Gr.11 Isotopes, Trends, & Atomic Theory Flashcards
What is an Isotope?
Same element atoms - same # of protons, different # of neutrons
What is the unit for isotopes
u - unit ot amu - atomic mass unit
How do you find abundance
- Get the avg mass of the element on periodic table
- iso¹(x) + iso²(1-x)
- sub iso² into the brackets
- put x with x’s on one side
- solve for x
- x × 100 -> = abundance minus 100 for y abund
OR y = 1 - 0.00 (x) (y=1-x)
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
Who are the 6 forefathers of atomic theory
Democritus, John Dalton, J.J. Thomson, Ernest Rutherford, Niels Bohr, and Erwin Schrödinger
What was Democritus’ time and contributions
400 BC, Greece
- started the search for a description of matter
- theorized matter would become indivisible at some point, the point which he named “atomos” - not to be cut
- atoms are infinite, always moving, and can join together
Why was Democritus ignored
Outshone by the more eminent philosophers of that time - Aristotle and Plato
What was Dalton’s time and contributions
Early 1800’s, England
- his experiments lead to the acceptance of the idea of atoms
- this recognition is known under “Dalton’s Law”, a pillar of modern chemistry; which includes the following:
• all elements are made up of atoms
• atoms are indivisible and indestructible
• same elements are alike, differents are different
• compounds formed by the joining of two atoms
What was Thomson’s time and contributions?
1897, England
- plum pudding model, the first hint that an atom had even smaller particles in it
- concluded that negative charges came from within the atom
- that meant there was particles smaller than an atom
- which made the atom divisible!
- old electrons were called corpuscules
- he figured positive charges existed too since the gas was neutral, but he couldn’t find them
Describe the experiment that guided Thomson to finding that atoms are divisible
In an experiment involving a neutral gas tube and an electric current: from the current, a negative charge came through, so a particle smaller than the atom had to exist - where else would they have come from?
What is the Plum Pudding model and who created it
J.J. Thomson. It said that atoms were made of a positively charged substance scattered with negative electrons, like raisins in plum pudding
What was Rutherford’s time and contributions
1908, England
- made a popular atomic model
- Conducted the gold foil experiment which lead to the discovery of the nucleus (coined that name too)
- all pos charges were inside the nucleus, neg charges were scattered outside the nucleus around the edge
- the atom is mostly empty space
- father of nuclear physics
Describe the gold foil experiment and who conducted it
Ernest Rutherford.
He send positively charged bullets through gold foil. Some bullets went straight, others went awry and different places as if it hit a solid. Knowing pos repels pos, he concluded that the center of the atoms had a condensed, positively charged nucleus!
What was Niels Bohr’s time and contributions
1913, Denmark
- proposed an improvement to Rutherford’s model which assigned electrons to a specific energy level
- it was the first successful model of the atom
○ it was made with thoughts of relating atoms to the solar system, electrons orbiting the nucleus
○ and, the orbital energy levels were located at certain distances
What is the wave model?
Modern Day Chemistry
- disproved Bohr’s idea of orbitals and location of electrons
- based off the principles of wave mechanics
- concluded that it is impossible to determine exact location of an electron
- probable location is based on energy amount of the electron
Describe the modern atomic model
A positively charged nucleus surrounded by enough electrons to make a neutral atom
What is an electron cloud
The space where electrons are likely to be found. Electrons do not move randomly, probable location may depend on the amount of energy the electron has
Low energy: closest to nucleus
High energy: furthest from nucleus
What is Erwin Schrödinger’s time and contributions
1935, Austrian-Irish
- considered a founder of quantum mechanics
- best known for Schrödinger’s Cat and Schrödinger’s Equation
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