Atomic & Molecular Structure Flashcards
what role does the neutron play in an atom?
they ensure the atom’s stability because without them, the protons would repel each other and make the nucleus unstable
what’s the atomic number?
it’s how many protons are in an element
the number of protons defines the element
what makes up the atomic mass of an atom?
the number of protons and neutrons it has
the mass of electron is considered negligible
differentiate between core and valence electrons
core electrons are closest to the positively charged nucleus. tend to be the most stable and are lowest in energy
valence electrons are the furthest from the nucleus. they are found in the highest energy level and have higher energy than core electrons.
since valence is further away from the nucleus, they do not feel the attractive forces of the nucleus as strongly and are loosely held. this is why valence electrons are more reactive and are involved in bond formation
what formula can be used to determine the maximum number of electrons each energy level can have?
2(n^2)
the first energy level will have 2 electrons, the second can carry up to 8, etc…
what’s an isotope?
isotopes are atoms of the same element that have the same number of protons but different number of neutrons.
many isotopes exist in nature with varying levels of stability. they are also found in different abundances in nature.
the atomic mass, also known as the atomic weight, of an element is calculated by taking the weighted average of the element’s naturally occurring isotopes, taking into account their
respective abundances.
for example, carbon’s
atomic mass is 12.011 amu. this is because
carbon-12 is much more abundant in nature
than carbon-13 or carbon-14. this means that
the mass of carbon-12 contributes more
towards the atomic mass of carbon.
what’s the law of constant composition?
the law of constant composition tells us that
elements within a compound always combine in a fixed proportion
for example, the compound “water” will always have 2 hydrogens bound to 1 oxygen to form H2O. if the proportion of
hydrogen to oxygen changes from being 2
hydrogens : 1 oxygen to 2 hydrogens : 2 oxygens, the resulting compound is not water
how does a chemical reaction differ from a physical reaction?
a chemical reaction involves the substances undergoing a chemical change whereby a new substance is created.
unlike a physical reaction, in a chemical reaction,
intramolecular bonds between atoms are created or destroyed
for example, oxygen and
hydrogen atoms create bonds with each other to form water.
what are the (5) types of chemical reactions? briefly describe them
synthesis
- occur when two or more atoms or molecules combine to form a single compound. this reaction usually involves the release of energy
decomposition
- occur when a compound breaks down into two or more products. this reaction usually requires the input of energy.
single displacement
- occur when one element is replaced by another in a compound
double displacement
- also called exchange reactions, involve the exchange of bonds between two reacting chemical species. some common types of double
displacement reactions are neutralization and precipitation reactions
combustion
- when a substance reacts with O2 gas to produce light and heat
what are the (2) types of combustion reactions?
there are two types of combustion reactions you should be aware of: combustion of hydrogen and the combustion of hydrocarbons. in the case
of a complete combustion of hydrocarbon, water and carbon dioxide are always the products, regardless of
which type of hydrocarbon was the reactant.
explain bohr’s model
originally believed that electrons follow a fixed circular path around the nucleus. the centripetal force from the attraction of a negatively charged electron to the positively
charged protons of the atom was thought to cause this effect.
this, however, is the out-
dated Bohr’s model of the atom!!!!!
describe the modern quantum/atomic theory and the heisenberg uncertainty principle
the modern quantum theory has replaced the
outdated Bohr’s model for describing the electronic structure of an atom.
electrons are actually
localized in specific regions of space around the nucleus known as an orbitals.
modern atomic theory uses four quantum numbers that help describe the electrons of an atom
the Heisenberg uncertainty principle describes that it is impossible to perfectly find both the momentum and the location of an electron in an atom. we can only figure out one or the other. as such, orbitals describe the most likely
location of an electron around an atom.
what are the (4) quantum numbers? what do each of them represent?
principle quantum number (n): the energy level the electron occupies
azimuthal quantum number (l): the shape of the subshell/orbital
magnetic quantum number (ml): the orientation of the orbital
spin quantum number (ms): the angular momentum of the electron
what are the requirements for the principle quantum number? (n)
represents the main energy level
occupied by electrons
—
is a positive integer, greater than or
equal to 1
what are the requirements for the azimuthal quantum number? (l)
describes the shape of the subshells
or the orbital shape within each
principal energy level
—-
possible values of the azimuthal
quantum number are all integers
between zero and n–1
for example, a principal quantum number of 3 would have potential azimuthal quantum numbers of 0, 1, and 2.
the subshells of the azimuthal
quantum number carry a letter
designation such that:
subshell l = 0 is “s,”
subshell l = 1 is “p,”
subshell l = 2 is “d”
subshell l = 3 is “f.”
- these subshells can hold 2, 6, 10,
and 14 electrons, respectively.
what are the requirements for the magnetic quantum number? (ml)
- the p-subshell for example, splits
into three unique orbitals. one along the z-plane (pz), one along the x-plane (px), and one along the y-plane (py).
the magnetic quantum number ranges between the negative and positive magnitude of the azimuthal quantum number. for example, since a p-subshell is l = 1, it would have ml values of -1, 0, and 1.
what are the requirements for the spin quantum number? (ms)
describes the angular momentum of
an electron
——
denoted as either +1/2 or -1/2, representing an upward or
downward spin. the assignment of a
positive or negative value to the spin
is arbitrary.
electrons in the same orbital must
have antiparallel spins.
what’s does the pauli exclusion principle state?
states that no two electrons in an
atom can have the exact same set of four
quantum numbers. these numbers are hence unique to each electron of a atom.
what’s does the aufbau principle state?
states that subshells tend to get filled from lower to higher energy levels.
thus, the 4s subshell gets filled BEFORE the 3d subshell because it is lower in energy. so, when dealing with
transition metals, just remember that the 3d orbital has slightly higher energy than the 4s which is why the 3d orbital is filled after the 4s.
what does hund’s rule state?
all orbitals of a subshell must first receive an electron before pairing can occur.
additionally, all the electrons within singly occupied orbitals must have the
same spin. thus, when drawing the orbital diagram of oxygen, all three 2p orbitals are filled as upward arrows before the remaining electrons are paired.
what are some exceptions to hund’s rule?
the first exception is exemplified with chromium (Cr). the 3d subshell is one electron away from being half-full. thus, chromium borrows an electron from the 4s subshell and places it in the 3d subshell to get an electron configuration of [Ar]4s1 3d5. both the s-subshell and d-subshell are half-filled, which satisfies our rule. also applies molybdenum (Mo),
the second exception is exemplified
with copper (Cu). the d-subshell is one electron away from being completely filled. thus, copper borrows an electron from the 4s subshell to make the 3d subshell completely full. the electron configuration of copper is hence [Ar]4s1 3d10. Gold (Au) and silver (Ag) also behave like copper in this regard.
so basically making d half full or full
what are isoelectronic species?
ions and atoms can have the exact
same electron configurations…
an isoelectronic species is when two or more species have the same electron configuration, it means that they have the same arrangement of electrons. they are known as isoelectronic species
e.g. Ca 2+ ion and Ar
what are ionic salts?
ionic compounds form
crystalline structures which are
incredibly hard to break, maximizing the interactions between the cations and anions
what are (4) properties of ionic compounds?
the cations (atom that lost electrons)
and anions (atom that gained electrons)
that result from ionic bonding are held
together by the electrostatic attraction
of their charges.
ionic compounds have very high
melting and boiling points due to the
strong electrostatic attractions between
their atoms.
these compounds are soluble in water,
where they dissociate into cations and
anions.
ionic compounds conduct electricity
when dissolved in aqueous solutions or
when they are melted. in both cases,
the ions are able to freely move around
in the aqueous or molten solution.
what are the (3) properties of ionic bonds?
since covalent bonds are weaker than ionic bonds, covalent compounds have lower melting and boiling points. As such, these compounds often exist as liquids or gasses
these compounds are insoluble in water.
covalent compounds do not conduct
electricity in aqueous or molten form.
