Chapter 24: Atomic & Molecular Structure Flashcards
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?
- Elements are composed of small atoms which are identical in size, mass, and chemical properties
- Compounds are composed of atoms of more than 1 element
- 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
58-Ni
- Atomic mass is 28 = 28 protons and electrons
- 58-28 = 30 neutrons
60-Ni-2+
- 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
A-X-Z
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
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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?
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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
