which results in energy absorption at different wavelengths


What did Bohrs model not explain?

The structures of atoms containing more than one electron - does not take into consideration the repulsion between multiple electrons surrounding one nucleus


What is the modern explanation of electrons?

They are in a state of rapid motion within regions of space around the uncle called orbitals which represents the probability of finding an electron within a given region


What is the Heisenberg uncertainty principle?

States it is impossible to simultaneously determine, with perfect accuracy, the momentum and position of an electron


What are the quantum numbers?

1) n - size

2) l - shape

3) ml - orientation

4) ms - spin


What is the Pauli exclusion principle?

No two electrons in a given atom can possess the same set of 4 quantum numbers


What is the principle quantum number?

What occurs as the value of n increases?

Denoted by the letter n
- Can take on any positive integer value and represents the shell where an electron is present in an atom
- Number corresponds with the elements period (row)

The higher the energy level, and the higher the radius of the electrons orbit


What is the azimuthal quantum number?

What occurs as the value of l increases?

What is the equation for the maximum number of electrons that can exist within a sub-shell?

Denoted by the letter l
- Tells us the shape of the orbitals
- For any given number of n, the value of l can be any integer in the range of n

The greater the energy of the sub shell

4l + 2


What is the magnetic quantum number?

Denoted by the letter ml
- Describes orientation of the orbital
- Possible values of ml are all integers from l to - l including 0


What is the spin quantum number?

What is the difference between parallel and paired spins?

Denoted by the letter ms
- Describes the spin
- The two spins are -1/2 and +1/2
- Must be opposite when in the same orbital

Parallel: Electrons in different orbitals (different ml) with the same ms values
Paired: Electrons with opposite spins (different ms) in the same orbital (same ml)


What is electron configuration?

The pattern by which subshells are filled and the number of electrons within each principal level and sub shell are designated by


How does electron configuration notation work?

First number denotes principle energy level, the letter designates the subshell, and the superscript gives the number of electrons in the subshell


What is the Aufbau principle?

What rule is used to rank subshells by increasing energy? What does it state?

What happens if two subshells possess the same (n+l) value?

Subshells are filled from lowest to highest energy, and each subshell will completely fill before electrons enter the next one

(n+l) rule is used to rank subshells by increasing energy
- It states that the lower sum of the first and second quantum numbers, the lower energy of the sub shell

The sub shell with the lower n-value has lower energy and will fill first


Draw out the chart used to determine the sub shell filling order



Which will fill first, the 3d subtle or the 4s subshell?

For 3d:
- n = 3
- l = 2
- (n+l) = 5

For 4s:
- n = 4
- l = 0
- (n+l) = 4

Therefore, 4s will fill first because it has a lower energy and will fill first


How do you determine which sub-shells are filled?
- Uncharged?

You must know the number of electrons in the atom
- Uncharged atoms: The number of electrons equals the atomic number
- Charged atoms: The number of electrons is equal to the atomic number plus the extra electrons if the atom is negative or the atomic number minus the missing electrons if the atom is positive


What are the written electron configurations for Nitrogen (N) and Iron (Fe) according to Hund's Rule?



What is Hund's Rule?

States that within a given sub-shell, orbitals are filled such that there are a max. number of half filled orbitals with parallel spins - electrons prefer empty orbitals to half-filled ones because a pairing energy must be overcome for two electrons carrying repulsive negative charges to exist in the same orbital


What happens if the material has unpaired electrons?
- Paramagnetic?
- Diamagnetic?

A magnetic field will align the spins of these electrons and weakly attract the atom to the field
- This is called paramagnetic
- Diamagnetic: No unpaired electrons and are slightly repelled by a magnetic field


What is a valence electron?

Electrons that exist in the outer most energy shell or that are available for chemical bonding


Which are the valence electrons of elemental iron, elemental selenium, and the sulfur atom in a sulfate ion?

Elemental iron:
- Has 8 valence electrons - two in 4s and six in 3d sub-shell

Elemental selenium:
- Selenium has six valence electrons = two in its 4s sub-shell and four in its 4p sub-shell
- Seleniums 3d electrons are not part of its valence shell

Sulfur atom in a sulfate ion:
- Sulfur in a sulfate ion has 12 valence electrons - orignal six plus more from oxygen to which it is bonded
- Sulfur's 3s and 3p sub-shells can only contain eight of these electrons; the other four electrons have entered the sulfur's atom's 3d sub-shell which in elemental sulfur is empty