Isotopes and Trends Flashcards
What is an Isotope?
atoms of the same element - same # of protons, different # of neutrons
How do you find abundance? state what x represents
formula:
Abundance = mass of iso¹ (x) + mass of iso² (1 - x)
*x represents the abundance of the first isotope, and since it’s a % (1 - x) is essentially 100 - x in order to find isotope 2 (so do that)
What is the unit for isotopes
u - unit or amu - atomic mass unit
How do you find avg atomic mass
(Mass of iso¹ × abundance¹/100) + (Mass iso² × abundance²/100) = avg atomic mass
What are the 5 sorts of trends of the periodic table?
Atomic radius, ionization energy, electron affinity, electronegativity, and the shielding effect
What is atomic radius?
It is the distance from nucleus to nucleus with 2 atoms’ valence shell touching each other.
What is atomic radius measured in?
Picometers (pm)
What happens to atomic radius when moving left to right and why
It decreases. Electrons and protons are added 1 by 1 to the same shell and can’t shield each other from being attracted to their opposite. This makes nuclear charge (protons basically) go up which decreases atomic radius
What happens to atomic radius when moving up to down and why
It increases. Increasing electrons means increasing shells and electrons further away from the nucleus. Just think radius; by design it sort of makes sense. bigger circle = bigger radius
What is ionization energy?
The energy required to remove the 1st valence electron from a neutral atom. The closer the electron is to the nucleus the more energy is required for it to be removed
What is ionization energy measured in
KJ/mole (kilojoule)
What happens to ionization energy when moving left to right and why
Increase. This is because atomic radius decreases, which means the valence is closer to the nucleus and more strongly drawn in
What happens to ionization energy when moving up-and-down and why
Decrease. Because the atomic radius increases, so valence becomes further away so the nucleus has less of a pull
Why does group I have low ionization energy?
Because when an electron is lost it forms a stable octet, so the hold on the valence isn’t so strong. They all want to be stable all the time.
What is electron affinity?
It is the ability of an atom to accept an electron, and the energy absorbed or released in the process.
Which family has the lowest electron affinity and why
Alkaline earth metals. You’d think it’s Group I, but they’re quick to lose an electron and become positive, which attracts electrons. Group II isn’t as quick to do that, so they attract the least electrons
What is electronegativity?
It is the measure of attraction of an atom to the electrons in a chemical bond. Closely related to ionization energy.
What happens to electronegativity when moving from up to down
It decreases. Atomic radius increases making electrons further from the nucleus and the nuclear charge decreases as well
What happens to electronegativity when moving left to right and why
It increases. Atomic radius decreases and nuclear charge increases, attracting more electrons to itself
What is effective nuclear charge and what should you know about it
The attractive positive charge of nuclear protons acting on valence electrons
- The effective nuclear charges is always less than total # of protons present in nucleus due to the shielding effect
- Effective nuclear charge is behind all other periodic table tendencies
What is the shielding effect charge and what should you know about it
The lessening of attraction between nuclear protons and valence electrons by partially or fully filled inner shells
- Shielding effect increases with the number of inner shells of electrons
- Same shell electrons do not shield each other
What is isotopic abundance?
the amount of a given isotope of an element that exists in nature, expressed as a percentage of the total amount of this element
how to find average atomic mass? (isotopes)
A = (mass of iso¹)(% of iso¹)+(mass of iso²)(% of iso²)
*repeat equation with mass x % if theres more isotopes
what happens to x in an equation of one isotope if there is 3 isotopes you need the abundance of? (2 are the same abundance)
1 - 2x
because it is x, but 2 are the same so it will be -x, and -x, which is 2x minus 100, so, 1 - 2x
