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.
