Atomic and Molecular Structure Flashcards
Atom
the basic building block of matter, representing the smaller unit of a chemical element
Nucleus
formed by the protons and neutrons, it is the core of an atom
Orbitals
this is where the electrons are and is located outside of the nucleus
Elements
- composed of very small particles called atoms
- identical in size, mass, and chemical properties
Compounds
-composed of atoms of more than one element
Chemical Reaction
involves only the separation, combination, or rearrangement of atoms
Protons
- carry a single positive charge and have a mass approximately one unified atomic mass unit (amu or u)
- amu is equivalent to one dalton
Atomic Number (z)
equal to the number of protons found in an atom of that element
Neutrons
-carry no charge and have a mass only slightly larger than that of protons
Electrons
- carry a charge equal in magnitude but opposite in sign to that of protons
- has a very small mass
Valence Electrons
- shell furthest from the nucleus
- the farther the valence electrons are from the nucleus, the weaker the attractive force of the positively charged nucleus and the more likely the valence electrons are to be influenced by other atoms
Mass Number (A)
- equal to the total number of nucleons (protons and neutrons)
- mass number (A) = number of protons + number of neutrons
Molecular Weight
the weight in grams per molecule per one mole of a given element (g/mol)
Mole
is a unit used to count particles and is represented by Avogadro’s number (6.02x10^23)
Isotopes
atoms with the same number of protons but different numbers of neutrons
-ex: 14 C 6 has 6 protons and 8 neutrons
Standard Atomic Weight
a weighted average of all the isotopes of an element found naturally on Earth
Example Problem (isotopes)
Element Q consists of three different isotopes, A, B, nad C. Isotope A has an atomic mass of 40 u and accounts for 60% of naturally occurring Q. The atomic mass of isotope B is 44 u and accounts for 25% of Q. Finally, isotope C has an atomic mass of 41 u and a natural abundance of 15%. What is the atomic weight of element Q?
0.60(40u) + 0.25(44u) + 0.15(41u) = 24 u + 11 u + 6.15 u = 41.15 u
The atomic weight of element Q is 41.15 g/mol
Quantum Theory
- energy emitted as electromagnetic radiation from matter comes in discrete bundles called quanta
- Energy value of a quantum is calculated by the equation: E=hf , h= Planck’s constant 6.626 x 10-34 Js, f= frequency
The Bohr Model
E= -Ry/n^2 , Ry = 2.18x10^-18
Electromagnetic Energy
E= hc/lambda, c= 3.0x10^8 m/s
Line spectrum
each line on the emission spectrum corresponds to a specific electronic transition
Balmer series
-four wavelengths in the visible region , n>2 to n=2
Lyman series
-higher energy transitions into the UV region
n>1 to n=1
Orbital
- a representation of the probability of finding an electron within a given region
- a specific region within a subshell that may contain no more than two electrons
Heisenberg uncertainty principle
states that it is impossible to simultaneously determine the momentum and the position of an electron
Quantum numbers
n (size of the orbital), l (shape of the orbital), me (orientation of the orbital), ms
Pauli exclusion principle
no two electrons in a given atom can possess the same set of four quantum numbers
Energy state
the position and energy of an electron described by its quantum numbers
Principal Quantum number
- the first quantum number
- denoted by the letter n
- the maximum n that can be used to describe the electrons of an element at its ground state corresponds with that element’s period (row) in the periodic table
Azimuthal Quantum number
- the second quantum number
- designated by the letter l
- tells us the shape of the orbitals and refers to the subshells or sublevels that occur within each principal energy level
- for any given n, the value of l can be any integer in the range of 0 to n -1
- the maximum number of electrons that can exist within a subshell is given by the equation 4l + 2
Magnetic Quantum number
- the third quantum number
- designated me
- describes the orientation of the orbital in space
- specifies the particular orbital within a subshell where an electron is highly likely to be found at a given point in time
- p subshell has 3 possible ml values (-1,0,+1)
- d subshell has 5 possible ml values (-2,-1,0,+1,+2)
- f subshell has 7 possible ml values (-3,-2,-1,0,+1,+2,+3)
Spin Quantum number
- the fourth quantum number
- denoted by ms
- the spin of a particle is its intrinsic angular momentum and is a characteristic of a particle
- the two spin orientations are designated +1/2 and -1/2
- whenever two electrons are in the same orbital, they must have opposite spins due to the Pauli exclusion principle
- electrons in different orbitals with the same ms values are said to have parallel spins
- electrons with opposite spins in the same orbital are often referred to as paired
Electron configuration
- the first number denotes the principle energy level, the letter designates the subshell, and the subscript gives the number of electrons in that subshell
- ex: 2p4 indicates there are 4 electrons in the second subshell of the second principal energy level
Aufbau Principle
subshells are filled from lowest to highest energy, and each subshell will fill completely before electrons begin to enter the enxt one
(n+l) rule
states that the lower sum of the first and second quantum numbers, the lower the energy of the subshell
Hund’s Rule
states that within a given subshell orbitals are filled such that there are a maximum number of half-filled orbitals with parallel spins
