Atomic Structure and Periodic Trends Flashcards
what is the smallest unit of any element?
an atom
all atoms have a central nucleus that contains:
protons and neutrons
what are nucleons?
protons and neutrons
what is contained outside the nucleus in an atom?
electrons that are held by the electrostatic attraction of the positively charged nucleus
atomic number Z
the number of protons in the nucleus of an atom (subscript)
mass number A
the number of protons plus the number of neutrons in the nucleus of an atom (superscript)
what is another way to write the mass number?
as a number after the name of the element
isotopes
two atoms of the same element that have the same atomic number but different mass numbers due to their difference in the number of neutrons
atomic weight of an element
the weighted average of the masses of its naturally occurring isotopes
anion
a negatively charged ion
cation
a positively charged ion
strong nuclear force
the force that holds protons and neutrons together, the strongest force (stronger than the electrical force between charged particles)
radioactive
unstable nuclei
radioactive decay
a process radioactive nuclei undergo to make them more stable; by altering the number and ratio of protons and neutrons or just lowing their energy
what are the three types of radioactive decay?
alpha, beta (-, +, electron capture), gamma
parent
the nucleus that undergoes radioactive decay
daughter
the resulting more stable nucleus after radioactive decay
alpha decay
becomes more stable by reducing the number and neutrons by emitting an alpha particle (containing 2 neutrons and protons)
each type of beta decay involves:
the conversion of a neutron into a proton or vice versa through the action of the weak nuclear force
why are beta particles more dangerous than alpha particles?
they are significantly less massive so have more energy and greater penetrating ability
beta- decay
occurs when an unstable nucleus contains too many neutrons: converts a neutron into a proton and an electron (beta - particle), the beta- particle is ejected
what is the effect on atomic number and mass number of beta-decay?
atomic number is 1 greater, mass number is the same
which is the most common type of beta decay?
beta- decay
beta+ decay
occurs when an unstable nucleus contains too few neutrons: converts a proton into a neutron and a positron which is ejected
what is the effect on atomic number and mass number of beta+decay?
atomic number is one less, the mass number remains the same
electron capture
allows the unstable nucleus to increase its number of neutrons by capturing an electron from the closest electron shell to convert a proton into a neutron
what is the effect on atomic number and mass number of electron capture?
the atomic number is one less, the mass number remains the same
gamma decay
a nucleus in an excited energy state (after alpha or beta decay) relaxes back to ground state by emitting energy in the form of photons of electromagnetic radiation (gamma photons)
why are gamma photons the most dangerous?
they have neither mass or charge and a very high frequency/energy, therefore they penetrate matter most effectively
what is the effect on atomic number and mass number of gamma decay?
no change in atomic number of mass number
half-life
the time it takes for one half of some sample of the substance to decay
how does the amount of a radioactive substance change over time?
it decreases exponentially
nuclear binding energy
the energy released when individual nucleons (protons and neutrons) were bound together to form the nucleus, also equal to the energy that would be required to break up the intact nucleus into individual nucleons
the greater the binding energy per nucleon…
the more stable the nucleus
mass defect
the difference in mass resulting from conversion of some mass to energy when the nucleons bind to form a nucleus
the mass defect’s energy equivalent is:
the nuclear binding energy
what sort of mass defect should a stable nucleus have?
positive
Planck’s constant
h=6.63*10^-34 Js
describe the Bohr model
electrons orbit the nucleus in circular paths, distance from nucleus was related to energy of the electrons, only orbits at certain distances were allowed; corresponding with quantized energy states to support the specific wavelengths observed in emission line spectra. ONE ELECTRON ONE ATOM MODEL
ground state
lowest possible energy level of an electron, n=1
excited state
when an electron absorbs a photon corresponding to energy difference between levels, allowing it to jump to a higher energy level
what does the Bohr model not account for?
electron-electron interactions in many-electron atoms
orbital
a three-dimensional region around the nucleus in which the electron is most likely to be found
what are the three basic rules for electron configuration?
1) electrons occupy the lowest energy orbitals available (Aufbau principle)
2) electrons in the same subshell occupy available orbitals singly before pairing up (Hund’s rule)
3) there can be no more than two electrons in a given orbital (Pauli exclusion principle)
diamagnetic
an atom that has all of its electrons spin-paired, contains an even number of electrons and have all of its occupied subshells filled: NO NET MAGNETIC FIELD
how do diamagnetic atoms behave in the presence of an external magnetic field
they will be repelled
paramagnetic
electrons are not all spin-paired
how do paramagnetic atoms behave in the presence of an external magnetic field
they will be attracted
some anomalies in electron configurations have atoms that prefer a filled or half-filled d subshell, some examples include:
- chromium (fill d shell with 5e-, Z=24)
- copper (fill d subshell with a 4s e-, Z=29)
- molybdenum (Z=42)
- silver (Z=47)
- gold (Z=79)
where do atoms go in anions?
the first available orbital, the one with the lowest available energy
isoelectronic
atoms with the same electron configuration
which atoms are removed/ionized from an atom first?
always comes from the valence shell (highest n shell) and the highest energy orbital within that level)
which electrons are responsible for the chemical reactivity of each group in the periodic table?
the valence-shell electron configuration
nuclear shielding effect
each filled shell between the nucleus and the valence electrons shields the valence electrons from the full effect of the positively charged protons in the nucleus
effective nuclear charge, Zeff
the charge felt by valence electrons after nuclear shielding
first ionization energy IE1
the amount of energy necessary to remove the least tightly bound electron from an isolated atom
second ionization energy IE2
the amount of energy required to remove the least tightly bound electron from the cation
is IE1 or IE2 always greater?
IE2 is always greater than IE1
electron affinity
the energy associated with the addition of an electron to an isolated atom
what does it mean if the electron affinity of an atom is negative?
energy is released when the electron is added
what does it mean if the electron affinity of an atom is positive?
energy is required in order to add the electron
electronegativity
a measure of an atom’s ability to pull electrons to itself when it forms a covalent bond
